基于GNSS测量的天宫二号质心确定

由于轨道机动燃料消耗，科学载荷加载、分离，以及伴飞小卫星在轨释放等原因引起天宫二号空间站质心(COM)发生位移，从而影响天宫二号的动力学质心定轨精度。针对这一问题，提出了基于全球导航卫星系统(GNSS)测量数据的简化动力学质心估计方法。燃料消耗是引起天宫二号质心发生位移的主要原因，质心在本体坐标系X轴方向位移最为显著。利用GNSS测量数据对天宫二号进行质心估计和精密定轨，在三轴对地稳定姿态下，本体坐标系X轴方向与轨道切向重合，定轨结果对本体坐标系X轴方向的质心位移并不敏感。但在连续偏航模式下，本体坐标系X轴在轨道法向上有较大分量，X轴方向的质心位移对基于GNSS测量计算的精密定轨结果有较大影响。定性和定量分析结果表明:偏航姿态模式下天宫二号本体坐标系X轴方向质心位移估计具有可行性。天宫二号实测数据计算结果表明:与未做质心估计的定轨结果进行对比，质心估计后表征轨道动力学建模误差的经验加速度补偿水平在轨道径向、切向和法向上分别降低62%、50%和65%；载波相位后验残差标准差降低0.04 cm；精密轨道与全球激光测距数据比较精度提高0.86 cm。所提方法可以应用于大型低轨航天器在轨质心估计。 

Center of mass estimation of Tiangong-2 spacecraft using GNSS measurement

Due to fuel consumption of orbital maneuvers, payloads' load and separation, and the release of small satellite, the Center of Mass(COM) of Tiangong-2 space laboratory moves. To solve this problem, a reduced orbit dynamic determination and COM estimation method is given based on Global Navigation Satellite System (GNSS) measurement data in this paper. Fuel consumption is the main reason for the COM of Tiangong-2 moves. The COM mainly moves along the X-axis of Tiangong-2 body-fixed coordinate system. The COM estimation and precise orbit determination of Tiangong-2 are performed using GNSS measurement data. And in a three-axis earth-pointing stabilization attitude mode, the orbit determination results are not sensitive to the displacement of COM in the X-axis of Tiangong-2 body-fixed coordinate system since the X-axis of Tiangong-2 body-fixed coordinate system coincides with the tangential direction of the orbit. However, in a yaw-steering mode, the X-axis of Tiangong-2 body-fixed coordinate system has a large projection on the orbital normal direction, which makes the displacement of COM in the X-axis of Tiangong-2 body-fixed coordinate system have a greater impact on the precision orbit determination results based on GNSS measurement calculation. And the qualitative and the quantitative analysis results show that the COM estimation is feasible in a yaw-steering attitude mode. Compared with the results without considering COM estimation, the Tiangong-2 measurement data calculation results considering COM estimation show that the empirical accelerations which represent orbital dynamics modeling error in the radial, tangential and normal directions are reduced by 62%, 50% and 65%, respectively, and the standard deviation of post-residuals of the carrier phase is reduced by 0.04 cm. Besides, the comparison accuracy of precision orbit data and the global laser ranging improves by 0.86 cm. The method proposed in this paper can be applied to COM estimation of the large-scale low-earth-orbit spacecraft.