Ambiguity-fixed real-time orbit determination of LEO spacecraft using RTPPP correction

Abstract

Precise knowledge of a satellite's orbit in real-time is becoming increasingly important with increasingly populated Low Earth Orbit (LEO) orbits and growing accuracy requirements for various tasks. At the same time, the capabilities of GNSS Signal Augmentation are increasing as well, and access to correction data is getting easier. Numerous system providers are planning to or already started to broadcast GNSS corrections via satellites, which makes them accessible for LEO satellites as well. Currently, GNSS-based real-time orbit determination works with ambiguity-float solutions, but the in-orbit availability of all corrections required for single receiver ambiguity-fixing is only a matter of time. This Thesis aims to evaluate the potential improvement that could be obtained through ambiguity fixing in combination with real-time augmentation. For this a ambiguity fixing approach based on a widelane-narrowlane ambiguity resolution using the LAMBDA method for narrowlane resolution is implemented. The basis for this are real-time corrections provided by the Centre national d'études spatiales (CNES), which can clearly improve the overall orbit accuracy. However, they also suffer from varying quality and outages. Ambiguity fixing based on these corrections introduces a high risk of wrong ambiguity fixes, resulting in degraded orbit quality. Different methods are applied within this thesis to prevent these wrong fixes, but the introduced instability can ultimately not outweigh the potential accuracy improvement - which is shown to be rather small even on days with good fixing rates. Nevertheless it can be shown that the presented fixing approach works well with precise correction data obtained via post-processing. This shows that single-receiver ambiguity fixing may still be an interesting option with more accurate real-time correction data.