Simple Sensitivity Analysis for Orion GNC

The Orion GNC entry team is analyzing the performance of Orion flight software in part by running Monte Carlo simulations of Orion spacecraft flights. The simulated performance is checked for conformance with flight requirements, expressed as performance constraints. Flight requirements include guidance (e.g., touchdown distance from target) and control (e.g., control saturation) as well as performance (e.g., heat load constraints). The Monte Carlo simulations disperse hundreds of simulation input variables, for everything from mass properties to date of launch.

We describe in this paper a sensitivity analysis tool ("Critical Factors Tool" or CFT) developed to find the input variables or pairs of variables which by themselves significantly influence satisfaction of requirements or significantly affect key performance metrics (e.g., touchdown distance from target). Knowing these factors can inform robustness analysis and where engineering resources are most needed, and could even affect operations. The contributions of this paper include the introduction of novel sensitivity measures, such as estimating success probability, and a technique for determining whether pairs of factors are interacting dependently or independently.

The tool found that input variables such as moments, mass, thrust dispersions, and date of launch are significant factors for success of various requirements. Examples are shown in this paper as well as a summary and physics discussion of EFT-1 driving factors that the tool found.