GNSS has come to play an increasingly important role in satellite formation‐flying and rendezvous applications. In the last decades, GNSS measurements have been frequently used to determine the relative position of cooperative satellites in low Earth orbit. More recently, GNSS data have enabled formation‐flying in highly elliptical orbits with apogees at tens of Earth radii well above the GNSS constellations. Current research aims at distributed precise relative navigation between tens of swarming nano‐ and micro‐satellites based on GNSS.
This trend is due to two main reasons. On one hand, GNSS receivers are very common devices onboard spacecraft. On the other hand, GNSS relative navigation benefits from a high level of common error cancellation. This allows the exploitation of the integer nature of carrier‐phase ambiguities in carrier‐phase differential GNSS (CDGNSS). This technique allows a substantially higher accuracy in the estimation of the relative motion than can be achieved in single‐spacecraft navigation. Following historical remarks and an overview of the state of the art, this chapter addresses the technology and main techniques used for spaceborne relative navigation both for real‐time and offline applications. Flight results from missions such as the Space Shuttle, PRISMA, TanDEM‐X, and Magnetospheric Multi‐Scale (MMS) are presented to demonstrate the versatility and broad range of applicability of GNSS relative navigation, from precise baseline determination on‐ground (millimeter‐level accuracy), to coarse real‐time estimation onboard (meter‐ to centimeter‐level accuracy).