On-line trajectory planning and guidance for terminal area energy management of reusable launch vehicle

On-line trajectory plan methods are of no guarantee of real time for using optimization searching algorithms. They are unpractical to be adopted in engineering application for reusable launch vehicles (RLV) in terminal area energy management (TAEM). An prediction and acquisition straight line (PASL) phase is added before the heading alignment cone (HAC) to accomplish the TAEM trajectory on-line planning in advance, thus decreasing the requirement for the real time performance. The vehicle's initial states of the TAEM phase referred to as the terminal states of the PASL phase can be predicted by calculating the analytic solution of three-degree freedom motion equations with zero aerodynamic angle. Taking dynamic pressure, normal acceleration and bank angle as constraints, it is transformed into a non-linear planning problem to generate the TAEM trajectory. The objective function is to search for the optimal HAC position with a minimum heading error to enter the HAC. In addition, a pneumatic-angle directive (PD) feedback tracking law is designed, where the open-loop commands are available once the trajectory is obtained. Finally, an illustrative example is given to confirm the efficiency of the TAEM method based on trajectory prediction.