How Satellites avoid breaking up in space due to cold temp ?

Ale

That is basically the question I have been having for a while.
If I submerge a piece of something in liquid nitrogen (-196 °C) and hit it, it breaks. The how do they keep things from breaking in space where the temp is around -270 °C ? Do they keep _everything_ every piece of pipe, wall and so on thermalized ?

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Post Edited (Ale) : 11/19/2009 12:15:31 PM GMT

BradC

I always believed they had a small heat source to keep things warm. The beauty of not having an atmosphere is there is very little there to conduct the heat away, so some pretty speccy insulation and a small heater would keep things comfortable for the electronics.

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Unknown

The same way the Moon doesn't break up in space because of what it is made of. You probably want to study textiles or the heat shield on the original Apolo 1 spaceship. I'm sure you have to calculate volume and density and find an equation to see how much you would need to build a basic heat sink. Then you can figure out how long it will last. If you put it in orbit, it is hot for some of the time and cold for some of the time. If you can balance it out, you can probably find a happy medium temperature. You probably have to keep contaminants like skin oil from touching it. When I changed projector bulbs for a theater, we had to use gloves to touch the bulbs because our skin oil would burn a hole through the bulb and sometimes they would explode if we were unlucky.

I suspect the reason why some satellites are in low orbit is because they are using the Earth as a shield to make them last longer.

mctrivia

Actually they often have trouble with to much heat. With almost no atmosphere the small amountof heat generated by electronics is hard to get rid of. Also with almost no atmosphere the cold does not have a chance to cool the shell.

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mctrivia

Low earth orbit is easier to acheive and has lower lag time

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Ale

Thanks guys, so it is as I thought

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ElectricAye

Keep in mind that in space there are two major modes of heat transfer: conductive and radiative. Conductive heat transfer happens when thermal energy moves through matter, whether it be a piece of metal, a gas, or a textile, etc. If one end of the material is hot and the other end is cold, you have conductive heat transfer through the material. In space, however, a satellite is existing almost in a vacuum, so the satellite as a unit has nothing connected to it that can conduct heat to or away from it.

So that leaves radiative thermal transfer. Anything above absolute zero emits thermal radiation. That include clouds of warm gas, planets, stars, etc. Thermal transfer via radiative processes takes into account the sum of thermal energy received from the environment minus the sum of energy lost from your object. In other words you have photons leaving your object and other photons hitting your object, and the resulting sum of photons lost and gained is what will determine if your satellite is going to heat up or cool down.

Now let's say your satellite is floating infinitely far away from any planet or star, and it is wrapped in a black blanket that perfectly absorbs all photons and is forever stuck at absolute zero. Such a blanket would emit no photons, so the satellite would get nothing from this blanket. The satellite, however, would be emitting photons that the black blanket would perfectly absorb. Over time, if there are no energy sources inside the satellite, the satellite would approach the same temperature of the blanket, absolute zero.

You can think of the cosmos as being that black blanket, except instead of being at absolute zero, there is a background energy that was left over from the Big Bang (plus star light, etc). The photons streaming in from all directions makes the cosmos appear like a black blanket at a few degrees above absolute zero, so from the standpoint of radiative heat transfer, the cosmos "looks" like roughly -270°C or whatever.

Of course, if your satellite is floating around in sunlight, that's a whole different story. It will be awash in photons, and because the satellite has nothing to conduct away the incoming thermal energy, it must rely on reflective shields and, sometimes, heat transfer systems that pick up the energy from the hot side and pump it to the cold shadow side where it can radiate the energy into the black blanket of space.


Keep in mind that if you were wearing a thin glove and reached out and "touched space", it wouldn't necessarily feel cold. Much would depend on whether your glove were in shadow or sunlight and on how good of an insulator the glove material happens to be and whether or not it is reflective, etc. You'll notice space suits don't come in fall fashion colors.

hope that helps,
Mark

Moskog

ElectricAye said...
Now let's say your satellite is floating infinitely far away from any planet or star....

Then it's probably no longer a satellite. Like the New Horizons, Voyager 1 & 2 and Pioneer 10 & 11 escaping·the solar system in different directions. A better name would be spacecraft or something like that. A satellite is orbiting something, like the Earth.

ElectricAye

Moskog said...

ElectricAye said...

Now let's say your satellite is floating infinitely far away from any planet or star....

Then it's probably no longer a satellite. Like the New Horizons, Voyager 1 & 2 and Pioneer 10 & 11 escaping the solar system in different directions. A better name would be spacecraft or something like that. A satellite is orbiting something, like the Earth.

Oops, of course, I forgot to mention that it's a satellite of the Local Group.

en.wikipedia.org/wiki/Local_Group

John R.

I like this simple (but useless) explantion to the original question:

Just like anything else: Duct Tape, Chewing Gum, and Velcro (especially Velcro)

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John R.
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stephenwagner

I can't speak for the entire earth orbiting satellite/vehicle, however, the electronic hybrids of the vehicle payload are specified to meet the requirements of MIL-PRF-38534.