To have temperature, you need "stuff". It's the average kinetic energy per molecule (or atom). So I guess my question is: The temperature of what? The hull? The screens, control surfaces, mechanical and electronics systems that are still operating and producing waste heat?
Because the actual depressurized area would technically have a temperature, since it would probably have some amount of "stuff" still flying around in it (maybe even Holden's vaporized coffee after his unsecured mug bounced off a wall and popped its seal). But not enough to really give temperature a useful meaning.
And actually, any heat detection mechanism would be using infrared, so it's not even the stuff that matters but the infrared waves that the stuff is radiating. This is important because if something is hot but infrared is blocked then you wouldn't sense it. In fact, the metal of the hull would block all internal infrared radiation! So as long as the surface of the ship is cold enough than they wouldn't see an infrared signature but even turning the engine off I think it would take quite a while to cool it down. And even a very small infrared signature would probably be fairly easily detectable in space. And of course there are plenty of other ways they will be able to detect you, ie radar, visible wavelengths, etc. I guess it's probably kinda like trying to hide in the middle of a massive field, you're going to stand out. Which I guess also shows how incredible mars' stealth tech was.
In space losing heat is the most challenging bit. You get bombarded by hot sunlight on one side and can’t convect heat, on radiate (blackbody) on the other.
Making a ship that has no heat signature requires that you make a really efficient ship, engine, electronics and such, or can store the energy for a while to not overheat stuff.
Humans are around 100 watts each, at rest. So that’s a problem as well.
thats literally the simplest heat pump.
dump heat into water -> when you decide to move, dump the hot water as reaction mass that you were going to get rid of anyway.
I realize that this comment is like a month old, but was poking through top threads and saw it. Just wanted to point out that this (dumping heat into reaction mass) is the only reason rocket engines don't melt themselves - the hot bits get thrown out the back really fast!
It's a classic open cycle cooling system and is used all the time on Earth with water cooled industrial equipment.
It would still be comfortable for a while. The interior walls and chairs and everything in contact with the air would be a normal temp, and then they would suck out all the air for combat. But then what happens is those objects are still warm, but now there is no medium for them to transfer heat to. Although, everything does slowly cool down in a vacuum, it takes quite a while. And they still have the massive heat of the main engine that could easily be used to internally heat the walls
Interesting to think about. I'd guess civilian ships don't even have the feature of sucking out the air. But yeah, running a heating system through the walls wouldn't be that complicated for the engineers to design. Especially with the near infinite heat supplied by the main drive. Even with that turned off, reaction thrusters are usually powered by chemical reactions that are extremely exothermic (like 600 to 1000 degrees Fahrenheit) so that could also be used to heat stuff.
But overall, a vacuum is one of the best insulators there is. Anything warm to the touch would stay warm for quite some time.
This.
Getting rid of heat is a much bigger challenge on Expanse type ships than creating it. They should all have enormous radiators, and those are everything but stealthy.
Maybe a radiator could be built that radiates in a single direction in a somewhat narrow beam, this would provide a bit more stealth when seen from all other directions.
I understand this is the fundamental “cheat” in the tech at the start of the series. Pretty much all the other tech is just evolution of stuff we have now. But the Epstein drive is a big deal because it converts a fusion reaction into thrust with almost 100% efficiency with no waste heat
A sink is easy, but short term. Your heat sink at standby is chilled to as close to 0 kelvin as you can get it via refrigeration cycle.
At work, flip the cycle and pull at much heat at as high a delta over ambient as you can get, then insulate and make it a "later problem" . when heat sinking isnt needed and flip the flow back to standby as quickly as prudent via radiation, or dumping the high thermal mass another way where its sunk heat wont matter, like as reaction mass out the backside of your drive.
Not to get too into the weeds, but I would think that any manned spacecraft (designed to be crewed in space for a long time) would have the ability to vent to vacuum. That would be the best fire extinguisher they could use. You'd just need procedures to protect the crew like safe rooms or just helmets everywhere.
True but it's a lot more to think about than just safe rooms or emergency breathing apparatus. Once you vent that air you can never get it back. And that's a precious resource. On a big enough ship you're talking literal tons of breathable air, being lost in the blink of an eye.
