Formationkeeping for a pair of satellites in a circular orbit

Certain future missions will require that a pair of satellites - master 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 formationkeeping 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 geosynchronous orbit are used as an example to present closed-loop formationkeeping simulation plots. The results show that formation is maintained to within the + or - 21 m allocated requirement in the in-track and out-of-plane directions.