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Microsystems in Spacecraft Guidance, Navigation, and Control 205

TABLE 10.1
Typical Spacecraft GN&C Attitude Sensing and Control Devices

Attitude Sensing Devices Attitude Control Actuation Devices
Sun sensors Thrusters
Earth sensors Momentum wheels
Horizon sensors Reaction wheels
Magnetometers Control moment gyros
Gyroscopes Magnetic torquers
Accelerometers Antenna pointing gimbals
Fine guidance sensors Solar array drives

While GN&C engineering and technology development efforts are primarily
directed towards both controlling launch vehicle (i.e., booster) dynamics during
ascent and controlling space platform dynamics in the microgravity environment of
free space, they also entail the navigational aspects of maintaining precise timing (and
the associated time transfer and time synchronization functions). MEMS technology
can certainly be applied to the development of miniaturized spacecraft clocks and
oscillators for navigational functions. Table 10.1 defines the typical set of sensing and
control devices typically used to perform spacecraft GN&C functions.

10.2 MINIATURIZED MODULAR GN&C SUBSYSTEMS
FOR MICROSATELLITES

Several future science and exploration mission architectures share common
interests and technological requirements for microsatellites. Some envision
economically mass-produced microsatellites as a means to enable new robust,
flexible, and responsive space architectures for Earth (or planetary) observation
and coordinated space communications and navigation functions. Others foresee
clusters of microsats as affordable and reconfigurable platforms for performing new
types of in situ or remote sensing science measurements or observations.
Consequently, many industrial and federal R&D organizations are spearhead-
ing the development of the breakthrough subsystem and component technologies
needed to implement next generation microsatellites. Using data from various flight
projects and cost models, some researchers have investigated the relative costs of
small satellite subsystems as a way to refine the identification of technologies,
which are key to reducing overall spacecraft cost. One such analysis, performed by
NASA’s New Millennium Program (NMP), determined that the largest cost frac-
tions were associated with both the electrical power subsystem, 34% of total cost,
and the GN&C subsystem, 27% of total cost, with the other small satellite subsys-
5
tems costs being significantly less. A general observation can also be made that,
excluding the payload, the GN&C and the C&DH, in the range of 25 to 30% of total

© 2006 by Taylor & Francis Group, LLC