Heat loss in a spaceship

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Heat loss in a spaceship

Postby FLESHGRINDER » Sat Feb 19, 2011 2:37 pm UTC

My friends and I where watching Firefly, and we had just seen the episode where the engine blows up; Because the engine malfunctions, the life support shuts down, and the ship gets extremely cold after a few hours. So I had said that I didn't think a spaceship would lose any heat, which started an argument, and I decided to ask the most reputable source of scientific information on the internet: the xkcd forums.

Their arguments where (to the best of my memory):
1 - When a molecule bounces around, every time it hits something it loses some of its kinetic energy, in the form of heat (not KE becoming heat through irreversibilities, but KE=heat), so after a while, the molecule would have very little kinetic energy, and the ship would lose its heat.
2 - Space is cold, so unless the engine is constantly adding heat, you'd lose it all to the surroundings.

My rebuttals where:
1 - When the molecule bounces around, its smacking into other molecules, so when its losing some kinetic energy, another molecule is gaining it. Space being really empty, I said the effects of molecules outside bouncing off the ship would be negligible; also, any sort permanent energy loss due to irreversibilities, would be in the form of heat being added to the system.
2 - Again, space is extremely empty, so there's really nothing around the ship, and you can consider the ship to be a contained system, meaning there should be zero heat transfer. A few minutes later I remembered that out of the 3 heat transfer methods (convection, conduction, and radiation), radiation would still cause the ship to lose energy. But even if the ship was losing heat due to radiant energy, I don't think the effects would be noticeable.

So here I am, not to prove I'm right to them, but to ask what would happen to a space ship heat content if life support where suddenly turned off.

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Re: Heat loss in a spaceship

Postby Stacy S. » Sat Feb 19, 2011 3:08 pm UTC

the folks in Apollo 13 almost froze to death.

I don't think the radiative heat loss would be insignificant.

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Re: Heat loss in a spaceship

Postby gmalivuk » Sat Feb 19, 2011 4:12 pm UTC

It would depend on the heat capacity of the materials in the ship itself, but yeah, there would be heat loss. It just wouldn't be as fast as if it were in an atmosphere.
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Re: Heat loss in a spaceship

Postby Hawknc » Sat Feb 19, 2011 4:34 pm UTC

FLESHGRINDER wrote:Again, space is extremely empty, so there's really nothing around the ship, and you can consider the ship to be a contained system, meaning there should be zero heat transfer. A few minutes later I remembered that out of the 3 heat transfer methods (convection, conduction, and radiation), radiation would still cause the ship to lose energy. But even if the ship was losing heat due to radiant energy, I don't think the effects would be noticeable.

The rate of heat transfer is dependent on the equation:
Image

So the rate of heat transfer is dependent on the temperature of the radiating body, but it would definitely be possible to lose heat from a spaceship at a noticeable rate since there is very little radiating heat back to it. (Actually the wikipedia article from which I grabbed that equation is worth reading, particularly the "interchange of energy" part.)
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Re: Heat loss in a spaceship

Postby Mr_Rose » Sat Feb 19, 2011 8:04 pm UTC

We should also note that most spacecraft humans build today are designed to passively radiate heat as much as possible since in normal operation every system on board is generating waste heat that must be dealt with, in addition to the extra input from the Sun. This is why the Apollo CM was wrapped in bacofoil and the LM descent stage was so shiny. Now obviously this becomes less of a problem the smaller your engine and the further away from the local star you get, and is reduced even more if you don't bother with crew, but Serenity was not designed like that at all, being a cargo shuttle designed for travel between planets in the habitable zone.
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Re: Heat loss in a spaceship

Postby Tass » Sun Feb 20, 2011 6:38 pm UTC

Yeah you are certainly right on point one. And partly right on point two. There will be radiative heat loss, but it is not as fast as often assumed. The cooling time scale is likely to be days rather than hours.

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Re: Heat loss in a spaceship

Postby Technical Ben » Sun Feb 20, 2011 9:22 pm UTC

Mr_Rose wrote:We should also note that most spacecraft humans build today are designed to passively radiate heat as much as possible since in normal operation every system on board is generating waste heat that must be dealt with, in addition to the extra input from the Sun. This is why the Apollo CM was wrapped in bacofoil and the LM descent stage was so shiny. Now obviously this becomes less of a problem the smaller your engine and the further away from the local star you get, and is reduced even more if you don't bother with crew, but Serenity was not designed like that at all, being a cargo shuttle designed for travel between planets in the habitable zone.

