A formation flying strategy for CloudSat/Picasso-Cena

For CloudSat and Picasso/Cena to collect nearly simultaneous data over the same territory CloudSat's ground track must stay within /spl plusmn/1 km (in cross-track) of Picasso/Cena's. The Department of Defense Space Test Program (STP) is responsible for CloudSat mission operations and its contractors must determine and execute orbit maneuvers approximately once per week to maintain the ground track separation. This paper derives an optimal path for CloudSat relative to Picasso that minimizes the average cross-track separation. Using historical atmospheric data, the paper then shows that simple parabolic fits of the satellites' relative locations, determined from GPS data, can be used to calculate the size and timing of the maneuvers. With a judicious selection of the relative location thresholds to trigger the maneuvers, this simple approach meets the cross-track and maneuver frequency requirements. Furthermore, this approach does not require highly accurate orbit propagation or atmospheric density models.