Abort Guidance during Powered Descent for Crewed Lunar Missions

摘要

During powered descent of a crewed lunar landing mission, should any contingency or unplanned event render the landing infeasible or unacceptably risky, the guidance system must be able to switch from powered descent guidance to abort guidance to ensure that the vehicle can transition into an ascent trajectory and insert into a clear pericynthion orbit. Unlike a typical launch ascent problem, the initial condition of such an abort is one where the vehicle is still in descent and it can be anywhere during the powered descent. This is thus a considerably more difficult problem and the guidance system should be fully autonomous and adaptive. In this work, the complete abort operation is divided into two phases once abort is commenced. The first phase is a pull-up maneuver, where the vehicle is guided from the initial condition on the powered descent trajectory to achieve a specified non-negative flight path angle, while maintaining nearly a constant velocity. The next phase is fuel-optimal ascent where the vehicle ascends from the end of the pull-up phase to the insertion into a specified final orbit. This paper describes the guidance strategy, develops the guidance laws for pull-up phase, and reviews the fuel-optimal ascent guidance algorithm. End-to-end simulation results are presented from the start of powered descent, abort at an arbitrary time during descent, to the insertion into the specified orbit. The viability of the abort guidance approach is demonstrated by extensive Monte Carlo simulations.