I'd guess the fusion engines would give off tons of heat too. Or whatever it used. So you might be right there. What if the power supply and engines are separate from the rest of the system?
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Re: Heat loss in a spaceship

Postby idobox » Mon Feb 21, 2011 9:28 am UTC

As your signature states, a human body produces about 100W of heat. The various electronics, life support system are probably going to produce more heat than that (a simple computer does). You will quickly get a kW, to dissipate per crew member.
It seems much easier and reliable to design your ship so that it looses as much heat as you can, and use waste heat from the engines to regulate temperature in the habitable zones.
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Re: Heat loss in a spaceship

Postby Roĝer » Mon Feb 21, 2011 11:25 am UTC

Also, a tiny craft such as Apollo 13 has a lot of surface compared to its volume, whereas a large ship would have relatively less surface.
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Re: Heat loss in a spaceship

Postby Sir_Elderberry » Mon Feb 21, 2011 2:03 pm UTC

You probably got this opinion in reaction to not having another misconception, the vision of space as a flash-freezer. Space can't steal heat that quickly--as has been pointed out, one major problem with our spacecraft is getting rid of all the heat our systems generate. That said, heat still radiates. I don't remember quite how cold it gets--below freezing?--or how long it takes--like half a day?--so who knows if the numbers actually work. Point is, the ship gets cold, yes.
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Re: Heat loss in a spaceship

Postby gmalivuk » Mon Feb 21, 2011 4:16 pm UTC

Sir_Elderberry wrote:I don't remember quite how cold it gets
About 2.7K in the shade.
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Re: Heat loss in a spaceship

Postby Adacore » Mon Feb 21, 2011 4:30 pm UTC

I'm going to assume the ship has a surface area of around 10,000 m2 and a volume of 25,000 m3 (which seems reasonable for the suggested dimensions I can find for Serenity).

The maximum possible rate of cooling would be in the following conditions (pre-post edit: spoilered out because the assumptions are silly):
Spoiler:
- Perfect heat transfer between the radiative outer surface and the internal sections, so no insulation at all, giving an initial surface temperature of ~293.15 K;

- Black body emissivity, such that epsilon = 1;

- There is no radiation of any kind striking the ship itself, either from internal interchange or from an external energy source;

- The average heat capacity and/or density of the ship being extremely low, at (say) 1 kJ kg-1 K-1 and 1.2 kg m-3 respectively (in effect, a box of air). I'm going to assume these are constant in the range 250 K to 300 K to simplify things.

In this heavily idealised (to the extent of impossibility) scenario, the ship would have a total thermal energy of H = V * rho * Cp * T = 8,794,500 kJ, and a radiative power loss of about 4,188 kW. That would result in the loss of around 8 K per minute, and the flying-box-of-superconductive-air would freeze in around three-four minutes.

More realistic assumptions, still aiming for fairly rapid heat transfer, might be to say:

- Assume a constant 50 degree difference in temperature between the outer surface and the core temperature (in reality this could be almost anything depending on the level of insulation and, thus, thermal conductivity between the core and the hull surface);

- Take a more realistic combined emissivity and view factor of 0.5 (if you were trying to reduce heat loss, this could be 0.05 or lower with highly reflective surfaces, but I don't remember Serenity being particularly clean and shiny);

- Keep the heat capacity at the reasonably realistic 1 kJ kg-1 K-1, but use a mass figure for Serenity of 270,000 kg (around an order of magnitude higher than above) based on numbers I found from a google search.

In this scenario, the heat loss will be of the order of 0.1-0.3 K per minute, taking a couple of hours to cool from 25 C to freezing. Now, given the volume you've got to play with, and the potential for decent insulation, you could well have an even larger temperature difference and far lower emissivity. With 100 K temperature difference and an emissivity of 0.1, for example, you could have temperature loss at around 0.01-0.02 K per minute, which would mean about 24 hours for the ship to cool to freezing.

I think, from going through the calculation, that it's actually reasonable for Serenity to cool to freezing in a few hours (and way below in a few more), if you don't take any explicit precautions against it (making an insulated 'nest' in the core of the ship, for example). I don't think it had a huge amount of thermal insulation, and it wasn't reflective to the extent that it would have extremely low emissivity. The big question, of course, is the insulation - the more complicated (and correct) version of the above would use a thermal conductivity to calculate the non-steady-state surface temperature and core temperature as a function of time, but there's no way I have time for that maths now - I'm not even sure I could remember how to do it.

