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.