两行根数辅助的SLR单站定轨

单站测距资料定轨的困难限制了漫反射SLR(Satellite Laser Ranging)测距资料的应用.为此,提出利用两行根数模拟多站SLR测距资料作为辅助,实现单站SLR测距资料定轨的方法.该方法对卫星Ajisai单站SLR测距资料定轨并生成5 d预报轨道,误差小于40 m,实现利用单站测距资料的轨道改进,验证了方法的可行性.     

两种观测技术综合精密定轨的探讨

利用T／P卫星的SLR和DORIS实测资料,对两种观测技术综合精密定轨中的加权及其对定轨影响的问题作了初步的探讨。根据所提出的一种经验性的加权方法进行了综合定轨计算,结果表明：对于两种不同技术的观测,相对权选取的恰当与否将影响综合定轨的精度;综合定轨的最优加权不仅依赖于观测资料的精度,还与观测资料的多少和几何分布有关;通过选用最优加权,可使得综合轨的精度优于仅用其中一种技术的定轨精度,综合定轨能有效地提高定轨精度。     

Space Event and Outlier Detection Based on Expectation Maximization Algorithm

The United States provide Element Sets (ELSET) database in Two-Line Element (TLE) format for public use, which plays an important role in the inversion of atmospheric density in the thermosphere, ballistic coefficient estimation, early-warning and so on. Due to large uncertainties existing in the TLE generation process, space environment changes, and space events, ELSET database contains a large number of abnormal TLE data to be filtered, such as corrected TLE, orbital element outlier, and Bstar outlier. The existing methods to filter out the outliers lack general applicability and are very complicated, which are only applicable to a few space targets in certain orbit regions. To overcome the shortcomings of the existing methods, a filtering method is proposed based on Expectation Maximization (EM) algorithm employing a sliding window and polynomial fitting method, which can detect outliers for different orbital elements and space events. The research shows that the algorithm can effectively single out the outliers in TLE sequences and is suitable for all orbital debris.     

Application of variance component estimation to precise orbit determination for ERS-2

Variance component estimation (VCE) is applied to precise orbit determination (POD) of the ERS-2 satellite. Twenty 5-day long arcs in the early three months in 1998 were calculated using the SLR and PRARE data. In the data the adjacent arcs overlap for two days except the intervals for orbit maneuver. The effect of VCE orbit determination on the calculation is investigated by an analysis of residuals and comparison of overlapping arcs, and the mean a posteriori standard deviation of each group of measured residuals is given. It is shown by the residuals analysis that the fitting of the measurements is significantly improved by VCD. However, according to Abbey criterion, VCD is not able to eliminate the systematic errors due to errors in the dynamic and geometric models. The results of the comparison of the overlapping arcs show that (1) VCE reduces the mean range deviation of overlapping arcs, especially where there are obviously unreasonable deviations, so that the orbit obtained has a more uniform precision; (2) By using VCE, adjacent arcs tend to close up and this is more apparent in the transverse direction. From the mean a posteriori standard error of each group of measurements, it can be seen that as far as the single normal point measurement is concerned, the data of some SLR stations are more important than other measurements in POD calculation. Generally speaking, determination of weighting by using VCE is more reasonable than by using initial standard deviation.     

方差分量估计方法在ERS—2卫星精密定轨中的应用

将方差分量估计（VCE）方法应用于ERS－2卫星的精密定轨,用SLR和PRARE资料计算了1998年前3个月的23个长度为5天的弧段（除了调整轨道的时段外,相邻弧段有两天的重叠）,从观测值残差分析和重叠弧段比较两个方面,考察VCE方法对定轨计算的影响,并给出了各组观测值的平均验后均方差,对观测值残差的分析表明,使用VCE方法明显地改善了观测值的拟合程度,但从阿卑（Abbey)标准对观测值残差的检验结果来看,使用VCE方法不能消除轨道中由力学模型和几何模型误差引入的系统差,重叠弧段比较的结果表明：（1）使用VCE方法缩小了重叠弧段的平均距离差,并改善了一部分权段明显不合理的偏离,使最后得到的轨道具有更均匀的精度,（2）相比较而言,VCE方法使相邻弧段靠拢的趋势在轨道切向体现得较为明显,由各组观测值的平均验后方差可见,说单个标准点观测值而言,部分SLR台站的观测资料在定轨计算中占有比其他观测资料更重的地位,纵观全文,使用VCE后得到的观测值的平衡验后均方差来确定资料的双重将比使用均方差更为合理。     

