Decentralized Relative Navigation for Formation Flying Spacecraft using Augmented CDGPS

Chan-Woo Park, Philip Ferguson, Nick Pohlman, Jonathan P. How
Proceedings of the ION-GPS Conference, Salt Lake City, UT, Sept 2001.

Autonomous formation flying of multiple vehicles is a key technology for both deep space and orbital applications that involve multiple spacecraft. Many future space applications will benefit from using formation flying technologies to perform distributed observations (e.g., synthetic apertures radars and stellar interferometry) and to provide improved coverage for communication and surveillance. One of the key requirements of formation flying is accurate real-time knowledge of the relative positions and velocities between the vehicles. Several researchers have shown that carrier-phase differential Global Positioning System (CDGPS) is a viable sensor to perform this relative navigation. This paper extends the previous work by presenting a decentralized algorithm for this CDGPS relative navigation, without degrading the estimation performance. Furthermore, it is shown that a decentralized implementation adds robustness and improves mission flexibility. The paper also considers spacecraft formations that have local RF ranging devices onboard the vehicles, which was recently proposed to overcome possible limitations associated with a NAVSTAR-only relative navigation sensor (limited availability and accuracy). These additional RF measurements couple the states in the system, thus rendering the previous decentralization scheme inapplicable. This problem is addressed by using an approximate decentralized approach, called Iterative Cascade Extended Kalman Filter (ICEKF). This new estimation approach is compared to a centralized estimation scheme using a typical LEO simulation. The results clearly show that the decentralized ICEKF approach substantially reduces the computational load, eliminates many of the implementation problems associated with the centralized algorithm, and reduces the communication requirements amongst the vehicles in the fleet.

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Professor Jonathan P. How

Chan-woo Park