Quote:
Originally Posted by drhex
But what is the source of cold? Is the near-vacuum around the spacecraft really sufficient?
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Remember technically there is no source of cold. Cold is just "less thermal energy".
Heat transfer occurs through conduction, convection, and radiation. In space you only have radiation. Effiency of radiation depends upon the emissivity (at a wavelength >1000 nm), the size of the radiator, and the temperature difference between it and what it is pointed at. This last can be important since a temperature difference of 370 K upon night side Earth orbit can go down to 90 K or less when the radiator is facing the Earth during the day side of orbit.
Suffice it to say that a radiator in space would have to be many times larger than one operating in the Earth's atmosphere at the south pole (for the same thermal transfer rate). A radiator immersed in water would be smaller yet.