The objective of this dissertation is to solve an optimal deorbit guidance problem given initial orbit and vehicle parameters as inputs. Currently, the problem is computationally intensive to solve and approximate methods such as impulsive maneuvers are utilized. The problem is formulated as a fuel-optimal control problem that allows for a variety of terminal conditions at entry interface (EI). Using optimal control methods, the engine on time, engine off time as well as the direction of the thrust vector are solved for a variety of circular and elliptic initial orbits. Single and multiple burn maneuvers for both circular and elliptic orbits are explored. The J2 gravitational term is added as part of the solution process. The numerical solution is obtained using an analytical multiple shooting method. The results show promising potential of the proposed method and are comparable to NASA's Shuttle results.
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