Stationkeeping Strategy and Possible Lunar Halo Orbits for Long-Term Space Station

A new long-term stationkeeping strategy is presented for a low-thrust space station in a lunar halo orbit for the Earth-Moon unstable collinear libration point L2. The approach is a sequence of optimal control problems for adjacent half-revolutions. The method utilizes the high-fidelity ephemeris model. An iterative single shooting algorithm of a differential correction is used. This is based on a discrete pseudo-impulse set method as an optimization technique. The partial derivatives are numerical computed along a reference orbit. Three possible quasi-periodic orbits with continuous visibility of the station from the Earth are considered. Two types of stationkeeping maneuvers are utilized. The first is a basic orbit correction in the Earth–Moon plane. The second consists of combined maneuvers that include out-of-plane motion correction (coordinates and velocity). The combined maneuvers are performed periodically for a threshold value of the out-of-plane coordinate. Simulation and comparative results of the long-term stationkeeping strategy for one year are presented. The algorithm can be used for an estimation of the required thrust-to-weight ratio for the space station.