Time-Optimal Collision Avoidance Via a Greedy Polynomial Backward Sweep
This work addresses the need for time-optimal collision avoidance maneuvers in low-thrust satellites, offering a computationally efficient solution for onboard use.
The paper presents a greedy backward-sweep method to compute the latest safe maneuver initiation time for low-thrust spacecraft collision avoidance, achieving near-optimal results with runtimes suitable for onboard implementation.
Spacecraft collision avoidance for low-thrust satellites often requires determining not only how to maneuver, but also how late a maneuver can begin while still ensuring safety. This paper presents a greedy time-optimal (GTO) backward-sweep method to find the latest maneuver initiation time. The method starts from the nominal time of closest approach and iteratively propagates the maneuver backward in time, selecting at each step the thrust direction that locally minimizes the chosen danger metric. Differential algebra is used to efficiently propagate state sensitivities and update the time of closest approach online. The method is tested on a large dataset of conjunctions, using both miss distance and probability of collision as safety metrics. The approach achieves accurate results and only a small loss of optimality relative to an optimal-control benchmark, while retaining runtimes suitable for on-board implementation.