Optimal Pose Design for Close-Proximity On-Orbit Inspection

Abstract

Close-proximity on-orbit inspection is a critical ability to initiate on-orbit servicing operations, required technology for space exploration missions. It is challenging to solve an optimal inspection trajectory planning problem that provides a complete target observation due to major difficulties. First, the inspection requirements must be defined and imposed on the problem as a set of path constraints that result in a nondeterministic-polynomial-time-hard problem. Second, the optimization problem, including highly nonconvex constraints, is very difficult to solve directly using an optimal control solver. Additionally, it requires proper initialization of states and control variables, which is critical in such problems. To overcome these difficulties, this paper proposes a novel formulation and method of solution for a full six-degrees-of-freedom optimal inspection motion planning problem. Optimal inspection trajectories are designed for a rigid-body spacecraft, which performs close, continuous, and complete observation of rigid, nonrotating, and nonaccelerating known targets. The inspection and collision avoidance constraints are defined in explicit forms that rectify the nondifferentiability of the problem and satisfy the inspection requirements. A pseudospectral optimal control solver is implemented to numerically solve the trajectory optimization problem. The proposed methodology is applicable to any robotic inspection mission. Simulations are presented as a validation of the proposed methodology and the achieved optimality.