Optimization of Thrust Vector Direction for Direct Thrust Estimation Uncertainty Minimization

Direct in-space thrust estimation provides cost-effective evaluation of a spacecraft's in-situ thruster performance, with applications in maneuver design for in-space technology demonstrations, mid-mission propulsion system health monitoring, and cost-effective validation of estimates from alternative measurement techniques. The minimization of the uncertainty in the estimation of a spacecraft's thrust is thus desirable as a means of improving the accuracy of these techniques. However, techniques to design optimal maneuvers that minimize uncertainty are underdeveloped, and the relationship between estimation uncertainty and maneuver parameters are poorly understood. This paper expands on prior work to present analysis on the impact of a critical maneuver parameter, thrust vector direction, on estimation uncertainty under a range of orbit and maneuver parameters. Methods to derive the estimation uncertainty for a given maneuver are presented and validated, then applied to generate the optimal thrust direction for a given mission. Results indicate strong correlation between the optimal thrust vector direction and other, easily-measured mission parameters, indicating potential for efficient integration of uncertainty minimization into cost functions for optimal control. In a random sampling of simulated maneuvers across realistic LEO mission profiles, the optimized thrust vector direction enabled significant improvement (>1.0%) in 36.4% of cases; among these maneuvers, the median improvement in estimation uncertainty was 9.60%. The mean improvement in estimation uncertainty across all sampled maneuvers was 83.5%. These results indicate that thrust vector direction optimization is a viable strategy for improving the accuracy of direct estimation methods for maneuvers in certain mission profile classes. Methods for application to real-world maneuver design are discussed, with recommendations for three common mission scenarios provided as examples.