非合作目标激光测距预报的实时修正方法研究

非合作目标的激光测距预报一般是基于双行根数(TLE)外推出来的,往往有较大偏差,对激光测距的成功率有较大影响。结合空间目标的轨道理论和实测的数据分析,预报的偏差主要是预测模型外推的空间目标在运行轨道上的平近点角与实际平近点角存在偏差。根据非合作目标在望远镜跟踪视场中的脱靶量,利用相关算法可以找到一个最佳的时间根数偏差量修正空间目标的平近点角。经过修正,空间目标的视位置偏差得到改善,距离偏差能够从几百米减小到几十米,提升了预期回波到达时刻的准确度,可以给单光子探测器提供更高精度的距离门控,提高测距成功率。     

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     

GEO空间碎片光度测量标定方法的研究

基于GEO卫星、太阳和观测站的空间几何关系,建立了消除太阳赤纬角对地球同步轨道( Geostationary Orbit,GEO)卫星光学特性的影响的方法.以三轴稳定GEO盒状卫星缩比模型为研究样本,在不同太阳赤纬角下进行仿真实验光度测量,研究太阳赤纬角和相位角的空间几何关系,得出消除太阳赤纬角对其辐亮度值以及以相位角...     

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.     

采用重置参数的轨道改进算法

当使用精度差的初始根数作定轨计算时,被估值的模型参数会吸收初值中所含误差而偏离其合理数值(如CD约为2.2),使定轨计算过程的RMS已不再变化,但轨道收敛到与实际状态有偏离的轨道上。文中给出的算例采用重置被歪曲的估值模型参数方法,首先以TLE根数为初值用精密定轨程序解条件方程,然后以第一轮迭代计算结果作为初始根数并重置模型参数,再进行第二轮迭代计算,使定轨计算结果收敛到正确轨道上,文中还使用另一颗激光卫星的双行根数作初值验证了该方法的有效性。较好地解决了因初值不准所引起的定轨计算不收敛,或收敛到与实际状态有偏离的轨道上的问题。最终得出的RMS达到厘米级精度。文中图示了两次定轨计算的RMS变化曲线图、残差分布图,迭代过程的资料采用率及定轨计算结果。     

CCD测角与激光测距技术综合测定空间目标的轨道

空间目标包括在轨卫星、空间碎片等,对其测定轨是空间攻防和空间利用的重要前提。由于地面测站资源有限,单站测量是目前对空间目标尤其是空间碎片测定轨较常用的方式。卫星激光测距(satellite laser ranging,SLR)技术测量精度很高,可达米级(非合作目标),甚至厘米级(合作目标),但不能单独用于单站短弧定轨;电荷耦合器件(charge coupled device,CCD)天文定位技术可观测距离较远的目标,但测量精度为角秒级,换算至空间距离不如SLR技术高。两者的联合为空间目标的高精度定位和跟踪提供了可能,并成为未来空间目标地基测量的发展方向。作为空间碎片单站监测的前期工作,对合作目标的单站定轨精度进行了评估。处理了1500 km高AJISAI低轨卫星的实测数据,分析了单站CCD测角和激光测距数据对低轨空间目标的联合定轨能力,并充分考虑两类不同类型观测数据的精度,数据综合时对其进行合理加权。利用全球激光站资料进行精密定轨,并以此作为参考轨道,采用上海佘山站AJISAI卫星2010年、2011年4天6圈的实测激光测距数据,以及CCD测角数据,开展了单站单圈和单站多圈定轨和预报试验。试验结果表明,测距数据的加入对定轨精度和24小时预报精度的改善非常明显,可提高至少一个数量级;单站单圈联合定轨和24小时预报的精度分别为20 m以内及数百米,单站多圈联合定轨和24小时预报的精度分别在米级及数十米。期望实验结果为中国未来的空间碎片望远镜建设提供参考。     

双行根数编目体系轨道误差研究

大量空间目标的真实轨道无法精确知道,目前只能通过跟踪观测的数据进行定轨来得到估计轨道,而估计的轨道就会有误差.双行根数(TLE)是广泛使用的一种特殊编目轨道根数,其配套的轨道模型为Simplified General Perturbations 4(SGP4)/Simplified Deep-space Perturbations 4(SDP4)模型.编目轨道的精度主要依赖于相应的观测模型和动力学模型,这些模型一般都不会非常准确,往往会有误差,有些误差可能直接导致编目定轨结果在局部为有偏估计.通过理论研究和仿真模拟,分析了动力学模型中地球非球形引力位田谐摄动项对编目轨道精度的影响,发现TLE编目轨道中存在随时间周期变化的系统差,该系统误差甚至可以达到千米量级.几何构型较好的测站分布在一定程度上可以削弱编目定轨中产生的系统误差,由于力学模型的限制,无法彻底消除.     

SGP4/SDP4模型预报可靠性分析

以激光测距资料精密定轨结果为参考轨道,分析了两种典型版本SGP4/SDP4模型对低、中、高轨道卫星预报误差的放大规律,当预报超过一定的圈数后误差成指数增长.数值试验结果表明:对低、中、高轨卫星预报误差无显著放大圈数分别是(h≤300 km),40;(300 km≤h≤1 200 km),150;(1 200 km≤h≤10 000 km),300;半同步卫星(19 000km≤h≤22 000 km),55;同步卫星(33 000 km≤h≤38 000 km),10.并图示出参考卫星轨道预报误差的放大规律,供工程中利用双行根数和SGP4/SDP4模型作轨道预报时参考.     