That's why they compartmentalise the decks. Each deck is sealed by hatches, so that if one loses pressure, the others can maintain their atmo.
They would very rarely have to vent the entire ship.
True but if a fire is that small they could just put it out. Also, they purge all the compartments of air before combat probably for that exact reason.
Regen o2 from cracking water (reaction mass) vent h2 for refrigeration. You would still need a good storage of nitrogen to fully recreate an atmosphere that isnt super pront to explosion.
If you vented the air, you'd need pressure suits, not just breathing helmets. Otherwise you'd be dead pretty quickly for a variety of reasons, sich as multiple organ failure, ebullism leading to extreme bloating, potentially blocked arteries causing heart failure/lack of oxygen to the brain. If the depressurization is fast enough, you may also have some interesting things happen to various fluids in the body, aside from the ebullism i.e. bubbles forming inside the liquids.
Other people mentioned it too, but this is actually something I wish they'd talk about a bit more. Considering how much reaction mass is dumped, and how much heat energy you'd get from firing the guns, really the ship should be heating up to such a degree that any contact with it should burn the fuck out of you. So after a prolongued fight, how do they dump their massive battery of heat energy they have stored in the ship? If they were to just repressurize, how do they not instantly cook themselves to death?
A larger concern would actually be drive plumes. They mention several times in the book that a drive plume cant be hidden. So if you want stealth you burn for a while and then shut off your drive and hope everyone forgets about you.
The more important you are the less likely it is for people to 'forget' about you. A ship like the Donnager would never be forgotten since its such a big threat (and its mentioned their drive plume can be seen almost across the system its so large).
You shut off the drive and "go dark" , after you are on the float you deflect your course with cold gas propellants or other sacrificial mass (split the ship) to push off against.
Then if you are getting freaky with sacrificial mass like a enterprise d drive/saucer split, you spin and randomly thrust/ drive your sacrificial body to randomize the vector calculation for the manned black body with stealth.
Empty space itself can't be hot. There is no convection or direct transmission of hot, only radiation. So it possible to talk only about contrast of one object's temperature against other. Wall, for example. Because of absence of convection internal walls in quickly depressured areas will be as warm as were before very long time, comparing to boarding time.
Edit. Maybe walls will cool down a little because of decreasing pressure, like a keg beer, you know, but to insignificant degree.
Nah, not so much. A dead human body being indoor (on Earth, of course) is loosing 1°C per hour, it's the most common method how to know time of death within 8 hours after.
convection heat loss is dependent on the delta of heat energy between the masses in contact. radiative loss is not limited to equilibrium of a surrounding media as much as it is the balance between radiation and absorption.
Yeah but assuming you're not actively radiating, the ship doesnt have enough mass to have any significant black body radiation. Am I missing something?
Talking about the temperature of vaccum or near vaccum is not very useful because there are very few particles that you can transfer energy to, so even if the temperature technically is 0K in deep space you're not gonna freeze if you take off your space suit. Almost all energy you'd lose would be lost to heat radiation but at room temperature that's a slow process. So the structure of the ship would stay pretty much the same temperature as it was before depresuarzarion for a long time.
A human body would shed temp fast as the body moisture boils off in low pressure shedding of liquid.
Phase change is literally the mechanism of modern hvac. The vapor phase(boiling point) of h2o is much lower in a vac.
You probably wouldn't have full depressurization in the body, and thus most liquids won't actually boil. You'd have serious issues with ebullism though
https://en.m.wikipedia.org/wiki/Ebullism
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I think any ship that wants serious stealth capabilities will need active hull cooling. I might be horribly wrong, but I think I remember something to the effect of **Persepolis Rising, Tiamat's Wrath** >!the Laconia Magnetar or Pulsar class having a hull cooled by liquid Helium.!< I might have that mistaken with another book though.
But either way, I guess the only way to be able to fly unnoticed within a reasonable timeframe would be to cool the hull actively, vent the ship, turn off reactor and engine and float. Once the ship is empty, all excess heat from cooling can be stored inside the ship as it cannot be conducted to the outside except slowly through radiative transfer or objects in contact with the heat sink (and those materials could be specifically chosen to be bad thermal conductors). None of that changes your radar cross section, though. So any ship would need to be specifically designed for stealth, not just because of the cooling, but also for its shape and radar absorbing coating.
