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Thread: Why is it 'cold' in space?

  1. #1
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    Why is it 'cold' in space?

    I've always been puzzled by Apollo 13. When they had to conserve power, they had a big problem with cold in the spacecraft. But I thought you'd have the opposite problem.

    If you are in direct sunlight on the surface of the Earth, it's hot. Sunlight is about 1kW/sq metre. We loose heat by convection in the atmosphere, but in space you are surrounded by the very best insulator there is: a vacuum.

    When I leave my car parked in direct sunlight it can get VERY hot -and a car is a metal box with windows just like a space capsule. It's surrounded by air which cools it by convection, but a space craft is almost totally insulated by vacuum.

    So why is it not "hot", at least in near-Earth orbit space?

    Note: I appreciate a vacuum cannot have a temperature. I'm asking why it is not hot within vessels in space, rather than cold, without any active heating or cooling.

  2. #2
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    Because the main engineering problem of a cislunar spacecraft is the rejection of internally-generated heat.

    Humans and electronics (especially 60's-era electronics) generate a lot of heat. That has to be gotten rid of. The last thing the designers wanted was a lot of extra solar gain to get rid of as well. So they designed the Apollo spacecraft to reflect away as much of the insolation as possible, and provided insulation (for thermal protection during reentry and radiation shielding).

    But when Apollo 13 lost its oxygen, it also lost its power source. The electronics had to be turned off. The astronaut's bodies didn't make enough heat to keep the cabin warm, and (by design) the Sun's energy was largely reflected, not absorbed. What heat there was, radiated away over the several days after the accident.

    I hope that was clear.

  3. #3
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    very interesting.
    Does this still hold true for the newer space crafts? Like soyutz(actually this is old lol), shuttle, ISS... ?

  4. #4
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    Quote Originally Posted by Jorge
    very interesting.
    Does this still hold true for the newer space crafts? Like soyutz(actually this is old lol), shuttle, ISS... ?
    Why astronauts are cool

    You may notice that the payload bay doors are open. In fact, almost any picture you see of the Space Shuttle in orbit will show these large doors open. [...] If you guessed that the payload bay doors have something to do with the radiators, then you are right. On the inside of the doors are heat radiators. This is a special system that allows heat from the Shuttle to be released into the cold vacuum of space. Liquid Freon loops are used to circulate heat from the Shuttle’s cabin and equipment to the radiators.
    The Space Station uses a similar system. Perhaps, you’ve noticed something on the ISS that looks almost like a crumpled-up solar panel. The ISS currently features five radiator panels (with four more awaiting deployment), attached to the Station’s trusses.
    Last edited by 01101001; 2005-Sep-29 at 07:40 PM.
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  5. #5
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    Deep Cold Space? Apollo BBQ?

    Some thing doesn't quite fit here yet..

    I understand the idea that spacecraft should be warm in space, and that they are designed to cool things off.

    But with the Apollo 13 example, most of the ship wasn't working, and it was freezing inside the capsule. I find it hard to beleive that the capsule was SO good at reflecting solar heat that it actually began to freeze.

    (i'm using the movie for refrence but it was supposedly made of the transcripts of the event and fairly accuate)

    why were the astronaughts freezing and cold? how could the ship "reflect" sooo much that it managed to actually nearly freeze the astronaughts. and why do the parachutes need heaters? why are they freezing in space? wouldn't it be easyer to just put them in the sunlight ? were they refrigerated or something?

    The way it is explained, to me it seems like the astronaughts should be cooking in their malfunctioning capsule, not freezing. I realize it's designed to reflect the heat, but is it so well designed that it actually reflects enough heat to require the ship to need a heater?

    I'm confused.

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    I think I'll try this...

    There is convection heat and radiation heat.

    Convection heat is contact heat: air, metal, wood, plastic, transferring heat from one thing to another. In that regard, space is very cold.

    Then there is radiation heat, like "light" heat, direct radiation coming from the sun.

    Way out in space, away from the sun, with no convection heat, everything is very cold.

    Near the sun, the side of, let's say the moon, that is lit up by the sun is hot (because of radiation heat), while the side in the dark side is cold (no radiation and not much convection heat, just a small amount of convection heat stored in the rocks from the last time the rocks were in the direct sunlight).

    If the spacecraft has a lot of big windows, and the windows face the sun, then it will get hot inside the spacecraft very fast because of radiation heat.

