Automated Method to Compute Orbital Reentry Trajectories with Heating Constraints

Abstract

An algorithm is presented that is designed to compute reentry trajectories for unpowered lifting reusable launch vehicles. The algorithm uses self-contained trajectory simulation and root finding techniques to determine the appropriate control sequences for solving reentry problems. For orbital reentries, the solution process breaks the trajectory into two distinct parts. The first part begins where the deorbited vehicle first encounters substantial atmosphere and can exercise trajectory control through the manipulation of aerodynamic lift. This phase of the flight is governed by an analytical, constant heat-rate following, bank angle control law. The second and final part of the trajectory begins where heat-rate control is no longer desired. During this time trajectory control is used to meet terminal range and altitude targets and is governed by a linear bank angle control law. The planning algorithm determines the value of the individual trajectory control parameters that shape the reentry. The planned trajectory is then used by a profile following guidance algorithm during actual flight. Test results for a variety of orbital and suborbital missions are shown.