GNSS systems were originally designed for earth-based positioning and navigation. Despite this, real-time spacecraft navigation based on spaceborne GNSS receivers is becoming a common technique for low-Earth orbits and geostationary orbits, allowing satellites to self-determine their position using GNSS, reducing dependence on ground-based stations.
The space community started experimenting with spaceborne receivers very early in the deployment of the GPS network.The first spaceborne GNSS receiver was deployed in Landsat 4 in July 16th 1982. The GPSPAC receiver deployed with Landsat 4 was also deployed with Landsat 5 and 2 other US Department of Defense missions and despite the few number of GPS satellites deployed (at that time only 6 Block I satellites were deployed), the GPSPAC was able to demonstrate the feasibility of using GNSS for space navigation.
Nowadays, GNSS is a major asset for space navigation in low Earth orbits which provide means for orbit precise determination, real time navigation and a precise onboard time reference. The application of the GNSS in space navigation enables research in different areas:
Precise orbit determination
Autonomous real time navigation
Multi-satellite payload synchronization