Accurate attitude determination of the LACE satellite

SUMMARY The precision pointing and imaging capability of the UVPIhas been used to improve the LACE spacecraft attitudesensing and determination. Utilizing these capabilities, theinstrument was used to determine attitude in real time,estimate offsets, and to more accurately characterize thespacecraft's attitude sensing system. This was accomplishedby viewing stars which were near the normal to the orbitplane, and by tracking a ground target with a knownlocation. Based on these results three conclusions werereached: (1) There was an offset between the attitudereference frame and the imaging instrument of 0.7 ° in theroll direction, (2) The roll and pitch provided by thespacecraft attitude sensors were better than expected, and (3)The total variation in the yaw was much less (+0.4 ° vs._+_1.0°) than the spacecraft sensors indicated. These resultswere then implemented into instrument operations resultingin improved camera pointing accuracy.The experience with the LACE spacecraft and the UVPI hasdemonstrated that a precision pointing instrument can beoperated from a spacecraft with simple and inexpensiveattitude control and sensing systems. The imaginginstrument itself can be used to improve the spacecraftattitude determination.Dean Bakeris of BFEC and John Ivory of RSI for help inunderstanding LACE attitude sensor data.Paul Flynn of BFEC, Don Horan of NRL, Lowell Plackettof BFEC, and Tony Smathers of NRLWork for this paper was done for the Naval ResearchLaboratory under contracts N0014-89-C-2011 and N0014-91 -C-2316.