That's not how plane crashes work. 

...It's also not accomplishing anything to sit here in the wet silty mud, getting wet and muddy, and mentally yelling at Reality that the situation she's apparently perceiving is physically impossible and doesn't make any sense. 

"Tsi-imbi," Merrin says to the quiet empty air, almost absentmindedly.

It's a strange kind of quiet. She can hear water moving, a quiet whispering from nearby and a louder rushing off in the distance, and that's the only sound. ...When she concentrates, she might also be able to hear a distant sighing that could be wind. She concentrates even harder, and can pick out very soft...clicking or popping noises? Coming from the sand around her, at irregular intervals. 

That's it. No other sound at all. 

...The tide seems to be on its way out, and the irregular popping-crackling might be the sound of the newly-exposed tidal flats literally freezing, because it's shockingly cold. Enough that Merrin's brain seems to be trying to reject it as some kind of bizarre sensory illusion, because it doesn't fit with anything else in her surroundings. The - ocean? - is apparently liquid. 

She stands up, to avoid getting any wetter, and looks around. 

Her Exception Handling wilderness survival and emergency medicine kit boxes are haphazardly scattered around her, some on rocks, some with their corners sunk into the wet silt. It's almost as though some capricious giant randomly dropped her, and them, out of the sky. 

NOTHING ABOUT THIS SITUATION MAKES ANY SENSE. 

...Also, if she just stands here repeatedly rejecting all of her sensory input as impossible and not making sense, then - well, she has no idea really, because she doesn't even have a hypothesis yet for what's actually happening, but if she's actually in an environment with ambient temperatures of at least -30º C, which is what it feels like, then she will DIE of HYPOTHERMIA with her emergency survival supplies right there. 

Merrin is going to provisionally give up on forming any coherent hypotheses for where she is, or how or why she ended up here, and instead focus on locating and unpacking the box with her power armor in it as fast as she possibly can. It's amphibious, with a built-in air supply, and rated to handle -50º C air temperatures, though operating in conditions that cold will drain the battery pretty fast. 

It's designed to be quick to put on with help, and possible to get into solo, but doing it solo is not as fast as she might hope, especially when she's starting out in comfortable clothing suitable for long-range air travel and now somewhat covered in wet mud and she needs to strip out of that first while her hands are already in the process of rapidly losing dexterity. By the time she has the armor on, her brain has stopped disbelieving the "cold" sensory signals in favor of FREAKING OUT about them and shivering uncontrollably. 

But the suit heating is on, and she should warm up from here without needing further actions from her. 

Merrin turns around on the spot to get a proper look at her surroundings. 

That doesn't look like anywhere. 

Merrin sits down, after a few moments, and stares stupidly at the horizon, which does not resemble any geographical location she's ever heard of. Why is everything purple. Why does the sky look wrong.

Why is she here, alone, with her survival kit and no sign of anything or anyone else, and not True Dead???? 

It takes Merrin what is in hindsight a really embarrassingly long time to piece together several disparate observations into a theory. 

The observations:

- This does not look like anywhere in dath ilan 

- She could gather more data by climbing to the top of the ridge and yet she's not doing that. She's sitting here on the tidal flats, which are rapidly frosting over, because she's tired. 

- She's really, really, really confused and failing to find traction on any of the pieces of her confusion

- She...has...a headache...? 

....This isn't dath ilan.

Therefore, it's a different planet. 

Merrin is having trouble thinking or doing things and has weird symptoms.

...And she's sitting here breathing the air normally, having not actually sealed the helmet fully out of some unthinking "not really liking how it restricts her peripheral vision" motivation, and also something on the suit panel is beeping an alarm, but Merrin puts it together in the second before she actually looks to see what the alarm is. 

There's no reason to assume that an entirely different planet, even one with air that initially seems breathable, has air with the same oxygen content. And so, by Merrin looks down and sees that the alarm is 'low oxygen detected', this is no longer particularly a surprise and she just feels very silly. 

She seals the helmet and the suit takes care of things from there. 

A minute or so later, she has less of a headache and feels a LOT more capable of being vertical. 

Wow. Merrin was aware that hypoxia can be hard to notice internally, because it impairs the metacognition that you need to notice you have a problem in the first place, but she has TRAINING for this and yet it took LIKE FIVE MINUTES for her to diagnose the problem and she was in fact completely tuning out the alarm trying to alert her of the problem and all of that is really quite embarrassing. She'll have to bring it up in the - 

- debrief.

That almost certainly isn't going to happen.

Because this isn't a training simulation, this is...something else. 

Put together the information she has. 

Her last memory is of a plane crashing. Merrin's understanding of the world confidently predicted that she would, at that point, cease having any experiences. 

Instead she's - apparently experiencing the actually-quite-recognizable fiction trope of finding herself on an exoplanet with various intriguing and plot-generating environmental hazards? With her Exception Handling gear all inexplicably along with her, which...is at least hopefully hinting at the version of the trope where the main character can, with great ingenuity, use the resources she has to survive? 

Merrin kind of still wants to yell at Reality that this is incredibly silly and doesn't make sense and should therefore not be happening. 

However, just because Reality is apparently insane, doesn't mean that Merrin would be making particularly sane choices if she reacted to all of this by closing her eyes and saying "tsi-imbi" repeatedly until someone rescued her. 

This appears to be the situation that exists to be interacted with. And...if she just rolls with the premise, it is in fact true that Merrin is rather unusually prepared for the "survival on an exoplanet" story trope. The reason it keeps feeling like a training scenario that she's going to get to debrief afterward is because it's totally one that Exception Handling would throw at her, if it were possible. 

Though even if it were physically within the capabilities of Civilization to arrange this for a training scenario, which Merrin really doesn't think it is, she doesn't think that Exception Handling would arrange to have her experience it without warning like this. It feels out of character. There are scenarios they might throw at her by surprise, where she's not necessarily prepared has to improvise with non-optimized equipment, but not 'surprise: you're on another planet'. If Exception Handling had access to instantaneous-travel to other planets with different atmospheres, Merrin is pretty sure she would get at least a briefing beforehand and a list of the situations in which she could expect them to call off the scenario and rescue her.

So she should not be expecting to be rescued, if she gets herself into something she can't handle. 

Okay. Time to focus, and stop wasting mental cycles on disbelieving that any of this is really happening, and instead use her entire brain toward surviving it if it is. 

There's no particular reason to think that 'low oxygen atmosphere' and 'subzero temperatures' are the only life-threatening hazards. Merrin needs to orient, and form hypotheses about what sort of planet this is and what its properties are, and then test those hypotheses, and then make plans to survive both the immediate and the longer-term dangers. 

She accesses the wrist panel on her power armor to check what environmental parameters it's picking up. 

The basic suite is pretty straightforward. Ambient air temperature: -38.1º C. She was not wrong that it's really cold.

Ambient pressure: ...pretty normal. Slightly low for literal sea level, but not for, say, 1000m altitude, which would not give anyone altitude sickness. 

Atmospheric oxygen fraction, though: 13.5%. Eep.

That's not, actually, quite low enough that she would have progressed to unconsciousness and seizures if the suit hadn't warned her. It's a level that causes "subtle" impairment and less subtle exertion-intolerance, not brain damage, but...she's actually rather fortunate that it was so cold. If she'd arrived to a comfortable balmy temperature, she might have started exploring without first putting on the armor and switching it on for the heating. She probably would have realized what was wrong before the subtle impairment made her do something incredibly stupid and/or she exerted herself too hard, failed to notice the problem due to impairment, and collapsed, but...possibly not actually in time to fix it while already impaired. 

....Well, she's gotten as far as analyzing the hazards she already knows about and that's already enough to alert her to some very serious problems!

Namely: at these temperatures, her suit has maybe 18 hours of battery life. And less oxygen supply than that. And she's not predicting a rescue in the next 18 hours. 

Okay. What are her solutions. 

She has a field oxygen concentrator, in the extended medical kit. And one caniser of compressed oxygen, for use in conditions where for some reason she can't set up the oxygen concentrator. She can adapt the various components to refill her suit's tank from the canister, and then fill the canister from the oxygen concentrator, and that gives her mobility. If she doesn't need mobility, she can park herself next to the oxygen concentrator and pipe it directly into her suit; it produces slightly more than she'll need at rest, so she could even still accumulate some extra for storage. Or, given that she needs to figure out shelter anyway once the suit runs out of battery, she could just sit around with nasal cannula on her. The atmosphere isn't toxic, it wouldn't even kill her to breathe as-is, it just doesn't have quite enough oxygen for her, an unacclimatized human, to be functioning mentally at her best, which she needs to be right now because she's in a situation where the slightest moment of carelessness might well get her killed. 

The oxygen concentrator also needs power to run. 

She has batteries. At 15º C she could power it for a couple of days just off stored power. 

Merrin has no reason to think her situation will end in a rescue in two days. 

She has a portable kit with solar panels. The sky looks clear, so if she's lucky, and she can find a nice undisturbed place to set up camp, she can generate solar power to refill batteries during the day, use stored power at night, have some backup stored oxygen (as a backup for her backup, she does have three sodium chlorate candles which will generate 6h of oxygen each, but if she has to use them, they're gone.) 

...Great. Progress. She's broken it down to 'if she can find a place to camp, she can indefinitely keep breathing air with enough oxygen in it.' She also needs water, and food, but she has some of each with her - enough water for several days, enough food for a month - and she has a filter and purification tablets if she can find freshwater locally, and she doesn't have a pre-built kit to evaporate and distill seawater but she knows how they work and she has a lot of emergency medical equipment and supplies that she doesn't need and can instead repurpose for survival. ...She'll need a heat source, she can't evaporate enough water by the heat of the sun if it's winter - it has to be winter, if it were this cold all the time there wouldn't be liquid oceans -

- actually, no, she's confused.

It's -38º C. There should be icebergs. Not just frost on the ground and some delicate icing-over of the little river flowing down the center of its channel, surrounded on either side by hundreds of meters of silt and rocks. There should probably be snow??? A desert might be completely bare of snow even in the depths of winter, but deserts are usually in the continental interior, not coastal. She's standing right in the intertidal zone. There should be regular precipitation, here, and if it's this cold it should be coming down as snow, so where is the snow? 

...She checks the suit readout again. You know, just in case she hallucinated it the first time or something. 

Still -37.4º C. 

That's...about half a degree warmer, actually, which is maybe hopeful that the winter days are warmer than the winter nights. She arrived more or less right at dawn. She's been here for...twenty minutes? Huh, it feels like it must be less than that, or the sun would have covered more distance, it's still only a little ways above the horizon. 

Merrin navigates to see the temperature trend. 

It's definitely getting warmer! By about 0.6º C per ten minutes. Well, that's at least hopeful in terms of the peak afternoon temperature being less frigid. The coldest temperatures are usually going to be shortly before dawn, so if it warms up enough and takes long enough to cool fully overnight, then -40º C is probably the worst she has to deal with, and she might even be okay in just warm clothing for the warmest part of the afternoon. She'll absolutely need to figure out some kind of shelter by nightfall, that's still the next step, and by tomorrow she ideally needs a good place for solar panel setup...

The obvious constraint on where she can set up shelter is that it needs to be above the high tide line. So, next up: figure out where that is. 

She leaves the boxes where they are - she will need to haul them with her, she absolutely needs all of her gear to survive this - but for now she's just exploring. 

The silt is rapidly freezing over, and crunches under her feet. 

The exposed rocks are covered in some sort of purple biofilm, which seems to be resisting the frost, and incredibly slippery. There are also armored limpet-like organisms, some almost as large as her fist, with radial ridges that look razor-sharp. 

The exoplanet has multicellular animal life!!!!

 ...That was something Merrin probably had visual evidence of earlier - the weird little holes in the silty part of the tidal flats look like something left by burrowing invertebrates - but she hadn't quite fully and explicitly made the observation and inference, because at the point when she was paying attention, she also hadn't explicitly thought through the "being on another planet" part. 

The primary photosynthetic pigments in the local equivalent of...prokaryote algae?...are purple. Dark purple, a lot of it is closer to black with purple undertones, and iridescent blue-green from some angles when it catches the light. She...can probably infer things about the planet's sun, from that, once she has a chance to dredge up her not-strictly-human-medicine-related biology knowledge. 

The time for that is probably not right now. ...A lot of dark pigment might hint at high UV levels? Which is useful to know - and makes perfect sense, a lower-oxygen atmosphere would mean somewhat less ozone production and a thinner ozone layer - but if she's wearing the power armor for heating anyway, she's not going to get a sunburn. 

(There's no reason to assume the animal life is edible for her. Or the plant life, for that matter. It might all use completely different amino acids and undigestible sugars. ...Reasoning off fiction tropes rather than physics - which Merrin is making SO many mental faces about doing but this is SUCH a tropey situation to be experiencing - then it depends on the author's taste and the flavor of story they're going for, it might be the case that this biosphere is just mysteriously compatible with dath ilani life. Maybe given time she can figure out how to repurpose her field blood-test lab equipment to figure out the composition? ...Off the top of her head Merrin has no idea how to do that but if she uses her brain and doesn't DIE STUPIDLY then she might have time to figure something out...) 

(Life!!!! Alien life on another planet!!!!!!!! Merrin might not have chosen to be in this situation and might - pointlessly, she's aware of that - resent Reality enormously on multiple levels, but also, ALIEN LIFE ON ANOTHER PLANET is really superheated cool.) 

The tidal flats slope gradually upward for a while. Eventually Merrin reaches the edge of the (probably limestone? definitely some kind of sedimentary rock with visible strata) valley walls, and when she looks back, the boxes are definitely at least four or five meters lower than her current elevation, over maybe 300 meters of horizontal distance. 

The valley walls aren't cliffs. Fortunately, or it would be a lot harder to climb up. It seems like it was once a V-shaped valley - carved by a river, maybe, at some point in the past when the river was a lot larger, or maybe it is larger in non-winter seasons. The erosion pattern produces a step-like effect. The stone is also crusted with (much smaller) limpet-like molluscs, and more of the purple probably-algae-biofilm. Here, it's been exposed long enough that the surface has dried out to the texture of waxed leather, and is no longer particularly slippery, but when Merrin touches it, there's still a feeling of gelatinous squishiness underneath: there's water present under the waxy surface, and it's still liquid. 

That's really cool. It's probably full of antifreeze proteins or something! 

She starts hiking up the slope. 

...The gravity on this planet is not right. 

It was less noticeable on the flatter area; the power armor gives her some help, to avoid her exhausting herself just hauling around its weight, and it probably recalibrated automatically, and the default panel readout doesn't list local gravity because, like, why would it, the suit is not rated for space. She was falling down kind of a lot, but it was easy to blame it on the insanely slippery mucilaginous biofilm stuff all over the rocks. 

Merrin digs through suit readout menus and determines that the suit sure is estimating an effective gravity of 1.18G.

She eyes the sloping limestone. It's going to be even more annoying than she thought to haul eight entire boxes of gear to the top. She's really not going to want to carry them any further than necessary. And she doesn't know how close the tide was to fully out; if it's already turning, she doesn't have that long to work. 

She climbs. 

Eventually she's covered another ten meters of elevation, over maybe fifty meters of horizontal distance. 

There's less of the algal film - and what there is looks more thoroughly dessicated, it's firm rather than gelatinous - but the rocks are still crusted with limpet-like and barnacle-like molluscs. 

....She's still below the high tide line. 

Merrin looks down into the valley. There are her boxes of gear, near the bottom, looking small and sad, especially when she thinks about the fact that that's all she has. 

She turns and looks out toward the ocean. 

...It's further out. It's a lot further out. And still going out, judging by the smooth outflow rather than turbulence of rising-tide-against-river-current. 

Her suit clock thinks it's been about two hours since she put the suit on. It's not trivial to eyeball from here, but when she appeared she was just above the high tide line, sitting in mud that had been covered until recently enough that it hadn't yet frosted. The water could easily have dropped three or even four meters since then. 

Great! She's managed to figure out the next environmental hazard while it's still getting further away from her rather than closer to her! 

In dath ilan, most coastal areas have a tidal range of less than five meters. Based on what she knows right now, this planet has a tidal range of at least twenty meters. 

And she's in a river valley. Even with just, like, eight meters of tidal range, river valleys can act like a funnel, squeezing the incoming tide into a tidal bore wave of pretty significant height and force. 

She doesn't want to be anywhere near the bottom of the valley when the tide comes back in, and she doesn't know how long she has to work.

...How much higher than this does she need to get?

Looking up, she can see a couple of different debris lines; this planet doesn't seem to have trees, there's no driftwood, just shredded bits of what must be some kind of seaweed, dried onto the rock. Probably the most recent high tides line up with the lower debris lines, given how thoroughly dried-out the higher ones are, but she doesn't know that for sure. 

Time to scramble up faster and see what's at the top of the valley walls! 

Incidentally, the sun isn't actually all that high in the sky yet, but her suit thinks the ambient temperature is now up to -31º C. Still chilly, but a seven-degree increase. The suit power expenditure on heating is very slightly lower. 

Maybe by afternoon it won't be all that far below freezing! 

It takes Merrin another fifteen minutes to reach the top of the cliff. She checks the suit readout again; the temperature is up almost another degree. 

There...isn't much...on land, in terms of signs of life. It's basically just patches of lichen and more biofilm-like stuff. 

The rocks have very noticeable bleaching patterns on the areas that Merrin can predict would be sun-facing. There's also a lot of cracking, of the kind you might expect from repeated cycles of frigid temperatures - with water freezing and expanding in tiny cracks - followed by heat expansion of the rock itself. 

It sure does look like the photosynthetic life goes for purple pigment, and occasionally orange. 

...It does not look like a hospitable place to make camp. Merrin has gear for that, in one of the boxes, she's not stuck making her own shelter out of local materials – which is GOOD because this planet doesn't have WOOD – but she's not sure she has a great setup to anchor a tent into cracked and UV-damaged bare stone. She could improvise carrying slabs of broken rock to weight it down, but - it's so exposed, up here... 

She turns around and eyes the terrain upstream. 

There's a cave. 

...Which Merrin can't even slightly use for shelter because it's blatantly going to flood at high tide. Probably flood explosively when the tidal bore squeezes its way up the river channel. In fact, she wonders if the cave exists directly as the result of water erosion from the regular gigantic tides blasting their way into an obstacle in the river channel and finding a region of softer stone. This is a silly way to feel, but Merrin is almost mad at the cave, sitting there practically offending her with its tempting yet treacherous offer of protection from the elements.

