New methodologies for onboard generation of Terminal Area Energy Management trajectories for autonomous reusable launch vehicles

Abstract

Onboard trajectory generation capability greatly increases an autonomous reusable launch vehicle's capacity for recovering from unexpected disturbances or anomalous conditions. Such capability dispenses with the routine of pre-defined, mission specific trajectories and contingencies, which has been in use since the early days of the Shuttle. Newer guidance techniques, employing modem computing power and faster algorithms, can therefore provide savings in both operational cost and design time, while enhancing both mission robustness and efficiency. Weaknesses in the current Terminal Area Energy Management phase guidance scheme are identified and shown to be remedied with an onboard trajectory generator. Subsequently, new methodologies are presented as well as an approach to attaining onboard trajectory generation capability using the NASA/Orbital X-34 gliding reentry vehicle as the representative testbed model. The approach utilizes the full nonlinear equations of motion to rapidly generate 3- degrees-of-freedom descent trajectories for a low lift over drag, gliding reusable launch vehicle from any portion of the Terminal Area Energy Management flight regime to the AutoLanding Interface. Full coupling of the longitudinal and lateral aspects, as well as actual vehicle dynamic capabilities and constraints, will result in guidance outputs that are both realistic and flyable. Key technology components are identified and preliminary results and comparisons are presented.