  Closed-loop attitude steering can be used to implement a non-standard
attitude maneuver by using a conventional attitude control system to track a
non-standard attitude profile. The idea has been employed to perform
zero-propellant maneuvers on the International Space Station and minimum time
maneuvers on NASA's TRACE space telescope. A challenge for operational
implementation of the idea is the finite capacity of a space vehicle's command
storage buffer. One approach to mitigate the problem is to downsample-and-hold
the attitude commands as a set of waypoints for the attitude control system to
follow. In this paper, we explore the waypoint following dynamics of a
quaternion error feedback control law for downsample-and-hold. It is shown that
downsample-and-hold induces a ripple between downsamples that causes the
satellite angular rate to significantly overshoot the desired limit. Analysis
in the $z$-domain is carried out in order to understand the phenomenon. An
interpolating Chebyshev-type filter is proposed that allows attitude commands
to be encoded in terms of a set of filter coefficients. Using the interpolating
filter, commands can be issued at the ACS rate but with significantly reduced
memory requirements. The attitude control system of NASA's Lunar Reconnaissance
Orbiter is used as an example to illustrate the behavior of a practical
attitude control system.

Systems and Control;Systems and Control;Dynamical Systems;Optimization and Control