AN APPROACH TO POSTLAUNCH VECTOR-SENSOR ALIGNMENT CALIBRATION IS PROPOSED WHICH PROVIDES OPTIMAL ESTIMATES OF SENSOR MISALIGNMENTS BASED ON GROUND-TESTING RESULTS AND INFLIGHT DATA.

AN APPROACH TO POSTLAUNCH VECTOR-SENSOR ALIGNMENT CALIBRATION IS PROPOSED WHICH PROVIDES OPTIMAL ESTIMATES OF SENSOR MISALIGNMENTS BASED ON GROUND-TESTING RESULTS AND INFLIGHT DATA. TWO TYPES OF ALGORITHMS ARE PRESENTED WHICH WOULD BE APPLICABLE EITHER TO SPACECRAFT WHICH DETERMINE ATTITUDE FROM VECTOR SENSORS ALONE OR TO SPACECRAFT WHICH USE VECTOR SENSORS AND THREE-AXIS GYROS. THE APPROACH IS BASES ON MAXIMUM LIKELIHOOD ESTIMATION, WHICH IS A WELL-ESTABLISHED PARAMETER ESTIMATION TECHNIQUE, AND USES A REALISTIC PROBABLISTIC MODEL FOR SENSOR MEASUREMENT ERRORS. A SUFFICIENT STATISTIC IS USED TO PROVIDE COMMANALITY BETWEEN THE TOW ALGORITHM TYPES, TO GREATLY REDUCE THE COMPUTATIONAL BURDEN,AND TO ALLOW OPTIONAL SUBOPTIMAL MISALIGNMENT ESTIMATES (WHICH PROVIDE USEFUL DIAGNOSTIC INFORMATION) TO BE CALCULATED WITHOUT REPROCESSING THE DATA. REDUNDANCY AND CORRELATIONS BETWEEN DERIVED MEASUREMENTS ARE TREATED EXACTLY SO THAT IT BECOMES POSSIBLETO CALCULATE CONFIDENCE BOUNDS CORRECTLY, PERHAPS FOR THE FIRST TIME. THIS ANALYSIS LEADS TO AN EXTREMELY EFFICIENT, FLEXIBLE, MODULAR AND USER-FRIENDLY SOFTWARE PACKAGE WHICH YIELDS THE BEST POSSIBLE ESTIMATE OF THE MISALIGNMENTS AND IS FAST ENOUGH TO BE USED INTERACTIVELY OR EVEN BE IMPLEMENTED ON AN ONBOARD COMPUTER.