By the way, am I right in thinking that thin multiple hulls with intermediate vacuum layers would be extremely good insulation when you're worried about radiative heat loss in space? Thermal conduction could only occur down the (small) support columns, and moer than 50% of radiation from each layer would be reflected or re-radiated back to the inner layer, right?

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Re: Heat loss in a spaceship

Postby Sir_Elderberry » Mon Feb 21, 2011 4:34 pm UTC

gmalivuk wrote:
Sir_Elderberry wrote:I don't remember quite how cold it gets
About 2.7K in the shade.

I meant how cold Serenity got in "Out of Gas"
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Re: Heat loss in a spaceship

Postby Mr_Rose » Mon Feb 21, 2011 5:38 pm UTC

As I recall, the final problem wasn't so much the cold as the lack of oxygen and the being-shot-in-the-stomach so the temperature didn't get mentioned much after condensation started frosting on the windows.
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Re: Heat loss in a spaceship

Postby Adacore » Mon Feb 21, 2011 5:56 pm UTC

Mr_Rose wrote:As I recall, the final problem wasn't so much the cold as the lack of oxygen and the being-shot-in-the-stomach so the temperature didn't get mentioned much after condensation started frosting on the windows.

This did occur to me, another interesting thought experiment may be the amount of time it takes for oxygen levels to become too low to breathe (with adequate CO2 scrubbing), or CO2 to build up to lethal levels (without scrubbing).

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Re: Heat loss in a spaceship

Postby thoughtfully » Mon Feb 21, 2011 7:30 pm UTC

Adacore wrote:
Mr_Rose wrote:As I recall, the final problem wasn't so much the cold as the lack of oxygen and the being-shot-in-the-stomach so the temperature didn't get mentioned much after condensation started frosting on the windows.

This did occur to me, another interesting thought experiment may be the amount of time it takes for oxygen levels to become too low to breathe (with adequate CO2 scrubbing), or CO2 to build up to lethal levels (without scrubbing).

Given how much volume inside the ship is air, compared to the number of crew, this seems to me to be often overstated in a lot of scifi. I don't have any good figures, though. I guess one could back-of-the-envelope something without too much trouble.
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Re: Heat loss in a spaceship

Postby Technical Ben » Mon Feb 21, 2011 8:09 pm UTC

A "get out of jail free" card for any instance would be a fire on ship though. Just have it the exact right size, with fuel, to last the same time it takes to rescue the crew. As they always get a last minute rescue right?
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Re: Heat loss in a spaceship

Postby thoughtfully » Tue Feb 22, 2011 4:18 pm UTC

On the plus side, a fire would keep things warm :)
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Re: Heat loss in a spaceship

Postby DrSir » Tue Feb 22, 2011 11:28 pm UTC

Technical Ben wrote:A "get out of jail free" card for any instance would be a fire on ship though. Just have it the exact right size, with fuel, to last the same time it takes to rescue the crew. As they always get a last minute rescue right?


You would use up your Oxygen doing this though, so that would be bad if that was an issue also..

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Re: Heat loss in a spaceship

Postby gmalivuk » Tue Feb 22, 2011 11:32 pm UTC

But only if you had abundant fuel. Sure, if oxygen is the limiting resource then it'll mostly get used up, but if there's only enough fuel for a quick bit of fire (or say, an explosion), it'll only use up part of the oxygen.
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Re: Heat loss in a spaceship

Postby tms » Wed Aug 23, 2017 11:17 pm UTC

Say I want to include conduction and radiation, which I suppose would be sort of accurate. I have superficially understood the Stefan-Boltzmann Law (black bodies, gray bodies), but after doing several hours of reading many sorts of texts on or grazing the subject, I'm still at a loss how to incorporate conduction in such a way that I'm not just using one thing for the inner and the other for the outer layer. Or would that be sort of close?
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Re: Heat loss in a spaceship

Postby Eebster the Great » Thu Aug 24, 2017 12:49 am UTC

You would need the temperature of the interior of the ship, the temperature of space (or more accurately, the temperature of the radiation hitting the hull), the total thickness of the walls (including all the insulation and whatever else inside them), and the effective thermal conductivity of the walls.

Honestly, as others have been saying, I doubt the ship would be insulated. It is usually going to be a priority to dispose of heat rather than to conserve it. It would make sense to design a ship, especially one that large, to dissipate heat as quickly as possible, because you can't really have AC in space.

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Re: Heat loss in a spaceship

Postby eSOANEM » Thu Aug 24, 2017 11:14 am UTC

Also, adding to what Eebster's saying, vacuum (even one of not particularly high quality) is a really good insulator. Radiation is going to be far and away the biggest mode of heat loss for a space ship
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Re: Heat loss in a spaceship

Postby speising » Thu Aug 24, 2017 12:34 pm UTC

You need some isolation to protect the side in sun shine, though.

