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142 MEMS and Microstructures in Aerospace Applications

ments are quite large and consume a lot of power. Miniaturization would allow
these instruments to be incorporated onto small multiple entry probes, autonomous
rovers, and sample handling systems such as robotic arms, booms, and drills.
Accordingly, MEMS is an attractive technology for developing highly miniaturized
versions of these instruments, if they can maintain the performance of existing
space flight instruments. In addition, new instruments based on technologies such as
lab-on-a-chip have been proposed to provide the ability to carry out analytical
chemistry in a miniature, integrated package.

7.4.1 MICROMACHINED MASS SPECTROMETERS
A mass spectrometer consists of a sample handling system, an ion source, a mass
filter, and a detector. After being introduced to the instrument by the sample
handling system, atoms in gaseous, solid, or liquid states are ionized by electron
bombardment, electrospray ionization, laser ablation, or other methods. The ions
are then separated by their charge to mass ratio in a mass filter. Common mass
filters include: magnetic sectors, in which ions of different masses are deflected
differentially in a magnetic field; quadrupoles and ion traps, which are scanning
devices in which ions of a particular mass exhibit stable trajectories at a given RF
frequency; and time-of-flight, in which ions of constant initial kinetic energy but
different mass are separated by their flight times due to their differences in velocity.
Work on MEMS-based mass spectrometers has been reported, including magnetic,
quadrupole, ion trap and time-of-flight mass filters. 70–79 In all cases, instrument
performance has fallen far short of the requirements for a space flight mass
spectrometer, and the need for additional research and development in this area is
clear.

7.4.2 MAGNETIC RESONANCE FORCE MICROSCOPY
Nuclear magnetic resonance is a very sensitive way to detect the presence of water,
and therefore is a desirable instrument on any explorer mission. There has been a
recent push to develop imaging magnetic resonance microscopes to be able to
measure spin distributions and identify molecules. These methods are based on
magnetic resonance force microscopy, where the force applied by the spins rotating
in an RF field on a micromachined resonant cantilever beam with a magnetic
particle is measured via interferometric techniques. Such instruments could be
potentially built entirely on a MEMS or microelectronics platform and used in
space exploration as element detectors for landers. 5,80–82

7.5 CONCLUSION
While it is difficult to imagine the instrumentation for future spacecraft that will be
enabled or improved by the integration of MEMS, it is obvious from the examples
that it is already being done, and that there are devices that can be inserted into
space systems as well as devices that have already been designed and fabricated for

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