Space borne attitude measurement units

Inertial and opticoinertial attitude reference units are characterized, and the design and test results of the system being developed for the SPOT spacecraft are presented. The general characteristics of the strapdown gyroscope configuration are reviewed, and the classical gyro packages used in OTS, ECS, TC1, TVSAT, and TDF1 are described. The present SPOT inertial platform, consisting of six gyrometer/thermal regulator/adapter units in a dodecahedral configuration, is shown to provide complete roll, pitch, and yaw information with accuracy sufficient for the short run. The hardware and software of the advanced unit, which uses optical sensors to make absolute attitude corrections for the long run, are discussed. Attitude information from inertial and optical systems is optimally mixed by a microprocessor employing a nonstationary sixth-order Kalman filter. A simulation test using the breadboard prototype indicates the feasibility of the approach and the broad applicability of the attitude-measurement package once it is perfected.