Spacecraft Attitude Estimation Under Agility Constraints

Agility describes the ability of a spacecraft to arbitrarily and rapidly reorient itself inspace. In recent years the desire for increased agility has turned into more and more ofa necessity to further enhance the capabilities of particularly Earth-observing satellites.Assuming agile conditions changes the way of looking at the topic of attitude estimation,since many real sensor signals experience degradation during times of increasedrotational rates.This thesis covers the topic of spacecraft attitude estimation under agility. The sensorsbeing employed are star trackers and gyros, the latter being of both rate- andrate-integrating type. For being able to accurately estimate attitude during periods ofhigh slew-rates, multiple error sources as well as misalignments of the sensitive axis ofthe gyros are considered and specifically modeled in the Kalman Filters used for calibrationas well as the corresponding sensor models. The observability of the physicalcalibration parameters of the gyros is analyzed. It is found that gyro calibration filterswhich are used for the calibration of gyro units with more than three sense axes, in additionto attitude measurements, also require null-space measurements in order to notsuffer a loss of observability. Furthermore a suitable calibration maneuver is requiredto provide full observability of all calibration parameters. Simulation results demonstratethe performance of the calibration filters developed. Monte Carlo simulationsprove consistent operation of the filters. Finally the filter-performance is compared tothe covariance-tuning solution used prior to this work.Validerat; 20151013 (global_studentproject_submitter