Onboard Optimization Of Three-Dimensional Constrained Reentry Trajectory For RLV

Determining how to find the best controls of a re-entering reusable launch vehicle (RLV) so that it can safely reach Terminal Area Energy Management (TAEM) involved the solution of a two-point boundary value problem. This problem, which was considered to be difficult, was traditionally solved on the ground rather than onboard. The optimal controls were found regardless of computing time by the most of algorithms. But it was very necessary to find the optimal controls quickly for some flight tasks. Traditional trajectory optimization algorithms can not perform this fast optimization task. In this paper, according to the features of three-dimensional constrained reentry trajectory, a new hypothesis was introduced. The dynamics and kinematics equations of motion were divided into two sets and only one of those was involved in iterations of optimization algorithm, which improved the efficiency of optimization greatly. Then the methods of multipliers was used to deal with the terminal constraints. Later the Conjugate-Gradient Method was applied to evaluate the optimal reentry trajectory. Successful results show that this algorithm is able to generate a feasible reentry trajectory of about 2200 s flight time in 20-50 s on the desktop computer. The optimal trajectory can be used as the reference needed by guidance system.