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Re: Heat loss in a spaceship

Postby morriswalters » Thu Aug 24, 2017 1:57 pm UTC

Staying Cool on the ISS
Without thermal controls, the temperature of the orbiting Space Station's Sun-facing side would soar to 250 degrees F (121 C), while thermometers on the dark side would plunge to minus 250 degrees F (-157 C). There might be a comfortable spot somewhere in the middle of the Station, but searching for it wouldn't be much fun!

Fortunately for the crew and all the Station's hardware, the ISS is designed and built with thermal balance in mind -- and it is equipped with a thermal control system that keeps the astronauts in their orbiting home cool and comfortable.
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Re: Heat loss in a spaceship

Postby Soupspoon » Thu Aug 24, 2017 3:30 pm UTC

Serenity's 'world' is a strange one, anyway, from what I recall. I think the mechanics have been worked out to death on it, by both canon and fanon sources that I've not spent too much time looking at, but (IIRC) the star system it's based in is a compact poly-stellar system in order to have Loads And Loads Of Planets within easy (sublightspeed) cruising distance of each other, consisting of many different Goldilocks Zones around many different subordinate stars.

This suggests to me that it is many 'cold' stars, the many and various Earth-surrogate worlds tucked tightly in (often a little on the warm edge of the zone), and the shepherding central mass isn't particularly dominant except by gravity. The cummulative radiative temperature profile across random intra-stellar parts of space is going to be odd, in the way that doesn't match the 1AU from Sol profile.

Minds (and memories!) greater than mine will have rationalised this situation, but there's obviously something at play.

(Apart from anything else, with a typical sci-fi power output already required to operate the Serenity's engines and its many systems there must be a highly efficient inherent heat-sink so as not to fry the occupants. So, let's say that this is at least partly passive, via some kind of device using an unobtainium/frinkonium junction-matrix around a ship-wide sleeve to push an enhanced Peltier transfer of heat out of the cold side using the power from a differently-facing Seebeck power source. Entirely self-contained and self-controlling, it might have not been engineered and configured to dial-down in the absence of engine-bled heat, when not safely sat on a planet with a thermo-smearing envelope of atmosphere to remove sufficient thermal gradient of imperative. Or something.)

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Re: Heat loss in a spaceship

Postby CorruptUser » Thu Aug 24, 2017 6:26 pm UTC

First off, it's a work of fiction it won't make sense :P

That said, the whole thing crumbles pretty quickly when you think about it. The verse is made up of about a hundred planets and moons, orbiting gas giants, etc. It's stated that humanity has made everything as earth normal as they could, including gravity. HOW?! Did they smash a bunch of moons together? Did they replace all the planet cores with tungsten? Such a project even if possible would basically render all the planets as lavaworlds for hundreds of thousands of years, and it's far cheaper to just build space habitats than to terraform it all the way. It's done because having most of the moons have ,1g would be virtually impossible to film and keep the stories. So yeah, ignore that, and ignore the similar issues with the breathable atmosphere.

Next issue, the simple farmers. The outer colonies rely on horses and plows for subsistence farming. Yet they clearly are in contact with spaceships. A society that can manufacture all those space ships can easily manufacture a simple machine plow, and then power it with that aluminum foil from Heart of Gold. And really, solar power that reflects light? Not a fan of that episode. But anyway, Mal could make a killing buying up simple machines like that, and trading them for all those cows, then selling the herds elsewhere. And even without the high tech stuff, there still shouldn't be such backwater places. It's mentioned in Bushwacked that sometimes ships are modified for one-way trips. If that's the case, the people would have dismantled the ship for parts, using the engine as a generator capable of powering a small city, even if the generator required uranium fuel rods. Given that Mal must've been handling a fortune with that small herd, since just setting up the deal apparently involved a small fortune according to badger, the communities could trade livestock for fuel. So no, the economy doesn't make sense.

So just calm down, it's just a show.

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Re: Heat loss in a spaceship

Postby morriswalters » Thu Aug 24, 2017 7:49 pm UTC

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Re: Heat loss in a spaceship

Postby Soupspoon » Thu Aug 24, 2017 8:43 pm UTC

CorruptUser wrote:First off, it's a work of fiction it won't make sense :P

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Re: Heat loss in a spaceship

Postby wumpus » Sat Aug 26, 2017 6:20 pm UTC

gmalivuk wrote:
Sir_Elderberry wrote:I don't remember quite how cold it gets
About 2.7K in the shade.


