Improving the orbit accuracy of BeiDou maneuvered satellites and AutoNav

Abstract

BeiDou satellites, particularly GEO/IGSO, are frequently maneuvered to maintain them in their designated orbits. As the precise maneuvering periods and thrust forces are unknown, in current operation practice, satellite broadcast ephemeris and precise ephemeris are interrupted for several hours and 1-2 days after each maneuver respectively, which severely affects satellite usability and orbit accuracy. Precise estimation of thrust forces acting on satellites would provide continuous ephemerides during maneuvering periods, and could significantly improve orbit accuracy immediately after maneuvering. In this study, we only use BeiDou ground stations to estimate the thrust forces acting on BeiDou satellites during the maneuvers, through a comparison of the kinematic orbit and the integrated orbit free from thrust forces. The characteristics of BeiDou satellite maneuvering types have been analyzed, and a piece-wise linear thrust force model has been proposed. Based on this new model, the continuous POD of the maneuvered satellites in a 3-day arc has been conducted. Evaluation of the orbit determination result shows that the accuracy of obtained precise ephemeris on the maneuvering day is comparable to that of precise orbits in normal cases. Moreover, to make up for the 5-8 h gap in maneuvered satellite broadcast ephemeris and achieve the timely recovery of satellite orbit, we have provided 1-h orbit prediction after the maneuver using the data of IGS MGEX network. The accuracy of the predicted orbits 1 h after maneuvering for both IGSO and GEO has achieved the similar level as normal broadcast ephemerides. Inter-satellite links (ISLs) are available for the newly launched BeiDou satellites. They are critical for enhancing the observation geometry of GEO and IGSO satellites and are the main observables of the emerging technique of BDS autonomous navigation (AutoNav). However, the BDS could suffer from the constellation rotation problem in the AutoNav mode due to the rotation unobservability when using only ISLs. In this study, onboard accelerometers are proposed for use to measure the non-conservative forces in BDS AutoNav mode. Simulations have been carried out with full BeiDou constellation. The results show that the AutoNav orbit accuracy with onboard accelerometers can significantly improve orbit determination accuracy over a long period and it can satisfy the 2 m standard positioning accuracy requirement over a 180-day period, versus only 100 days meeting the same accuracy requirement if only ISLs are used.