On-board three-dimensional constrained entry flight trajectory generation

This dissertation presents a method for on-board generation of three-degree-of-freedom (3DOF) constrained entry trajectory. Given any feasible entry conditions and terminal area energy management (TAEM) interface conditions, this method generates rapidly a 3DOF trajectory featuring a single bank-reversal that satisfies all the entry corridor constraints and meets the TAEM requirements with high precision. First, the longitudinal reference profiles for altitude, velocity, flight path angle, and the corresponding controls with respect to range-to-go, are designed using the quasi-equilibrium glide condition (QEGC). Terminal backward trajectory integration and initial descent approaches are used to make the longitudinal references intrinsically flyable. Then the 3DOF entry trajectory is completed by tracking the longitudinal references with the approximate receding-horizon control method, while the bank-reversal point is searched such that the TAEM heading and distance to the Heading Alignment Circle (HAC) requirements are satisfied within specified precision. For extreme entry cases that marginally allow a single bank-reversal or no bank-reversals, a terminal reference ground path tracking method and a terminal open-loop trajectory search method are developed respectively to complement the on-board 3DOF trajectory generation method. The overall computational load needed by this method for any entry trajectory design amounts to less than integrating the 3DOF trajectory five times on average. Simulations with the X-33 and X-38 vehicle models and a broad range of entry conditions and TAEM interface requirements demonstrate the desired performance of this method. The on-board entry guidance scheme is then completed and tested by integrating this trajectory generation method with a state of art reference trajectory regulation algorithm on a high fidelity simulation software developed at NASA Marshall Space Flight Center. Instead of preloading a reference trajectory, this method generates a 3DOF entry trajectory from the current state in 1 to 2 seconds on the simulator. Then this freshly generated trajectory is used as the reference for the guidance system. The results demonstrate the great potential of this innovative entry guidance method.