2010年上海天文台卫星激光测距观测报告

介绍了2010年上海天文台卫星激光测距的常规观测和白天千赫兹激光测距情况。在国际上首次对同步轨道卫星开展了千赫兹激光测距,作用距离达38800多千米,测距系统性能达到国际先进水平。利用2套独立的激光测距系统,开展了激光收发分离测距实验,为行星际异步应答式激光测距模拟试验提供了实测数据。最后概述了空间碎片目标激光测距进展情况。     

太阳质量损失对流星群轨道改变的长期影响

将作者在变质量天体力学所得理论结果应用于太阳质量损失对流星群轨道根数变化的长期效应上。太阳质量损失包括光子辐射和太阳风造成的质量损失。利用G—M型变质量天体轨道根数变化方程的一阶和二阶解对15个流星群轨道半长轴、近日点距离、轨道周期和近日点经度因太阳质量损失造成的每世纪的长期改变效应做了数值计算,并得出计算结果。其计算结果表明,太阳质量损失使流星群轨道半长轴每世纪的改变效应较明显,它们同太阳距离的扩大影响值得关注,但对轨道周期的拉长每世纪的影响甚小,对近日点经度只有量级变化小到可以略而不计。     

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．     

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.     

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.     

On the cause of the discrepancy between groundbased and spaceborne lightcurves of Ganymede and Callisto in the <Emphasis Type="Italic">V</Emphasis> band

Properties of the surfaces of Jupiter’s satellites—Ganymede and Callisto—are shortly described. Their images acquired in space missions are shown. Causes of the discrepancy between orbital lightcurves of the satellites obtained from the earth and spaceborne maps of the satellites are considered. The groundbased observations were carried out under phase angles of solar illumination ranging from 0° to 12°, and the maps were built from images acquired from spacecraft in a wide interval of solar phase angles. We suggest that the main cause of the discrepancies between the lightcurves is the coherent backscattering effect observed only at small phase angles of the sun.     

LAGEOS Satellites Germanium Cube-Corner-Retroreflectors and the Asymmetric Reflectivity Effect

We propose a new analytical theory to explain the physical cause of the asymmetric reflectivity effect observed for the LAGEOS satellites. To achieve this result we have modelled the reflection of the Sun visible light from the four germanium Cube-Corner-Retroreflectors of these satellites. The position of the Cube-Corner-Retroreflectors play a crucial role in defining the characteristics of the effect and its impact in the satellites orbit. With this new approach we have been able to reproduce the temporal variation of the asymmetric reflectivity effect acceleration for LAGEOS, and to determine the main characteristic of the effect in the case of LAGEOS II. When considering the orbital elements, we have been able to reproduce the time evolution of LAGEOS eccentricity vector excitations and perigee rate. In the case of LAGEOS II, the asymmetric reflectivity effect need to be modelled with an analytical expression different from that previously introduced for LAGEOS.This revised version was published online in October 2005 with corrections to the Cover Date.     

激光测距中单光子雪崩二极管的动态范围问题及解决办法

叙述了云南天文台1．2m望远镜激光测距系统中应用多种手段，如：机械快门、发散角调整、距离门、光谱滤波、空间滤波，解决了可门控的雪崩二极管的动态范围问题，实现了远、近卫星的黑夜激光测距和部分近地卫星的白天激光测距。     

Equivalence of energy-time and momentum-position phase spaces of the solar system

In the first step, equivalence of energy-time and momentum-position phase spaces is discussed for simple periodic systems having a central force. The discussion concerns the phasespace areas taken as a whole, as well as their fragments. It is demonstrated that some fragments of the phase space areas can fit together with a considerable accuracy. This suggests similar equivalence of the corresponding fragments of the phase-space areas of the solar system. The hypothesis is examined in respect to the planet orbits and the orbits of some planet satellites.     

The magnitude and color of the Saturn system

Brightness measurements made during 1963-1965 and 1991-2009 are used in constructing models of the brightness of the Saturn system in the Johnson B, V, R and I system. The models cover nearly the full range of phase angles and ring opening angles visible from the Earth and are believed to be accurate to 0.03-0.05 magnitudes. A U-filter model is also selected which covers ring opening angles of between 4° and 14°. The model is the first such one that treats the light from the rings as a function of the saturnicentric latitude from the Earth and Sun in a way that is consistent with observations and theoretical considerations. Six conclusions of this work are: (1) the Saturn system brightens as the solar phase angle decreases, (2) the Saturn system has an opposition surge, (3) the opposition surge increases as the ring opening angle increases, (4) the solar phase angle coefficient increases as the ring opening angle increases, (5) the B-V, V-R and R-I color indexes change by up to 0.2 magnitudes as Saturn orbits the Sun and (6) the V-filter model in this report is a better fit to the 1963-2009 data than the one proposed by Harris (Harris, D.L. [1961]. In: Kuiper, G.P., Middlehurst, B.M. (Eds), Planets and Satellites. Univ. of Chicago, Chicago, IL, pp. 272-342].     

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.