Optimal plane change during constant altitude hypersonic flight

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76829/1/AIAA-20715-865.pd

Optimal Nodal Transfer and Aeroassisted Transfer By Aerocruise.

In view of the increasing human activity in space, the maneuvering between different orbits is going to be a regular and also an important part of the space transportation. The objective of this dissertation is to provide some contributions to the problem of minimum fuel, time-free transfer between non-coplanar elliptical orbits both in the pure propulsive mode and the aeroassisted mode. We have the following results: (1) The "reference plane" introduced in Chapter 3 gives a good initial guess and we can solve all the two-impulse time-free orbital transfer problems, and have a better evaluation between the propulsive transfer and the aeroassisted orbital transfer. (2) From the discovery of the closeness between the minimum nodal transfer and the true optimum transfer in Chapter 4, we can use the former as a good approximation and checkout the latter. Also the general view about the permissible thrust angles and the impulse position restriction can give a guide in designing a near-optimal orbital transfer. (3) The optimal control problem in aerocruise at constant altitude reveals that the optimal control strategy, by modulating both the thrust magnitude and the bank angle, is better than the result from parameter optimization, not only for the plane change ability but also in reducing the acceleration load. Furthermore, this flight program is particularly efficient for cruise at very high altitude when several orbital revolutions are required for completing the plane change.Ph.D.Aerospace engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161419/1/8712155.pd

Optimal time-free nodal transfers between elliptical orbits

This paper presents the necessary conditions for the minimum fuel, time-free transfer between two non-coplanar elliptical orbits. It is shown that the solution is obtained by solving a system of three non-linear equations for three unknowns. In the second part, we discuss the case where the impulses are applied along the line of nodes. In general, this nodal transfer is non optimal, but the characteristic velocity for the best nodal transfer, called the minimizing nodal transfer, is reasonably close to the one for the optimal transfer for it to be useful as a substitute for a practical transfer. Furthermore, when we continuously vary the relative position of the two terminal orbits, the two characteristic velocities, for the minimizing nodal transfer and the optimal transfer, exhibit the same trend in the sense that they pass through their maxima and minima at nearly the same relative position. This makes the set of explicit formulas for computing the minimizing nodal transfer, as presented in this paper, a useful tool for designing a minimum fuel transfer between several orbits.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27209/1/0000213.pd