Improving BDS Autonomous Orbit Determination Performance Using Onboard Accelerometers

Autonomous orbit determination is a crucial step for GNSS development to improve GNSS vulnerability, integrity, reliability and robustness. The newly launched BeiDou (BD) satellites are capable of conducting satellite to satellite tracking (SST), which can be used for autonomous orbit determination. However, using SST data only, the BD satellite system (BDS) will have whole constellation rotation in the absence of absolute constraints from ground or other celestial body over time, due to various force perturbations. The perturbations can be categorized into conservative forces and non-conservative forces. The conservative forces, such as the Earth non-spherical perturbations, tidal perturbation, the solar, lunar and other third-body perturbations, can be precisely modeled with latest force models. The non-conservative forces (i.e. Solar Radiation Pressure (SRP)), on the other hand, are difficult to be modeled precisely, which are the main factors affecting satellite orbit determination accuracy. In recent years, accelerometers onboard satellites have been used to directly measure the non-conservative forces for gravity recovery and atmosphere study, such as GRACE, CHAMP, and GOCE missions. This study investigates the feasibility to use accelerometers onboard BD satellites to improve BD autonomous orbit determination accuracy and service span. Using simulated BD orbit and SST data, together with the error models of existing space-borne accelerometers, the orbit determination accuracy for BD constellation is evaluated using either SST data only or SST data with accelerometers. An empirical SRP model is used to extract non-conservative forces. The simulation results show that the orbit determination accuracy using SST with accelerometers is significantly better than that with SST data only. Assuming 0.33 m random noises and decimeter level signal transponder system biases in SST data, IGSO and MEO satellites decimeter level orbit accuracy can be achieved over a service life of two months using SST data and accelerometers. If only SST data are used, the orbit accuracy is 3~6 m with the same time period, which is an order worse.