Application of Accelerometer Data in Precise Orbit Determination of GRACE -A and -B

We investigate how well the GRACE satellite orbits can be determined using the onboard GPS data combined with the accelerometer data.The preprocessing of the accelerometer data and the methods and models used in the orbit determination are presented.In order to assess the orbit accuracy,a number of tests are made,including external orbit comparison,and through Satellite Laser Ranging (SLR) residuals and K-band ranging (KBR) residuals.It is shown that the standard deviations of the position differences between the so-called precise science orbits (PSO) produced by GFZ,and the single-difference (SD) and zero-difference (ZD) dynamic orbits are about 7 cm and 6 cm,respectively.The independent SLR validation indicates that the overall root-mean-squared (RMS) errors of the SD solution for days 309-329 of 2002 are about 4.93cm and 5.22cm,for GRACE-A and B respectively; theoverall RMS errors of the ZD solution are about 4.25 cm and 4.71 cm,respectively.The relative accuracy between the two GRACE satellites is validated by the KBR data to be on a level of 1.29 cm for the SD,and 1.03 cm for the ZD solution.     

Applications of IGS products in GPS time comparisons

When the GPS CV (common view) technique is used for the high-precision time comparisons, the effects of the error of the satellite orbit and the ionospheric delay of the received signal are not negligible and have to be IGS precise ephemeris and CODE global total electron content maps in the GPS time transfers, and it is shown that by using these IGS products the accuracies of the single-station time determination and long-distance time transfer can be effectively improved.     

基于CEI测量的GEO目标快速轨道恢复

连线干涉测量(Connected Element Interferometry, CEI)是一种全天时全天候的被动测角技术, 已用于空间目标的跟踪监视. 地球静止轨道(Geostationary Earth Orbit, GEO)卫星需要频繁机动以保持轨位或完成其他任务, 其机动后的快速轨道恢复能力对于监视预警极为重要. 针对基于CEI的GEO短弧定轨和预报, 分析了定轨算法的形亏和数亏, 在附加先验轨道约束的短弧定轨基础上, 提出了轨道半长轴初值的自适应优化方法. 利用亚太七号卫星的CEI仿真和实测数据进行了短弧定轨和预报, 实验结果表明, 采用优化后的半长轴初值, 30min短弧定轨和10min预报的卫星位置分量精度均优于4km, 能够满足非合作GEO目标机动后快速轨道恢复的需求.     

日月轨道计算对TLE深空编目目标预报精度的影响

双行根数(Two Line Element, TLE)作为一类广泛使用的空间物体编目数据, 其预报精度和误差特性是TLE编目 在空间碎片研究中所要关注的问题之一. TLE编目需要配合SGP4/SDP4 (Simplified General Perturbations 4/Simplified Deep Space 4)模型进行轨道预报, 对深空物体来说, 主要考虑带谐项$J_2$、$J_3$、$J_4$摄动、 第三体日月摄动和特殊轨道共振问题修正等. 其中, SGP4/SDP4模型第三体摄动计算时, 对日月轨道近似采用了长期进动根数和 简单平运动的方式, 在外推10d时存在约2$^\circ$--3${^\circ     

Study on the Orbit Prediction Errors of Space Objects Based on Historical TLE Data