Maybe at some later point she'll have time to explore. For now, she'd better get her gear out of the path of the GIANT TIDAL BORE before the tide starts turning. 

She starts scrambling back down, which does at least go faster than climbing up. 

Still, by the time she's at the bottom, the temperature is all the way up to -26º C. 

The sun still hasn't covered all that much of the sky, given that it's now been three hours since dawn. 

.....Merrin is starting to have. A little bit of a suspicion. 

She can't easily test it now. The valley floor, soon (hopefully not too soon) to be submerged, is not a good place to set up any kind of observation station. It'll have to wait until she's dragged herself back above the high-tide line again. 

She reviews her supply kit. 

Each of her boxes has an inset on the side where a laminated inventory card can be swapped in, and each card lists all the boxes, with color coding shown, before listing the full detailed inventory of the individual box. 

CASE 1 (RED) - CRITICAL MEDICAL SUPPLIES 
20 kg
Trauma supplies: tourniquets, hemostatic gauze, chest seals, airway management, IV access, critical injectable medications (epinephrine, morphine, ketamine). 4L IV fluids. Oxygen concentrator, main battery pack (5 kWh), backup O₂ generators, pulse oximeter.

CASE 2 (GREEN) - WATER & FOOD
25 kg
15 days emergency rations (3500 kcal/day), 5L drinking water, water filter, purification tablets, UV sterilizer, collapsible containers, cooking gear, fuel canisters.

CASE 3 (BLUE) - SHELTER & THERMAL
15 kg
Tarp, sleeping bag, insulated pad, 100m paracord, emergency blankets, chemical heat packs. 

CASE 4 (ORANGE) - TOOLS/POWER
22 kg
Solar panels (100W), backup batteries, 50m climbing rope, harness, carabiners, knife, axe, multi-tool, sewing kit, tactical lights.

CASE 5 (PURPLE) - EXTENDED MEDICAL
30 kg
Antibiotics, oral medications, additional wound care, suture kits, surgical supplies, diagnostic equipment, decontamination supplies.

CASE 6 (GREY) - EXTENDED PROVISIONS
30 kg
30 additional days of emergency rations.

CASE 7 (GREY) - REDUNDANT MEDICAL
25 kg
Redundant medical supplies: extra IV fluids (6L), gauze, sutures, medications, gloves, emergency blankets, reference materials.

CASE 8 (BLACK) - POWER ARMOR 
80 kg (full)
(However, currently empty except for a 5kg spare power pack in a 4kg box) 

Okay. 

Merrin needs Case 1 because the atmosphere isn't breathable, that's non-negotiable. She needs power, or she dies after the battery power runs out for the oxygen concentrator; Case 4 is also non-negotiable. 

She needs shelter. She does not have the option of building one with local materials. 

She needs food. Ideally all of it, to buy more time to figure out which local lifeforms are edible with what processing. 

Honestly, the only boxes she doesn't really desperately need are Case 5 and Case 7, all the backup medical supplies. Except that, one, she might well end up injuring herself, and two, her trope-sense is tingling and insisting that it would be TOTALLY ON THEME for this stupid survival scenario to somehow also involve someone showing up with a medical emergency. Merrin does not THINK that's how any of this works, because it would be so incredibly silly, but given her spectacular levels of uncertainty around everything she thought she knew about Reality, she's not SUFFICIENTLY CONFIDENT in that to entirely discount it. 

Since transport would also be a significant issue in the survival scenario she had been expecting to need this gear for, the boxes lock together, and in theory she can lock together four of them and lock that onto a harness and the power armor would let her carry that many at once. 

In theory. In normal gravity, on reasonable terrain. Merrin is absolutely not going to risk it at 1.2G when needing to scramble up uneven, potentially slippery slopes. Too much risk that she would at some point slip and fall and tumble end-over-end all the way to the bottom of the valley again, which could injure her and might damage the power armor and would definitely set back the timeline. 

Two at a time, then, and she'll just have to keep an eye on the receding tide and do as much as she can. 

Even laden, it's a little faster; she has her route planned, and the terrain is steadily drying out; the mucilaginous rock films retain water remarkably well, but the surfaces eventually dry out to a waxy texture. They're surprisingly tough, too. Even with all the extra mass she's carrying, the treads of her boots don't shred them. 

Well, they have to go through a lot, what with the violent tides blasting up and down this riverbed on a twice-daily basis. 

It's now slightly less than five hours after dawn.

The sun is...higher. It doesn't look anywhere near the zenith of its arc through the sky. It's noticeably an angled arc – which makes sense, for winter at a temperate latitude – and it's a little hard to judge when Merrin keeps changing position and viewing it from different angles, but eyeballing it, the sun is maybe a third of the way up the arc its tracing. 

Eyeballing it isn't good enough for planning purposes. Merrin is going to pause for five minutes, despite the time pressure, and kludge together a sundial out of fragmented bits of shale and, when it doesn't want to hold together as sturdily as she prefers, a mouthful of water from the built-in drinking bladder in her power suit, mixed into one of the exposed patches of hard-baked dry clay to make it into, instead, sticky wet clay. 

She marks the sun's current shadow with an indelible marker - she has one of those in the small light front-pack clipped to her suit where it's not in the way. 

And then back down. ...Temperature check? 

It's now -17º C. 

That's a twenty-degree increase in five-ish hours.

If she's eyeballing it right, solar noon might not be for another ten hours, and the temperature will probably peak a little after that. 

...Merrin now has a hypothesis for why there aren't any icebergs. 

Again, it takes about an hour to scramble all the way back down and return to her remaining boxes. 

(The tide, so far as she could tell, was even further out when she was climbing down and had a good view. From her current angle she can no longer see ocean at all, just the river itself, still working on icing over but in another five hours that's going to start reversing course.)

Almost three hours per trip, once you take into account loading and unloading. She won't have to climb down on the last one, but that's still eight hours to get everything else and that's assuming she doesn't rest at all. 

She has longer than she feared. This ridiculous planet clearly has a longer day-night cycle than what she's used to, and the tidal cycle should be (approximately) (at least, assuming there's just one moon) tied to the length of the day. With high tides specifically twice a day, she thinks - yeah, she's remembering that right, the "tidal bulges" are on the side of the planet facing the moon and, symmetrically, on the opposite side, and rotate as the planet rotates under the moon. 

...She hasn't seen the moon, so the last high tide must have been the tidal bulge opposite the moon; otherwise, low tide would correspond to moonset, implying the moon had previously been visible the entire time. (She thinks "low tide is always moonset" holds? She doesn't know how long a full orbit of the moon would take - it depends how fast the moon is moving relative to the planet, on dath ilan the "lunar day" determining tides is almost an hour longer than the solar day as the planet "catches up" with a moving moon - oh, no, and she's also doing some approximation, she thinks moonrise-to-moonset isn't always exactly half of the lunar day period, it varies based on...stuff...that she knew some facts about once that she cannot retrieve right now and probably can't figure out on the fly for another planet anyway so it's irrelevant and she'll need to determine it empirically...) 

- approximation is better than nothing. Low tide is moonset or moonrise. She hasn't seen a moon yet, ergo, it's not yet low tide, the tide is still going out. Once she sees the moon, she'll know its on its way back in. 

...The tide seems to have been draining out at a rate of somewhere between one and four meters per hour depending how far she trusts her eyeballing. In theory, knowing that the "lunar day" is closeish to the solar day should, once she has a sundial measurement to sanity check her sun-eyeballing, let Merrin estimate the duration between high tides and, given the per-hour rate of water dropping, get an estimate of the total tidal range that way. Ish.

Merrin is really hoping it's closer to 1-2m, because 4m and a day that might be 30 hours long - a winter day! in addition to her first uninformed wild guess that it surely can't be -40ºC in summer or she would be in a glacier right now, the sun's trajectory is compatible with winter-at-temperate-latitudes, though she has no way to estimate her actual latitude without knowing the planet's axial tilt - anyway, if a winter day is 30 hours, then who knows maybe the night is 50 hours and an 80-hour solar day divided by four is twenty and twenty times four meters an hour would mean EIGHTY METER TIDES and that's pessimistic wildly-approximate-math, it's probably more like her 95%-confidence-interval for maximum tidal range than her 50%-confidence-interval, but it sure is a terrifying 95%-confidence-interval upper bound to be assigning. 

For now: there's still no moon in the sky. Not low tide yet. She should focus on hauling boxes. 

Two hours later - seven hours after dawn - and she's dropping off more boxes at the top of the slope and making a mark on her sundial. It's not an accurate enough sundial to be certain yet but it does, in fact, look compatible with "sunrise to sunset will take about 30 hours". 

...Check on ambient temperature trends? 

-9 º C. 

The ocean is....just, barely, visible, as a strip of glimmering purple-maroon that might be a whole ten kilometers away. 

STILL NO MOON. Not that Merrin wants a moon, because she doesn't want it to be low tide yet, but it's still mildly driving her nuts not knowing.

She mostly hasn't been itching too much about the lack of prediction markets - she's done a whole run of training sims recently with only low-bandwidth voice-on-radio backup, specifically to practice decisionmaking under stress without all the smartest people in the world feeding her advice via prediction markets, and she managed to successfully discount it as not worth being mad about - but right now Merrin would REALLY LOVE if the twelve most excited astrophysicists in dath ilan were eagerly debating every single data point available and narrowing down probabilities. She's pretty sure she could be doing more with observations she could make if she knew to make them, and it's just that she's not a superheated expert in tides, or in any of the several thousand fields of expertise that are not specifically emergency medicine but would be A LOT MORE HELPFUL right now. 

...At least Merrin is unusually well-prepared for one element here, which is repeatedly hauling very heavy storage crates of life-critical emergency supplies up a giant limestone slope, while under the effects of 1.2G, and also keeping the suit power-assist as low as she can cope with to save on battery life, and resisting the temptation to bump her air up to 25% oxygen for the stamina boost because she doesn't know how many problems she'll have with solar generation, and doing all of that for what's going to end up being nearly twelve hours straight. 

It really feels like the universe is trolling her.

Cases 1, 2, 3, and 4 are now at the top of the slope!!!! Merrin has oxygen, power for the oxygen, the makings of a shelter, and 15 days of food! 

Merrin scrambles down as fast as she can. She's definitely going to have time to grab Extended Provisions and Extended Medical. Whether she has time for the box her armor came in - light, since she's wearing the others, but unwieldy enough that she doesn't want to attempt to paracord-tie it on top of two other crates - or for the Redundant Medical Supplies, depends on when she sees a moon and how scary the incoming tide looks. 

Tidal bores are unpredictable, is the thing. You don't get a steady flow, you get a small incoming tide – because most of it is getting hung up in the narrowing river-mouth inlet - and then you get a wave bringing tens of meters of tide all at once. She thiiiinks she read one time that you can get tidal bore waves nearly as high as the total tidal range in a region, though that takes very specific conditions and geography and she's probably not that unlucky. Unless the universe is trolling her. 

Anyway: there's a discontinuity, turning a smooth water-level graph into a step-function, and there might be physics to determine when the step happens but Merrin doesn't know it and it would rely on measurements she has no way to take. She suspects it means that the point where her stuff is will be flooded sooner than it would otherwise, because it's at least ten meters below high tide and at least ten above low tide and so, approximation, it's exactly in the middle, and probably the step-function jumps from "tide is below what the naive math predicts" to "tide is above that" across the middle of the tide graph?

...Or possibly Merrin is incredibly confused because she's trying to visualize hypothetical graphs of water levels in her head while hauling stuff up a hill. 

She's halfway up the limestone slope - moving a bit more slowly, now, she's starting to risk fatigue - when she sees the moon. 

It is a superheated enormous moon. ...Well, strictly speaking Merrin has no way of knowing if it's larger than dath ilan's moon or just closer, just that the angular diameter as seen from the planet's surface is sure making her feel like it is More Of A Moon. (There's probably some sort of astrophysics where one is related to the other but she doesn't know it and cannot rederive it from basic principles on the spot in her head while hauling crates up a hill.) 

That...would in fact explain the enormous tides, wouldn't it. 

Top of the hill. An hour later, according to her suit clock, and it's now been ten hours in total since dawn. 

The temperature is now 0.2° C. Positive 0.2° C. The ice is about to start melting. 

The sundial, and also Merrin's eyeballs, think the sun is about two-thirds of the way to its zenith. More likely to be a bit more than that than a bit less, but...call it a 30-hour day.

Merrin should try to estimate how close in angular degrees the zenith is to "directly overhead", once the sun is there, that'll let her do some math and figure out roughly how much longer the night is than the day? ...Is that true, or would it need to be stupid guesswork math because she can't untangle "different axial tilt" from "exact latitude" or "exact season relative to winter solstice and nearest equinox"? - no, she thinks if she can get a sense of where the sun rises and where the sun sets and estimate that as a fraction of the total...horizon circumference? there's got to be a better term than that? - but if she knows how "small a bite" of the sun's arc happened above the horizon, relative to if it were passing directly overhead at a 90 degree angle and the day and night were exactly equal, she can figure out how much of the circle is left "under" the horizon and thus the relative durations of day and night?

This is definitely math she needs writing materials for, it's been a while since she had any reason to do math like this. Fortunately, her gear includes a reasonable quantity of (tough, waterproof) paper, plus writing utensils for it. She'll run out food before she runs out of notebook space. 

...And low tide was an hour ago. 

She can almost certainly make it down and back. The ocean still looks very far away and she still can't see or hear the roar of a wave surging up the inlet. It seems likely that the interval between low tide and high tide is, like, fifteen hours or something, and ten hours ago her nearby spot was already above water, so it's probably more than halfway up in terms of elevation. She doesn't have another ten hours, because of the tidal bore effect, but it would be really quite baffling if she had less than two hours. The tide looks like it's gone out past the eroded cliffs at the mouth of the river inlet, so initially it's going to be rising normally without encountering obstacles to concentrate the forces. 

It's worth a tiny risk, for the benefit of backup medical supplies that could mitigate other risks later. And it would be really nice to have a way to store her armor securely where it can't get damaged by the elements.

Merrin isn't certain, though, and so it's going to be an intensely nervewracking last trip. 

The trip down is rapidly becoming noticeably more difficult than the previous three trips were.  

The thing is that the ground was previously frozen, and froze within seconds to minutes of being exposed by the tide. Which created its own hazards, of course, but the black-ice tidepools were visible and possible to avoid, and much of the rest ended up freezing with a sandpaper texture that did not create additional slipping hazards. 

Now the little pockets of trapped water are melting. They'll almost certainly dry out the rest of the way under the bright, increasingly hot sun, but in the meantime, it takes Merrin 50% longer to safely make it down. 

By the time she's back at her stuff, the air temperature is still only up to 4° C, but the surface level of the frozen tidal silt is absorbing the sunlight and melting. It's quickly becoming very squishy. 

Merrin - somewhat unusually for her social group - has spent enough time near oceans to have an intuitive-level prediction about how long it would take for the silt-mud to bake in the sun and dry out a bit and have less of a tendency to try to eat her boots. 

...Longer than she expects she has. 

Well, nothing for it but to load up again and trek back. 

Merrin plus power armor weighs around 130kg. (It's not the kind of armor that would deflect high-energy projectiles; it's designed to make her able to carry more with less fatigue and to safely operate underwater and survive being banged around a bit, but it's also optimized to be lightweight and have as long a battery life as possible, for scenarios where she's a long, long way from Civilization and a reliable power supply. The armor itself still weighs more than she does, but only slightly more.) 

Another 35kg of boxes is "just" a 27% increase in mass. But it's mass in a location that shifts her center of gravity, and the thawing ground is trying even harder to eat her feet.

...Merrin might, perhaps, have prioritized suboptimally here, though admittedly there's also an element of poor luck. 

She could have done this ten hours ago, no problem. She would be having a somewhat easier time now if she had EATEN MORE CALORIES, which she hasn't, because she would have to unseal the suit helmet to eat a meal bar and she didn't prioritize taking half an hour to set up the oxygen concentrator, partly because she was worried about leaving it exposed to the frigid cold and draining its battery life, but she could have caught onto the trend like SIX HOURS AGO if she had been PAYING ATTENTION and guessed that there would be a window of totally innocuous temperatures. 

Anyway. She's had maybe 800 calories worth of meal replacement liquid, by dint of just pouring it directly into the drinking bladder built into her suit, which she can do without removing the suit though she's perhaps going to regret it when she has to clean it later, normally she sticks to electrolyte powder in there.

(She can, fortunately, pee in the suit, and it doesn't even involve having to catheterize herself, there's a pad of super-absorbent material that wicks the moisture away. She'll have to dry it out later and reuse it, she only has one spare.) 

She does have a couple of meal bars in her front pouch but the problem remains that she would have to unseal the helmet, and either breathe low-oxygen air or, like, override the "open helmet" alarm and waste a lot of the air supply blasting oxygen out the front of her open helmet. And stopping to eat won't actually fix the whole problem. Her body doesn't just need a meal in her stomach; her muscles need rest. 

And she can't afford to stop here, because it's POSSIBLE that she has only ONE OR TWO HOURS until an enormous wavefront that could be up to 25 meters high and will be moving at 50 km/h bears down on her. 

(She probably has longer than that, and it might not be quite that high; tidal range varies. But if Merrin makes a habit of taking risks because it's 95% likely to be fine this one time, then all those 5% risks of disaster will RAPIDLY COMPOUND. She has no backup, here.) 

...Can she manage without the boxes, or has she just thoroughly misjudged her endurance and doomed herself here? 

She can manage a lot more easily without the boxes! It's still an intense workout, keeping her balance while the silty mud tries to swallow her boots, but she can do it. 

Okay. 

Merrin does not think she can afford to risk another laden trip up the slope.

(For one, if she gets caught in the wave, she...will have a significantly better chance of surfing it upstream and surviving the adventure if her suit has the hydrodynamics she's used to. She's never actually done a training that involved challenging water conditions with several boxes of gear strapped to her suit and completely ruining its streamlined profile, let alone what more or less amounts to attempting to surf a tsunami. 'Getting caught in the tidal bore' is still a huge risk, to be clear, her challenging-water-training took place in the open ocean and not in a river channel full of dangerous obstacles, but she might be able to manage it if she can trust her power armor's water functions to be at top performance.) 

