Electronic Implementation for Semiactive Attitude Control System

On August 9, 1969, the National Aeronautics and Space Administration launched a little publicized but successful control system, utilizing the second stage of the Delta booster used to inject the Orbiting Solar Observatory into orbit. This experiment demonstrated the feasibility of a new low-cost attitude control system with potential for making platforms for earth-oriented experiments out of otherwise expended boosters such as the OSO-Delta. Utilizing the gravity gradient torque available from the long thin booster, the Delta packaged attitude control (PAC) system is a semiactive three-axis system that utilizes no expendables. The system is based on the use of a gimbaled reaction wheel scanner loosely coupled to its mounting by a soft spring and a damper. The control system uses only one motor which provides gyroscopic action, provides a reaction torque by accelerating in response to a pitch error, and rotates the optics in an infrared optical system whose cone scanning action locates the earth's horizons. The motor's magnetic pickoffs furnish speed information and vertical reference data. The electronics, tailored to enable the motor to achieve its objectives, is based on hardware developed for the Nimbus D attitude control system which was launched in April, 1970.