Two line element (TLE) released by the North American Aerospace Defense Command (NORAD) is widely used by aerospace workers, and the matched SGP4/SDP4 (Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4) model is used to propagate it. Nevertheless, no corresponding information about its accuracy and covariance is clearly given, thus the application of the TLE data is greatly restricted. In this paper, the determined and predicted orbits are compared to generate the orbit error data, based on the historical TLE data obtained from the Space-Track website and the SGP4/SDP4 model. By dividing different time bins, the fitting coefficients of the variation of orbit prediction error with time are given for each space object, and the characteristics of the error evolution are further discussed for the different types of orbits. The mean analytic model of the orbit prediction error evolution with time is given respectively for the four orbit types of space objects, which provides a valuable reference for extending the application of the TLE data.     

Orbit determination of space debris: admissible regions

The main problem in the orbit determination of the space debris population orbiting our planet is identifying which separate sets of data belong to the same physical object. The observations of a given object during a passage above an observing station are collectively called a Too Short Arc (TSA): data from a TSA cannot allow for a complete determination of an orbit. Therefore, we have to solve first the identification problem, finding two or more TSAs belonging to the same physical object and an orbit fitting all the observations. This problem is well known for the determination of orbits of asteroids: we shall show how to apply the methods developed for preliminary orbit determination of heliocentric objects to geocentric objects. We shall focus on the definition of an admissible region for space debris, both in the case of optical observations and radar observations; then we shall outline a strategy to perform a full orbit determination.     

DTM94大气模型及其应用

简述了ＤＴＭ９４ 大气模型, 并以其旧版本ＤＴＭ７８ 为对照进行了初步考察和分析, 其中给出了两种模型的大气密度随地磁指数ｋｐ 和太阳辐射流量（Ｓｏｌａｒ Ｒａｄｉｏ Ｆｌｕｘ） 变化的情况, 并对２０ｄ （ 天） 弧长Ａｊｉｓａｉ 卫星的全球ＳＬＲ观测资料进行处理, 结果表明ＤＴＮ９４ 对近地卫星Ａｊｉｓａｉ 的精密定轨是十分有利的。     

Application of the extended Kalman filter in satellite prediction

The extended Kalman filter is used in this paper to process single-station laser ranging data over a few revolutions to improve the satellite orbit. The aim is to provide accurate short-term predictions of the satellite position. The dynamical model includes the perturbations due to the Earth's oblateness, air drag, solar radiation pressure and the gravitational attractions of the Sun and the Moon.The proposed method is tested with simulated and real LAGEOS data. The results show that the above aim is achievable. Moreover, the computing program based on the present method can be realized on mini-computers.     

SGP4/SDP4模型精度分析

本文基于最新发布的SGP4/SDP4(Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4)模型设计了一套定轨方案,从空间目标库中挑选出不同类型和轨道参数的1120个目标进行计算,定量给出了SGP4/SDP4模型处理不同类型空间目标的定轨预报精度.结果表明:近地目标定轨精度为百米量级;半同步和同步轨道定轨精度平均为0.7和1.9km.椭圆轨道目标的定轨精度与偏心率有关,除少数e>0.8的椭圆轨道目标,绝大多数椭圆轨道目标定轨误差均小于10km.用SGP4/SDP4模型对近地目标预报3天,半同步轨道预报30天,同步轨道预报15天,椭圆轨道预报1天,预报误差一般不超过40km.     

Geostationary Satellite Orbit Determination by LEO Networks with Small Inclination

In view of the limitation of ground-based Tracking Telemetry and Command (TT&C) system in covering the geostationary satellite in space and time, the method of determining the orbit of the geostationary satellite by the LEO (Low Earth Orbit) multi-satellites network with small orbit inclination was proposed. According to the space environment and optical viewing conditions, the simulation data were screened to simulate the real observation scene. The precise orbit determination (POD) of geostationary satellite was calculated by using the optical angle measurement data and the numerical method. By comparing with the reference orbit, under the condition of platform’s orbit accuracy of 5 m, measurement accuracy of 5-arcsecond, and 12 hours of observation, the POD accuracy of geostationary satellite by two LEO satellites can reach the order of kilometers, while the POD accuracy by four LEO satellites can reach the order of 100 meters. Therefore, the POD accuracy has been greatly improved with the increase of the number of LEO satellites.     