...She's genuinely pretty upset at the prospect of losing the last two boxes. The backup medical supplies aren't just useful for emergency medicine; she could turn the gauze into textiles for clothing, use the sute needles as...fishhooks? does this planet have actual fish or just simple invertebrates?...she hasn't thought through everything that could be improvised into something, but eight boxes of gear is all she has and it's viscerally painful to think about losing it. And her armor box is, in addition to a safe place to keep her precious and essential armor suit, an insulated, waterproof, and highly durable storage location for arbitrary objects. She doesn't have the manufacturing ability to make any more. 

The boxes might wash upstream and be findable later? If she's willing to spend the next several months looking? They're really durable; Exception Handling toughened wilderness gear is dath ilani manufacturing at its finest. The contents might pick up some damage if exposed to extreme g-forces, but the medical supplies in particular are not very fragile and are packed in a way where they ought to survive being literally airdropped from 5,000 meters without a parachute.

The main cost is that she would have to scour every meter of riverbank, and meanwhile they would move with every tide, and...yeah, she might find them before she dies here, or she might not. 

...Can she somehow wedge them in a place where they'll still be there once the tide drops? Put them somewhere where the incoming tidal bore will just push them harder against the wedging surface, and hope that the speed and turbulence of the current from the outgoing tide is less intense and they stay put? 

Well. She's actually pretty much right beside the river channel. And the very bottom of that channel, already submerged, is going to be the place least disturbed by the violently incoming tidal waters. And she is wearing a suit that's designed for underwater operations, and taking a break from the gravity might actually count as a bit of a rest. 

She slips down into the water. 

(It doesn't feel cold. It must be frigid - the suit will have a record to peruse later - but the armor takes care of heating.) 

....It's beautiful. It's really, really pretty. 

It's an ACTUAL EXOPLANET with ALIEN LIFE!!!!!!!! Merrin has not had a huge amount of time to think about the positives of her extremely ridiculous current situation, but it continues to be really cool!!!!!!!!

There are more, and larger, mollusc-like organisms down here. Some of the shells - a little like clamshells or oystershells in shape, but remarkably dense and heavy and thick - are slightly open, with delicate fronds waving, but if Merrin's shadow passes over them - or maybe it's not her shadow at all, it still happens even in the dimness under rock overhangs, maybe it's the water disturbance vibrations of her passage - they immediately snap shut with rather a lot of force. You could lose a finger that way. If Merrin tries tugging on them, she'll find them glued to the rock with a very impressive stubbornness; it would take a sharp knife, or possibly underwater explosives, to dislodge them from their anchors.

There are algae biofilms plastered flat against the stone everywhere, and in a wider range of colors – not just the deep maroon-purple-black, but vivid crimson reds and even deep rosy pinks, the photosynthetic pigment present with less of the melanin-analogues for UV absorption. 

There are...tubeworms? Short, segmented, heavily armored bases, with long delicate tendrils waving in the water that, again, instantly curl up and vanish inside the armored tube when Merrin's shadow passes over them. 

There aren't all that many mobile fishlike organisms. A few semi-translucent wormy things, no larger than Merrin's pinky finger, that stick close to the rock surfaces and corkscrew into crevices when her movement disturbs the water near them. She sees one larger organism – a segmented-worm body with bilateral rows of flat paddle-like limbs, like a bizarre combination of a fish and a centipede. It's about twenty centimeters long and swims slowly, radial mouthparts opening and closing in the algae-hazy water. 

Cooooooooool!!

(This planet is...probably a lot earlier in the history of complex multicellular life, Merrin thinks? It would make sense of the lower oxygen, if there just hasn't been enough photosynthesizing biomass for long enough to complete the shift from a low-oxygen to a high-oxygen atmosphere. The centipedefish is the only organism she's seen that looks like it has a genuine nervous system, and probably not much of one.)

There are also larger, thicker mounds that, on closer examination, seem to be some kind of sea sponge. They're flattened, not structured like coral on dath ilan, but they're hardened - calcium-like deposits, or some kind of very tough hard keratin-like protein, or both, or something else entirely, Merrin has no way to determine the exact chemical composition. 

There's also seaweed! It's the most complex and structured plant life she's seen by far. It's sort of kelp-like, with a root-system anchor and fronds that extend into the water column. No sign of air bladders for buoyancy, though, and the fronds mostly hang downward from rock overhangs into the current, though they're anchored in ways where it doesn't look like it would risk dislodging them if the incoming tidal current were to tug them the other way.

Unsurprisingly given the forces they're regularly subjected to, the root-anchors are huge and extensive. If Merrin swims up close and paddles against the gentle river current to stay there for a while, and uses her headlamp, she can see that the roots aren't just stuck to the rock, but at dozens or hundreds of points seem to have eaten into it. This particular patch has an anchored-root-system base a good two meters across, securing a bundle of fronds less than four meters long. 

They're very secure. Merrin can grip a frond and plant both feet and use the suit power as well as her own muscle strength to pull as hard as she can, and it doesn't budge at all. 

Hmmmmmmmmmmmmmm. 

...Merrin is going to swim downstream a bit and check out some of the other seaweed patches. 

Here's one where the root system is anchored on the floor of a shallow erosion-depression, not quite an underwater cave yet but on its way there. There appear to be several of the plants, with root systems overlapping and reinforcing each other. The fronds are particularly long, maybe as much as five meters, undulating in the current; if the current switches, they'll be plastered against the arch of the would-be cave. 

Hmmmmmmmmmmmmmmmm. 

.....The straplike fronds are flexible enough to tie into knots. And the root system has points where one could slide a loop of paracord under a particularly thick root and secure additional ropes. 

Yeah. Merrin thinks she has a scheme for where to attempt to secure her last two crates. Though she had really better hurry. 

When she re-emerges, she still can't see any ocean, and she doesn't hear the roar of an approaching tidal bore wave, though of course at the point when she did hear one it would be at most minutes away. 

....Merrin has an unforeseen problem, which she could have foreseen if she had thought about it for ten entire seconds. 

The full box of redundant medical supplies is neutral-to-negative buoyancy. Merrin won't have any trouble swimming down to 10m of depth with it and holding it against the current while she ties it into place with the 10m of paracord she has in her front pouch. (Because she was being dumb and did not think through the fact that she might want to secure anything at the bottom of the river channel, and she has a lot more paracord than that but it's at the top of the riverbank, which right now might as well be the Moon.) 

The empty power armor crate is sealed full of air. And thus rather buoyant. She does not think she can easily haul it deep underwater, and its buoyancy will strain the attachment points even when there's no current. 

...She'll swim down with the first box and secure that and use the time to think of solutions. 

The seaweed frond material is really remarkably tough. Merrin tries dissecting one down the middle to split it into two halves, so she can knot it in more places without using paracord, and her small multitool knife is having a lot of trouble with it. (She has sharper knives, and a lightweight hatchet, but both are in the toolbox at the top of the hill.) 

She gives up on that plan and just knots what she has; it's a thick, flattened, slightly twisted ribbon, as wide as her wrist and almost a centimeter thick at the center, leathery rather than woody, and she thinks there's silica incorporated too. The edges of the ribbon are sharp and it's a very good thing her suit gloves are sturdy. 

....And then she's going to saw through one frond at the base, to try to take with her. Because this planet might not have any trees, but this ultrasturdy seaweed might have real promise as a building material. She'll want to see what it's like when it dries. 

By the time she makes it back to her last remaining crate, her suit clock thinks it's been 13 hours and 20 minutes since dawn. Eyeballing it from this angle, it looks like the sun is nearly at its zenith. 

The temperature is up to almost 18° C. The tidal flats must be getting even hotter; some areas are steaming as water rapidly evaporates. 

The moon is still a long way behind the sun, in terms of making its arc across the sky. Not a spring tide, assuming that "spring tides" on this planet also correlate with a lunar-solar syzygy. She still can't see or hear the ocean. 

Okay. 

She has two options: 

- Try to carry the crate up the hill - it's not heavy - and, if she hears the roar of ocean approaching, ditch it for streamlining in case she doesn't make it and has to surf 

- Load it up with rocks???? 

...There is, unfortunately, a complete lack of nicely sized stackable rocks, down here. Some of the "exposed rock" might belong to large boulders embedded in sediment, rather than being directly attached to the bedrock, but she doesn't know which ones to try to dig up, and they might all be too big to even fit in the crate. Any small rocks have clearly been thrown around by the tide until they were eroded down to pebbles and grit. 

(Filling it with water - with pure water of neutral pH - might not irreversibly degrade the lining, but it's not really meant to be totally waterproof from the inside. She has lots of collapsible-waterproof-container water storage; she wasn't supposed to need to adapt the boxes as cisterns. And, of course, she hasn't had a chance to fully analyze the seawater; the suit has sensors for pH and osmolality, once she gets around to digging around in the menu, but it was not designed to give her a full analysis and readout of the chemical composition of seawater on ANOTHER PLANET. Also, if she wanted to weigh down the box by filling it with water, she would have to remove the spare suit battery and rig something to carry that, if she wants to use it; it's water-resistant, dropping it briefly in a puddle wouldn't destroy it, but it's really not specced to survive sitting around in mineral-filled seawater for days.) 

...Okay. Merrin's climbing-relevant muscles do actually feel somewhat rested, after taking a break from the gravity and using different muscles.

Harnessing the empty box to her back and going as fast as she can, that's what the plan will be. (And the seaweed frond she cut is wrapped a few times through the harness webbing to secure it along with the box.)

It takes significantly longer. Before, when the ground was frozen and she wasn't so exhausted, she'd been able to make it from her landing spot to her box cache at the top of the bank in about 100 minutes. Exhaustion alone would probably have brought it to two hours. 

This time, three and a half hours pass - it's now been 16 hours since dawn, the sun is clearly trending back down in the sky, and her suit has flipped over to cooling mode because the outside temperature is up to 28° C - and she's still not up to the highest debris line, let alone all the way back to her cache. The stone is dry, here, it's no longer slippery, and she would be making faster progress, but it took her more than two hours just to cross the silty tidal flats, and she's very close to exhaustion.

And now she can hear a roar in the distance, and feel the vibration of it conveyed through the rock and into her bones. 

Perhaps Merrin is not quite on the edge of exhaustion after all! The adrenaline produced by sheer terror for her life can eke out a bit more speed! 

(She's really close to what she thinks is the true high-tide line, and she might already be above the current high-tide line, if she's right that this isn't the highest the tides will get. It doesn't quite seem worth ditching the box, especially since it's not really slowing her that much at this point, on stable rocky ground, and she would really like to have the spare suit battery for tonight.) 

She makes it, with - probably minutes and not literal seconds to spare, but still - and she flops down beside her haphazard pile of boxes, and she watches the tidal bore wavefront roll in. 

[AUTHOR'S NOTE: please ignore all the ways in which this image is not quite physically plausible, this is attempt #6.] 

....Eeeeeeeep.

Merrin is very, very glad that she knows enough about a hundred kinds of basic planet-related science to have predicted that the tempting cave is, in fact, a DANGER CAVE.

It's actually pretty majestic and epic and awesome to watch, and all that. Given that she survived it. 

(Merrin spends a little while wondering whether having just barely made it is evidence that the Literary Tropes Theory is applicable to her situation and the universe is, in fact, trolling her, before she concludes that it's stupid to be wasting mental cycles on that right now.) 

The wave settles. It's not yet high tide; the water level is more than halfway up the limestone banks and still rising, with the incoming tidal current completely overwhelming the underlying river current flowing the opposite way. 

Her suit temperature sensor picked up a peak of 29.3° C – and coinciding with almost 60% humidity, from the giant evaporating tidal-flats surface, meaning the calculated dry-heat-equivalent for predicting heat stress without the suit was 37° C. But the sun is sliding down the sky, and the inrushing water brought some cooler wind with it, and the temperature is now past its peak, down to 26.6° C and will, presumably, continue to drop.

Merrin missed her chance to mark solar noon on her sundial - or measure the exact highest angle of the sun - but at a guess, noon was a bit over two hours ago, so about 14 hours after dawn, and sunset will be in 12 hours. And then there will be a long winter night of unknown duration, and the temperature will drop, and drop, and probably reach a low of around -40° C just before dawn. 

...Which means that the 24h average temperature would be below freezing. 

Why is that relevant? Because seawater should (slowly) approach the average seasonal air temperature.

Merrin does have some other guesses now about what explains the lack of visible giant icebergs; the tidal turbulence would dash them to pieces, and fragmented sea ice would both be difficult to see in the distance and also much faster to melt in the heat of the day. (The lack of snow on the ground is no longer confusing. For all she knows, it did snow a week ago, but if the temperature spikes to a high of 30° C each afternoon, even if the 24-hour average is below freezing, snow on the ground wouldn't even last a single day-cycle; it would melt into water, flow away into cracks and hide out there contributing to rock weathering, and mostly end up right back in the ocean.) 

...But another thing about seawater, especially when the shallower and deeper layers are undergoing such thorough mixing, is that it lags behind the seasonal temperature. If the planet had no axial tilt and this latitude was always its current "season" - which, Merrin is realizing, is not in principle impossible, a zero-degree axial tilt and a high polar latitude could result in the sun-angle she's observing? - but if that were the case, the sea ought to reach an equilibrium at around -5° C. 

And she can confirm, with her suit data, that it's not that cold and somehow liquid anyway. She was getting readings between 1° and 3° C. 

One very obvious explanation is that this is winter, as opposed to summer, and that in summer the average temperature is significantly higher, and right now the ocean with its enormous heat capacity is still slowly cooling after last summer's heat, and won't quite get down to a below-zero average before it's spring and the temperatures are rising. 

....Which, if true, is a fact that predicts very serious problems for Merrin in...some fairly large but unknown number of planetary days (she doesn't know how long the year is.) 

The problem is that right now, the average daily temperature is below zero - unless the rate of heat loss is really nonlinear, Merrin was admittedly doing Stupid Approximate Math and should instead, like, get a full day and night trend and then graph it and get the actual area-under-the-curve - anyway, the low is further below zero than the high is above zero, and the high is still hot enough that, without her suit, she would not be able to do any serious physical labor without risking heatstroke. 

The peak summer temperatures on this planet could easily be another twenty or even thirty degrees higher, and that's flat-out not survivable even for a few hours a day. 

...But, of course, today Merrin's most immediate-term survival threat is the winter night and the cold.

Which means she cannot afford to waste any more time resting. She'll have at least thirty hours of night to rest, later. Right now, she needs to be frantically using the remaining hours of sunlight to generate power, and erecting an insulated shelter soon so it's starting out full of warm air and will cool more slowly than the ambient temperature... 

Merrin's gear has, again, been heavily optimized, with a huge number of specialized labor-hours from dozens of different fields of expertise going into filling a storage crate with 18 kg of as much utility-across-a-wide-range-of-possible-situations-including-unlikely-ones as they can cram in. (And many of those experts were having a lot of fun with it.) 

Most relevant to Merrin's current purposes is the modular solar power array. Four panels, both remarkably lightweight and remarkably durable; they wouldn't survive a tree falling on them but they would survive falling off a cliff, and being rained on won't even inconvenience the setup. (She might have to leave it up at her camp to generate and store power while she went off to rescue a casualty, and what if there was a sudden rainstorm while she was away!) The protective coating is extra-slippery, and most dirt or dust will slide right off it. There are six different standardized, documented configurations to use it in, ranging from "in treetops" (if she's in a forest and the ground gets minimal sunlight) to "in four different locations, with localized power storage" to "arranged on the back of her suit to power it while she walks". 

Right now Merrin just needs the most boring one. All four arranged in a square, tilted toward the sun's current descending angle. It's pretty much ideal circumstances for solar power generation, at least: clear sky, no obstacles to block the sun before it sets. There's some wind, up here on the rocky plateau, but not enough that she needs to do anything fancy to secure the panels. 

(Though Merrin really should try to do some mental climate modeling and figure out if this planet is likely to get regular hurricane strength gales. Not that she's going to be able to take any protective measures about that by tonight; she's barely going to have time to set up the basics.) 

The sun and sky are cooperative. There are some cute fluffy clouds on the horizon out over the ocean, but they don't seem to be in such a hurry to blow in that they'll catch up to the sun before it sets in...still probably more than eleven hours. Maybe the clouds will catch up; the longer day is going to be throwing off Merrin's instinctive judgement on that sort of thing. 

There is not actually anything Merrin can do to optimize over whether the sun goes behind cloud cover before it sets, so there's not much point thinking about it. She'll get the power she gets, and she should have empty battery storage to actually keep all of it, so that's better than turning it directly into stored oxygen if she doesn't know what she's most likely to need it for yet. 

She'll definitely have enough to power the oxygen concentrator all night, just in existing stored battery power – she has two dath ilan days worth of battery power, so even if the winter night is forty-eight hours long, she would make it. And she thinks it probably won't be quite that long. She hasn't done the math properly yet, and would have to approximate it anyway since her measurement system was fully manual and she missed solar noon by being in the wrong place, but the "bite" of a circle that was the sun's arc above the horizon felt fatter than she would expect if the night were approaching twice as long as the day. 

Her suit has six hours of battery-power-at-max-heating left. It's stretched longer than she feared – she's been using it for sixteen and a half hours, it just wasn't necessary for heating or cooling for most of that time. 

The cooling overnight will be gradual, and might even be close to linear once the sun sets. If she makes a very rough guess that it'll cool down to 15º C by sunset, which feels plausible for a day on dath ilan in a desert (low heat retention in the atmosphere) where the daily high reached 30° C, and she also guesstimates the night duration at 40 hours, and makes an assumption that by the end of those 40 hours it will hit -40º C...

- ugh, she's too tired for math - if it were 10° C at nightfall (plausible, with the longer stretch of late-afternoon and early-evening) and the night were 50 hours, that would be a degree per hour. The temperature would hit -15° C halfway through the night, with 25 hours left to go. 

