GAAF在星载GPS实时定轨中的应用研究

为确保高精度星载GPS实时定轨算法能够应用于较低轨道卫星,提出了用地球引力近似函数法(GAAF)代替传统球谐函数递推法来计算地球引力加速度,在不降低实时定轨精度的同时,大幅减小高阶次重力场模型的轨道积分计算负荷,以满足计算能力有限的星载处理器的在轨处理要求。分析了影响GAAF计算精度的两个因素:伪中心位置拟合多项式的次数选取和经纬度格网大小的最优确定。用CHAMP卫星的实测GPS数据模拟实时定轨试验,结果表明,采用二次及以上伪中心拟合多项式,格网纬度小于0.75°、经度小于1.5°的GAAF时,实时定轨的轨道精度要优于70×７０阶次重力场模型直接参与实时定轨,且大幅降低实时定轨的计算负荷。

Application of a Gravity Acceleration Approximation Function in the PreciseReal-Time Orbit Determination Using Space-borne GPS Measurements

In order to minimize the computational burden of the onboard precise real-time orbit deter-mination system,a Gravity Acceleration Approximation Function(GAAF)is introduced to computethe gravitational acceleration replacing the traditional spherical harmonic representation of the gravityfield.The appropriate order of the polynomial to fit a set of pseudo-centers on various heights at afixed location is discussed in detail,as well as the optimal geographic grid size.Then,GAAF is em-bedded in the SATODS software for real-time orbit determination using space-borne GPS measure-ments.A simulation test of real-time orbit determination was carried out using space-borne GPS dualfrequency pseudo-range data from the CHAMP satellite.Results show that the GAAF can improveorbital accuracy with quadratic polynomial fitting and a global grid where the latitude increment is nomore than 0.75degrees and the longitude increment is less than 1.5degrees,as compared with thetraditional recursive method using a 70× 70gravity field model. The proposed method reduces the computational load of orbit determination significantly.