Onboard longitudinal trajectory planning for terminal area energy management of reusable launch vehicles

An onboard trajectory planning algorithm is presented in this paper for the terminal area energy management (TAEM) phase of a reusable launch vehicle (RLV). To satisfy the multiple constraints in the TAEM phase, a profile in the flight-path angle vs. range-to-go space is planned. The optimization of this flight-path angle profile is described as a one-parameter search problem and solved by the Newton iteration method. With the optimized flight-path angle profile, a satisfied longitudinal flight trajectory is generated based on the flight dynamics. Testing for the trajectory planning algorithm is performed in missions with different terminal flight-path angle constraints. The onboard algorithm is indicated effective to generate a constrained longitudinal flight trajectory in 0.5 seconds on a PC. The Monte Carlo simulations are employed in dispersed cases, and the planning algorithm is shown robust in trajectory generation with large initial condition errors of the TAEM phase.