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Microsystems in Spacecraft Thermal Control 195

FIGURE 9.4 Radiator assembly. (Courtesy: JHU/APL.)

To qualify the MEMS louver, several environmental tests were conducted on
the final flight articles. The device needs to pass various performance tests (burn-in,
various vibration tests, and thermal vacuum) to verify its survival. In addition, life
cycling tests, performance measurements (both effective IR emissivity and solar
absorptivity), cycling in vacuum (over 1000 times), and exposure to a simulated
space environment in solar wind and ultraviolet (UV) facilities were conducted.

9.4.3 MEMS THERMAL SWITCH
A conventional thermal switch, sometimes referred to as heat switch, is an active
thermal control device. Heat switches are devices that allow the connection or
disconnection of the thermal contact between two surfaces. Thermal switches are
typically installed between an insulated spacecraft structure and an external radiator
or mounted between spacecraft components such as the battery on the Mars rover
and the structure or the radiator. Various types of paraffin are often used in the
thermal switches to create conduction paths when melted materials expand and
bring components in close contact. A pedestal thermal switch designed by Starsys is
38.1 25.4 mm, weighs 100 g, and has a thermal conduction range from 1 to 100. It
uses a paraffin actuator, which uses the thermal expansion of paraffin when it is
melting to bring two thermally conductive surfaces into contact. The effectiveness
of a thermal switch is usually characterized by a thermal conduction range which is
an indicator of the improvement in effective thermal conductivity of the conduction
path.
Another new variable emeltance technology, which also will be flown on the
4
ST5 mission, uses an electrostatic thermal switch as a radiator. In this design, a thin
film with a high emissivity surface is suspended, thermally isolated, above
the radiator. Once a voltage is applied between the radiator and the film, it is

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