Electronic Heat Rejection on Spacecraft

Adapted from the JPL D-8160 Thermal Environments

Passive Control:

One of the more common methods of rejecting electronic heat is to mount the electronics just inside the spacecraft bus structure. Thus, the energy is conducted over a short path to an external spacecraft thermal control surface (frequently refered to as a radiator and sometimes as a shearplate). This surface is usually coated with a low solar absorptance/high infrared emittance coating (usually a white paint). Such surfaces are usually positioned by spacecraft orientation to point to deep space. Thus, the natural environment is minimized or eliminated and maximum heat rejection occurs.

Active Control:

More often than not, there is a louver system external to this radiator. The louvers allow almost maximum heat rejection under hot conditions, but retain most of the energy when needed to keep the equipment from getting too cold. Each louver blade is usually polished aluminum, thus having a low infrared emittance. Each blade has its own bimetallic mechanism which opens and closes the device as a function of the bimetal spring temperature which is essentially at the temperature of the shearplate.
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