Microcosm, under funding from the Air Force Research Laboratory Space Vehicles Directorate, has developed the first on-orbit demonstration of autonomous, on-board intrack and cross-track orbit control. The flight demonstration was conducted on the Surrey Satellite Technology Laboratory’s (SSTL) UoSAT-12 mission. The satellite is in a 650 km, near circular orbit at 65 deg. Navigation data is provided by an experimental GPS receiver built by SSTL. The first full orbit control test was initiated Sept. 23, 1999, and lasted for 29 days until other propulsion system experiments were initiated. During the test period, thrust calibration was initially off by a factor of 2 and was corrected midway in the testing. Due to active work on the GPS software, GPS data outages occurred that were as long as 8 hours, with as much as 11 hours out during a 24 hour period. In spite of these unexpected anomalies and lack of data, OCK maintained a time late at the ascending node to within a standard deviation of 0.12 sec, equivalent to ± 0.93 km in-track over the entire 29 day test run. This is in contrast to an in-track slippage of approximately 4,500 km over the preceding 4 month period. During the test period, OCK applied a total ΔV of 73.3 mm/sec in 53 burns. All burns were in the positive direction (i.e., provided drag make-up). The total ΔV was equivalent to or slightly less than that which would have been required to return the spacecraft to its initial altitude had all of the thrust been applied at the end of the test period.
Wertz, J.R., J.L. Cloots, J. Collins, S. Dawson, G. Gurevich, B.K. Sato and J. Hansen. 23rd Annual AAS Guidance and Control Conference, Breckenridge, CO. February 2–6, 2000.