She can handle -15° C with nothing except her tarp shelter - she'll want to make the smallest-internal-volume configuration, so her body heat and the small amount of waste heat from a running oxygen concentrator go as far as possible - and a sleeping bag. The sleeping bag is rated down to -20° C even with no other shelter! The temperature inside a well-sealed sleeping-shelter compartment will lag behind the dropping air temperature, so even if the outside air gets down to -20° C twenty hours before dawn, it could take - ugh this needs math - it'll take longer. Some amount longer. She might only have to endure ten hours of an interior temperature below what her sleeping bag is rated to handle... 

...she can actually improve the insulation a bunch. She has six emergency blankets, the kind that are waterproof and have a super-engineered layer of insulation that weighs almost nothing and can be packed down to the size of a small drink container and is nonetheless very effective, and are lined with equally super-engineered reflective material to reflect body heat back at the person inside. She does not need them for wilderness first aid, right now, so she can instead line the entirety of her sleeping cubicle with extra insulation. 

It might be a pretty uncomfortable night. But she's probably not going to be freezing to death with more than six hours to go until dawn. 

...Wait she forgot about wind-chill effects. Ugh, she’ll need to recalculate using a different effective-temperature with wind chill, in case it gets a lot windier than this overnight, out on the horribly exposed flat plain with no trees or vegetation to serve as windbreaks. 

She does, as a backup, have chemical heat packs. She would rather not use all of them on the literal first night, because they’re one time use and she can’t make any more unless she develops advanced chemical manufacturing literally on her own and that’s a lower priority than, you know, FOOD, and really she should just assume she has no more ever once the current supply is gone, since “in several years, if she first solves twelve more urgent impossible problems” is not germane to her current situation.

But she does have options. Costly ones, if she misjudges the wind chill and night duration enough, but she will very likely still be alive in the morning unless, like, a volcanic eruption gets her which would be really stupid and unsatisfying as the plot of a science fiction exoplanet-survival novel  that is not actually an argument, but in terms of direct physical causality, an unfortunately timed volcanic eruption is barely more likely than a meteor strike.

Merrin is already working on the shelter. She has a tarp, also very optimized – she can just use it as a sheet, 4m x 6m, but it comes with six different predesigned configurations that she can set up by arranging the lightweight aluminum tent-poles differently inside different color-coded sets of built-in tubes sewn in place, and one of those configurations is for a single-person capsule.

It's meant for confined spaces, more than "reducing internal volume", and she isn't really supposed to seal the thing as hard as possible for air-circulation reasons, but in this case she does not actually want to use the ventilation system it comes with, because the whole point is to keep the air inside exactly where it is and the air outside separate. It's not going to be airtight anyway, she won't literally suck all the oxygen out of the air, and she's going to be sleeping hooked up to extra oxygen.

The CO2 levels will probably get a little high. She can adapt one of the emergency-medical monitors to set off a loud alarm before it gets high enough to make her drowsy and harder to wake...

The tidal bore wavefront is past, but that was just the initial water-turning-around getting hung up in the narrowed inlet. The tide is still rising, steadily now, maybe a meter an hour. 

And rising, as the sun sloooooowly moves down the sky toward the horizon. 

(Occasionally there's another, smaller wavefront, and the waterline approximates a step-function again and jumps by a meter within less than a minute.) 

The temperature is dropping, not fast but steady. The tide is still rising. 

And rising... 

It almost looks like a normal river. Almost. Except that when you look closely, the current is wrong, there are too many eddies of weird turbulence, and also Merrin can clearly remember climbing like thirty meters up the erosion-stepped limestone valley walls, and looking down on the tidal flats and little winding river from a great height.

 Not just that, but at actual low tide the ocean was out of sight downstream.

And there are now less than ten meters between the waterline and the place where the valley walls give way to the to the more gently sloped shale plateau. 

She closes her eyes and pulls up the visual memory as clearly as she can, and then opens them and looks at the high-tide "river" again.

Merrin looks down wistfully at the impassible wall of purple water. It's so purple! ...Her vague recollection is that in dath ilan, algae blooms tend to die off due to nutrient depletion of the water – the "dead zone" that results happens afterward, when all that biomass decomposes and thereby depletes the oxygen in the water, killing all remain oxygen-breathing heterotrophs that live there. The algae itself just needs light - and nitrogen and phosphorus. It makes sense, given the rapid weathering of the rocks here by the twice-daily massive tides, that the nutrients in the coastal waters are regularly replenished. The waters aren't ever deep enough that no light would reach the bottom, and in any case, any given cubic centimeter of water might well end up back at the surface next tide, with all that mixing, and the algae currently getting less light at the bottom can probably survive until then, and any algae that does die will decompose with plenty of oxygen, given the regular mixing.

So: no big algae die-offs. Extremely superheated purple water. 

Her final box of gear is down there. Was down there. She's not sure whether to dare to hope that it's where she left it. 

This planet is terrifying. Merrin would like to trade her mysterious post-True-Death-waking-up-somewhere-else scenario in and get a different, easier, starter-mode exoplanet, please 

...She had better focus. This looks like high tide, but unrelatedly the sun is getting low in the sky and she probably has less than two hours of daylight left. And her shelter is finally assembled and lined with emergency insulated-reflective blankets, but it's not properly secured yet and there might be horrible nighttime winds to go with the horrible tides. 

She can't afford to use artificial lighting tonight, not knowing how many hours of night she has to budget her stored battery power for. So she had better finish everything while she still has natural light to work by. 

Merrin's shelter kit has a very advanced tent-stake system. With the right tools and power supply from the relevant crate, she could anchor her tent to granite bedrock. 

She does not think it's specced for stone that's been so weathered and cracked by the high UV and routine seventy-degree temperature swings that she can feel it trying to shatter under her feet. (She can walk, carefully, keeping her center of gravity exactly above the foot she's stepping down onto, but she wouldn't want to run.) 

For now she'll just rig up a temporary solution and anchor the guylines to her storage crates. It's not an ideal permanent solution since she'll want to at some point unpack them, but this isn't an ideal campsite anyway and she's going to be using most of the next endless long day to find a better one. Full, the set weighs over 200 kg. And she's effectively getting 20% more weight from the same mass, given the slightly higher gravity. Her own weight will be helping, too, and she's going to be sleeping with her armor right beside her in case she needs to get into it to survive the coldest part of the night. 

With the sun floating just above the horizon, Merrin has everything secured, and it's time to pack up for the night. 

She puts away the solar panel kit in its box; the box is in use, as a weight, but the securing guylines are fastened under and around it - there are convenient harness points for carrying it - and it's upright, she can access it without problems. 

The solar generation system comes with four auxiliary rechargeable batteries, each with a capacity of 500 Wh* (and stored uncharged, unlike the main 5000 Wh battery which has a full charge, so far unused).

She has managed, with twelve hours of afternoon sunlight, to partially fill one of them. She missed the peak hours of sunlight, so that's not necessarily indicative of how much power she can generate and store given an entire planetary day without cloud cover, which is good because over that time period her suit has used more than 1500 Wh – and it's not even concentrating the supplementary oxygen she's been breathing, it's getting that from storage. 

She carries the 5000 Wh main battery unit into the back of the tent. And the auxiliary suit battery (only 400 Wh), to swap in if she needs more suit power to get through the night. And the partially charged additional battery cell, which will give her maybe another 300 Wh. 




*assume translation convention from whatever units dath ilan actually uses. 

She unpacks the oxygen concentrator from the medical equipment box, and brings that into the tent, and connects it to the main battery – it has an internal battery but only enough to power a couple of hours of usage – and she switches it on. Conveniently, it has a backlit screen, though she can switch the display off later to save that tiny bit of power. 

...Right, and in all her approximate-math she'd been forgetting that she can run it at different settings. If she wants to generate 4L/min of oxygen, the maximum rate, it'll draw 180 W, and her battery will last...she can totally do math...oh right her hands are not busy now she can do calculator math (and also she has this in the written protocol somewhere but apparently not MEMORIZED, for that specific number, which makes sense because she is not sure she's literally ever had a training scenario OR a real scenario where her only power usage was oxygen and heating, normally she's using a lot more of the equipment to, you know, keep someone who's badly injured alive).

Highest setting is less than 30 hours. If she runs it at the very lowest setting, though, 0.5 L/min, then...in theory her battery ought to last over 100 hours, but at cold temperatures it'll be less efficient. Almost certainly still at least 70 hours? 

Her suit storage - it's a fully built-in oxygen "tank" that stores the equivalent of about 400L of O2 - is down to 15%. She could generate extra from the concentrator and siphon some off to refill it...but the medical compressor also uses power...and she would need to. Do more setup. Her equipment's default quick-setup protocol assumes that she's either running the oxygen concentrator at the rate her patient(s) need or replenishing her more portable storage, not trying to do both at once. And she's running out of light to do any setup. 

So not that. She'll breathe directly from the oxygen concentrator tonight. In the morning she'll either have to refill her suit's built-in tanks from the other medical oxygen canister, or do her siphoning-to-compressor setup and then park herself here for...a while...in the morning. Or not do as much wandering around. 

...How much oxygen does she need? This is not, actually, perfectly clear from the rate of suit consumption. The suit is topping up the air she's breathing with exactly the additional oxygen necessary to keep the partial pressure at normal-for-dath-ilan, and so what she's used is almost exactly what her metabolism has burned over that period, with close to no waste. If she's breathing from a nasal cannula, there will inevitably be a bit of waste. 

Well. Time to get out of the suit and put a pulse ox on herself and spend a while calibrating. ...And set up the CO2 monitoring for overnight, before it's dark. That also uses power aaaaaaa Merrin has stupid problems because this is a STUPID PLANET. 

(She hasn't actually started generating oxygen yet; it's just on standby mode, which is very low power usage.)

The outside air temperature was about 9° C, when she went into the tent. The tent itself was set up when it was hotter and has been absorbing sunlight-heat and is very well insulated; it's actually warmer than is really comfortable, reading at 24° C. 

GOOD. Merrin will NEED THAT HEAT LATER. 

...She sits cross-legged on the insulated sleeping pad and stares at the number on the pulse ox. 

Breathing ambient air, while sitting still not burning extra oxygen, Merrin's O2 saturation reading eventually drops to 89% and steadies out there. 

....Okay. That could be worse. It would almost certainly settle lower when she's asleep – right now Merrin is trying not to deliberately breathe more than she would otherwise, but that's sort of hard to actually do, and respiratory drive is a little lower during sleep, and her sleeping body would be going off CO2 levels – but she wouldn't die. Probably. 

She still shouldn't sleep without oxygen on her literal first night here. She needs her brain and cardiovascular system functioning optimally.

But humans can and do acclimatize to altitudes with an equivalent partial pressure of O2 to "sea level but with an atmospheric O2 percentage of 13.5%." It takes...about thirty days?...to acclimatize fully, for the average person, but she's fitter than average. 

She turns on oxygen generation at 0.5L/min and waits some more. 

It's already pretty dark in her tent, with the flaps sealed, but it's getting darker, too. The light outside is fading. 

It's too bad Merrin can't walk around outside for a while. On a planet with zero light pollution, the stars - in their alien constellations - are going to be spectacular. 

Astronomy can wait. Merrin has urgent problems to get a handle on first. 

...93%. Eventually, 94%. 

Yeah, that's fine. If she can manage to sleep without dislodging the pulse ox, it'll start alarming if she goes below 90%, but even if it didn't, she's not going to die of hypoxia in her sleep. Not even if she dislodges the nasal cannula, she would just wake up a bit stupid but she almost certainly wouldn't have given herself permanent brain damage from a night of sleeping with her sats in the high 80s.

Merrin has been awake for well over 24 hours now and is really very ready to finally get some sleep. 

...She makes herself eat a meal bar first. In the dark, by feel. 

(1200 calories, and it has all of the key nutrients - essential amino acids, essential fats, vitamins, minerals, etc - that she would need per day. In theory, if she can find anything on this planet that contains human-digestible calories at all, she could top up the rest of her diet with that and get it down to one bar a day rather than the three her stores budget for. ...Three in a 24 hour day, that is, and her supply would last 45 days on dath ilan, not that she's ever had a real or simulated wilderness scenario last anywhere close to that long, normally the extended food crate is the one she would ditch first because 15 days is already a long time for any of her sims, but she's very glad that Exception Handling overprepared her, here.) 

...Water. She needs to figure out water. She's consumed 80% of what's in the 3L drinking bladder in her suit, with all the activity today, she wasn't rationing herself at all. (Note to self she also needs to CLEAN THE RESERVOIR she put meal replacement powder in it.) 

She has another 5L. That's enough for 48 hours, unless she rations it and dehydrates herself a bit. Two days, on dath ilan. But, in fact, she needs to solve her water problem tomorrow, because the days on this stupid planet are at least 60 hours long. 

And she's not prepared for a lost-at-sea training scenario, for which they would have given her a desalination kit of one form or another. She can purify fresh water, but she has no idea how far she would have to go to find reliably fresh water. She'll need to build a still.

Fortunately, guess what she has a whole bunch of: various tubing for medical purposes! And lots of plastic, and ways to make a seal. And this planet has no shortage of daytime heat to evaporate seawater by. She just needs to make sure she actually handles that early in the day, because if she has another active day she'll drink most of her water before it's even nightfall.

...Actually, Merrin is very silly, isn't she. She didn't unpack any of her water, because she had not thought through the fact that she's not going to just sleep through a "night" that could be two dath ilan days long. She knows exactly where it is, outside the tent, in the main provisions box, but now it's completely dark outside...

- stars, hopefully? Clear sky? And she's night-vision-acclimated. She'll just need to breathe ambient air for five minutes, since she didn't prep for mobile O2 and it's not worth putting her suit back on and power-cycling it, its systems are entirely switched off right now and booting up the power takes more than just keeping it running. 

The stars are very bright - at least, to Merrin's darkness-acclimated eyes - and very beautiful, and there are no recognizable constellations at all. 

(They do not actually shed much useful light - she can't super see her own feet - but she can see the shadow of the tent against the horizon, and pick her way around it.) 

...If Merrin has to be in the situation of having DIED IN A PLANE CRASH - that should not have happened in the first place because the base rate of that happening is really actually very low - and then had this inexplicably result in being STRANDED ON AN EXOPLANET that seems to WANT TO KILL HER - well, the planet itself is obviously not sapient and cannot have intentions unless Reality here works really very differently than her model of Reality in dath ilan, but it sure feels like the situation has been optimized for deadliness by some kind of agent - 

- anyway. If she has to be in this situation which she hates. She is at least going to enjoy the small upside of staring at alien stars. 

...For thirty seconds. It's getting cold out here. And she's not breathing enough oxygen and shouldn't let that continue longer than necessary.

She knows exactly where she put all of the crates, and which one is primary provisions, and how its contents are arranged. It takes her two minutes to retrieve two liters of water, properly seal the box again - what if there's a dust storm? or a normal storm? - and carry them into the tent. 

- actually, you know what, first she's going to set them down right outside the closed flap and go walk ten meters away and pee. She has the camping-supply-pouch on the inside of the tent tarp and it includes a collapsible bucket but she should save the bucket capacity for later in the night. 

Arghhh there might be a rainstorm and in that case she would really want to have caught some of the rain but she. Does not, actually, have the energy to go unpack any more gear and rig up a rain-collection cistern. Whatever. She'll sleep, and wake up, and it'll still be night, and if she hears rain she can put on her armor and go out in it and do it then. The extra power usage would be worth it, for water. ...Scratch that, nighttime precipitation will almost certainly come down as snow, she'll...figure something out...if she emerges in the morning and finds a lot of pristine snow that she might be able to collect before the day warms up and it melts...

Merrin's thoughts are getting pretty loopy, and it's probably not lack of oxygen - back in the tent, her sats are only down to 90% at the point when she restores the pulse ox to her finger and switches the oxygen concentrator back from standby to lowest-rate generation, she was probably subconsciously overbreathing a little bit - it's just. That she's been awake and active for way too long. 

She manages to get at the drinking tube via the helmet of her armor suit and drink everything else in there. It'll get gross if she leaves it. 

And then she unpacks the sleeping back from its pouch, shakes it to re-expand the insulation lining fully - it packs down small - and wriggles in, and lies down. 

She's asleep in under a minute. 

When Merrin wakes up, the temperature in the tent is definitely around the freezing point. She can tell because she drooled a tiny bit in her sleep, and now it's frozen. 

Ugh. 

...What time is it. Or, rather, how long has it been. She's going to want to figure out how to reprogram her dath ilan-manufactured wrist timepiece for a longer day. She turns on the backlight to read it, realizes that she did not actually fully consciously register the time-in-dath-ilan last time she looked at it, and goes to instead switch the backlit oxygen concentrator screen back on and see how long it's been running. 

(Merrin is not, in fact, particularly disoriented about where she is at the moment of waking. Last night was very memorable, and she's pretty good at orienting instantly on waking if she...the best way to put it is "knows she's in a high stakes emergency or a training for one" and yesterday wasn't not something that smells like an Exception Handling training. It was, in some ways, not even that weird a day for Merrin. The part that takes her longer to fully reorient to, and hits her with an almost physical-feeling force, is the part where she DIED IN A PLANE CRASH and apparently the result of True Death was not in any way what she had expected and now she's here.) 

It's been 13 hours. 

The camping-gear-pouch has a temperature sensor in it. Small, low power use, non-rechargeable internal battery, runs for ten (dath ilan) days once switched on. (She has a few extra in the tools-and-power crate.) 

Merrin finds it by feel and switches it on and holds it up realllly close to the backlit oxygen concentrator screen, because the sensor itself is not wasting any power on things like a backlit screen readable in near-complete darkness. 

It's -2° C inside the tent. 

The cold isn't actually what woke her. The parts of her body inside the sleeping bag are perfectly cozy. She mostly woke up due to having slept as much as she needed even with her exhaustion going into it, and due to REALLY NEEDING TO PEE.

...Collapsible bucket next. It'll probably freeze solid by morning, won't it. At least that will mean slightly less of a disaster if she's dumb and knocks it over by mistake. 

Urgent bodily functions dealt with and a major source of distraction removed: ...what are her sats on the pulse ox? What's the trendline like?

She doesn't have the rest of her basic field monitoring suite set up, which includes both an actual small display screen and controls and also a computer that can store - well, she's never run out of memory for medical data - so she has to use the built-in menu navigation side button on the pulse ox, and she only has the what it can store in its built-in memory chip, which she had apparently last set to every-five-minutes point readings but at least she has them for the whole 13 hour period she was asleep. 

