Six-DOF trajectory optimization for reusable launch vehicles via Gauss pseudospectral method

Abstract

To be close to the practical flight process and increase the precision of optimal trajectory, a six-degree-of-freedom (6-DOF) trajectory is optimized for the reusable launch vehicle (RLV) using the Gauss pseudospectral method (GPM). Different from the traditional trajectory optimization problem which generally considers the RLV as a point mass, the coupling between translational dynamics and rotational dynamics is taken into account. An optimization problem is formulated to minimize a performance index subject to 6-DOF equations of motion, including translational and rotational dynamics. A two-step optimal strategy is then introduced to reduce the large calculations caused by multiple variables and convergence confinement in 6-DOF trajectory optimization. The simulation results demonstrate that the 6-DOF trajectory optimal strategy for RLV is feasible.