Real-Time Navigation of Formation-Flying Spacecraft

Abstract

Spacecraft formation flying is commonly considered a key technology for advanced space missions. Compared with large individual spacecraft, the distribution of sensor systems to multiple platforms offers improved flexibility and redundancy, shorter times to mission, and the prospect of being more cost effective. The present study describes the design and prototype implementation of a navigation system that enables high-precision relative navigation of multiple formation-flying satellites in real time using representative space hardware. A fully decentralized system design has been adopted, in which each spacecraft is equipped with its own single-frequency global-positioningsystem receiver and navigation computer. A continuous exchange of raw measurements between any two satellites in the formation is achieved through a communication architecture using multichannel radio modems operated in a time-multiplexed manner. Multiple Kalman filters running concurrently on each navigation computer provide estimates of both the local spacecraft’s absolute state vector and the relative state vectors of all remote satellites in the formation. Using live global-positioning-system signals generated by a signal simulator, the proper operation of the navigation process and the communication architecture has been validated in a realistic environment. Real-time relative navigation could first be demonstrated for a formation of up to four spacecraft with an accuracy of 1.5mm (position) and 5 µm/s (velocity) over a 4-km baseline.