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118 MEMS and Microstructures in Aerospace Applications

Unbiased-
OFF

A A'
Biased-
ON

(cross section through A-A')

FIGURE 6.5 Scanning electron micrograph of the Rockwell Science Center RF MEMS
switch. On the right are cross-sectional schematic views of the switch in the ‘‘off’’ and ‘‘on’’
states. (Source: J. Jason Yao et al., MEM system radio frequency switches, Smart Material
and Structures, 10, Institute of Physics Publishing (2001) pp. 1196–1203. With permission.)

have shown no fatigue after 60 billion cycles and ‘‘hot’’ switching at ~ 1 mA has
been demonstrated for tens of millions of cycles.
Given the significant advantages of MEMS switches for space RF transceiver
systems, this device was an excellent candidate for a LEO technology demonstra-
tion flights via the PICOSAT missions (see below). Two PICOSAT-based flight
demonstrations of the RSC RF switches were conducted: The first in February 2000
and the second in September 2001. In both of these missions the RF switches were
not part of the functional RF communication system but comprised the test payload.
The mission objective to actuate the switches while in orbit was successfully
accomplished on both missions. No detectable degradation in performance from
the baseline performance prior to launch was found for the RSC MEMS RF
switches.

6.2.7 MICROCHEMICAL SENSORS
NASA’s Glenn Research Center (GRC) has spearheaded the development of mini-
aturized chemical sensors based on MEMS and nanomaterials technologies. 15
GRC’s most successful technology is a microfabricated hydrogen sensor that won
the 1995 R&D 100 award. It has been successfully demonstrated on the STS-95 and
STS-96 missions as a point contact sensor for the detection of hydrogen fuel leaks.
Fuel leaks have led to the grounding of the Space Shuttle while on the launch pad.
No commercial sensors were available that operated satisfactorily for the detection
of hydrogen over a wide range of partial pressures, and that could detect the
presence of hydrogen in inert environments (He purged environments) or in air.
Commercially available sensors often needed oxygen to operate or needed the
presence of moisture. The GRC hydrogen sensor remains highly sensitive in both
inert and oxygen-bearing environments and can operate over a wide concentration
range of hydrogen as shown in Figure 6.6. Since it is a microfabricated device, it has

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