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Microtechnologies for Space Systems 121

Infrared radiation

Pinhole Internally supported
absorber

Corrugations

Membrane
Tip
FIGURE 6.7 Tunneling infrared sensor flown on a Stanford University satellite called
SAPPHIRE. The sensor was used as a horizon detector. The MEMS-based sensor combines
the principles of the Golay cell infrared sensor and scanning tunneling microscopy. The
three-chip device (bottom cross-sectional view) consists of two chips enclosing a small
volume of air. Infrared absorption causes the enclosed air to expand, pushing out the lower
membrane. The membrane movement is sensed by a quantum-mechanical tunneling elec-
trode tip. The top view shows a 2-pixel device (red square marks a single 1.5 1.5 mm
pixel). (Source: NASA/JPL.)

resistively heated to 600 K. The thrust levels per slot are in the range of tens of
mN, and can be adjusted by either changing the ambient temperature of the
propellant or by changing the dimensions of the slot. These extremely low thrusts
could be utilized for spacecraft attitude control or for precise station-keeping
applications. Such low-level, precision thrust is needed for ensembles of spacecraft

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