Observability Analysis and Filter Design for the Orion Earth–Moon Attitude Filter

Abstract

The Orion attitude navigation design is presented, together with justification of the choice of states in the filter and an analysis of the observability of its states while processing star tracker measurements. The analysis shows that when the gyroscope biases and scale factors drift at different rates and are modeled as first-order Gauss–Markov processes, the states are observable so long as the time constants are not the same for both sets of states. In addition, the inertial-measurement-unit-to-star-tracker misalignments are modeled as first-order Gauss–Markov processes and these states are estimated. These results are used to finalize the design of the attitude estimation algorithm and the attitude calibration maneuvers.