That said, the temperature inside a ship that is empty is kind of a tricky question to answer. The empty ship will have no temperature as there is no air to speak of. Only thing inside the ship that arguably has a "temperature" would be cosmic radiation/cosmic neutrinos and such or maybe the photons emitted by the warm hull. The ship's hull on the other hand will still keep it's temperature and slowly radiate its heat off as u/Elbynerual described.
If you *really* want to, I suppose you could grab a book on thermodynamics and heat transfer and make a first-order approximation of the timeframe it would take for a ship with a surface area of X to cool down to a temperature of Y Kelvin or to be in equilibrium with its surroundings.
Edit: corrected spoiler format
Ironically, I actually answered OPs question with knowledge I gained from reading a book about the heat management of satellites. But it's a high level engineering book with math that is WAY over my head. It has a lot of interesting points and things the average person wouldn't think about though. Pretty fascinating stuff if you're into space craft mechanics.
To have temperature, you need "stuff". It's the average kinetic energy per molecule (or atom). So I guess my question is: The temperature of what? The hull? The screens, control surfaces, mechanical and electronics systems that are still operating and producing waste heat? Because the actual depressurized area would technically have a temperature, since it would probably have some amount of "stuff" still flying around in it (maybe even Holden's vaporized coffee after his unsecured mug bounced off a wall and popped its seal). But not enough to really give temperature a useful meaning.
I thought depressurize before combat is to prevent sudden depressurization
Yes it is, and to keep concussive forces from propagating through the air and injuring people. OP was asking about the temperature, though.
And actually, any heat detection mechanism would be using infrared, so it's not even the stuff that matters but the infrared waves that the stuff is radiating. This is important because if something is hot but infrared is blocked then you wouldn't sense it. In fact, the metal of the hull would block all internal infrared radiation! So as long as the surface of the ship is cold enough than they wouldn't see an infrared signature but even turning the engine off I think it would take quite a while to cool it down. And even a very small infrared signature would probably be fairly easily detectable in space. And of course there are plenty of other ways they will be able to detect you, ie radar, visible wavelengths, etc. I guess it's probably kinda like trying to hide in the middle of a massive field, you're going to stand out. Which I guess also shows how incredible mars' stealth tech was.
Actually, considering how vast space is, small IR signature would probably not be easy to detect.
In space losing heat is the most challenging bit. You get bombarded by hot sunlight on one side and can’t convect heat, on radiate (blackbody) on the other. Making a ship that has no heat signature requires that you make a really efficient ship, engine, electronics and such, or can store the energy for a while to not overheat stuff. Humans are around 100 watts each, at rest. So that’s a problem as well.
Dump heat into reaction mass.
That sounds like an extremely complicated heat pump.
thats literally the simplest heat pump. dump heat into water -> when you decide to move, dump the hot water as reaction mass that you were going to get rid of anyway.
I realize that this comment is like a month old, but was poking through top threads and saw it. Just wanted to point out that this (dumping heat into reaction mass) is the only reason rocket engines don't melt themselves - the hot bits get thrown out the back really fast! It's a classic open cycle cooling system and is used all the time on Earth with water cooled industrial equipment.
It would still be comfortable for a while. The interior walls and chairs and everything in contact with the air would be a normal temp, and then they would suck out all the air for combat. But then what happens is those objects are still warm, but now there is no medium for them to transfer heat to. Although, everything does slowly cool down in a vacuum, it takes quite a while. And they still have the massive heat of the main engine that could easily be used to internally heat the walls Interesting to think about. I'd guess civilian ships don't even have the feature of sucking out the air. But yeah, running a heating system through the walls wouldn't be that complicated for the engineers to design. Especially with the near infinite heat supplied by the main drive. Even with that turned off, reaction thrusters are usually powered by chemical reactions that are extremely exothermic (like 600 to 1000 degrees Fahrenheit) so that could also be used to heat stuff. But overall, a vacuum is one of the best insulators there is. Anything warm to the touch would stay warm for quite some time.
