MAGNETOMETER-ONLY ATTITUDE AND RATE ESTIMATES DURING THE EARTH RADIATION BUDGET SATELLITE 1987 CONTROL ANOMALY*

The Earth Radiation Budget Satellite (ERBS) experienced an uncontrolled tumble on July 2, 1987, with spacecraft rates of the order of 2 deg/sec. The high rates made the Sun and Earth sensors unreliable and the gyro telemetry saturated, so that the three-axis magnetometer (TAM) was the only useful attitude sensor. ERBS attitude and rates for the high-rate period are estimated using TAMONLY—a recently developed system lhat estimates attitude and rates using a TAM and sp i ecraft dynamical models. The spacecraft rates estimated by the Kalman filter and by the deterministic algorithm in TAMONLY agree closely, both algorithms confirming rates as high as 2 deg/sec. Comparisons with valid gyro data indicate rate accuracies of 0.1 deg/sec, and the TAM residuals indicate attitude accuracies of 2.5 deg. The effects of models of thrusters, spacecraft mass properties, and filter noise parameters are described.