Formation Flying

In recent years, a growing number of space missions have been identified which will utilize distributed systems of satellites. There has been a great level of interest in both the scientific and defense communities to develop mature systems and software for autonomous rendezvous and formation flying. Examples include the TICS, F6 and Orbital Express programs at DARPA, the DART, MMS, SIRA, MAXIM and TPF missions at NASA, the Proba-3, Darwin and Cluster missions at ESA and commercial missions like OLEV. The applications range from automated rendezvous for equipment and fuel delivery, to long-duration precise formation flying of distributed sensors, which could enable the detection of distant Earth-like planets. A common thread for all such missions is the need to autonomously perform coordinated operations among multiple free-flying spacecraft.

Princeton Satellite Systems (PSS) has worked for several years on the problem of designing autonomous guidance and control systems for formation flying satellites. For the Air Force TechSat 21 project, we developed the Cluster Manager software, which was an agent-based distributed software system responsible for orbit guidance and fault management. This led to innovative work on the design of formation flying escort vehicles for on-orbit protection of space assets. We were later awarded Phase 1 and Phase 2 SBIRs by NASA Goddard to develop a decentralized formation flying GN&C system, capable of supporting any type of periodic formation geometries in any central body orbit, for arbitrarily large formations. Throughout these efforts, we have developed efficient and robust algorithms to perform optimal maneuver planning and general multi-vehicle coordination tasks in a distributed software architecture.

More recently, PSS has worked with the Swedish Space Corporation (SSC) / OHB Sweden to develop new methods for collision prediction and avoidance. This work was done in support of the PRISMA mission, which was launched in 2010 to demonstrate Guidance, Navigation, and Control strategies for advanced autonomous formation flying. The safe guidance mode, based upon algorithms developed by PSS under a CRADA, has been an integral part of the PRISMA mission. Proximity detection algorithms identify when the two spacecraft are too close and switches to the safe guidance mode. This mode is also used routinely during nominal operations to transition between formation flying experiments and when experiments are not being performed. While in the safe guidance mode, relative station-keeping maneuvers are continually planned to keep the spacecraft on a safe relative trajectory.

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