Y-Biasing: A New Operational Method for Cassini to Control Thruster Usage while Managing Reaction Wheel Momentum

Abstract

As NASA’s Cassini spacecraft continues its 6 th year in orbit around Saturn and 13 th year of flight, the spacecraft operators have increased efforts to control the ways in which the Reaction Wheel Assembly (RWA) and Reaction Control System (RCS) thrusters of the aging spacecraft are used. Thrust degradation from at least one of Cassini’s Z-axis aligned RCS thrusters led to interest in developing a method of Y-Biasing; that is, using only the spacecraft’s Y-axis aligned thrusters to alter the momentum of Cassini’s reaction wheels, thereby preserving the health of the Z-facing thrusters by limiting their use. Further analysis of the Y-biasing technique demonstrates that this method of reaction wheel biasing not only greatly reduces the use of the Z-facing thrusters, but it also offers as much as a 3035% savings in hydrazine consumption compared to the previously used method.