    If the spacecraft has small or no windows, and it is designed to reflect the radiation heat away from it, then it will get cold inside. If the cold spacecraft gets closer to the sun, it could heat up inside because of more intense radiation heat coming in from the outside, warming up the skin and body of the spacecraft and that heat is then transferred inside the spacecraft by convection through the metal, plastic, and other material in the walls of the spacecraft.

    The tiles on the underside of the Space Shuttle are designed to reduce or minimize the convection heat carried from the outside of the tiles to the inside of the shuttle.

    Of course if we move a space craft a long way away from the sun, it will become very cold inside, because space itself lacks convection heat, and the sun's radiation heat is weak at great distances.

    So, I would say the Apollo spacecraft radiated out more heat than it radiated inward from the sun, and that's why it cooled off so much inside.

  7. #7
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    so say that the apollo capsule is in space, totally turned off, due to its nature, and the nature of the vacuum, the capsule will cool off and probably freeze over?

    that same capsule say, in a desert here on earth would heat up just like any car would right?

    in short, had the capsule been designed diffrently it could have just as easily sat in space and gotten very hot right?

  8. #8
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    Quote Originally Posted by KingNor
    why were the astronaughts freezing and cold? how could the ship "reflect" sooo much that it managed to actually nearly freeze the astronaughts.
    What we sense as hot and cold is actually a fairly narrow range of temperatures. For instance, ‘room temperature’ is about 22-degrees C while water freezes at 0 C. However, on the absolute temperature scale (Kelvin scale) room temperature is 295 K and the freezing point of water is 273 K. Thus you don’t need to reflect that much solar energy to make what is really a fairly modest drop in temperature.

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    Quote Originally Posted by KingNor
    so say that the apollo capsule is in space, totally turned off, due to its nature, and the nature of the vacuum, the capsule will cool off and probably freeze over?

    that same capsule say, in a desert here on earth would heat up just like any car would right?

    in short, had the capsule been designed diffrently it could have just as easily sat in space and gotten very hot right?
    There are several reasons for that. A desert on earth is already warm and stays warm for several reasons. Natural earth heat from below, radiation heat from the sun in the day, stored radiation heat in the rocks at night, and convection heat of the air.

    If you move the capsule up to a high mountain top, with little air up there, it will get cold, and there are “deserts” in the arctic which are very cold. The hot deserts are closer to the equator and receive more direct radiation rays of the sun.

  10. #10
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    One time I put a high-temp thermometer out in the hot sun where I live. I’m at 5,000 feet in the Western US. In the direct sunlight, the temperature reading of the thermometer went up to 160 degrees F. In the shade it went up only as high as about 95 degrees F. So, it picked up about 65 degrees by just being moved from the shade, out into the direct radiation of the sun.

    Out here in the West, we have “high deserts” at high altitudes. They are very hot in the day and very cold at night. In the winter here, they can collect snow on the cactus, especially at night.

    A snowfall where I live, in January, will melt in the desert sunlight in a day or two, but the snow in the shadow of a hill will remain for many weeks, maybe a couple of months, because of the lack of direct radiation heat.

  11. #11
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    Quote Originally Posted by Sam5
    There is convection heat and radiation heat.

    Convection heat is contact heat: air, metal, wood, plastic, transferring heat from one thing to another. In that regard, space is very cold.
    Umm, no. In that regard, space has no temperature. It is a pretty good vacuum and there is no material touching the spacecraft to transfer heat.

    Then there is radiation heat, like "light" heat, direct radiation coming from the sun.
    And also radiation cooling. The spacecraft absorbs on the sunlit side everything that is not reflected (heating) and emits radiation in every direction (cooling).

    In that regard space is very cold. Look at any section of the sky and mostly you will see a radiation temperature of few degrees above absolute zero. Unless the section of the sky includes a planet (warmer) or the sun (very hot).


    To maintain a given temperature there are three factors that have to be kept in balance: Absorption of solar radiation, internal heating (electronics, humans, etc.) and emission of radiation. I don't know much of the Apollo CSM temperature control, but if it was mostly passive by designing the heat flow to accomodate the internal heating (possibly including heaters) then that system would be thrown off balance by drastically reducing the internal heating.

