星载加速度计增强北斗自主定轨性能

Abstract

卫星自主定轨是提高全球卫星导航系统（GNSS）可靠性、稳健性、完整性和生存能力的重要保证。新一代的北斗卫星已可以进行星间链路测距，从而达到提高卫星全球跟踪能力以及实现整个卫星导航系统的自主定轨。然而由于卫星运行会受到多种摄动力的影响，如果不能对这些摄动力进行精密的改正，在没有地面或其他天体提供绝对约束的条件下，导航系统会随着自主定轨时间的延长出现星座整体旋转。卫星所受摄动力分为保守力和非保守力两部分：对于保守力，如地球非球形摄动、潮汐摄动、太阳月球和其他三体引力，现在已有的力学模型可以很精确地进行改正；而非保守力（如太阳光压摄动），则难以用精确的模型进行改正，因此成为影响卫星定轨精度的主要因素。星载加速度计可以高精度地测量非保守力，并已成功应用于重力卫星（CHAMP、GRACE、GOCE）的重力场反演与大气研究中。本文研究主要探讨采用星上加速度计提高北斗卫星自主定轨精度和延长自主定轨时长的可行性。利用模拟的卫星轨道和星间链路数据，以及现有的星载加速度计误差模型，对北斗卫星系统分别使用星间链路数据和星间链路与加速度计组合数据，进行自主定轨与精度评定。计算结果表明，使用星间链路与星载加速度计数据进行自主定轨，较单纯使用星间链路数据精度具有明显改进。在模拟的星间测距观测数据具有0.33 m随机噪声以及分米级系统误差，自主定轨两个月的情况下，联合使用加速度计数据的自主定轨IGSO和MEO卫星精度为分米级，而仅使用星间链路数据的定轨精度约为3~6 m，比使用加速度计精度低一个量级。 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.