OPTIMAL EXPLICIT TERMINAL GUIDANCE FOR A LAUNCH VEHICLE

It is observed that general explicit guidance schemes exhibit numerica l instability close to the injection point. This difficulty is normall y attributed to the demand for exact injection which, in turn, calls f or finite corrections to be enforced in a relatively short time. The d eviations in vehicle state which need corrective maneuvers are caused by the off-nominal operating conditions. Hence, the onset of terminal instability depends on the type of off-nominal conditions encountered. The proposed separate terminal guidance scheme overcomes the above di fficulty by minimizing a quadratic penalty on injection errors rather than demanding an exact injection. There is also a special requirement in the terminal phase for the faster guidance computations. The faste r guidance computations facilitate a more frequent guidance update ena bling an accurate terminal thrust cutoff. The objective of faster comp utations is realized in the terminal guidance scheme by employing real istic assumptions that are accurate enough for a short terminal trajec tory. It is observed from simulations that one of the guidance paramet ers (P) related to the thrust steering angular rates can indicate the onset of terminal instability due to different off-nominal operating c onditions. Therefore, the terminal guidance scheme can be dynamically invoked based on monitoring of deviations in the lone parameter P.