Entry guidance and trajectory control for reusable launch vehicle

An entry guidance concept, similar to that of the Space Shuttle, is considered for the reusable launch vehicle (RLV). But the reference trajectory defined by drag profile is parameterized and optimized as piecewise linear functions of the energy. Analytical expressions for accurate downrange distance prediction and a performance index, the accumulated heat load, are obtained. A regularization technique is employed to achieve desired properties of the optimal drag profile. These results enable fast design of constrained optimal trajectories for both offline studies and possible onboard application. A nonlinear control law is derived for trajectory tracking, which guarantees globally asymptotically stable tracking of the reference drag profile. Numerical results for a conceptual RLV are provided to demonstrate the optimal design of drag profiles and the performance of the trajectory control law under a variety of off-nominal conditions and navigation errors in altitude rate.