Her lowest reading was 89%, and it's a single reading with 91% on either side, it might have been sensor error. The average was around 92% and a few times it went as high as 95%. 

She in fact feels fine, cognitively speaking. Well, except for the part where sitting in near-complete darkness is making her feel less than fully awake, but she thinks her metacognition and mental math abilities and all that are working fine. Physically, she's pretty sore – she did almost twenty-four hours straight of physical labor, with the bare minimum power assist from the armor so she could stretch its battery life. 

She is incredibly ravenously hungry, which is very unsurprising, she has to be running a massive calorie deficit from yesterday.

Food is...going to be a problem...but not in the near-term. It's prooobably worth it to eat as much as her appetite wants during the initial few days when she's still figuring everything out on the fly and really can't afford to be mentally-low-energy. 

The dense chewy nonperishable complete-nutrition bar she eats is possibly the most delicious thing she has ever eaten in her entire life. 

After eating a bar slowly and drinking a lot of water and waiting a while, she's still ravenously hungry. She'll eat a second one. 

...Now how long as it been since about-sunset? 

13 hours 40 minutes!

...She should check the outside temperature. For information value. 

Merrin manages to unseal a tiny strip of tent flap, and hangs the temperature sensor out on a bit of cord. (She has eighteen different lengths, thicknesses, and stretchinesses of Small Rope in the camping-gear pouch.) 

It's about -16° C outside. 

...Well, at least that's some reason to think her insulation is effective, and will hopefully continue to be effective and keep the indoor temperature more than 10° C above the outdoor temperature? 

It's already cold enough that being even partially out of the sleeping bag is uncomfortable, and there's no reason to. There's not, actually, much that Merrin can productively do, except lie here and not die of hypothermia. 

(She should turn off the pulse ox entirely, actually, now that she's awake and she knows the reading was stable when she was asleep. Operating independently on only its internal battery, it'll last for 24 hours of continuous use, but she's already spent almost 14 of those hours and she's in "use as little electricity as possible" mode right now.) 

She stows it in a zipped tarp pocket where it won't get lost, and then wriggles fully into her sleeping bag again and lies down. 

She's boooooooooooooooored. 

This is not, actually, a problem that Merrin is used to having! At all! 

Most dath ilani have a higher need for novelty and cognitive stimulation than Merrin does, and have less stamina. She actually almost never has the "bored but too tired to do anything sufficiently stimulating" problem. And her life is stimulating! She's generally really busy. She's often relieved to spend a rest block aimlessly not doing that much. 

However, "aimlessly doing not that much" actually does usually involve reading (easy) material about topics she finds interesting, or looking at cool pictures, or text-chatting with friends. 

Apparently, actually doing nothing, while fully awake, with an unknown duration of darkness and boredom ahead, and with a lot of problems to solve that feel urgent and don't feel tractable to solve in her head versus by actually working on them, is not at all the same. 

Arghhhhhhh. 

Okay. She'll lie here and mentally plan out exactly how she's going to build a still for seawater desalination out of the materials she has. 

...Merrin gives in to the impatience and briefly turns on the backlight for the oxygen concentrator screen and checks how long it's been running now. 

15 hours, 53 minutes. 

She probably could learn something by looking at the stars for a while, but - long term things. If she sets up something to approximate star-trail photography, or sets up the right equipment to repeatedly measure the exact position of a bunch of stars she can reliably find, she can use that to find celestial north (or south, if she's in the southern hemisphere; she doesn't know yet, she could figure it out by unpacking a compass and checking what side of the sky the sun is on, but she did not do that.)

Anyway. If she knows the celestial pole, she just has to measure how many degrees it is above the horizon and that's - no, is that the latitude or is she getting confused about when she needs to know the axial tilt - no, the axial tilt is actually not relevant to the celestial pole, she doesn't think? It's about the angle of the axis of rotation - the imaginary line drawn between the north and south poles - relative to the sun, but the axis of rotation could exist with or without a sun present at all, it's relative to the other stars...

That's a useful thing to know but it's not worth compromising her already-pretty-questionable shelter's heat retention. 

She'll spend a while thinking about how to set up to do various astronomy measurements that would give her potentially useful data about the planet.

She can turn it into some random mental tangents - her thoughts are getting a bit weird and loopy, with all the lying-in-the-dark - which is fine, she's not trying to think on a deadline, she's just trying to pass the time doing something that isn't totally unproductive. 

....Now how many hours has it been? 

17 hours, 27 minutes. 

Chemistry! She's going to need to rederive as much organic chem as possible from information that exists in her own personal brain plus the reference materials she has with her. The reference materials have stuff that's relevant to, like, pharmacology in the context of a human metabolism, and in general are mostly quite specific to medical purposes, but it's not nothing. 

Can she recall enough of the basics to design experiments that would narrow down the composition of various samples of local plant and animal life, to determine:

1. If digestible calories are present. 

2. If poisonous toxins are present. 

She can determine seawater composition, probably, by literally just using her existing equipment for measuring electrolyte levels in human blood. ...Possibly with a distilled-water dilution protocol and doing calculations from there, she thinks that even seawater on dath ilan would max out those tests on electrolytes like magnesium. And she'll need to read the fine print in her digital reference guide to check if there are weird adjustments to make because blood has plasma proteins and seawater doesn't, from memory she has no idea. (The electronic tablet "book" to read it takes power but not a lot if the backlight is off, she can afford tons of hours of reading with external light sources for every hour of oxygen generation or suit heating.) She also has tests for heavy metal contamination. She should test the seawater, definitely, to know how careful she needs to be about swimming without a suit... 

She cannot think how to test for every possible toxin. There's just a really very large space of molecules that would be toxic to a human metabolism. 

...She can use logic to infer that the intertidal plant life is almost certainly going to be packed full of both antifreeze compounds - and heat-stress-related enzymes, to handle the temperature swings in the other direction - and UV-protective pigments. And, like, on priors weird biomolecules doing specific things like that are more likely to be toxic to her than biomolecules that just store energy or whatnot. 

To find local life that's the least likely to be full of toxins that only might be made safe with enough cooking and processing, she'll need to...go deeper underwater? The molluscs-or-whatever that are always submerged in deep water will be adapted to living in water pretty consistently close to 4° C - the temperature at which water is densest, so on a planet with liquid oceans that never freeze all the way through, the deeper ocean water will tend toward that temperature year-round. 

The tidal situation is going to make it really inconvenient to safely access further down the continental shelf. She....probably wants to do it when the tide is at its highest point, swim down the river along with the current, but if the tidal currents are strong enough she might have trouble getting back to shore until the tide turns, so that's budgeting LIKE SEVENTEEN HOURS of ocean swimming.

She can do it, if her armor is starting out with its battery fully charged, but she doesn't have 17 hours of air supply. She would need to alternate diving and helmet-open treading water at the surface. Which means she should really do it in a week or two when she's acclimatized. (Acclimatizing mostly doesn't mean her lungs will get better at extracting oxygen from the air; her bone marrow will just start producing more red blood cells, so that even a lower hemoglobin saturation still gets adequate oxygen to her tissues, which annoyingly means she can't track acclimatization just off her measured O2 sat readings, and has to figure out what measurements and subjective symptoms to be tracking...) 

It sounds kind of ridiculously dangerous, actually, now that she's thinking through the logistics. A suit electronics failure would straight-up kill her and send her to respawn on ANOTHER random exoplanet because APPARENTLY that's how Reality works

...She has plenty of time to think through the risk-benefit analysis. But she probably has to, sooner or later, or she'll run out of food and die in 45 days. 

What a productive block of thinking-ahead while lying in a sleeping bag in complete darkness! 

...Now how many hours has it been since sunset? 

19 hours, 2 minutes! 

ARGHHHHHHHHH

Merrin is starting to feel like ACTUALLY the greatest hazard of this planet is that at some point she will LITERALLY HAVE A PSYCHOTIC BREAK triggered by SHEER AGONIZING BOREDOM while she's trying to wait out the e n d l e s s night.

Merrin is at this point really, really tired of trying to reason through critical survival-related problems while she feels like she's floating in a causally isolated sensory-deprivation bubble. 

She's just going to lie here replaying the plots of the last eight media series she's consumed over several years in her head. 

NOW HOW MANY HOURS HAS IT BEEN

21 hours 33 minutes!

She's still not freezing in her sleeping bag with the hood up and zipped and only the ventilation slits letting in the ambient air, but when she emerges to check the oxygen concentrator screen, it's now feeling really pretty cold. 

....Temperature sensor check? 

Inside the tent, it's now down to -13° C. 

Outside the tent, when she checks that again, it's -24° C. 

Ugh. Still warmer inside than out, but by a somewhat smaller margin. She really needs to optimize her shelter better. That and water. And acclimatizing so she can breathe the air. And heat that doesn't use electricity, there's got to be something here she can turn into fuel and then keep warm with a CAMPFIRE like some sort of PREHISTORIC ANCIENT HOMINID. 

She curls all the way up in her sleeping bag again. So far it's holding up just as well as was promised in the specs. She has a brief silly urge to write a nice review, which of course she cannot do because she's NEVER GOING HOME. Unless Reality is even weirder than she thought, but...she died. She definitely died. It came as news to her that this resulted in respawning on a random exoplanet, but...she doesn't, actually, see how it could physically work to get home from here. It kind of seems like the best she can do, if she's also lucky about the existence of digestible calories in any local biomass, is eke it out for a year or two until she either dies of some sort of essential amino acid or other micronutrient deficiency, or fucks up from the starvation-related cognitive impairment or isolation-triggered psychosis and has a fatal accident. 

And then, maybe, this happens again? Merrin has no idea! 

...She's going to think about something else now, actually. It's really depressing, and Merrin is not a Keeper and does not have the mental discipline to think about incredibly depressing things and not have it screw up her brain. Which she needs. To survive as long as possible. 

Look on the positive side! While she's slowly running out of the essential micronutrients available from her limited dath ilan-sourced food, she might have the opportunity to learn some really cool biology facts about the alien life here! 

Time for more replays of fiction in her head. 

She's going to mentally draft an entire fanfiction of that one story she liked that one time. It's already got characters going through interesting life-changing experiences and fun clever problem-solving and an interesting adversary and a romance, but WHAT IF she added a totally unnecessary medical emergency. What if she added THREE extraneous random medical emergencies, at this part and that part and that part... 

Maybe she needs to invent an alphabet she can mark in wet clay tablets to reread by touch, just so she can write stupid fanfiction to avoid going INSANE during all the nights she's going to have to wait out. 

...Orrrr she could figure out how to make a light source that doesn't need electricity! She actually totally knows how to improvise an oil lamp, and surely some organism on this planet produces flammable oil. Actually, come to think of it, the intertidal plants probably produce a ton of long-chain waxes of some sort, she noticed their outer surfaces would dry out into a waterproof leathery skin and retain the moisture underneath. She can scrape a whole bunch of the various sorts of biofilm off rocks and...boil them? And render out the wax into a semi-purified form, and then test if it burns clear enough to use as a candle. ...She shouldn't do that until she's fully acclimatized and also has some kind of ventilation system that doesn't compromise the heat retention of her shelter, fire will use up all her O2 and she needs that. But later. It's a possibility! 

Eventually, she does drift off to sleep again, half by accident.

The last time she remembers checking the time, it had been 24 hours and 49 minutes since she started running the oxygen concentrator at around sunset. 

She is eventually woken by the fact that it's now -23° C inside the tent! And the highly optimized sleeping bag is doing a really very good job of trapping her body heat and preventing her from becoming hypothermic, but she is still eventually going to be shivering. 

Oh no. In order to check how long it's been now, she has to. Let one of her limbs leave the cozy enclosure of the sleeping bag. And let in a ton of cold air! Merrin doesn't wannnnnnnnna. 

...She's gonna, though. If she can't get warm again afterward, she had a plan for that, that's why she has the backup suit battery in here already. 

It's been 30 hours and 37 minutes since sunset-ish! 

There is absolutely no sign of outside light. (Well, probably the stars are still in the sky, but her heavily insulated tent with all its extra reflective-blanket lining also serves as highly effective blackout curtains.) 

If she checks the exterior temperature again, she'll learn that it's apparently -32° C. Her tent insulation is working! The gap between the interior and exterior temperature is narrowing but only very slowly! 

Mrgggggh. 

...Merrin is really cold. She tries burrowing back into the sleeping bag and sealing everything except the ventilation slits and she's still really cold. 

Fine. Time to PEE in a BUCKET on top of the existing partially-frozen pee in the bucket, and drink a bit of water, and then stuff herself back into her power armor and turn on the heating. 

At this point there's an argument that she might as well go stargaze, but the suit will still burn more power if she's heating from -32° C rather than just -23° C. And also if she's walking around. (She can turn down the power assist pretty far to stretch the battery life, if she doesn't need to move fast or carry extra weight, but it's literally heavier than she is, weight-optimized or not, she cannot actually walk in it without the servos active.) 

Merrin switches the oxygen concentrator off. And overrides a bunch of warnings to turn her suit-air-supply target O2 percentage down to 18%. She is, after all, trying to acclimatize, so she should be taking gentle steps toward that, and she'll still need to switch her suit regulator to use oxygen from the storage canister if night goes on too much longer, but she can at least put that off. It'll be annoying. 

She tests whether she can actually fit in her sleeping bag with the armor on, to reduce the heating needs. 

She can! Which makes sense, she has literally crammed herself plus another person into this sleeping bag at some points in the past. 

Merrin will lie here and try to develop on the spot some kind of mental discipline that would let her not experience boredom as suffering quite so much. Probably Keepers are capable of not experiencing "no external stimuli" as literally more unpleasant than physical pain.

(Possibly Merrin is a bad test case for that comparison. Wow, she's really going to start missing her boyfriends after a year of this. Alternating life-threatening stress with interminable boredom, and then combining that with a complete lack of sadism in her life ON TOP of the complete lack of, you know, any other human company, would not have been something Merrin chose to opt into.) 

Merrin ends up spending a while scheming how to dissect one of the emergency blankets in order to sew the reflective lining to her rain poncho and make UV-proof robes for eventual daytime operations not in the suit. It'll work fine in cold weather, is the thing, the part of the morning when the UV is already high but the temperature is still on its rise, but for afternoons she either wants something breathable - she can turn medical gauze into textiles, maybe? and dye it a lovely purple with boiled rendered local-biofilm-wax full of UV-protective pigments? - or, possibly, she just wants to avoid being out in the open at all in the peak-UV period and instead take a nap. She's going to need to sleep at least twice per "day", probably, unless her underlying circadian rhythm turns out to be wildly more adaptable than she expects... 

She also spends a while playing around with body-awareness meditation and trying to see if she can lower her own heart rate on purpose, she thinks this might be in theory trainable but she's never had to wait out a more-than-thirty-hour night with no reading material and so she has never experimented with it. She also, eventually, spends some surprisingly long periods of time not thinking much at all.

And eventually there's faint light leaking through the ventilation-mesh strip around the sealed tent flaps. 

...How long has it been since sunset now? 

36 hours, 12 minutes. 

...It's going to be really cold out, but Merrin does still want to duck out for a few minutes and see the world. 

[AUTHOR’S NOTE: imagine the tide significantly higher than this, the image model did not want to oblige me on that]

…It is beautiful. 

It’s so quiet. Even the ocean isn’t making much noise, right now, the flow is very smooth - the tide must have turned a few hours ago - and for the moment there’s barely any wind. - the silence is kind of uncomfortable, really, as a reminder that she’s not just the only human on this planet, she’s the only terrestrial life form larger than a worm.

Merrin sets up the solar panels. They won’t produce anything yet, but the sun will be up soon, and this way she’ll be able to stay inside and conserve heat while the sun comes up and the auxiliary batteries start charging. It’s not going to get above freezing until late morning, and “dawn until late morning” is all day by the standards of a day on dath ilan.

She goes back into her tent, seals the flap, and gets back into her sleeping bag to save on suit-heating while she thinks about her morning plans. 

…Where’s her battery life at, actually? Both the suit and the main battery unit?

She ran the oxygen concentrator at the lowest setting for 30 hours, since she did turn it off when it got too cold to stay in the sleeping bag. Running the equipment while cold drains the battery a bit faster, both via the equipment drawing more power and the battery holding charge a little worse; she’s down to 3100 Wh in her primary storage. 

Her suit main battery is still at 10%! She ran it for six hours, but she was only heating from the temperature inside the sleeping bag for most of it - the wrist temperature sensor trend-history thinks it was initially around 1 C and eventually trended down to around -4 C, nowhere near the -33 C that the interior of the tent is down to. (Outside was, apparently, -40.2 C, during the few minutes the suit was out there to read it.)

Her suit is very close to out of its stored compressed oxygen, though.

She can fix that! The protocol for refilling it directly from the medical oxygen canister already exists, she doesn't need to do weird improvisation for that. (Usually that backup oxygen is for patients, whether real or simulated, but Exception Handling did prepare her for the scenario where, instead, she's surviving a weird dangerous situation on her own.) 

...Aaaand she should go dig around in the biometric data in the suit memory to see how she did on 18% oxygen for the last sixish hours. (She also has biometrics for the entire day yesterday, and hasn't looked at them at all mostly because accessing it entirely via the wrist panel is annoying and she was very busy, and not actually worried about her own vital signs.) 

She sure did do a lot of intense exertion yesterday! Tons of very high heart rate measurements. 

She's been doing fine on 18% oxygen. O2 sat reading mostly at 94% and 95%. Admittedly she was lying still not doing anything for most of that, and it did drop to 93% when she was briefly up and about. Her heart rate stayed low while she was resting - well, higher than her usual resting heart rate while asleep, mostly between 63 and 68 bpm rather than in the low 50s, but she was awake and probably worrying on and off, and she had a very intense and very long day of exertion yesterday, that would fully explain a slight rise and it doesn't look like her cardiovascular system is being additionally stressed by insufficient oxygen from trying to acclimatize too fast. 

Okay. Good.

Merrin doesn't have an urgent sameday deadline, today. She has tasks, but it's a marathon now. She's going to leave her suit at the fixed 18% – which will be an adaptive usage rate, she'll still burn more oxygen if she breathes faster due to higher metabolic oxygen needs from exertion and the suit will top up faster to compensate, but if breathing faster isn't cutting it, she'll just have to notice and slow down.

