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.