GPS Based Relative Navigation

Abstract

The use of Global Positioning System (GPS) measurements provides the primary technique for determining the relative position of cooperative, formation-flying satellites in low Earth orbit. Similar to terrestrial applications, the relative navigation benefits from a high level of common error cancellation. Furthermore, the integer nature of double-difference carrier phase ambiguities can be exploited in carrier phase differential GPS (CDGPS). Both aspects enable a substantially higher relative accuracy than can be achieved in single-spacecraft navigation. Following an overview of spaceborne GPS receivers, the dynamical and measurement models for relative navigation using single- or dual-frequency measurements are presented along with a discussion of estimation schemes for real-time and offline applications. Actual flight results from the TanDEM-X and PRISMA missions are presented to demonstrate the feasibility of mm-level post-facto baseline determination and cm-level real-time navigation using CDGPS.