  12. #12
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    Quote Originally Posted by Andreas
    Umm, no. In that regard, space has no temperature. It is a pretty good vacuum and there is no material touching the spacecraft to transfer heat.
    I thought I covered that. In a vacuum there is no convection heat. Convection heat comes from hot moving molecules touching other molecules and passing along the heat energy. Thats why I said a spacecraft gets very cold when it moves a long way from the sun, because there is no convection heat out there in deep space and very little radiation heat.

  13. #13
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    Quote Originally Posted by Sam5
    I thought I covered that. In a vacuum there is no convection heat. Convection heat comes from hot moving molecules touching other molecules and passing along the heat energy. Thats why I said a spacecraft gets very cold when it moves a long way from the sun, because there is no convection heat out there in deep space and very little radiation heat.
    But heat isn't something that just goes away when there is no heat source. So regarding convection heat space isn't cold, it isn't warm, it has no temperature. Without material in contact, there is no means to transport heat to or away from the spacecraft by convection. And a working spacecraft produces heat internally it needs to get rid of.

    Only radiation heat applies. That is inefficient for cooling compared to convection transfer. The spacecraft doesn't necessarily get cold. It all comes down to balances - if it absorbs and produces more than it radiates away it will heat up.

  14. #14
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    Sam5,

    While there is such a thing as convection heating (and cooling), it is not what you ae describing.

    Convection heating is the movement of fluid (liquid or gas) from a hot region to a cooler one.

    What you are describing is conduction heating (the movement of heat within a solid).
    Last edited by Kaptain K; 2005-Sep-30 at 03:23 AM. Reason: typo - did not close a parentheses

  15. #15
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    Hi, Kaptain K. What might be a good idea is for you and Andreas to start at the top of this thread and try to answer the original questions of kzb and KingNor.

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    Maybe this can be helpful.

  17. #17
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    Quote Originally Posted by Sam5
    Hi, Kaptain K. What might be a good idea is for you and Andreas to start at the top of this thread and try to answer the original questions of kzb and KingNor.
    1) The original question has already been adequately answered by others.
    2) It serves nobody any good to answer a question with incorrect physics.
    3) If I had made such a mistake and you had caught it, my response would have been "Oops, sorry about that. Thank you Sam5"!

  18. #18
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    [spellcheck]

    it's astronaut; we'd really like to avoid the implications of "astronaught." see . . . er, I can't remember which thread but it's in conspiracies somewhere, for lots of discussion on the subject.

    [/spellcheck]
    _____________________________________________
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    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

  19. #19
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    Although no one has mentioned it, one of the most perfect examples of what happens to a space craft that doesn't have its insulation in place is Skylab. Because the craft was damaged when it was launched, it had lost a large section of insulation material from the top of the housing. When the first mission arrived the station was over 50°C and they had to raise what was basically an umbrella that was designed to protect the damaged section by refecting away the heat.

    With Apollo 13, the system had all of it's insulation still, so the ship was losing heat into space. Essentially the design that normally removed the excess electronics and body heat was cooling the ship. The effect drastrically increased because the crew blocked the windows so they could sleep. Without any sunlight coming through the windows, the heat in the LM was basically sucked out of it with little replacing it. The CM was cold because it had no there was nothing heating it at all, which is also why the parachuttes might have frozen.

  20. #20
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    if you step out of the space ship and into a vacume... assuming your not in the light.

    the first thing that will happen is the rapid evaporation of every drop of water from your skin, and below it..... below your skin... and from inside your lungs.
    the vacume will cause the water to rapidly boil.. and for every gram of water boiled off as a gas.. 2000 joules of heat are removed...
    so just from rapid evaoration you would quickly freeze...

    secondly.. dark space is a perfect black body collector..
    i.e.. every photon of infrared energy that you emit... just leaves.. and never comes back... i.e.. you are like a light bulb.. and you will radiate your energy until you reach an equialibrium with your enviorment.. which could be 2 degrees Kelvin.
    -MT

  21. #21
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    Quote Originally Posted by Kaptain K
    Convection heating is the movement of fluid (liquid or gas) from a hot region to a cooler one.

    What you are describing is conduction heating (the movement of heat within a solid).
    D'oh! I meant conduction heating, too.

  22. #22
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    Quote Originally Posted by Mosheh Thezion
    if you step out of the space ship and into a vacume... assuming your not in the light.

    the first thing that will happen is the rapid evaporation of every drop of water from your skin, and below it..... below your skin... and from inside your lungs.
    the vacume will cause the water to rapidly boil.. and for every gram of water boiled off as a gas.. 2000 joules of heat are removed...
    so just from rapid evaoration you would quickly freeze...
    This is not the case. Liquids under your skin can hardly boil because they are not exposed to vacuum. Anyway, that subject was handled in another thread.

