Space platform attitude control system

A discussion is presented of the preliminary design of the Space Platform System, which is being developed to support the Shuttle Orbiter in a sortie configuration with power, communications, and thermal and attitude control capability for up to 30 days while supporting payloads within the Shuttle bay or mounted directly on the platform. Three payload pallets can be supported for indefinite periods of time by the platform in a free flier mode. The vehicle is stabilized against gravity gradients and aerodynamic disturbance torques by the attitude control system. The attitude control system requirements are stringent, due to the need to counteract large aerodynamic disturbances despite the large platform size and low earth orbit altitude. The design of the control system allows it to control both free fly and sortie configurations, with differing inertias as payload pallets are changed.