Optimal transition from entry to cruising flight

Following a high angle-of-attack (α) "blunt body" entry from orbit, the space shuttle orbiter will rotate to a low a for flight to an airport and a conventional aircraft landing. It is likely that the transition trajectory will carry the vehicle through a region of aerodynamic instability at intermediate α. Transition trajectories which minimize operation within the unstable region through the use of a subsonic jump maneuver are investigated here. Angleof- attack penalties shape the control profile, which otherwise minimizes load factor while meeting terminal state conditions. Using a steepest-descent algorithm, the intermediate-a penalty is suppressed for the first several iterations, allowing the minimum load trajectory to be established. Increasing weighting on this penalty during succeeding iterations forces the control into the stable regions at higher and lower angles. These regions are then connected by a rapid (but continuous) jump through the unstable region. Numerical results for a straight-wing shuttle vehicle are obtained, including solutions for variations in initial and final conditions and for a range of lift/drag ratios and wing loadings. Small initial condition measurement errors are shown to be stable, and two forms of near-optimal control are considered.