Qualification in orbital flight at the Cactus high sensitivity accelerometer

The Cactus accelerometer of the Castor satellite is based on the measurement of the force necessary to maintain a test mass in levitation inside a cage. In-orbit qualification consisted of threshold verification and ground-calibration verification. The x-, y-, and z-components of the acceleration of the satellite in the vicinity of apogee and in the earth's shadow were measured. Threshold was found to be in the range (8-14) billionths m/sq sec. The projection of the satellite acceleration vector on the XY plane during day-night transition shows the effects of decreasing aerodynamic drag due to increasing satellite altitude, the effect of solar radiation pressure, gradual reduction of measured acceleration due to instrument response time, and the effect of earth infrared radiation pressure.