  23. #23
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    Quote Originally Posted by Andreas
    This is not the case. Liquids under your skin can hardly boil because they are not exposed to vacuum. Anyway, that subject was handled in another thread.
    well.. we do have pores, and if im not mistaken, stepping into a vacume would cause several parts of the body to pop open literally.
    -MT

  24. #24
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    Quote Originally Posted by Mosheh Thezion
    well.. we do have pores, and if im not mistaken, stepping into a vacume would cause several parts of the body to pop open
    Only in the movies. In the real world the human body doesn't fall apart so easily. You should read the thread linked to, above, and follow the references there.

    Grant Hutchison

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    I'm sure nasa can find someone willing to go out into space with only a helmet on... if they really want to

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    Well.. i can except having an exagerated view of the ramifications of stepping into a vacume.. but im pretty sure, our bowls will expand, and our eyes will bug out.
    and im also pretty sure we will suffer numerous capilary explosions on the surface of our skin.... er.. if nothing else.. all our pores will empty, since a vaume pump is a great way to suck out the pores of the face.
    But hea.. i can except being wrong.. and i would like to think we are made of tougher stuff..
    and i am most surely wrong about the boiling under the flesh... but one has to admit, that based on clear knowledge found in deep sea diving.. rapid pressure change will cause gases to form.. its a question of how quickly i suppose. And what gases.
    -MT

  27. #27
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    Quote Originally Posted by Mosheh Thezion
    Well.. i can except having an exagerated view of the ramifications of stepping into a vacume.. but im pretty sure, our bowls will expand, and our eyes will bug out.
    Our bowels would surely expand, because they have gas in them. But what would make your eyes bug out? (Apart from surprise and horror.)

    Quote Originally Posted by Mosheh Thezion
    and im also pretty sure we will suffer numerous capilary explosions on the surface of our skin....
    Only if parts of your body were decompressed, while the rest stayed under pressure. Your capillaries don't explode when you come to the surface quickly from 10m underwater, because the pressure drop is uniform throughout your tissues. In effect, your whole body changes volume very slightly, and the tissue pressure falls by one atmosphere uniformly. So there's no increased pressure gradient across the capillary walls.

    Quote Originally Posted by Mosheh Thezion
    all our pores will empty, since a vaume pump is a great way to suck out the pores of the face.
    Vacuum pumps don't suck anything out of the pores in your face, I'm afraid, appealing though the thought may be to some people. You need a pressure gradient to induce flow, and since the pores are blind-ended, the entire channel quickly drops to the sub-atmospheric pressure of the pump, and there's no flow. (Same thing applies to the idiotic practice of ear-candling, which doesn't suck wax out of your ears.)
    If you don't believe this, try getting peanut butter out of a small jar by closing your mouth around the rim and sucking.

    Quote Originally Posted by Mosheh Thezion
    but one has to admit, that based on clear knowledge found in deep sea diving.. rapid pressure change will cause gases to form..
    That's nitrogen coming out of solution - rather different from the "boiling" you mentioned in your first post.

    Grant Hutchison

  28. #28
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    Ok..
    But i have a vacume pump.. and it can suck out white and black heads like nothing else....
    And you do know ear candling uses heat to melt the ear wax out.. right?
    and its gravity that allows the clogged ear to drain..
    i knew a guy, who was deaf in one ear most of his life..
    then he got ear coneing.. and bamm.. just like that his ear worked just fine..
    he had just had a clog of wax built up... and it acted like an ear plug.

    -MT

  29. #29
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    Quote Originally Posted by Mosheh Thezion
    But i have a vacume pump.. and it can suck out white and black heads like nothing else....
    You surprise me.

    Quote Originally Posted by Mosheh Thezion
    And you do know ear candling uses heat to melt the ear wax out.. right?
    and its gravity that allows the clogged ear to drain..
    This is too off-topic to pursue here, and I regret bringing it up. Look here:
    Ear candles: a triumph of ignorance over science
    Ear candles: efficacy and safety

    Grant Hutchison

  30. #30
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    thanks for the info guys, i guess i'm just sort of impressed that the apollo spacecraft were that well desigend that they could radiate out that much heat. I think i've got a grasp on how it works now. :-)

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