Optimal Aerocapture Guidance

Aerocapture is the maneuver by an interplanetary spacecraft to fly through the atmosphere of a planet with the aim of attaining a specified orbit around the planet. By appropriately controlling the aerodynamic lift and/or drag force vectors, the spacecraft can exit the atmosphere and enter the target orbit without the need for large propellant consumption in post-atmospheric orbital correction burns. The focus of this paper is to develop an algorithm to guide the spacecraft accurately and reliably during the aerocapture maneuver with lift vector control while ensuring the least possible post-atmospheric propellant expenditure for inserting into the target orbit. The analysis of optimal aerocapture flight in this work shows that the optimal aerocapture trajectory in general has a bang-bang control structure in which the spacecraft first flies with the largest possible vertical lift up, then the largest possible vertical lift down. Based on this understanding, a two-phase numerical predictor-corrector guidance algorithm is developed. It is demonstrated that this algorithm not only exhibits the strengths of adaptivity and high accuracy of predictor-corrector guidance algorithms, but also produces an optimal performance in terms of propellant consumption that is significantly better than existing aerocapture numerical predictor-corrector guidance algorithms.