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Vision for Microtechnology Space Missions 17

FIGURE 2.1 The NMP ST5 Project is designing and building three miniature satellites that
are approximately 54 cm in diameter and 28 cm in height with a mass less than 25 kg per
vehicle. (Source: NASA.)

Center (GSFC), developed by the Johns Hopkins University Applied Physics
Laboratory (JHU/APL) and fabricated at the Sandia National Laboratory. In JHU/
APL’s rendition, the radiator is coated with arrays of micro-machined shutters, which
can be independently controlled with electrostatic actuators, and which controls the
1
apparent emittance of the radiator. The latest prototype devices are 1.8 mm 0.88
mm arrays of 150 6 mm shutters that are actuated by electrostatic comb drives to
expose either the gold coating or the high-emittance substrate itself to space. Figure
2.2 shows an actuator block with the arrays. Prototype arrays designed by JHU/APL
have been fabricated at the Sandia National Laboratories using their SUMMiT V 1
process. For the flight units, about 38 dies with 72 shutter arrays each will be
combined on a radiator and independently controlled.
The underlying motivation for this particular technology can be summarized as
follows: Most spacecraft rely on radiative surfaces (radiators) to dissipate waste
heat. These radiators have special coatings that are intended to optimize perform-
ance under the expected heat load and thermal sink environment. Typically, such
radiators will have a low absorptivity and a high infrared emissivity. Given the
variable dynamics of the heat loads and thermal environment, it is often a challenge
to properly size the radiator. For the same reasons, it is often necessary to have
some means of regulating the heat-rejection rate in order to achieve proper thermal

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