Orbital gyrocompass evolution

This paper gives a brief history of the Orbital Gyrocompass, especially as developed and used at Lockheed. The first Orbital Gyrocompass was developed by Lockheed in the fall of 1957 and first successfully flown on the Discoverer 1 on February 28th 1959. The original design consisted of three single-degree of freedom gyros and a horizon sensor. Gyro pitch and yaw drift errors were later identified and corrected on-board. The addition of a digital sun sensor (DSS) allowed the determination of gyro drifts in all three axes. This case also introduced an interesting stability example when switching between the two cases of the Orbital Gyrocompass, i.e. with and without the use of the DSS. Calibrations of the attitude reference system were done periodically on the ground. Included in the inputs to the ground filter were the residual outputs of the on-board flight filter. This provided an early operational example of one filter using the outputs of another filter.