OPTIMAL STEERING FOR NORTH-SOUTH STATIONKEEPING OF GEOSTATIONARY SPACECRAFT

The problem of north-south stationkeeping of geostationary spacecraft using electric thrusters is analyzed. Pure yawing with short-duration low-thrust arcs applied infrequently is assumed, and the dynamics are cast in continuous form to obtain an analytic steering law in the incl ination-node (i, Omega) space that brings the spacecraft back to the i deal initial orbit orientation for the initiation of a free-drift peri od that satisfies the inclination constraint for the longest possible duration, This problem is posed as a minimum-time navigation problem b etween two i, Omega pairs and is similar to the Zermelo problem of nav igating a ship in strong variable currents. The simple linear steering law thus obtained is easy to use and fuel optimal compared to other s uboptimal strategies for travel between two given (i, Omega) pairs.