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188 MEMS and Microstructures in Aerospace Applications

9.3 SPACECRAFT THERMAL CONTROL

The function of a TCS is to control the temperature of spacecraft components within
their operational temperature ranges for all operating modes and in satellite space-
craft environments. This is a demanding requirement if the limits are tight or the
environments extreme. Table 9.1 shows some of the typical temperature require-
3
ments for spacecraft components.
The thermal design of a spacecraft requires accounting of all heat sources, both
from within the spacecraft and imposed by the environment. Heat-producing space-
craft components include but are not limited to heaters, shunts, rocket motors,
electronic devices, and batteries. Environmental heating is largely the result of
solar radiation. Radiation from other heavenly bodies (such as the Earth or Moon)
is typically less, but must be considered for thermal design purposes. Other space-
craft components such as a solar array and deployed devices that are in a field of
view of a surface may impose a radiation heat load.
Once heat sources and environmental parameters are quantified, the thermal
engineer uses analysis for the thermal design of the spacecraft. For a spacecraft,
conduction (including interface conduction) and convection (if present) are con-
sidered as internal heat transfer processes. These processes affect the balance of
heat energy within the spacecraft itself and may be very important. Thermal
exchanges within the environment are almost completely caused by radiation
exchange. The radiator area and the coating surface properties are of great import-
ance in achieving proper thermal control. Fortunately, research has been devoted
into developing coatings with specialized properties. Desired surface properties
may be presented as a permanent surface coating or may be temporarily altered
according to design conditions.

9.3.1 SPACECRAFT THERMAL CONTROL HARDWARE
Thermal control hardware is employed to maintain components within proper
temperature ranges. Proper thermal design will maintain all components within
the required operating temperature range during the entire mission. The radiator is
an important element of the design. Radiators are areas on the surface of the
spacecraft with high typically emissivity and low solar absorptivity and a minimum

TABLE 9.1
Typical Spacecraft Component Temperatures 3
Component Operating Temperature (8C) Survival Temperature (8C)
Digital electronics 0 to 50 20 to 70
Analog electronics 0 to 40 20 to 70
Batteries 10 to 20 0 to 35
Particle detectors 35 to 0 35 to 35

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