Can windows frost over in space?

[CookieSalesman]

I thought about this pretty hard, can windows frost over in space? I'm pretty sure they don't or can't after giving it a bit of thought. This is just a curiosity of mine.

So first I believe the correct question that we're trying to answer is:
Can a window get colder than interior air faster than the interior air can? Because in order to cause condensation/frosting it's only possible if the window is much colder.

I think this leads to 2 scenarios, one where the spacecraft is in thermal equilibrium, roughly speaking, and another situation where it is cooling down over a significant period of time.

I've given it a bit of thought but I'm not clear what's going on. First, the spaceship is in a vacuum and simply does not lose heat due to kinetic loss. It can only lose heat due to electromagnetic radiation.

However, because the radiation passes from the inside air through the window, how could the window possibly lose enough heat? The radiation from inside and thermal contact with the window should bring the window into near equilibrium, I think.

Is this correct?There are depictions like in the iron man scene where iron man goes out into low stratosphere and his visor frosts, however this is only possible because the heat loss from physical contact first of all greatly exceeds that of EM radiation. Consequently his visor gets cold very quickly because it's the first interface with the extremely cold outside atmosphere. The inside is more insulated and much much hotter than the sub-zero outside temperature and visor. I believe this is very unequal to the spaceship cockpit situation.

 

[.Scott]

A window on the dark side of the spacecraft will itself radiate thermal infrared out into space. Then, air inside the spacecraft could condense water onto that window.

I would also note that it is not impossible for the outside of the window to become frosted - but that would be very unusual and temporary. If you have ever watched the second stage booster coverage of the SpaceX launches, you may have noticed "snow" accumulating on the machinery above the engine. That is actually solid oxygen. If you had a squirt gun in space and squirted water at a window, evaporation would send much of the water into space. But it would also freeze the remainder of the water. If that ice was then exposed to any warmth, it would slowly sublimate away.

 

[Ibix]

Apollo 13 apparently condensed up (I admit I remembered that from the movie, but real sources confirm - https://history.nasa.gov/SP-350/ch-13-5.html). Icing doesn't seem implausible on the inside if the temperature dropped further.

 

[russ_watters]

However, because the radiation passes from the inside air through the window, how could the window possibly lose enough heat? The radiation from inside and thermal contact with the window should bring the window into near equilibrium, I think.

I don't understand what you are saying here. If the window is warmer than 3K it radiates heat into space. It will be in thermal equilibrium based on radiation received, radiation emitted and heat generated inside. That's the normal state of the spacecraft .

Other than incredulity over the power of heat radiation, I see no reason why this is more difficult to understand than the windows in your house frosting up.

 

[russ_watters]

Apollo 13 apparently condensed up (I admit I remembered that from the movie, but real sources confirm - https://history.nasa.gov/SP-350/ch-13-5.html). Icing doesn't seem implausible on the inside if the temperature dropped further.

Agreed; Without looking it up, I would have to guess dehumidification is a major problem in spacecraft and a critical function of the environmental control system. We drink liquid water and exhale water vapor. It has to go somewhere.

Edit: Well, this is pure gold:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080031131.pdf

 

[CookieSalesman]

Sorry. Maybe more specific situations may explain where my disbelief comes from. Please help me out with this and explain flaws in thinking if I have them.

Specific responses:

If you have ever watched the second stage booster coverage of the SpaceX launches, you may have noticed "snow" accumulating on the machinery above the engine. That is actually solid oxygen. If you had a squirt gun in space and squirted water at a window, evaporation would send much of the water into space. But it would also freeze the remainder of the water. If that ice was then exposed to any warmth, it would slowly sublimate away.

I'm not sure I understand you. Do you mean snow on the inside? I'm actually not clear if you still talk about 'outside' the aircraft.
First that's pretty cool that solid oxygen can accumulate, however I really don't know what you meant by squirt gun. Why would part of the water evaporate but freeze some other portions?

Other than incredulity over the power of heat radiation, I see no reason why this is more difficult to understand than the windows in your house frosting up.

The reason I believe the window can't frost is because I think the only way a window can frost up is if it's colder than interior air. I think I've stated a few reasons why I think this is not plausible on this assumption.I understand that <https://history.nasa.gov/SP-350/ch-13-5.html>
Says the walls perspire and windows were wet however is this because the windows were colder than interior air, or because the liquid dripped onto glass?Let me explain the reason for this question. I was just arguing with a friend that if while we see iron man's visor frost up in high altitude, I was insisting that the circumstance would be very different in space.

EXAMPLE 1: For instance please explain what may be the situation if you were in a spacesuit in space. You will only be losing heat through EM radiation, but I also believe your visor has little reason to become extremely cold. Consequently you should not have issues with your visor frosting up, right?

EXAMPLE 2: Or let's just say you're in an empty metal box in space with a window, with you sitting comfortably inside. (With air inside) You start at a certain temperature. Suppose you teleport this big empty box with you in in it into empty space at room temperature. I'm assuming NO sun nearby. However, does that change the situation anyway?

