POINTING ALGORITHM FOR REENTRY ORBIT INJECTION WITH UNCONTROLLED LAST STAGE DOI 10.5028/jatm.2012.04031112
Keywords:Algorithms, Orbit transfer vehicles, Pointing control systems, Reentry guidance, Reentry vehicle, Trajectory analysis.
AbstractAn essencial requirement for a launcher with uncontrolled last stage is to compute the ignition time of that stage and its attitude, in order to obtain a proper orbit transfer from a nonpropelled trajectory to a desired orbit, since such stage it cannot change its velocity profile and its direction. This article presented an algorithm that allows achieving the proper conditions to inject a vehicle with uncontrolled last stage into a descent Keplerian trajectory, in order to permit its reentry through the Earth's atmosphere with strictly defined conditions of radius, velocity, and flight path angle at the entry interface. These specific conditions impose requirements to the configuration, performance, and trajectory of the launcher. This strategy considers that the total energy is applied instantly for the reentry orbit injection. Impulsive ignition time and necessary attitude for the last stage are obtained based on orbital parameters, having a match between the nonpropelled and reentry orbits, and boundary conditions at the initial state and at the entry interface. Impulsive ignition time was corrected for compensating the impulsive assumption and the calculated attitude related to an inertial frame. The obtained results show the efficiency of the algorithm involving reentry missions with uncontrolled last stage, as the Sharp Edge Flight Experiment (SHEFEX) program.
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