Space Shuttle Heat Transfer Question

[anthonyj915]

From what I gathered in Heat transfer, an object in space, ie space shuttle, can only lose cabin heat through the means of radiation (no conduction or convection off the surface...) So how would one go about determining what the emissivity is in space. Obviously there will be objects that are hotter (sun) but there is a lot of nothing.

Anyone have some insight as to how to ball park that figure?

The other think i was thinking about, was on re-entry the space shuttle gets hot. What is causing this heat? I know its the friction between the air and the shuttle, but doesn't the air flowing past also aide in the Convection heat transfer?

Thanks

 

[russ_watters]

The ball-park figure for space itself is Zero and you treat the sun separately and since it is so much hotter than objects such as the space shuttle, you just use the solar radiation flux (340w/m^2 iirc). For an object in orbit around the earth, you'd probably treat the Earth separately as well and use the S-B equation.

For re-entry, the heat is more from the compression of the air than from friction, so since the air itself is getting hot, the convection is what heats up the shuttle.

 

[bdrosd]

I believe the original post asks about the emissivity of space, which is probably about 1.0, and a ballpark figure for the temperature of space is about 0 (2.4 kelvin to be a little more precise). You will also need to know the emissivity of the shuttle itself, along with the surface area.
BTW, Isn't the intensity of solar radiation about 1500 w/m^2 at the top of the Earth's atmosphere?
As for heating during re-entry, even though the air molecules are traveling at a relatively slow speed (in Earth reference frame) which is consistent with them having a low temperature, from the shuttles' frame of reference, they are moving quite fast and hence have a very high temperature. In effect, the shuttle is surrounded by very hot gas and so it gets heated. Of course, the gas is mostly moving in a single direction, as compared to randomly for a "normal" hot gas.