Gyroscope spin axis direction control for the Gravity Probe B satellite

Presented is a technique which can control the orientation of the spin axis of an electrostatically suspended vacuum gyroscope (ESVG) using residual torques generated by the rotor's suspension system. A process of rotor shape "spin averaging" showed that the residual electrostatic torques take on a particularly simple form: they tend to cause the rotor to precess about the electrode axes. A time-optimal bang-bang control scheme was developed for the Gravity Probe B spacecraft which utilizes suspension voltages in the force null space to generate the torques which lead to controlled spin axis precessions. Laboratory tests confirm the spin averaged torque predictions.