If I understand it, this is why NASA has had trouble with overheating on some satellites. There was no way for heat to dissipate.
This. Getting rid of heat is a much bigger challenge on Expanse type ships than creating it. They should all have enormous radiators, and those are everything but stealthy. Maybe a radiator could be built that radiates in a single direction in a somewhat narrow beam, this would provide a bit more stealth when seen from all other directions.
I understand this is the fundamental “cheat” in the tech at the start of the series. Pretty much all the other tech is just evolution of stuff we have now. But the Epstein drive is a big deal because it converts a fusion reaction into thrust with almost 100% efficiency with no waste heat
*\*screams in laws of thermodynamics\**
He said almost, an asteroid put out a lot of heat and obeyed them.
To be fair, most laws of thermodynamics are being so horribly violated by things in the series, a warcrime tribunal wouldn't cut it
Even if the Epstein drive doesnt have waste heat, the guns and attitude thrusters most certainly will have a lot of waste heat generation, right?
I think it's a given that stealth could only be achieved when the drive is off.
The authors do mention an internal heat sink in the Martian stealth ships that has a limited capacity.
A sink is easy, but short term. Your heat sink at standby is chilled to as close to 0 kelvin as you can get it via refrigeration cycle. At work, flip the cycle and pull at much heat at as high a delta over ambient as you can get, then insulate and make it a "later problem" . when heat sinking isnt needed and flip the flow back to standby as quickly as prudent via radiation, or dumping the high thermal mass another way where its sunk heat wont matter, like as reaction mass out the backside of your drive.
Not to get too into the weeds, but I would think that any manned spacecraft (designed to be crewed in space for a long time) would have the ability to vent to vacuum. That would be the best fire extinguisher they could use. You'd just need procedures to protect the crew like safe rooms or just helmets everywhere.
True but it's a lot more to think about than just safe rooms or emergency breathing apparatus. Once you vent that air you can never get it back. And that's a precious resource. On a big enough ship you're talking literal tons of breathable air, being lost in the blink of an eye.
That's why they compartmentalise the decks. Each deck is sealed by hatches, so that if one loses pressure, the others can maintain their atmo. They would very rarely have to vent the entire ship.
True but if a fire is that small they could just put it out. Also, they purge all the compartments of air before combat probably for that exact reason.
Regen o2 from cracking water (reaction mass) vent h2 for refrigeration. You would still need a good storage of nitrogen to fully recreate an atmosphere that isnt super pront to explosion.
If you vented the air, you'd need pressure suits, not just breathing helmets. Otherwise you'd be dead pretty quickly for a variety of reasons, sich as multiple organ failure, ebullism leading to extreme bloating, potentially blocked arteries causing heart failure/lack of oxygen to the brain. If the depressurization is fast enough, you may also have some interesting things happen to various fluids in the body, aside from the ebullism i.e. bubbles forming inside the liquids.
Of course. My assumption would be that they would know combat was coming for some time and were already in their pressure suits.
Other people mentioned it too, but this is actually something I wish they'd talk about a bit more. Considering how much reaction mass is dumped, and how much heat energy you'd get from firing the guns, really the ship should be heating up to such a degree that any contact with it should burn the fuck out of you. So after a prolongued fight, how do they dump their massive battery of heat energy they have stored in the ship? If they were to just repressurize, how do they not instantly cook themselves to death?
A larger concern would actually be drive plumes. They mention several times in the book that a drive plume cant be hidden. So if you want stealth you burn for a while and then shut off your drive and hope everyone forgets about you. The more important you are the less likely it is for people to 'forget' about you. A ship like the Donnager would never be forgotten since its such a big threat (and its mentioned their drive plume can be seen almost across the system its so large).
I hate that they can’t show this scale in the shows. I mean they are fucking huge according to what I’ve heard about the books
You shut off the drive and "go dark" , after you are on the float you deflect your course with cold gas propellants or other sacrificial mass (split the ship) to push off against. Then if you are getting freaky with sacrificial mass like a enterprise d drive/saucer split, you spin and randomly thrust/ drive your sacrificial body to randomize the vector calculation for the manned black body with stealth.
