A system to maintain a phase difference is disclosed. Two or more aircraft fly in a continuous periodic trajectory. The system maintains a phase difference between the two or more aircraft. Telemetry information for a reference aircraft moving in a first periodic trajectory is received. A phase difference between a primary aircraft and the reference aircraft with respect to the first periodic trajectory is determined. A variance in the phase difference between the primary aircraft and the reference aircraft from the target phase difference is determined. A new trajectory for the primary aircraft that decreases the variance in the phase difference with respect to the new periodic trajectory is determined, and the primary aircraft is maneuvered to follow the new trajectory.