And she'll analyze her biometrics at the end of the day and if it's going okay then tomorrow she'll drop it to 17.5%. Half a percent drop per day - per local day, which she's estimating at 64 hours - means she'll be down to 13.5% in nine days. That's - calculator math she doesn't need to tire her math brain out for no reason - that's 24 "normal" days. Not unreasonable at all. She might even try going faster, if she can get to a point that she's not needing to push herself quite so hard with survival-critical tasks. 

So far she's been here for one day and she's used most of the 500L suit storage. (Huh, neat, she can calculate that it was averaging out to 0.25L/min suit usage, though of course the vast majority was yesterday while active and running at 21% oxygen, taking the the last six hours specifically it was more like 0.15L/min, so definitely more efficient than the concentrator and nasal cannula. Possibly enough efficiency gain that she should be wearing her suit as much as possible even if she's wearing it lying down in her tent, and eat the cost of running the medical compressor to refill its tanks, but guess what she needs to do MORE MATH to check...) 

Anyway, if she takes "about 0.25L/min" for granted and averages that over the entire 64h day, she needs...960L. (In actual fact she's used a total of 1400L, because for 30 hours of the night she was getting it direct from the oxygen concentrator with more waste.) 

She does not have that much right now. She has 400L in the compressed-oxygen canister currently being transferred to the suit tank. (Most of it, at least, eventually the pressure remaining on the canister side will drop low enough that it doesn't push through the system of one-way valves, and the rest is only usable the normal nasal-cannula way.) 

Mrgghhh.

WHY DO ALL OF MERRIN'S PROBLEMS REQUIRE MATH TO SOLVE.

...There is, at least, enough light in the tent now to write by. She can do math on PAPER. 

Okay.

While she's busy breathing the 400L of oxygen in her suit tank, she needs to generate another (slightly less than) 400L to fill the now-nearly-empty storage. How long will that take.

...Depends how fast she runs it. Normally - in hospital conditions, say - the power usage is supposed to be closer to linear, but running it in cold conditions means it's also spending power on not freezing solid - it's a smart system, it can run fine with an ambient air temperature of -30° C - but when it's doing that, it's substantially more efficient per-L-generated to run it fairly close to maximum. And of course she'll also have to run the compressor, which doesn't vary much in power usage based on how "hard" it's running, it's pretty close to a 150 W draw regardless - and she can't cycle it on and off, she has nothing set up to reliably and fully capture uncompressed oxygen for later compression and then make sure none is wasted. And the compressor uses...almost as much power as the oxygen concentrator at its maximum, and significantly more than the concentrator at lower power. So she really should be doing this as fast as possible. 

At 4L/min it'll take - exactly 100 minutes to fill the canister all the way, or realistically a little bit less since it's going to be 10% full already. Call it 90 minutes. That's 300 Wh for the oxygen concentrator at max power and 225 Wh for the compressor. 525 Wh total. ...Round up for cold-related inefficiency, she has never actually tested running this particular setup with temperatures this cold.

Call it 600 Wh. That leaves her at 2500 Wh in her main battery, from 5000 Wh starting out. 

...She is fundamentally just not going to get solar power production keeping up with that rate of usage. Maybe she'll get as much as 1000 Wh over an entire long sunny day. 

(Key question: it's winter, she thinks, but is it before or after the winter solstice? If the days are getting shorter, she...has serious problems, even if they're not as serious as the problems she eventually expects to have in summer. If the days are already getting longer and the sun's arc is already getting higher, then the summer heat problem is that much more imminent, but her near-term power generation problem is more tractable.) 

Ugh. 

Okay, ignore historical data i.e. what she used yesterday and overnight. (The answer is "approaching 4000 Wh", between nearly-draining her power armor battery and using 40% of the even larger main storage battery. It's a bad answer.) 

She needs about 1000L of oxygen in 64 hours. (Less, tomorrow, if she can keep weaning herself down.) 250 minutes of running the concentrator-and-compressor, that rounds to four hours, which is 1400 Wh. That's not (very) negotiable. 

She knows that the maximum power draw on her suit is, like, 500 W, but that's normally for very brief periods – sprinting, jumping, using the various powered swimming modes at top speed. It's very, very optimized for power efficiency, honestly moreso than her medical equipment. It's packed full of electronics, but those don't use much power at all compared to what you need to concentrate oxygen out of the air and squish it into a canister at very high pressure, and she spent a lot of yesterday using the absolute bare minimum of its mechanical-assist functions. She ended the day with a little over 20% battery left, so she spent 1600 Wh over the day, which somehow only averages out to 60W, and then 200 Wh (averaging to 28W) over the last coming-on-seven-hours of not doing much except breathing and declining to die of hypothermia. 

(Wow, her power armor is incredible technology. Walking around in it takes like 1/6th the power draw of refilling her oxygen cylinders! Merrin has never been so grateful for the sheer ridiculous quantity of engineering optimization effort that went into that in particular. ...Would be nice if the same were true for her other equipment, but in fact it's optimized for very reasonable things, probably, like "lightweight" and "unlikely to have mechanical problems" and "not exploding if dropped with a lot of force".) 

If she hooks up her backup battery (400 Wh), she can do about 10 hours of activity matching yesterday's profile - though some of that was breaks, the actual carrying period must have been higher - and then she's out. She already needs more than her solar power generation can keep up with just to get enough air to breathe. 

...She has problems, doesn't she. 

Okay. 

There are two strategies she can take, here: 

1. Hunker down and recalculate and find some way to get her needs down to only a bit more than 1000 Wh. Hope she can eke away at it and get to something sustainable before she runs out of the stored power she arrived with.  

2. Leverage her remaining stored energy into one more frantic day of fixing her situation, or at least improving it enough that tomorrow will be survivable on just solar power. 

She really, really needs shelter that isn't stupid. Where the geography is cooperating with her needs. If she can find that, and set up a shelter that retains heat well enough that she can survive in just her sleeping bag through the nights, she can actually hunker down for a while until she can handle a normal activity level breathing 13.5% oxygen, and then make steady progress from there with more minimal use of her power armor. 

....She needs a still first. And to fill the saltwater reservoir before the tide impractically far out and she has to climb for ages to haul water up. It's still cold out, but she can afford some amount of suit heating today, and she probably can't afford to waste more of her limited daylight. 

It's not complicated to make a smallish and not-perfectly-efficient setup, and she mentally planned it out enough during the endless night that executing on it takes minutes. She has a collapsible water tub that can hold 100 liters; she sets it up on a smoothish patch of rock. She also has a lightweight cooking pot that holds 3L. It goes in the middle. She has a bunch of tough waterproof plastic sheets, though "a bunch" is not nearly as much as she wishes she had, given the incredibly versatile usefulness of plastic and the fact that it's practically free to manufacture in dath ilan and impossible here. She has adhesive sealant strips that are "reusable" though only, like, a dozen times before they've picked up too much dust to re-stick well.

The annoying part is hauling water up the stupid valley side. It's a slope, not a cliff, and walking up isn't too bad, but walking down with too little cautious risks a tumble dropping her directly into the fast-moving current. It's probably only 15m of elevation but each trip is still taking a while.

(She does take the opportunity, on her first trip down, to rinse out the removed suit drinking bladder with seawater. She'll want to clean it more properly than that before drinking out of it again, but at least the gunk from the meal replacement shake won't get any more glued on or start to mildew in there.) 

She fills the tub to maybe 10cm deep. ...At which point it occurs to her that she should really stash it in her tent, which is warming up much faster than the ambient air as its insulated walls absorb heat, it's still well below freezing but the water probably won't freeze into a block of ice before the sun is hot enough to do any effective evaporation. She hauls it, with careful effort, and manages not to spill any, and then she places her pot inside in the middle - weighted with one of her stainless-steel metal tools at the bottom so it doesn't try to float, she doesn't know the local composition of the rocks or if she wants to risk any of it leaching into her drinking water. 

She uses a small rock from the ground to weight the middle of the sheet so it's pulled down in an inverted cone with its point over the pot. In theory, condensation will tend to trickle down and drip from the cone's point into her collection pot, though she'll lose some that will just drip right back into the seawater at the bottom. 

And then it's time to equip herself for a little sortie, and EXPLORE. 

Merrin packs another liter of water in her front pouch. ...She should probably actually be drinking more than she is, she's consumed 5 liters in...two and a half days, by dath ilani reckoning...which is less than the 2.5L/day minimum for an adult woman her size, and a lot of that was with high activity levels though she at least wasn't sweating much in the armor. The frozen pee in the bucket is a very deep yellow color, but she doesn't have a headache or feel lightheaded, her body seems to be coping with mild dehydration. She'll see how much drinkable freshwater she can get today with her stupid un-optimized still. 

She sets up the oxygen concentrator and compressor to start filling the now-mostly-empty O2 tank. She should be back in an hour; if she's not, the concentrator should detect a blockage once the compressor detects sufficiently high pressure and switches itself off, and it should switch itself off in turn. 

She makes sure the auxiliary suit battery is seated properly. (With it properly snapped into place, the seal should be waterproof, though she always feels like she can notice the change to her streamlined silhouette. The primary oxygen tank and battery are bulky as well as heavy, but the armor is custom-fit to her and the bulky necessary storage is smoothly incorporated into the suit's back.)

...She checks on the solar panel output. 

The sun is still at a low angle in the sky. Even with the panel tilted optimally, she's getting, like, 7W. 

OH RIGHT ONE MORE THING she's gonna spend fifteen minutes improving her sundial measurement apparatus, and improvising a sextant – she doesn't carry one with her supplies, anymore, since she knows how to make one out of general-purpose making-stuff supplies which she could in a different scenario with different needs make into something else.

She measures, and writes down as accurately as she can - it's not gonna be super accurate - the altitude angle of the sun in the sky, and then her even-less-accurate best guess of the azimuth angle given that she did not actually mark the spot where the sun first appeared since she was at that point hiding in her tent. She adds the exact time in minutes-since-dawn, realizes that she's stupidly wasting mental math capacity on generating that from the suit clock time-since-switched-on, and figures out how to manually change that to the actual estimated time since dawn (78 minutes, somehow she's already spent over an hour of her 28 hours of daylight...) 

There. She should be making regular trips back to this base camp today, she'll keep taking measurements, and then she'll have a baseline to compare tonight and judge if the day is getting longer or shorter. 

And NOW she will actually go explore her exoplanet surroundings! 

It's a plain of sedimentary rock – probably mostly limestone, it looks like, and definitely a kind that's partially soluble in slightly-acidic water and thus easily weathered and eroded by rainfall drainage.

No real mountains in view, just sort of rippled undulating hills. 

The lichen-like biofilms are tenacious, clinging to the rocks despite the current lack of any moisture whatsoever. The area clearly gets rain, to cause all the fascinating erosions patterns, but it's very unclear when it last rained. Maybe the lichens get some water from the humidity in the air, during the periods when the enormous intertidal zone is wet and exposed to the peak heat of the sun. 

The lichen - it's probably not technically a lichen by the dath ilani biology definition, which is a whole complex and specific symbiosis and who knows if this planet even has three distinct evolutionary branches for "plants", "animals", and "fungi", but whatever - anyway, it's got to be, like, 50% UV-protective molecules by dry weight, to not get all of its DNA-or-equivalent completely shredded by all those long endless days with zero shelter from the sun. 

Promising to boil into a dye and treat a bandage-derived textile to make herself a UV-proof robe? 

...That's a later priority. Merrin keeps walking. 

There's an area where wind and rain has eroded the stone in taller spire-like patterns! Not really tall enough to provide shelter, though, and it sure is a hint that this particular spot is perhaps subject to high-force driving winds during storms. 

And a bunch of them look like they're ready to fall apart the next time they're subjected to those forces. It's eerily beautiful, and Merrin takes a moment to savor the view because if she DOESN'T let herself indulge a little bit in the few parts of the situation that are fun and cool then she will GET REALLY DEPRESSED and MAKE POOR SURVIVAL DECISIONS. But it's not a good place for a camp. 

On her walk back, she finds a sinkhole! 

They're a pretty common feature of land like this. The water-erosion happens underground, too, the whole area is probably riddled with underground rivers - at least in the rainy season, if rain is strongly seasonal - and you get caves with awesome stalactites and stuff, and then sometimes they get too big and the ground above can no longer hold up and it collapses into a pit. 

This one doesn't appear to still connect to any cave systems. Judging by the water-marks on the inside, it does flood at the bottom, if not with every tide then at least at some point seasonally. 

Nothing usable yet. But there are promising signs! A sinkhole would do, she just needs to find one that's on slightly higher ground and has clearly been dry for at least the last few decades.

Merrin walks the rest of the way back to camp. She's been pausing to take notes, checking the angle of the sun to get an approximate sense of direction to draw a map. 

...It occurs to her once she gets back that she's very silly. She had been assuming that her suit location records would be completely useless because the GPS obviously isn't getting any kind of reading. 

But her suit does, also, have a backup magnetic compass, and inertial reference tracking software. She's literally done training scenarios where she had to turn off all the external-satellite-uplink functions because ""the entire planetary satellite network had gone down"". The magnetic compass is less reliable, it'll be thrown off if there happens to be a whole bunch of iron ore nearby, and also it is not necessarily even very close to the rotational axis of the planet, but she hasn't been covering enough distance for it to be likely that the reading is all over the place. 

Accessing the inertial "map" of all her activity since she turned the suit on for this "training scenario" is going to be incredibly frustrating on her tiny wrist panel screen. It miiiiight, in fact, be worth turning on her actual electronics for this, briefly, so she can copy stuff onto paper. Probably not now, she'll keep doing an approximate map, but later on she can fix all the angles and distances on it to be close to exact. 

...It is easy to pull up the compass reading. The sun is angled on the south per the magnetic compass readings. She already knew she would have been in the "northern" "hemisphere" if this were dath ilan, from the angle at which the sun's arc is inclined, but now she also knows that this planet rotates the same way, and that the magnetic pole isn't wildly off from the rotational pole; it won't match exactly, but with her shitty measurement setup she can't pin down the difference yet. 

Neat. Now she can navigate in cloudy weather, if for some reason she has to do that. 

It's now 2h57min after dawn. Her oxygen cylinder is full and the equipment has nicely switched itself off.

The outside temperature is already up to -29.9° C. The temperature inside the tent is warming even faster; it's just -6° C. The water in her tub has not at all started evaporating, unsurprisingly, but it's also not frozen. 

Her solar panels are now generating 13 W. The 500 Wh auxiliary battery they're hooked up to still has tons of space, of course. 

She has plenty of O2 and battery left on the suit. Walking around unladen on mostly-flattish ground didn't require too much power assist, even with the higher gravity, but it did give her enough of a workout that the suit detected her starting to sweat and turned down the heating, which BOTH stretches the battery life AND minimizes water loss from sweat. Super convenient, that.  

Time for further exploration and adding to her map!

(After quickly putting down another data point for the time and sun angles, for later analysis.) 

Another trip back and forth, with a water break in the middle. (It's actually really annoying not having the suit bladder in usable shape, she has to unseal the helmet to drink.) 

Meal break back at camp. 

Another trip. 

More notes. 

Back to camp. 

It's now been 6h since dawn. (Less than halfway to solar noon; the sun is still not actually that high, though the bright, unobstructed, too-bluish light makes it feel like it's closer to midday than it is.)

The outside temperature is up to -18° C; a glance at her suit analytics would show that today seems to be trending a little bit warmer than yesterday. The temperature in her tent is above zero. 

The tide is now down to around how she remembers it yesterday. 

Her solar panels are getting 24 W. She's banked a total of 80 Wh so far today. 

And it keeps feeling like she's getting close to halfway through her daylight and she ISN'T, she has 22 HOURS LEFT, she is in fact only TWENTY PERCENT of the way through today. 

...She should attempt to retrieve her box of backup supplies, rather than leaving it to endure ANOTHER tidal bore. Maybe it's still down at the bottom of the river channel? 

She might as well not cut it too close to low tide and the turning point, to avoid more STRESS. She can just wait, like, another couple of hours until the tidal waterline is solidly below her landing point. 

Time for another walk, then! 

Sinkhole that clearly drains rainwater into an underground cave system, dry now but layered with water-marks. 

Weird maze of deep crevices. Very cramped, very easy to get lost in if one did not have a magnetic compass and inertial reference navigation software. 

...They go on the map. 

Water break. Pee break.

Power and oxygen check? 

She's been drawing about 45 W on average with the armor, and is down to 330 Wh remaining between her main and auxiliary battery (there's some kind of smart pick-where-to-draw-power switch that she doesn't understand the engineering behind, to minimize draining any of the batteries fully.) Naively, that means she can do 7 more hours and then she's out of juice. It might be longer if the heating needs drop as the temperature warms, though. 

She's breathed about 70L of O2, out of 400ish in the tank, and indeed her suit thinks she has about 325L left. The math predicts 27 hours remaining. The tank is still too full for it to make sense to transfer her current full canister and fill another. 

Okay. She in fact flat-out doesn't have the option of exploring all day; at some point she'll have to return to base, park herself beside the solar unit, and recharge the suit directly. Maybe she can take a nap at the same time, she doesn't really want to stay awake for 28 hours straight again. 

But, for now, she has power and air to spare for a trip down to the river to check if her crate of supplies is intact. 

She picked a good time for it. The ground is still frozen solid and everything on the surface of the rocks is pretty well dried out. 

An hour later: yes! it is! 

It's a little dented, but it's spare consumable medical stuff, none of it is, like, flammable or super fragile. 

The knots on the rope - and the knots on the seaweed - have been drawn tight enough that there's no possible way she's getting them untied. She'll have to cut them. She'll have a bunch of really short bits of paracord rather than one longer piece, which is less useful, but oh well, it's not like it's useless, and it's a worthwhile trade for the supplies.

...She'll probably kill this entire seaweed plant in the process, she entangled basically all of its fronds in her paracord. Well, she might as well harvest it and carry it up with her. Come to think of it, what actually happened to the one she harvested yesterday - she can't remember if she thought to secure it, she was so tired, so it could easily have blown away overnight. 

She should name the particular plant, there are going to be lots of "seaweeds" and naming something is a good way to start keeping a distinct mental bucket for it. Strapweed? That sounds stupid. Strapwrack? ...Okay, sure. 

