AAS 98-168

STATION-KEEPING STRATEGIES FOR TRANSLUNAR LIBRATION POINT ORBITS

G. Gomez - Universitat de Barcelona, Spain; K. C. Howell - Purdue University; J. Masdemont - Universitat Politecnica de Catalunya, Spain; C. Simo - Universitat de Barcelona, Spain

Abstract

Spacecraft in orbits near the collinear libration points are excellent platforms for scientific investigations of various phenomena. Since such libration point trajectories are generally unstable, spacecraft moving on such paths must use some form of trajectory control to remain close to the nominal orbit. The primary goal of this effort is the study of two particular stationkeeping approaches applied to the maintenance of a spacecraft in a quasiperiodic Earth-Moon L2 halo orbit. The Target Point station-keeping method computes corrective maneuvers by minimizing a weighted cost function. The cost function is defined in terms of a corrective maneuver as well as position and velocity deviations from the nominal orbit at a number of specified future times; these state vectors are denoted as "target points." The target points are selected along the trajectory at discrete time intervals that are downstream of the maneuver. In contrast, the Floquet Mode approach incorporates invariant manifold theory and Floquet modes to compute the maneuvers. Floquet modes associated with the monodromy matrix are used to determine the unstable component corresponding to the local error vector. The maneuver is then computed such that it eradicates the dominant unstable component of the error. It is noted that both approaches have been demonstrated in a complex model, but neither of these methods has previously been applied in the Earth-Moon system.

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