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Microsystems in Spacecraft Guidance, Navigation, and Control 223

and maneuver in space and on lunar or planetary surfaces. Sensitive multisensor
‘‘skins’’ embedded with significant diagnostic resources such as pressure, stress,
strain, temperature, visible or infrared imagery, and orientation sensors could be
fabricated using MEMS technology for robotic control systems. A variety of
sensing mechanisms reacting to temperature, force, pressure, light, etc. could be
built into the outermost layer of robotically controlled arms and members. This
MEMS-based sensitive skin would provide feedback to an associated data proces-
sor. The processor would in turn perform situational analyses to determine the
remedial control action to be taken for survival in unstructured environments. This
is one of the uses of the multisenson skin envisioned for future science and ex-
ploration missions. Modest R&D investments could be made to design and develop
a working hardware robotic MEMS-based sensitive skin prototype within 5 years.

10.6.4 MODULAR MEMS-ENABLED INDEPENDENT SAFE HOLD SENSOR UNIT
Identifying and implementing simple, reliable, independent, and affordable (in terms
of cost, mass, and power) methods for autonomous satellite safing and protection has
long been a significant challenge for spacecraft designers. When spacecraft anomal-
ies or emergencies occur, it is often necessary to transition the GN&C system into a
safe-hold mode to simply maintain the power of the vehicle as positive and its
thermally benign orientation with respect to the Sun. One potential solution that
could contribute to solving this complex problem is the use of a small, low mass, low
power, completely independent ‘‘bolt on’’ safe hold sensor unit (SHSU) that would
contain a 6-DOF MEMS IMU together with MEMS sun and horizon sensors.
Specific implementations would vary, but, in general, it entails one or more of the
SHSUs being mounted on a one-of-a-kind observatory such as the JWST to inves-
tigate the risk of mission loss for a relatively small cost. ISC represents an enhancing
technology in this application. The low mass and small volume of the SHSU pre-
cludes any major accommodation issues on a large observatory. The modest SHSU
attitude determination performance requirements, which would be in the order of
degrees for safe hold operation, could easily be met with current MEMS technology.
The outputs of the individual SHSU sensors would be combined and filtered using an
embedded processor to estimate the vehicle’s attitude state. Furthermore, depending
on their size and complexity it might also be possible to host the associated safe hold
control laws, as well as some elements of failure detection and correction (FDC)
logic, on the SHSU’s internal processor. It is envisioned that such an SHSU could
have very broad mission applicability across many mission types and classes, but
R&D investment is required for system design and integration, MEMS sensor
selection and packaging, attitude determination algorithm development, and qualifi-
cation testing would require an R&D investment.

10.6.5 PRECISION TELESCOPE POINTING
Little attention has been paid to applying MEMS sensors to the problem of
precision telescope stabilization and pointing. This is primarily due to the perform-
ance limitation of the majority of current MEMS inertial sensors. However as the

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