But you also are a vacuum thermos bottle in 2.7K. In practice, this means only radiated losses. There is no conduction to 2.7K (making that number pretty meaningless).

If life support (and other critical functions) are still functioning, expect that the spaceship is producing enough power to require real work radiating it out. Apollo 13 had issues providing enough oxygen to the astronauts, so not only the heaters but other critical functions were turned off (it also must have been "day/not-shade" for most of the trip: don't expect either the moon or the Earth to block out much of the Sun for most of the way. Remember the "Big Blue Marble" picture? It won't get to "the size ISS sees" until a few days later).

Typically cooling a spacecraft is more of an issue, but that assumes that most systems are functioning.

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Re: Heat loss in a spaceship

Postby Eebster the Great » Sat Aug 26, 2017 8:33 pm UTC

wumpus wrote:
gmalivuk wrote:
Sir_Elderberry wrote:I don't remember quite how cold it gets
About 2.7K in the shade.


But you also are a vacuum thermos bottle in 2.7K. In practice, this means only radiated losses. There is no conduction to 2.7K (making that number pretty meaningless).

It's not meaningless. If your ship generates no heat (and nor does anything inside it, like people), then it will approach the temperature of the background radiation, which is 2.7 K. Only at that temperature will it be in radiative equilibrium.

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Re: Heat loss in a spaceship

Postby gmalivuk » Sat Aug 26, 2017 9:09 pm UTC

Yeah, it doesn't mean the same thing as being in contact with a physical object that's 2.7K, but that doesn't make it meaningless.
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Re: Heat loss in a spaceship

Postby morriswalters » Sun Aug 27, 2017 12:51 pm UTC

If it's anywhere close to a star it will never reach background. You can state Mal's problem as, his ship receives heat in a plane. While it radiates spherically. Fix Mal's problem by fixing that geometry. Put some reflectors on his dark side and get broadside to the sun, crew side closest to the sun. Or rotate the ship to even out the heat transfer across the ship. Or both.

Apollo did a barbecue roll on the way to the moon to even out the temperature regime. Conductive materials on the surface make you a more efficient radiator, the reflective characteristics of surface make you a better or worse at absorbing.

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Re: Heat loss in a spaceship

Postby Eebster the Great » Sun Aug 27, 2017 10:15 pm UTC

Although the medium near the Sun is very hot, that is almost irrelevant, since its specific heat is so low. In the shade, you can get close to the microwave background. Permanently shaded craters on the Moon have temperatures around 35 K in spite of being in contact with the rest of the Moon at a much higher temperature. And at that point, a few tens of kelvins really doesn't matter much.

If you are hiding behind an object that blocks out all sunlight, but not in contact with it, I imagine you could get very close to 2.7 K. Of course, the object itself will be heated by the Sun on the other side, so its dark side will still be warm, and that will radiate a little, but I doubt it would be all that significant.

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Re: Heat loss in a spaceship

Postby morriswalters » Mon Aug 28, 2017 1:24 pm UTC

I suppose I agree with you, but I see this as purely a heat transfer problem.
Eebster the Great wrote:Permanently shaded craters on the Moon have temperatures around 35 K in spite of being in contact with the rest of the Moon at a much higher temperature.
All that tells you is rock is a poor conductor of heat. What you've said is, that I radiate faster than I can conduct.
Eebster the Great wrote:If you are hiding behind an object that blocks out all sunlight, but not in contact with it, I imagine you could get very close to 2.7 K. Of course, the object itself will be heated by the Sun on the other side, so its dark side will still be warm, and that will radiate a little, but I doubt it would be all that significant.
Yep. You can use this fact to take CO2 out of air, it condenses first. How much heat you would get through a shield is measurable. Walk under a metal roof on a hot day. Up close to a rock in space in the shade, you're going to get chilly.

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Re: Heat loss in a spaceship

Postby Bloopy » Mon Aug 28, 2017 9:29 pm UTC

The 1993 movie Lifepod is hugely relevant to this thread. The one escape pod first gets annoyingly hot and then later freezing cold as they're battling trying to keep the systems working. I guess they were in the heat of the sun but drifting away from it. I can't remember the exact details.

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Re: Heat loss in a spaceship

Postby tms » Fri Sep 01, 2017 6:41 pm UTC

As for accelerating losses, a NASA published document puts an estimated upper bound at 12 kW per kg. So graphene or carbon-n-tubes would have that thermal emission capability.
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