Back up the stupid valley walls, wearing a whole lot of 3m and 4m strapwrack fronds draped over her suit and attached crate in various ways. 

That was a little more power-hungry and oxygen-hungry as an adventure. 2 hours 40 minutes, and she used almost 140 Wh on the suit and breathed 39L of oxygen. 

It's now been almost 9h since dawn. It still isn't that close to noon. The outdoor temperature is approaching 0° C.

Inside the tent is almost 20° C, and there are drips of humidity starting to ooze down the inside of her sill. 

Her solar panels are producing almost 40 W now. She’s banked 175 Wh. 

Redoing the calculations: she’s got 4 hours of suit power left, give or take. That’s the limit, not oxygen.

She kiiiind of suspects that once she stops moving she’s going to be stationary for a while. Might as well squeeze in one more exploratory hike before she takes an afternoon rest-and-literal-recharge break.

That shadow off in the distance might be promising…

It is! This sinkhole has a shallow slope into one side, filled in with packed gravel, and the other end is an actual overhang.

The cavity shelterer beneath the overhang isn’t huge, maybe four meters wide, two meters high, and one-and-a-half meters deep. …But it’s entirely below the grade of the plain, the sinkhole itself is at least four meters deep.

The giant slab of intact, uncollapsed stone forming the overhang had, at some point before the cave ceiling ahead of it collapsed, been eroded by a subterranean river into a natural arch shape. It’s cracked and bleached on the surface, like everything else, but it looks plenty stable.

The water-erosion was probably many millennia ago, and this part of the plateau has since been pushed upward by some geological force or other. It’s near the top of the local undulation, with no particular sign that it’s harbored more significant water flows that the rain falling directly into it in the last thousand years.

…The dark band at the base of the sheltered arch is not, on closer examination, actually a layer of different-colored stone. 

It’s a narrow crevice - no, a tunnel. The faintest air movement wafts near it. This sinkhole does still have a connection to the deeper network of limestone caves.

Merrin might be in love.

…With a cave. That’s kind of a silly way to describe it, isn’t it.

But this cave might well save her life every night from here on out, until such point as something else kills her.

She should really scope it out for hidden flaws before getting all attached, but…welp. She’s already attached. This cave will be her REPLACEMENT BOYFRIEND. It’s a deeply inferior replacement but at least it feels cozy and safe.

…Merrin is being very silly right now. But this is the first moment of genuine uncomplicated joy she’s felt since she DIED IN A PLANE CRASH. And, you know, who exactly is going to stop her from indulging in some emotional silliness? The Moon?

She trudges back to her camp, beaming to herself and already imagining exactly how she’ll set up her new out-of-the-wind, half-underground tent.

It’s been 10 hours and 35 minutes since dawn. 

The temperature is rising rapidly now. It’s already 10 C outside. 27 C in her tent.

Her solar panel output is up to 51 W. She has 252 Wh stored.

...It is pooossible that Merrin did not. Perfectly think ahead over her needs for the entire day. 

There are two ways to set up the multi-configuration tarp for her shelter: shiny side in, to stay warm, and shiny side out, to stay cool. For obvious reasons given her concerns last night, the shiny side is in right now. And there is not a super-easy standard protocol to flip it inside out without taking it apart, because on dath ilan you would not normally need to switch rapidly; either it's winter, and you're mainly worried about cold, or it's summer and you're worried about heat. 

She's storing up a ton of heat in her tent, and it'll be great twenty hours after sunset, but for right now she...is not going to be able to rest comfortably in there. Solar noon will be in three or four hours, the actual outside temperature will peak another couple of hours after that, yesterday it stayed pretty high for most of the afternoon and only started dropping more quickly after nightfall, and for that entire period her tent is going to be practically a furnace.

...You know what she should do, she should remove the big main storage battery right now. It's not great for holding charge for it to sit in temperatures above 30° C, she's supposed to Avoid That, and also she should probably only charge her suit part of the way and then just charge the main battery directly. It's sliiiightly better at holding charge than the smaller lighter batteries. 

When she's in the tent, she has the chance to notice that the bottom of her freshwater-collection pot is wet. There's not much standing water, yet, it's maybe 10 ml total, but the interior of the plastic is now continuously dripping condensation. 

...In a little while Merrin is going to dig a pit to set up a second still out here. It's working but she's getting quite low on drinking water and she has a very long night ahead of her. A long time ahead of her, admittedly, nightfall is still at least 17 hours away if she counted yesterday right, but she still doesn't want to make her bet on getting a liter to drink this afternoon and another two liters for the night. She's definitely not optimally hydrated, right now, which is admittedly convenient when peeing is a whole complicated thing. (She's avoiding just peeing in the suit absorption pad, since she does have slack to do the really annoying thing instead and she is, at some point, going to have to painstakingly clean and dry the stupid pads for reuse.) Anyway, it might be convenient but it's not, like, great for her organs long-term, and is generally best avoided. 

…For now she’s going to take a break from the suit, actually, to eat and pee and just…not be wearing power armor…it’s not that it’s uncomfortable, it’s very well fitted, but she does start to get tired of it after a while. And it’ll charge a bit faster if it’s not running while it charges, and she can sit with a pulse ox probe on her finger and see how long she can go before she feels unusually stupid. 

The air temperature is lovely, actually, however brief that’s going to last.

…Now seems like a good time to retrieve her multipurpose foldout screen for viewing digital materials, download all of her suit data to her main computer storage and wipe the suit memory (it’s not unlimited and will start erasing earlier recordings to make space after about 150 hours of use, which at this rate won’t take much longer to reach), and then, while the armor charges from the solar panels, she’ll pull up her route data as a map and recopy her hand-sketched approximate map with the correct distances and angles.

This is strictly speaking more effort than she needed to put into hand-drawing her map, it did not need to be an art project that somehow took her over an hour and it's possible she's just a little spacey with her pulse ox reading persistently at 89% and fugued on it. But, consider: it's preeeeeetty. 

[AUTHOR'S NOTE: length of distance arrows on the grid scale is REALLY borked, the written numbers are the correct ones.] 

....Suit back ON, for the O2, and she'll give herself 21% for fifteen minutes before turning it back down in case it unstupidifies her. 

(It doesn't actually seem to do much, so maybe it wasn't that. There are honestly a huge number of reasons why she might be in a weird headspace right now, from "this is a lot of social isolation for her, actually" – it's very rare that she does a sim with no radio backup that lasts more than a single dath ilan day – to "she's really stressed about the exoplanet trying to kill her and is missing all of her usual stress-relief humans", to "she DIED in a PLANE CRASH and that's probably traumatic or something.") 

Where are her numbers at. She has so many numbers to track but at least they're finally maybe sort of starting to become intuitive like vital signs. 

12 hours (and 5 minutes) since dawn. Rechecking the angle of the sun and doing a coordinate sketch of her measurements so far, it does look like solar noon will plausibly be in about two hours, which checks out for a 28-hour day. 

It's now 16.6° C outside, with a soft gentle breeze wafting up from the ocean. 

The temperature during her suit break was perfect, though she is realizing, belatedly, that she should really have been more careful to keep her hands out of even indirect sunlight. She was wedging herself into the shrinking patch of shade side of her tent, and she was still wearing the undergarment that goes with the suit which is pretty full-coverage and she grabbed a head and eye covering, but somehow hand sunburn did not occur to her and she did not have the backs of her hands covered the entire time. 

Well, the damage is limited now, and she'll have to remember that the UV here is not comparable to a "high UV" day in dath ilan. 

Her solar panels are getting 72 W now, and it's still rising. She's not going to be able to refill her suit battery even if she sits here all day, but every additional hour of being plugged in buys her another hour of active work (she's only net getting maybe 50 Wh in an hour now that she's running the air and basic monitoring and climate control, even if it's not needing to do any cooling for her yet.)

...She can walk far enough with the power armor still plugged into charge to peek into the tent. It's 38° C in there, and the pot inside her makeshift still now has half a centimeter of clear desalinated water at the bottom. 

...She'll make another still in a pit. She can do that without moving much, she barely even has to dig, just remove the broken rocks and gravel from one spot and pile them up in rings around that spot until she has an inverted cone. Line it with more of her precious waterproof plastic, put her eating bowl in there to catch drips... The most annoying part is carefully transferring over five liters of the now-bath-temperature seawater inside the tent, because there's no way it's worth going down the cliff again, she brought up like 10L of it and there's no way she's turning all of that into freshwater this afternoon. 

And then, apparently, Merrin is going to lie down, still wearing her power armor which is still tethered to the solar panel unit, and take a nap. She has been awake for around 19 hours at this point, and they were busy hours. 

Merrin wakes up after five hours to find her primary suit battery up to 480 Wh of charge (she has more like 600 Wh total, the auxiliary battery isn't fully drained). A glance over the analytics confirms that the solar power output peaked at 91 W, and is now descending but slowly. It looks like she will hit 1000 Wh today, albeit just barely. 

And she has work to do. 

The thing about surviving on a hostile exoplanet while completely alone, is that there is an approximately infinite queue of Tasks that will need to be Dealt With and the consequences if they are not Dealt With are lethal. 

A lot of them aren't that urgent! Many she's completely blocked on for now and can't even think about productively! But in any individual moment, there's almost always something. 

Merrin conserves suit power - no more exploration, she'll do setup at her NEW CAMP in the PERFECT CAVE tomorrow - but she is not at any point bored during the rest of that day; she has math to do, and documenting all of her thoughts and observations and plans on actual paper.

She plugs her main battery into the solar output to charge, and the 265 Wh generated over the remaining eleven hours of the day get its total charge up to almost 2800 Wh. Plus, of course, she's got the two random auxiliary batteries with awkward half-charges each, because she has NOT been organized about that so far.

Also, she has two and a half liters of water from her stills – rather, that's what's left after she drinks half a liter, after having finished all of the stored water she arrived with. This is all she's got until - realistically it's not "tomorrow morning" it's "sometime tomorrow afternoon." There are a lot of efficiency improvements on the basic design; she'll work on that once she has a permanent campsite that doesn't drop to -30° C inside at night. 

Her suit O2 reservoir is down to 60L, which would at her going rate last her five or six hours and run out while she's asleep. She ends up draining both of the half-charged backup cells entirely, plus about 100 Wh from the main battery, in order to run the oxygen concentrator and compressor and directly fill her main suit reservoir all the way to 500L. 

It's a pleasant 12° C outside – today definitely ran a little bit warmer than yesterday, though of course it takes more than one day to call whether that's a fluke or a trend. 

The tent is still a sauna inside – hot enough that her still is probably still working, in fact. And Merrin isn't desperately exhausted yet, after her noon nap. She seals the tent flap behind her to keep the heat in, because she will be glad of it at - ugh, she needs a time system for this stupid planet - at Minus Ten Hours In The Morning. 

She carefully writes down the exact time-since-dawn in hours and minutes for sunset and her best guess at the end of astronomical twilight – "dawn" is the most approximate number here, really, she was going off "the light woke her" which is later than astronomical dawn and earlier than actual sunrise, which she missed due to hiding. She'll try to catch it today, because "moment of sunrise until moment of sunset" is the single least-subject-to-measurement-error metric she can track for whether the days are getting longer or shorter, and if the sun-arc measurements point in the same direction after a couple more days, she'll be pretty confident of her result. 

And then she lies on her back on the rocky plane and stargazes. ...Actually, the simplest way to identify celestial north is to switch on the suit camera and review the footage to get the star trails. It's been off because she mostly doesn't keep it on for solo work in sims, and it's not like anyone except her will be able to use the footage, which the suit can only store six hours of anyway, video is much less compressible than biometrics and navigation vectors. 

(She has a separate miniaturized camera, packed with the medical diagnostic equipment, but it's a separate piece of electronics that she would have to power on, and besides, it's packed away in a box all the way over there.) 

Camera on. Lying still, looking at the sky. Four hours should hopefully be enough data to use later. 

It's beautiful. 

Merrin is not going to dwell on the overall depressingness of her situation. She's not. She has high baseline wellbeing, that's always been true, it's not just because her life was really great in every way and she did not appreciate how great it was until she DIED and ended up on a planet that really appears to have been optimized to kill her slowly so she can spend longer afraid of it. 

She doesn't understand the broader situation, but has she ever understood a broader situation in her life, really? She didn't understand Civilization. There was too much of it, too many people with vastly more thinkoomph than her. Really, she's never understood all the pieces of the important things, and - that's not actually what she's upset about, anyway. 

She's upset about obvious, concrete things. Never sleeping in her nice apartment in Default again. She liked her apartment. Never going on a date again! Ever! Or if she somehow does it'll be with ALIENS and then she'll be offended about how romance with aliens is a really stupid trope according to her, there's no reason for that to be workable.

She's never going to talk to her mom again. 

And she's not going to dwell on it all night and make herself miserable. She'll allow herself five minutes to notice that she's upset for incredibly reasonable reasons, and then she's going to look at the stars, and then eventually sleep. 

The strapwrack, it turns out, hardens as it dries into whatever shape it was left in, and has quite a lot of flex but snaps back to its hardened shape when released. 

Merrin isn't sure of this first thing in the morning, of course. At that point any moisture left in it is frozen solid, and she's not going to touch it and damage it while it's brittle. 

She's well-rested at dawn. She went to sleep maybe four hours into the night, slept for nine hours despite being in her armor in the sleeping bag, was awake for...a lot of hours, but at least a few of them were quite mentally productive, and she does seem to be getting used to the endless nights and was able to pass some number of those hours pleasantly in a sort of free-associating narrative-dream-logic state, thinking about fiction she likes...and at some point she slept some more, and eventually woke up and it turned out to be an hour before projected dawn. 

...Which ends up being almost fifteen minutes earlier than she was expecting. Could be her shitty approximate math from yesterday, or could be that the days really are getting longer and her near-term power generation situation is going to end up pretty good. Unless it's rainy here in spring. That would be bad. She really needs to figure out how to heat her cave by burning local biomass rather than running her power armor all the time. 

Merrin's suit is actually recharged to 1500 Wh; she left it charging from the main battery after its internal battery ran low, and fell asleep like that, and apparently had at some point set it to "charge to 3/4 and then pause". The main battery is down to 1020 Wh. 

She has 110L of oxygen left in the suit tanks - which, now that she's turned the percentage down to 17.5%, will probably last 7 hours even at higher exertion-related O2 consumption - and presumably still the last untransferable 40L or so in the medical canister. 

She sets up the solar panels - she'll carry them to the new site last, tonight, right before sunset when they're no longer generating anything to speak of - and then plans her move. 

First: packing up. Merrin had unpacked more than she'd realized; getting all the miscellaneous objects into the correct spots, and then dismantling the personal-pod tent and stowing the poles and guylines and tarp, takes two hours. 

It's about 650m from her current position to the surprisingly optimal (!!!!) sinkhole cave. The most direct route from it to the top of the riverbank might be closer to 550m.

The ground is flat enough that it's probably more suit-power-efficient overall to load herself up with the maximum four-box arrangement and make two trips rather than four. 

She takes it slow, doing as much as she can with muscle power. She's going to have to get stronger, so that once she's acclimatized to the lower oxygen, she can do the required ongoing physical labor during the tolerable-temperature windows of the day, without a suit. It'll burn more calories, but that's exactly why she needs to do as much as she can unaided, and save the power armor for the aquatic work needed to find something on this stupid planet that she can eat. ...Eat and also digest and metabolize, technically she can eat whatever she feels like but those parts are pretty important. 

Two hours later, though, everything but the solar panels is stowed in the cave. She walks back up the slope and can see the solar panels glinting in the sun, safe on the bank. The wind is slight and there's no megafauna here to disturb them. 

The tarp shelter kit comes with six standard configurations, but none of them are precisely designed to turn a sinkhole cave into an actual shelter. She'll have to improvise. 

Fortunately, the kit is also optimized to be friendly to improvisation. It might come up! With Merrin specifically it will and has come up a lot, actually! 

Merrin did a whole bunch of mental design while lying in her sleeping bag last night, and now it's time to find out how well it works!

(In the long run, she's actually mulling on replacing as much as possible of her dath ilani shelter kit with whatever she can find locally to use as building material. It'll be less optimized and less durable, but her shelter gear is not, actually specced for multiple months of intense UV exposure, and if the local materials break down quickly, well, she can just go get more. No way to get more fancy Exception Handling tarps.) 

Merrin's brilliant middle-of-the-night idea was that she doesn't need to switch which way the tarp is facing twice a day. She doesn't actually need the entire cave to be toggle-able between "day mode" and "night mode", because she's going to be spending the too-cold-to-be-out-of-her-sleeping-bag portion of the night sleeping. But she does need a larger work area that will stay a vaguely tolerable temperature for as wide a window as possible, during daylight, and it's going to become more and more true that the problem in daylight is heat and not cold. 

So: tarp facing shiny side out, in something midway between canopy and lean-to mode, joining with the hollowed-out arch to form the other half of a flattened hemisphere with the tent-flap as a "door" in the middle. This is a nonstandard pole arrangement and is actually really annoying to set up the geometry for; she totally screwed it up when working purely with visualization, and the forces were in the wrong place and the part at the top kept wanting to pull away from the lip of the overhang and gape. She doesn't want the tarp to be hanging from the arch, she would have to drill stakes into the arch for attachment points and it looks pretty stable but she has no desire to stress it more than she has to. She does another sketch on paper and eventually figures out a structure where the super-grippy rubber-gecko-foot-like swappable pole tips are actively pressed against the rock by the weight of the rest. 

Merrin really wishes she had some way of ever seeing a human being from dath ilan again, specifically whichever Exception Handling team designed her reconfigurable shelter tarp with sufficient adaptability that she was able to turn it into an exterior wall around a weirdly shaped sinkhole cave. So she could give them a HUG about it. It only took her like three hours! 

Six hours into the day. The temperature has already climbed by twenty degrees! ...Unfortunately, that does still leave it at a current temperature of -20° C. 

High tide appears to have arrived, and turned, a couple of hours ago. 

...Whoops, Merrin was deeply focused and also below-grade in the sinkhole and totally missed that. She needs a TIDAL GRAPH. Ideally a GIANT POSTER ON HER WALL but that's a little difficult when she can't just order one printed and delivered to her house. Maybe the hyperpigmented UV-resistant lichen can be turned into ink and she can paint her cave like a prehistoric hominid. That would be really cool, actually. Also not a today priority. 

