Optimal trajectories for the aeroassisted flight experiment
Doctor of Philosophy
The aeroassisted flight experiment (AFE) is to simulate a transfer from a geosynchronous Earth orbit (GEO) to a low Earth orbit (LEO). Specifically, the AFE spacecraft is released from the Space Shuttle and is accelerated by means of a solid rocket motor toward Earth, so as to achieve atmospheric entry conditions identical with those of a spacecraft returning from GEO. During the atmospheric pass, aerodynamic and thermal data are gathered for use in designing aeroassisted orbital transfer (AOT) vehicles. Following the atmospheric pass, the AFE spacecraft ascends to the specified LEO either directly or indirectly via an intermediate parking Earth orbit (PEO). The optimal trajectories are determined by minimizing the postatmospheric characteristic velocity if the entry path inclination is fixed or the total characteristic velocity if the entry path inclination is free. The final maneuver includes the rendezvous with and the capture by the Space Shuttle. The entry and exit orbital planes of the AFE spacecraft are identical with the orbital plane of the Space Shuttle. Under following two assumptions: (i) the instantaneous orbital plane is nearly identical with the entry orbital plane; (ii) the Earth's angular velocity is relatively small, the motion of the AFE spacecraft of order six (combination method) can be decoupled into two subsystems of order three, the longitudinal motion and the lateral motion (decomposition method). The results of optimal trajectories are nearly the same by using the combination method and the decomposition method. The optimal control is bang-bang if the entry path inclination is fixed and is constant if the entry path inclination is free. Finally, the optimal trajectories are advantageous over a nonoptimal reference trajectory in terms of the main quantities of interest, namely, the characteristic velocity, peak dynamic pressure, peak heating rate, and peak wedge angle.
Mechanical engineering; Mathematics; Aerospace engineering