基于历史TLE的空间目标轨道预报误差演化规律研究

北美防空司令部(North American Aerospace Defense Command, NORAD)发布的双行根数(Two Line Element, TLE)是广大航天工作者最常用的轨道根数,与其对应的轨道模型是SGP4/SDP4 (Simplified General Perturbation Version 4/Simplified Deep-space Perturbation Version 4)解析模型.由于TLE中并没有包含相应的轨道精度信息,编目轨道的应用范围受到很大的限制.基于Space-Track网站发布的历史TLE数据和配套的SGP4/SDP4动力学模型,采用定轨标预报的方法统计并生成了大量目标轨道的预报误差,通过对预报轨道的时间区间划分给出了每个目标的预报误差随预报时间变化的拟合系数,并进一步对不同类型轨道预报误差的演化规律和特征进行了分类讨论,给出了4种轨道类型目标的轨道预报误差随时间演化的平均解析模型,为拓展双行根数的应用提供有价值的参考.     

小倾角LEO多星天基平台光学跟踪GEO精密定轨

针对地基卫星测控系统(Tracking Telemetry and Command, TT&C)系统对地球静止轨道(Geostation-\lk ary Earth Orbit, GEO)卫星在空间和时间覆盖上的局限性, 提出小倾角低地球轨道(Low Earth Orbit, LEO)多星组网天基平台对GEO卫星进行跟踪定轨的方法. 根据空间环境和光学可视条件对仿真数据进行筛选以模拟真实的观测场景, 利用光学测角数据, 使用数值方法对GEO卫星的轨道进行确定. 结果与参考轨道进行重叠对比, 在平台轨道精度5 m、测量精度5rq\rq、 定轨弧长12 h的情况下, 两颗LEO卫星对GEO卫星进行跟踪定轨的精度可达到千米量级, 4颗LEO卫星对GEO目标进行跟踪定轨的精度可达到百米量级. 随着LEO组网卫星数量的增加, 定轨精度得到了较大的提高.     

LAGEOS卫星精密定轨及残差分析

介绍LAGEOS卫星用卫星激光测距(SLR)资料精密定轨和在精密定轨基础上的残差分析处理．SLR资料的分析处理方法、采用的力学模型和解参数的多少根据目标的不同而不同．对不同的方案进行了详细分析、比较．其关键是对LAGEOS卫星进行精密定轨．得出了目前上海天文台在SLR资料的分析处理中已采用的解算模式．作为例证，该解算模式分析处理了1998年12月31日至1999年6月29日LAGEOS卫星的SLR资料，得到每3天一个弧段的精密轨道．结果显示每3天一个弧段的定轨残差rms都小于2厘米．上海天文台从1999年10月1日开始了全球LAGEOS—l和LAGEOS—2资料的快速分析服务，结果可从APSG的网址：http：／／center．shao．ac．cn／APSG／result获得．     

加速仪数据在CHAMP卫星精密定轨中的贡献

通过用几个实例计算，评估了CHAMP卫星加速仪数据对SLR数据定轨精度的贡献．结果显示用加速仪数据代替非保守力对CHAMP卫星进行精密定轨时，其SLR的残差从原来的16．5cm减少到2．7cm，与精密轨道相比，卫星位置误差由18．9cm减少到6．2cm(一天资料)．     

海上移动站精密测轨方法

将人造卫星精密定轨理论应用于海上移动站精密定轨，根据移动站的特点，建立了相应的定轨条件方程，并在此基础上利用海上移动站某次飞船发射任务跟踪数据进行了实算，给出了定轨结果和讨论。