On-Board Correction Estimation for LEO-PNT Satellites

Abstract

Global Navigation Satellite Systems (GNSS) have become crucial for providing Positioning, Navigation, and Timing (PNT) services worldwide. Existing GNSS constellations such as GPS, GLONASS, BeiDou, and Galileo operate in Medium Earth Orbit (MEO) at around 20,000 km altitude. Low Earth Orbit Positioning, Navigation, and Timing (LEO-PNT) is an emerging satellite navigation concept to augment current GNSS by placing satellites closer to Earth, at around 600-1200 km altitude. This lower altitude results in a faster change in satellite geometry, which is primarily expected to reduce the convergence time of Precise Point Positioning (PPP). To fully realize this opportunity, accurate knowledge of the LEO-PNT satellite orbital positions and clock offsets at a low latency is required. For existing GNSS constellations, global networks of ground stations are generally used to determine the GNSS satellite positions and clock offsets. This information is then uplinked to the GNSS satellites for dissemination to users. Due to the closer proximity to Earth, LEO-PNT systems would require an extensive ground network to replicate the ground estimation approach of GNSS. However, being situated below MEO, there is an opportunity to leverage GNSS to perform real-time Precise Orbit Determination (POD) on board the LEO-PNT satellites. This thesis aims to quantify the impact on ground user positioning that the LEO-PNT satellites could have when using on-board POD.