Risk-Aware Mission Design Around Small Celestial Bodies

Abstract

Robotic exploration of small celestial bodies is integral to current and future space programs. However, complex, uncertain dynamical environments around small bodies pose challenges for spacecraft to safely navigate around them. For successful small-body exploration, the mission design process needs to be aware of potential risks (e.g., collision with the body, loss of science opportunities), appropriately quantify these risks, and mitigate them to ensure achieving the expected performance (e.g., safety, cost) in the presence of uncertainty. To this end, this dissertation develops risk-aware mission design frameworks for robust small-body exploration under uncertainty, by merging techniques and insights in the fields of astrodynamics, stochastic control, optimal control, and optimization. In particular, this dissertation is focused on developing frameworks for robust spacecraft guidance and space trajectory optimization under uncertainty. The developed guidance framework combines chance-constrained optimal control, convex programming, and local approximation of orbital dynamics, to optimize a sequence of guidance policies that guarantee, with a user-defined confidence level, precise control of spacecraft orbits about a reference trajectory in the presence of uncertainty. The framework for trajectory optimization under uncertainty leverages dynamical properties of orbital mechanics to enable efficient semi-analytical uncertainty quantification within the optimization routine, formulated as a class of the indirect method by applying the calculus of variations. Furthermore, this dissertation also develops an orbit control framework that exploits one of the major disturbances in small-body environments, solar radiation pressure, to effectively utilize the natural force as a primary source of orbit controls, allowing greater flexibility in mission design for small-body exploration. These frameworks provide mathematical and computational tools for the design of robust exploration missions under uncertainty, paving the way for better access to and safer operations at small celestial bodies in our Solar System.