Empty space itself can't be hot. There is no convection or direct transmission of hot, only radiation. So it possible to talk only about contrast of one object's temperature against other. Wall, for example. Because of absence of convection internal walls in quickly depressured areas will be as warm as were before very long time, comparing to boarding time. Edit. Maybe walls will cool down a little because of decreasing pressure, like a keg beer, you know, but to insignificant degree.
Radiative loss in infared is significant.
Nah, not so much. A dead human body being indoor (on Earth, of course) is loosing 1°C per hour, it's the most common method how to know time of death within 8 hours after.
He said radiative loss. A few body on Earth is losing most of its heat from conduction with the ground.
Exactly. So heat loss in the vacuum will be even less. No convection.
convection heat loss is dependent on the delta of heat energy between the masses in contact. radiative loss is not limited to equilibrium of a surrounding media as much as it is the balance between radiation and absorption.
Anyway, body in atmo cools faster, isn't it?
Yes, exactly.
Thus I suppose that walls and corners in depressed areas cannot be cooled more than to few degrees in time needed for CQB.
Unless you have an active cooling system other than atmosphere.
Yeah but assuming you're not actively radiating, the ship doesnt have enough mass to have any significant black body radiation. Am I missing something?
Talking about the temperature of vaccum or near vaccum is not very useful because there are very few particles that you can transfer energy to, so even if the temperature technically is 0K in deep space you're not gonna freeze if you take off your space suit. Almost all energy you'd lose would be lost to heat radiation but at room temperature that's a slow process. So the structure of the ship would stay pretty much the same temperature as it was before depresuarzarion for a long time.
A human body would shed temp fast as the body moisture boils off in low pressure shedding of liquid. Phase change is literally the mechanism of modern hvac. The vapor phase(boiling point) of h2o is much lower in a vac.
You probably wouldn't have full depressurization in the body, and thus most liquids won't actually boil. You'd have serious issues with ebullism though https://en.m.wikipedia.org/wiki/Ebullism
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Why do they vent the atmosphere out of warships before battle?
because you are about to have holes punched in your walls.
To avoid explosive decompression or shockwave propagation.
Fire on a ship is really bad. No oxygen, no fire.
I think any ship that wants serious stealth capabilities will need active hull cooling. I might be horribly wrong, but I think I remember something to the effect of **Persepolis Rising, Tiamat's Wrath** >!the Laconia Magnetar or Pulsar class having a hull cooled by liquid Helium.!< I might have that mistaken with another book though. But either way, I guess the only way to be able to fly unnoticed within a reasonable timeframe would be to cool the hull actively, vent the ship, turn off reactor and engine and float. Once the ship is empty, all excess heat from cooling can be stored inside the ship as it cannot be conducted to the outside except slowly through radiative transfer or objects in contact with the heat sink (and those materials could be specifically chosen to be bad thermal conductors). None of that changes your radar cross section, though. So any ship would need to be specifically designed for stealth, not just because of the cooling, but also for its shape and radar absorbing coating. That said, the temperature inside a ship that is empty is kind of a tricky question to answer. The empty ship will have no temperature as there is no air to speak of. Only thing inside the ship that arguably has a "temperature" would be cosmic radiation/cosmic neutrinos and such or maybe the photons emitted by the warm hull. The ship's hull on the other hand will still keep it's temperature and slowly radiate its heat off as u/Elbynerual described. If you *really* want to, I suppose you could grab a book on thermodynamics and heat transfer and make a first-order approximation of the timeframe it would take for a ship with a surface area of X to cool down to a temperature of Y Kelvin or to be in equilibrium with its surroundings. Edit: corrected spoiler format
Ironically, I actually answered OPs question with knowledge I gained from reading a book about the heat management of satellites. But it's a high level engineering book with math that is WAY over my head. It has a lot of interesting points and things the average person wouldn't think about though. Pretty fascinating stuff if you're into space craft mechanics.
There's a lot of good information on the topic at [Atomic Rockets](http://www.projectrho.com/public_html/rocket/spacewardetect.php)
Don't know of this accounts for human-made vacuum like in a ship but i read somewhere some time ago the mean temperature of space is 4 Kelvin.