How are satellites cooled?

  1. For example, most satellites will have CPU processors. On land, they require a heat-sink to transfer the energy to the air quickly so the CPU reaches ambient temperatures. But on a satellite there is no significant mass to absorb the generated heat from processing. So how are satellites kept cool?

    Thanks
     
  2. jcsd
  3. minger

    minger 1,498
    Science Advisor

    I'm not 100% positive, but I would guess the same way the sun transfers heat to us.
     
  4. Borek

    Staff: Mentor

    There are three methods of heat transfer, but only one can be used in vacuum.
     
  5. D H

    Staff: Mentor

    Short answer: The spacecraft is a heat sink for the electronics.

    So how is the spacecraft's temperature maintained? That is the subject of spacecraft thermal control. A full answer would require writing a book. Here is the first chapter of *the* book on the subject, Spacecraft Thermal Control Handbook: http://www.aero.org/publications/gilmore/gilmore-1.html.

    Here is a presentation on the issue of spacecraft thermal control: http://www.ieec.fcr.es/english/formacio/cva/apunts/P._Planas/Presentation.pdf.

    The European Space Agency has a good site on spacecraft thermal control, http://mechanical-engineering.esa.int/thermal/.
     
  6. I'm a pilot and I have an open cockpit aircraft. It is really cold at 5000ft msl. If its 80 degrees farenheit on the ground it's 40 degrees or so minus the wind chill. So its about zero. I would say in space it's probably a lot colder than that. I think the necessary question is how does a satellite keep from freezing???
     
  7. DaveC426913

    DaveC426913 16,138
    Gold Member

    Nope. High altitude and space are completely different animals. There is no atmo to transfer heat by convection or conduction. That leaves only radiation, and radiation is not very efficient.
     
  8. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    It's a pain with higher power CPUs and data processors. The tricky bit is to get the power from the chip to the radiators when you can't use fans or fluids+pumps. Especially on astronomy vehicles when you don't want to put any heat into the structure in case you change the shape.
    Theres a lot of work in building lower power FPGAs to reduce the amount of CPU you need.
     
  9. So your saying that even though its freezing up there the heat will stay in the same spot??? Not transfer to cool. Then how do comets collect ice?? Or why are they mostly ice. Why is there ice in space? Are you saying the matter that formed the ice was ice before it entered space?? Or do comets have an atmosphere??
     
  10. Borek

    Staff: Mentor

    Comets don't produce heat and they have millions of years to cool down. Satellite does produce heat and has to get rid of it in a short time span. These are completely different situations.
     
  11. Excuse my ignorance. I just didn't understand the heat dissipation part. The heat dissipates at a much slower rate than in atmospheric conditions. So it is tricky to remove the produced heat before it becomes to hot and burns out......
     
  12. DaveC426913

    DaveC426913 16,138
    Gold Member

    Correct.

    Also: while in direct sunlight, objects in space get very hot. The sun is an excellent source of heat radiation.

    Astronauts' suits are designed as much to cool them as to heat them.
     
  13. Q_Goest

    Q_Goest 2,967
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    Gold Member

    Hi Pitts. For any object, comet or satalite, they have a side that faces the sun and a side that faces away from the sun. Depending on how close to the sun it is, the sun side may get very hot. That's why comets begin to off-gas as they near the sun, but only on the sunny side. The black side is always cold as there's nothing to transfer heat to that side. On the sunny side, you have radiation heat transfer from the sun but on the dark side, any heat radiates to space which I believe is an equivalent of only a few Kelvin.
     
  14. Borek

    Staff: Mentor

    Not burns out, but melts down. Remember there is no oxygen around to burn in.

    --
     
  15. DaveC426913

    DaveC426913 16,138
    Gold Member

    I don't think "burn out" implies burning. When a component burns out, it does not combust (normally), even here on Earth.
     
  16. Borek

    Staff: Mentor

    Right, haven't thought about it this way.

    English difficulte langauge :devil:
     
  17. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Rust is still a problem.
    In vacuum, especially with repeated heating and cooling, all sorts of volatiles boil out of the plastics, lubricants, cleaning residues etc. these get zapped into free radicals by the UV and deposit themselves on the coldest part of the payload - which is always either the detector or the window into the detector.

    Because of the rarefied atmosphere, UV radiation and mix of reactants you get some weird chemical reactions that you never thought of in a lab. And they aways coat or attack the most sensitive bit of kit.
     
  18. I would think the processors are not so important for heat as the CCDs on satellites used to take pictures, which need to be kept so cold that thermal excitations are kept small so the pixels are less likely to falsely report an incident photon. Is there much need for processing power on a spacecraft, apart from sending the signals back to Earth? How hot do they get when fully operating, and surely this wouldn't damage a chip in 2.7 K surroundings!?

    Apart from that all they can do is shield the equipment from the heat (and wind) of the sun with the rest of the satellite body, or, do like WMAP does and live in constant shadow eclipsed by the Earth at L2, I guess they can just add metal conducting stiprs to conduct excess heat away to be radiated faster?
     
  19. Borek

    Staff: Mentor

    On Voyager, yes, on communication satellites - no.
     
  20. mgb_phys

    mgb_phys 8,952
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    Homework Helper

    The new solar panels for Hubble on the last service mission are about 2500W each. So around 5kW of electric power is being consumed in the spacecraft.
    Apart from a few 100w of microwave in the down link all that energy will end up as heat.
     
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