Precise formation flying control of multiple spacecraft using carrier-phase differential GPS

Formation flying is a key technology for deep space and orbital applications that involve multiple spacecraft operations. Imaging and remote sensing systems based on radio interferometry and SAR require very precise (sub-wavelength) aperture knowledge and control for accurate relative data collection and processing. Closely tied with the Orion and TechSat21 projects, this work describes the ongoing research to investigate precise relative sensing and control via differential GPS for multiple spacecraft formation flying. Specifically, we present an autonomous control architecture for formation flying that integrates low-level satellite control algorithms (formation keeping and relative error correction) with high-level fuel/time optimal formation coordination and planning. The basic features of this architecture are implemented on a nonlinear orbital simulation of Orion vehicles with disturbances and a realistic differential GPS measurement model. Also, we generalize closed-form solutions of passive apertures for constellations with mean formation eccentricity.