Improving GPS AutoNav orbit accuracy with onboard accelerometers

Autonomous navigation (AutoNav) is a crucial technique for enhancing the navigation satellite system, such as GPS, autonomy and decreasing systemic vulnerability. However, AutoNav using only inter-satellite link (ISL) observations can lead to constellation rotation problem over time, mainly due to the complex perturbations. The conservative perturbations, such as the Earth non-spherical perturbations, tidal perturbation, the solar, lunar attractions, etc. can be precisely modeled with latest force models. The non-conservative ones, mainly the Solar Radiation Pressure (SRP), on the other hand, are difficult to be modeled precisely and have become the main factors affecting AutoNav accuracy. Accelerometers onboard satellites are capable of measuring non-conservation forces and have been successfully used in the scientific missions, e.g., CHAMP, GRACE, and GOCE. This study investigates the feasibility of using accelerometers for GPS. Based on the IGS precise ephemerides, inter-satellite range measurements of decimeter accuracy (σ=0.31m) are simulated. AutoNav using only ISL measurements and ISL together with accelerometers have been carried out, respectively. The results show that AutoNav with accelerometer data can achieve 0.3 to 0.5m orbit accuracy in radial direction, less than 8m in the horizontal direction during the 180-day AutoNav period, several times better than that without accelerometer data. Also, the AutoNav performances of GPS and Beidou are compared.