Formationkeeping for a pair of satellites in a circular orbit

Certain future missions will require that a pair of satellites—ma ster and slave—fly in a fixed relative formation. Active control is required to maintain this formation in spite of disturbances such as aerodynamic drag and solar radiation pressure. This paper develops a closed-loop formationkeeping controller for satellites in any circular orbit using digital optimal control theory. A formationkeepi ng sensor concept, tradeoffs, design, brassboard demonstration, and modeling are discussed. The formationkeeping actuators are assumed to be chemical thrusters on the slave satellite. Two satellites flying in trail 700 m apart in geosynchronou s orbit are used as an example to present closed-loop formationkeeping simulation plots. The results show that formation is maintained to within the ±21 m allocated requirement in the in-track and out-of-plane directions.