Halo orbit station keeping for International Sun-Earth Explorer-C /ISEE-C/

The ISEE-C spacecraft must be kept close to an unstable 'halo' orbit with a series of discrete orbital maneuvers set at intervals at least one month apart. A numerical algorithm has been developed to compute a velocity correction at any point on the trajectory which will minimize the distance between the satellite orbit and the nominal halo path. This algorithm is used to generate a number of station keeping histories with fixed time intervals between maneuvers to ascertain bounds on fuel cost, tightness of fit to nominal path and expected duration between thrust applications. The difference between a third order analytic representation of the halo orbit and a numerically improved nominal path as a reference orbit in the station keeping scheme is investigated as well as the distinction between a tight control and a loose control. A simulation of an operational approach to station keeping is also presented which shows that intermittant propulsive maneuvers can be used to control the spacecraft with very modest fuel expenditure.