LEO卫星轨道根数型星历参数与接口设计

低轨卫星是导航增强系统发展的新兴力量,具有独特优势。广播星历参数是其实现星基增强的重要指标。中轨GPS星历采用16/18参数模型,若直接用于LEO的星历参数拟合,卫星沿迹方向的位置分量拟合误差大,且对小偏心率近圆轨道有潜在的拟合法矩阵病态问题。基于第一类无奇点根数,通过增加或修改轨道沿迹向和径向摄动参数,设计了适用于近圆低轨卫星的16～19参数的5种星历模型。基于300～1500 km高度LEO的拟合试验表明:提出的16/17/18/18~*/19参数星历,URE最大值分别优于10/6/4/5/2.5 cm。最后,根据拟合参数的变化范围,对5个星历模型进行了接口设计。在数据截断对URE的影响为毫米量级要求下,总比特位分别为329/343/376/379/396,其中16/17参数星历模型比GPS16参数模型减少了29/15个,18/18~*/19参数星历模型比GPS18参数星历模型减少了64/61/41个。

Orbital elements ephemerides and interfaces design of LEO satellites

Low earth orbit satellites, with unique advantages, are prosperous types of navigation augmentation satellites for the GNSS satellites constellations. The broadcast ephemeris element needs to be designed as an important index of the augmented LEOs. The GPS ephemerides of 16/18 elements cannot be directly applied to the LEOs because of the poor fitting accuracies in along-track positional component. Besides, the ill-conditioned problem of the normal-matrix exists in fitting algorithm due to the small eccentricity of the LEO orbits. Based on the nonsingular orbital elements, 5 sets of ephemerides with element numbers from 16 to 19 were designed respectively by adding or modifying orbital elements magnifying the along-track and radial positional components. The fitting experiments based on the LEO of 300 to 1500 km altitudes show that the fitting UREs of the proposed 16/17/18/18^*/19-element ephemerides are better than 10/6/4/5/2.5 cm, respectively. According to the dynamical range of the fitting elements, the interfaces were designed for the 5 sets of ephemerides. The effects of data truncation on fitting UREs are at millimeter level. The total bits are 329/343/376/379/396, respectively. 29/15 bits are saved for the 16/17-element ephemerides compared with the GPS16 ephemeris, while 64/61/41 bits can be saved for the 18/18^*/19-element ephemerides compared with the GPS18 elements ephemeris.