GNSS-based Real-Time Onboard Orbit Determination for Agile Satellites

Kurzfassung

The development of a GNSS-based real-time navigation system for the Capella synthetic aperture radar (SAR) constellation is described. Capella satellites are equipped with a commercial-off-the-shelf receiver offering concurrent tracking of all visible GNSS satellites from up to four constellation in multiple frequency bands. These data are presently processed on ground in a precise orbit determination (POD) supporting the SAR image generation as well as other high-level applications such as SAR interferometry. For future generations of Capella satellites, the ground-based POD will be complemented by an onboard navigation system enabling faster generation of SAR products and reduced ground system dependence. Compared to common remote sensing satellites in low Earth orbit (LEO), the Capella satellite offer a high level of agility and conduct frequent attitude maneuvers to switch between data takes, ground contacts, battery charging, and orbit maneuvers. This poses notable challenges for GNSS tracking and orbit determination. A prototype real-time navigation filter is described and validated with GPS and Galileo observations collected onboard a representative 3rd generation Capella satellite. The achievable real-time navigation accuracy are assessed in comparison with a ground-based POD. With a 20-cm 3D RMS precision the onboard navigation can support both high-resolution SAR imaging and reliable geo-coding