TABLE OF CONTENTS An understanding of satellite thermal control is not possible without a satisfactory knowledge of the principles of heat transfer. It is in using these principles that the thermal engineer determines the means of regulating the heating of a satellite to produce the desired temperatures.
There are three modes of heat transfer: radiation, conduction, and convection. Conduction and radiation are always present and account for heat exchange among satellite components in a vacuum with final rejection by radiation to space. Convection occurs mainly on the ground, during ascent, and in heat transfer from fluids in sealed containers. Situations involving energy transfer by satellite outgassing and venting into space, or interaction with atomic and electrically charged particles, are specialized and require separate analysis.
Radiation is heat exchange by electromagnetic energy (wavelength range from about 0.1 to 100 ?m) between a surface and its surroundings. It is the most complex of heat transfer modes, and its mathematical treatment must invoke many simplifying assumptions to make it tractable. The next chapter in this book, Chapter 3, is an extended discussion with emphasis on the connection to thermal control.
Briefly, all surfaces at temperatures greater than absolute zero emit radiation at rates proportional to their temperature to the fourth power. A black surface (referred to in physics as a blackbody) is by definition the most efficient emitter. Its radiation emission, q e b (W/m 2), at temperature T (K) is given by the Stefan Boltzmann law
or
where