Her next today-priority is the rest of her brilliant convertible-day-night-cave idea: a separate sleeping capsule, all the way at the back, lined with all of her emergency medical blankets this time with the reflective side facing inward. She can make it even smaller than the personal capsule tent, since she won't also need to cram, like, an oxygen concentrator and a battery and a pee-bucket and a collapsible tub full of evaporating saltwater into it; the larger cave is for daytime work, the capsule is only for sleep (and lying in the sleeping bag for eight hours in between her nighttime sleep blocks, until the summer nights get warm enough that it's still comfortable to work ten hours after nightfall and also she's solved the artificial lighting problem). Small means her body heat alone will go further toward keeping it warm inside, but if the rest of the cave stays cooler than the daytime high, it won't be starting out so hot that she can't fall asleep. 

...The alarm she preset in the suit controls is warning her that at current consumption rate she's down to two hours of supplementary O2 in the tanks. So actually her next priority is to turn 60% of the remaining charge in the main battery into a full suit oxygen tank. 

Down to 380 Wh, from 5000 to start. Her suit has 1150 Wh, though, and even at moderate activity levels (but with lower heating needs than the last-six-hours average, she's been pretty out in the open working) that should last her, like, 22 hours, which brings her to sunset. At which point she should have another 1000 Wh to pick up in the backup batteries currently with the solar panels, and that's...about what she needed for last night, isn't it. 

Not sustainable.

But decent shelter will cut tonight's power needs a whole bunch. 

...And there's the point that she's been here for more than five dath ilani days, when you actually add up the hours, and her body will be busy acclimatizing; she already suspected yesterday that she's no longer meaningfully cognitively impaired while breathing ambient air, just exertion-impaired. But once it's a comfortable temperature in her shelter, she might be able to sit inside doing low-exertion work all afternoon and not use any battery power at all. And if that goes fine and she's not feeling like soggy toilet paper after eight hours, it's probably also safe to sleep without oxygen. She'll still need supplementary O2 for intense exertion for a while longer, but...less, as time goes on. 

For now, the suit power is heavily being spent on heating and it'll actually spend less on that if Merrin is working out. 

Still sitting with the oxygen concentrator and compressor running and plugged into her suit (inefficiently in the cold, but she put emergency blankets over them to help a bit), she'll starts digging - well, rock-collecting-and-shifting - a new pit for her relocated still. She can make it more efficient later by, instead of waiting for the vapor to saturate the (hot) air and condense onto the (also hot) plastic, she can send it through a bunch of tubing that cools it and also traps all of it rather than letting droplets fall right back into the salty water. The obvious cooler location is underground. More digging. She can probably get to it today even if she needs an afternoon nap again, she has 22 hours. 

About 90 minutes later the suit tanks is full and Merrin puts the equipment away again. She has a snack break, and a water break (rationed sips of her remaining exactly 1.2L of water; she'll have more "soon" but "soon could be twelve hours away.) 

She finishes the pit to the depth she wants - she's going for wide and shallow, this time, for more effective evaporation and since she doesn't need to do the weight-it-with-a-rock plastic drip method if she's going to cannibalize a bunch of IV tubing instead. She lines it with previously used plastic sheeting (dirty side down), and builds a little rim-wall of nicely stacked interlocked rocks that naturally cracked into conveniently brick-ish shapes and sizes.

And then it's 9 after dawn and the temperature is up to 0° C and she might as well go haul a whole lot of seawater over, she won't get much evaporation for hours yet but it's not going to freeze. 

...That took longer than expected, with the 650m hike back very carefully carrying her collapsible tub with like 50L of water in it. (It has a lid but Merrin does not trust the seal if dropped, it's meant for stationary use and not necessarily specced to be watertight even under rough handling.) 

And now for Merrin's master plan!

Merrin is going to determine if dried and stiffened strapwrack fronds will soften again if dunked in the 30L of water left after she filled her evaporation basin to a reasonable depth. If so, she can take what she already harvested, soften it for manipulation, weave the wet fronds and arrange them over her storage crates, and once they re-dry in the baking afternoon sun, she'll have a frame to wrap in emergency blankets and use as a sleeping capsule tonight.

It's a hackish first try, but if it works as well as she hopes, she can harvest more! And do it again, better! The one single nice thing about being a solo human on an exoplanet is that there's no way she's going to drive strapwrack extinct by over-harvesting it.

The strapwrack DOES soften up again when soaked in a tub of water! (It takes a while, since a lot of it has dried into shapes that don't fit in the bottom of the tub. NOTE TO SELF next time she should, like, wrap it into spools to store, if she's planning to let it dry for later use.) 

Merrin spends pretty much the entire rest of the day on this project, alternating with:

- Digging an additional trench beside her seawater-evaporation pit, and rigging up a more efficient freshwater-collection system. She sacrifices a set of IV tubing to it, which makes it pretty easy to also attach a 1L IV bag for the actual collection - its existing contents can be mixed with her remaining freshwater, it's not very salty compared to seawater and she could probably use the electrolytes anyway.  

- Actually pulling up her camera recording on her screen and figuring out what setting to use to turn 4 hours 19 minutes of video into a file resembling one of those timelapse night-sky images with star trails. It turns out the software actually ALSO has a setting to just find the celestial pole for her! Merrin had forgotten it did that! She...spends a kind of annoying length of time figuring out exactly what direction her feet were facing and doing adjustment calculations and figuring out where true north is from here (it's unsurprisingly not identical to magnetic north, she calculates a declination of 11 degrees).

- Re-setting-up a sundial apparatus, this time actually facing true/celestial north. Her measurements will be imperfectly comparable to yesterday's, but from now on out she's staying put.

- Walking back to check on her solar cells, and retrieving one of the 500 Wh auxiliary cells, now filled up. She should fill up another over the afternoon. 

- Eating two more meal bars. 

- Taking a 3h nap

It comes out really nicely. It looks so cozy! 

And she's promptly going to make it much less pretty-looking by sacrificing two of her insulated-reflective emergency blankets for the cause. Both are reflective-side-in, but one is on the outside and one is on the inside, leaving a small air gap in between for its additional insulating properties. 

It's worth cutting them for this – very, very carefully, after sketching out her plan on notebook paper and carefully drawing her planned cuts in indelible marker on the blankets.

She has a basic sewing kit. She also has duct tape*.

That part takes four hours, but at the end of it she has a pod that will fit one (1) Merrin, in a sleeping bag, optionally still in her armor. Her sleeping pad fits perfectly into the flat bottom. 

And it's still probably three hours before sunset. 

(It's highly optimized Exception Handling general-purpose extra-tough extra-sticky utility tape, but that's basically duct tape.) 

...She'll spend her remaining three hours of light sitting in the back of her cave - where it is, in fact, a lovely comfortable temperature despite the high slowly dropping from 29° C outside - with her electronic screen up at minimum-backlight. She tapes four squares of notebook gridline paper together and, using a storage crate as a desk, copies over a star chart and names some constellations. 

Merrin does it out of the suit, breathing the ambient air; the temperature in her shaded cave did rise with the heat of the day, since she didn't have the flaps sealed and was in and out a bunch, but only up to a very pleasant 18° C now very slowly dropping, despite the outside temperature having hit almost 30° C today.

She feels...more or less completely normal? Well, once you account for the fact that it's now been, like, six and a half days in dath ilani reckoning since she last had a conversation with another human being and she's spent nearly all of that time agonizing over the dwindling power supply she needs for very basic Staying Alive. But she's satting mostly at 89-90% while at rest, and her resting heart rate is actually getting back down to 62 even while she's still awake and working, with good heart rate variability according to the suit analytics. However stressed she is, she's not actually running stupidly high cortisol levels right now. All the physical labor is probably helping. 

And shortly before sunset she dons the suit again and treks back over to the last remaining sign of her old campsite: the solar unit sitting by itself, a startlingly out-of-place piece of advanced technology, sitting there in an expanse of bleached and weathered limestone, on a planet where the most advanced terrestrial life consists of tiny segmented worms about the size of an individual suture needle. (Merrin spotted them when she was digging for her still.) 

The angle-auto-adjust feature worked well, and it was another clear day. She's gotten nearly 1040 Wh; the unit appropriately switched the relay over and started charging the third backup battery after the second was full. 

She carefully folds up the solar unit and carries everything back to camp. 

And back. The sun is down (she checks and memorizes the exact time, since her hands are full of solar unit, she didn't bother bringing the extra weight of its storage crate to clip on her back), but she has enough twilight to make it to camp before she can't see her feet.

...She can afford a bit of artificial lighting tonight, she decides, to sit in her cave and review her current status on all of her critical numbers. 

Her power armor is down to 290W of charge. It was a less heavy-exertion day, mostly work with her hands that didn't rely on the suit's servos, but it was, still, a long day, and for quite a lot of it she was using the climate control. 

BUT she actually has more than half of her O2 tank left from the midmorning refill. 315L. ...Which wouldn't quite stretch to cover the whole night, but she does, in fact, think that she's not going to give herself any medical problems if she sleeps without supplementary oxygen. 

Between her main battery, charged auxiliary cells, and the charge left on her armor, she has about 1800 Wh. (She's actually going to top up her suit battery immediately from the auxiliary battery that only got to 40 Wh, the transfer is pretty efficient so the loss is low and that way she can neatly separate out "full" and "empty" backup batteries. 

...She should check her records of daylight hours yesterday versus today. 

Even accounting for measurement error, it sure looks like today's sunrise-sunset interval was somewhere between ten and twenty minutes longer than yesterday.

It's spring. 

...Correction: it's very likely to be sometime after the winter solstice and before the spring equinox. But she doesn't know what percentage of the way she is from one to the other.

Or, come to think of it, how long the year is. She can calculate that, with a few more reliable data points on the changing sun angle and a lot of really annoying geometry. 

…She can trivially check her latitude, though. The software probably calculated it for her, it’s literally just the angle of the celestial north point above the horizon.

44 degrees north, apparently. Almost exactly halfway from the equator to the poles. 

SO MUCH MATH 

But: in the near term, it’s closer to good news than bad.

The days will get longer. The sun will get higher in the sky. Her per-day solar panel production will increase: eventually, she might be able to charge her suit to full every day. 

The ocean will get (a little bit) warmer. The nights will be more survivable, though given that even a summer night is probably not much less than 24 hours, she wouldn’t be surprised if even summer nights drop to below freezing. 

The daytime highs will be a problem, but…thanks to her lovely cave which she loves, not for a while. She can get it better sealed than it is now; she’ll design a structure she can make out of strapwrack. There are clearly deeper caves; maybe she can find some that aren’t too hazardous, and retreat to them during peak afternoon temperatures.

Food is a problem.

(Water is still not optimal, but it’s less of a problem. She has 2200 ml left of today’s production from her new still, to last her through until tomorrow afternoon or whenever it starts meaningfully evaporating again. She covered it with an emergency blanket as insulation, so it might not even freeze solid if the rocks keep radiating the absorbed heat of the sun for long enough overnight.)

…Food and water are tomorrow’s problem. It’s 90 minutes after full dark, she’s been working by the dimmest, bedtime-color-mode setting on her durable and power-efficient LED-strip portable light, and her nap was now 14 hours ago. Merrin is feeling pretty ready for her first sleep block.

It's actually too warm in her sleeping capsule to be in the sleeping bag. Merrin leaves it unzipped and flops on top of it and almost immediately falls asleep. 

Outside her sheltered cave, the temperature drops.

Inside the cave, the temperature also drops, but more slowly. She's thoroughly tucked out of the wind. The rock above her absorbed significant daytime heat, and now re-radiates it slowly. The deeper bedrock neither heats up nor cools down much with the daytime swings.

There's a very faint draft coming from the dark tunnel at the back of her cave. It's cold relative to the daytime outside temperature, but deep bedrock - and the air it surrounds, where there are caves - approximates the annual average temperature, and it's above freezing. Eventually, as the night goes on, that trickle of airflow becomes a warming rather than a cooling effect.

Her cave interior is eventually going to drop below zero, in the last stretch of the night, but not that far below zero. Her capsule, with the "door" flap at the head hanging down and Velcro-strip-sealed in place, is going to stay comfortably above freezing all night long. 

Merrin wakes up and checks her wrist timepiece and is informed that it's, like, 3 pm in dath ilan. She was using the timekeeping function on her power armor for her daytime timekeeping, since she was wearing it and her wrist timepiece wasn't even accessible. 

Great. She really needs to go dig into the reprogrammable-software options - which, to be clear, she has literally never done before, but it's probably set up such that a smart eight-year-old could do it, and Merrin is not smart but she's a grown adult who is capable of figuring things out even when it's really annoying. 

She vaguely recalls glancing at it at some point when she was midway through her star chart and noting that it was apparently little after midnight in dath ilan. So at a wild guess, it's been thirteen-ish hours since sunset and she's been asleep for eleven and a half hours. More than she should need, really, but she's not going to complain if her circadian rhythm is deciding it's time to adjust to the long nights. She does remember noticing that she wasn't as tired as she would naively expect, yesterday, staying up for - it must have been over 30 hours, with only that one three-hour nap, and she was only really crashing toward the end of it. 

Her circadian rhythm probably isn't going to fully adjust. She vaguely recalls reading about experiments with subjects living underground and never exposed to daylight cues, and that does often result in the 24-hour circadian rhythm stretching longer, but only rarely even as long as 48 hours. She does feel like she's sleeping enough, but she's probably going to continue to have two nighttime blocks with an annoying in-between period of lying awake in the darkness. 

She could probably justify turning on her reader tablet for a little while and reading something to pass the time, but actually Merrin is kind of inclined to instead train her Mental Discipline for Solitude With No Entertainment. If she survives long enough, eventually her electronics will stop working and she won't have a tablet to use at all. 

Seven hours pass....less painfully slowly than before. Merrin spends a lot of time mentally designing the better cave cover she can make out of strapwrack. She'll still want to use the tarp for this summer - she can't make a replacement UV-reflective surface - but if she survives the summer heat, in winter she can replace it with a whole lot of insulation made out of local materials. 

She's got time. She's got nothing but time to do arts and crafts and building with local materials, really. 

If she can solve the stupid superheated problem where she arrived with 45 days of food. Which is, like, seventeen planetary days. And she's already coming up onto day four.

Eventually (after a pee break, which is enough to notice that the interior is getting chilly but isn't even below freezing yet) she drifts back to sleep, and sleeps through until dawn. 

It's down to -3° C in her cave, but it can't have been below zero for that many hours of the night; her drinking water containers didn't freeze solid. 

It's totally safe to let them freeze - they're tough flexible plastic, and expand - but it's nice that her remaining water is drinkable straight away. Merrin is going to drink some, and eat a meal bar and try NOT to count down in her head what percentage of her remaining calories it represents, and check her O2 saturation reading. 

91%! Technically lower than expected in a healthy adult but she's fine, it's not going to be causing her any problems. Her resting heart rate taken by hand is a little higher, in the 70s, but that's actually adaptive in this phase of acclimatization. 

The more important question is going to be her exertion tolerance, so...she should do a small, controlled test of it here and now. It'll help her get warm. 

50 pushups? 

....Haha, just kidding, Merrin's body is firmly telling her after, like, twenty-six pushups that she should consider Stopping That. Her O2 saturation reading drops to 82% and takes a while to recover. She feels shockingly out of breath, completely disproportionately to the actual activity, and her heart rate is spiking a lot higher than it usually does from pushups. 

...All right, she's super not fully acclimatized.

Which makes sense, it's only been a week in dath ilan days, and she's probably delaying the process a bunch because she was paranoid about ANY cognitive impairment when she has to do constant high-stakes prioritization and gave herself extra O2 all through the first day, so really from her body's perspective she's been here for two planetary days, not three. And still giving herself some supplementary O2 in order to maintain her kind of ridiculous activity level.

Right now her body will have gotten used to breathing a bit more, her kidneys will be adjusting her bicarb levels to tolerate hyperventilation, and her body will be retaining less water to increase her relative red blood cell count, but her absolute red blood cell count is probably just at the start of its rise.

In another seven planetary days, if she slowly weans herself off using the suit and extra oxygen for walking around, she'll probably be as acclimatized as she's going to get, and her exertion tolerance will still be lower than it was at sea level in dath ilan – she might still want extra O2 when she's wearing her armor to do something super intense – but she should be able to handle, like, walking around and carrying objects up hills without getting absurdly winded. 

At least she's not accumulating too much delayed onset muscle soreness. The long enforced rest period helps a bunch; she woke up kind of stiff in the middle of the night and did a bunch of gentle static stretches during the Nothing Else To Do, and now she's fine. 

...Ohhhh right also this planet has 1.2G gravity. It's a small enough difference that Merrin has now completely stopped noticing it consciously, but yeah, pushups will be more tiring if she's suddenly "gained" 20% of her body weight. 

She puts her suit on and goes out into the chill morning air to set up the solar panels in her new location. 

She'll set it up beside the top of the archway. It's occurring to her that the best place to keep her main battery storage might be buried in a pit beside the solar panel unit; temperature extremes are bad for it and will degrade it over time, and the temperature a meter down will vary even less than the temperature "indoors". 

She has three meters of cable for it, plus a bunch more attached to various devices, not all of which she's ever going to need here, and she does in theory know how to splice cables together. She can create a permanent "power station" and run the cable directly into the cave to charge her suit.  

...That's a ton of digging and it's not a right-now project, she's just thinking ahead. There's so much thinking ahead to do. 

Aaaand time to go back into her cave and make a TODO LIST.

Somehow Merrin has not at any point managed to actually do that? It feels like she's spent the last three days prioritizing solely off "what does she need to do right now to avoid dying in the next 64 hours" and all of a sudden she's...not...especially at risk of dying at that timescale? She totally could spend a bunch of the day resting in her sleeping capsule, breathing ambient air, and finish the day with more stored power than she started out with. 

Saving her electrical power is not her highest priority anymore. If it's headed toward spring, then the days are going to get longer...and longer...and longer...and eventually she's probably going to be getting more solar power production than she can use or store. 

The things most likely to kill her, at this point, come down to:

1) Stupid accidents. 

2) Surprise hazards that she failed to predict in advance and was unprepared for. 

3) RUNNING OUT OF FOOD. 

4) SUMMER.