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130 MEMS and Microstructures in Aerospace Applications

FIGURE 7.2 Schematic of the different missions for ‘‘Living with a Star.’’ (Source: NASA,
http://lws.gsfc.nasa.gov/overview2.htm.)

instruments are large (20 kg for PEPE), require a large amount of electrical power,
are expensive, and could not be easily implemented into 20 to 50 small satellites.
A good overview on plasma spectrometers, how they work, and the drive to make
them smaller (thereby making the missions less expensive) is given by Young. 8
One of the first micromachined designs was used by Stalder et al., who used
9
micromachining techniques to generate an array of Bessel boxes. They have
reduced the dimensions of such a system from typically 10 cm to an array of 4
with a thickness of 2.6 mm, and shown an energy resolution of 1.2 eV at 100 eV
with an acceptance half-angle of 148. For this device, silicon wafers of different
thickness were wet-etched and bonded together. A different fabrication method was
used by Enloe et al., who fabricated an electrostatic analyzer out of laminated,
photolithographically etched stainless steel. 10 The analyzer worked without charge
multiplication and was about 5 cm 5 cm in size, with 1920 individual analyzer
elements. The acceptance angle was 58, with an energy resolution of 0.66 eV at 10
to 30 eV ion energies.
A similar analyzer design was used at the Johns Hopkins University Applied
Physics Laboratory (JHU/APL) and NASA Goddard Space Flight Center (GSFC) for
a flat plasma spectrometer to fly on the Air Force Academy’s Falcon Sat 3 mission
1
in 2005. This instrument, including sensor-head-array, printed circuit board with
amplifier array electronics, power supply, and chassis has been designed and built
3
to occupy a volume of approximately 200 cm in a 0.5 kg, 300 mW package. The
sensor head as shown in Figure 7.3 consists of an array of five identical spectrom-
eter modules, each with a different fixed field-of-view (FOV) consisting of a
collimator, electrostatic analyzer, energy selector masks, microchannel plates,
and anode plate for detection. Ions enter the instruments via the collimator,
which serves to select the entrance angle of the incident particles. It is comprised

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