What now?

My thoughts are: Everything in the box essentially begins at thermal equilibrium. The windows begin at room temperature, and I think they would not drop faster than the interior air would. The physical transfer of heat from air to window should exceed the loss of temperature from the window radiating heat. Right?

 

[russ_watters]

The reason I believe the window can't frost is because I think the only way a window can frost up is if it's colder than interior air.

Even if you don't believe the window can be much colder than interior air, you must believe the window is colder than interior air because you know/accept that heat is flowing out of the spacecraft . Heat only flows from warm to cold.

I think I've stated a few reasons why I think this is not plausible on this assumption.

The only thing I saw was some confused logic about layers of insulation (which doesn't even apply to the window). The heat transfer logic still holds: as you move out of the spacecraft , layer, by layer, each layer is colder than the one next to it. It must be.

I understand that <https://history.nasa.gov/SP-350/ch-13-5.html>
Says the walls perspire and windows were wet however is this because the windows were colder than interior air, or because the liquid dripped onto glass?

Again, since the spacecraft is losing heat, the walls/windows must be cooler than interior air. Condensation is water spontaneously forming on a surface that is cooler than the surrounding air.

My thoughts are: Everything in the box essentially begins at thermal equilibrium. The windows begin at room temperature, and I think they would not drop faster than the interior air would. The physical transfer of heat from air to window should exceed the loss of temperature from the window radiating heat. Right?

Thermal equilibrium just means the temperature gradient is set and unchanging, it doesn't mean the gradient doesn't exist. Condensation could form whether you are in thermal equilibrium or not.

Back to your OP:

However, because the radiation passes from the inside air through the window, how could the window possibly lose enough heat? The radiation from inside and thermal contact with the window should bring the window into near equilibrium, I think.

I'm not sure if you understand, but it isn't the interior air that radiates to outside (through the window), it is the window itself that is radiating to outside.

 

[russ_watters]

I may have figured out what the issue is, because it just came up in another thread: do you think the window is transparent to infrared light? It's not.

 

[.Scott]

I'm not sure I understand you. Do you mean snow on the inside? I'm actually not clear if you still talk about 'outside' the aircraft.

It's especially easy to see in the SAUCOM Launch late last year. Look at the video from the link below.

https://www.spacex.com/news/2018/10/07/saocom-1a-mission

Starting at around 20:00 into the video, they alternate between two shots of the second stage engine. One shot shows sunlight illuminating the engine at the top of the screen, the other at the bottom. The shots showing the sunlight at the top also show a steady dribble of snow forming and sliding down along the seam where either engine fuel or O2 is being used to cool the bell of the thruster. This is outside of the engine.

Later at 28:28 into the video, the engine has been shut down and the source of the leak is more visible. It forms a shape that grows and they falls off.

First that's pretty cool that solid oxygen can accumulate, however I really don't know what you meant by squirt gun. Why would part of the water evaporate but freeze some other portions?

When most fluids evaporate (water and liquid O2 being among them), the conversion from water to gas require heat - the latent heat of evaporation. So, in the same way that perspiration leaves you cool as it evaporates, so will the bulk of the water be cooled as the the water evaporates. And in a vacuum, this evaporation happens very quickly.

If you have ever put ethyl alcohol on a wound to clean it (which is no longer advised) and then blew on the wound, you would have felt instant cool. Blowing on the alcohol accelerates its evaporation and thus accelerates the cooling effect.

When the bulk of the water is cooled, its rate of evaporation slows. But not enough to prevent it from freezing. Once frozen, it will still sublimated - and that sublimation will further cool the main body of the ice and further reduce it rate of sublimation. There will only be enough heat energy in the original liquid water to evaporate a certain portion of the total liquid. Beyond that, there will be a certain amount of ice that will last until it can absorb heat from other sources.

The reason I believe the window can't frost is because I think the only way a window can frost up is if it's colder than interior air. I think I've stated a few reasons why I think this is not plausible on this assumption.

If I place a hot glass ball into orbit around Pluto (just to get it clear of the Sun), would you imagine that ball staying hot forever? It will not. It will continuously radiate thermal infrared radiation. And it will cool until the radiation it produces matches the radiation it is absorbing.

By the way, glass is transparent to light, but blocks almost all infrared. So it is effective at radiating thermally.
This also means that the interior air cannot radiate energy directly into space. Any infrared generated by the air (which is minimal anyway) would be absorbed by the walls of the spacecraft and by the windows.

My thoughts are: Everything in the box essentially begins at thermal equilibrium. The windows begin at room temperature, and I think they would not drop faster than the interior air would. The physical transfer of heat from air to window should exceed the loss of temperature from the window radiating heat. Right?

The air temperature will not drop at all until the walls or the windows cool down and, in turn, begin to cool the air. Moreover, the air may be heated to keep it at "room temperature" by adding as much heat as is being lost through the walls and windows.