MEMS Shutters for Spacecraft Thermal Control

As they are envisioned for future missions, small spacecraft, including nano and picosats, will require low power and light weight thermal control systems due to their small power and mass budgets. Variable emittance coatings, including micro-machined shutter arrays, will be flown as demonstration technologies on NASA’s New Millennium Program ST5 spacecraft. The latest prototype devices are arrays of 150 μm x 6 μm micro-machined and gold-coated shutters. Electrostatic comb drives are used to actuate the shutters to expose either the gold coating or the high emittance substrate to space. The prototype arrays have been designed and fabricated at Sandia National Laboratories using their SUMMiT V process. Present prototype die are 2.5 mm x 5 mm and consist of nine independent shutter arrays. For the flight units, 38 die, each with 72 shutter arrays will be combined on a radiator and independently controlled. It is expected that this will allow linear control of the effective emittance. The prototypes have undergone extensive thermal and lifetime testing, both in air and under vacuum. The paper will discuss the latest results including measurements of variable emittance, design aspects of the shutter arrays and the thermal control radiator, the ST-5 thermal conditions and the integration of the radiator into the spacecraft.