![]() ![]() For the atmospheric pass, a feedback control scheme is employed and the lift coefficient is adjusted according to a two-stage gamma guidance law. Next, attention is focused on guidance trajectories capable of approximating the optimal trajectories in real time, while retaining the essential characteristics of simplicity, ease of implementation, and reliability. The optimal trajectory is shown to include two branches: a relatively short descending flight branch (branch 1) and a long ascending flight branch (branch 2). The sequential gradient-restoration algorithm (SGRA) is used for optimal control problems. ![]() First, optimal trajectories are computed by minimizing the total velocity impulse (hence, the propellant consumption) required for AOT transfer. The presence of upper and lower bounds on the lift coefficient is considered. It is also assumed that, during the atmospheric pass, the trajectory is controlled via the lift coefficient. It is assumed that the initial and final orbits are circular, that the gravitational field is central and is governed by the inverse square law, and that at most three impulses are employed: one at HEO exit, one at atmospheric exit, and one at LEO entry. In particular, HEO can be a geosynchronous Earth orbit (GEO). The optimization and guidance of trajectories for coplaner, aeroassisted orbital transfer (AOT) from high Earth orbit (HEO) to low Earth orbit (LEO) are examined. Gamma guidance of trajectories for coplanar, aeroassisted orbital transfer ![]()
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