基于单站CCD漂移扫描光电设备的同步轨道目标测定轨

地基光电观测在同步轨道目标监测领域具有重要作用.为评估单站光电设备对同步轨道目标的实际测定轨能力,利用上海天文台佘山站1.56m望远镜,采用CCD漂移扫描光电技术,对3颗北斗同步卫星开展试验观测,基于卫星精密星历评估目标的测定轨外符精度.结果表明:同步轨道目标的天文定位在方位和俯仰方向上的外符精度均好于0.3";在单圈次观测情况下,尽管轨道预报精度较低,约为数千米量级,但是观测弧段内定轨精度可优于百米;在多圈次观测情况下,轨道改进效果显著,定轨精度优于50m,外推至4d的轨道预报精度为百米量级.此外,定量评估了每晚不同观测时间跨度下同步轨道目标的测定轨精度,为单站光电设备实际应用提供了参考.      

2010年4月地球同步轨道相对论电子增强事件分析

为研究2010年4月地球同步轨道相对论电子通量异常增强事件的原因, 选取了2004-2010年之间高速太阳风下7个类似事件进行对比分析. 探讨了多种可能导致此次异常事件的太阳风和地磁条件. 结果表明, 较弱的磁暴使得相对论电子高通量区域更接近同步轨道, 此外, 哨声波加速很可能在2010年4月地球同步轨道相对论电子通量异常增强事件中起到重要作用. 磁暴强度与种子电子的注入深度密切相关, 表现为Dst指数曲线的形态与能量为30～100keV的电子高通量区域的下边缘高度吻合. 能量为30～100keV电子的注入深度影响了能量大于300keV的电子出现的磁层区域. 此事件中, 由于磁暴相对较弱, 种子电子向内磁层注入的深度较浅, 更靠近同步轨道区域, 这使得相对论电子大量出现的区域也靠近同步轨道, 最终导致同步轨道相对论电子通量异常增强. 另外, 2010年4月地球同步轨道相对论电子通量异常增强事件中, 高强度的亚暴提供了充足的种子电子并加强了波粒相互作用, 这也是相对论电子增强的必要条件.      

A universal on-orbit servicing system used in the geostationary orbit

The geostationary orbit (GEO), a unique satellite orbit of the human beings, is a very precious orbit resource. However, the continuous increasing of GEO debris makes the GEO orbit more and more crowded. Moreover, the failures of GEO spacecrafts will result in large economic cost and other bad impacts. In this paper, we proposed a space robotic servicing system, and developed key pose (position and orientation) measurement and control algorithm. Firstly, the necessity of orbit service in GEO was analyzed. Then, a servicing concept for GEO non-cooperative targets was presented and a universal space robotic servicing system was designed. The system has a 2-DOF docking mechanism, a 7-DOF redundant manipulator and a set of stereo vision, in addition to the traditional subsystems of a spacecraft. This system can serve most existing satellites in GEO, not requiring specially designed objects for grappling and measuring on the target. The servicing contents include: (a) visual inspecting; (b) target tracking, approaching and docking; (c) ORUs (Orbital Replacement Units) replacement; (d) Malfunctioned mechanism deploying; (e) satellites life extension by taking over its control, or re-orbiting the abandoned satellites. As an example, the servicing mission of a malfunctioned GEO satellite with three severe mechanical failures was designed and simulated. The results showed the validity and flexibility of the proposed system.     

星载GNSS确定GEO卫星轨道的积分滤波方法

采用星载全球导航卫星系统（GNSS）确定地球静止轨道（GEO）,以解决目前应用星载全球定位系统(GPS)时导航卫星可见性差的问题。以风云卫星为例,分析了未来的GNSS相对于GEO卫星的可见性,针对GEO轨道上导航接收机采样间隔较长的问题,综合轨道积分和卡尔曼滤波方法的优点,提出了确定GEO卫星轨道的积分滤波方法。并利用STK软件仿真产生所需数据,用MATLAB对提出的算法编程并进行仿真验证,结果表明,提出的方法性能优越,定轨精度较高。     

An improved focusing method for geosynchronous SAR

More and more attention is paid to Geosynchronous Orbit (GEO) Synthetic Aperture Radar (SAR) in recent years due to its fine temporal resolution and large coverage, so that GEO SAR will play an important role in monitoring natural disasters, but its imaging is more difficult compared to lower Earth orbit (LEO) SAR because of the increase of orbit height. This paper mainly studies the coverage property and focusing method in GEO SAR. As is known to us, the coverage of a GEO SAR satellite can reach 1/3 of the whole Earth, and the revisiting time can reduce to 2 h, which will remarkably improve the capability in ocean applications, earth dynamics and natural hazards management and so on. Compared with the imaging in LEO SAR, a problem in GEO SAR is that the linear trajectory model can bring a big error due to the long synthetic aperture time, so that the classical imaging algorithms in LEO SAR cannot be directly applied in GEO SAR. Using the Norm method and Taylor expansion method, this paper gains an accurate slant range model, which can resolve the big error of the linear trajectory at perigee and collapse of the linear trajectory at apogee. Furthermore, this paper deduces a novel imaging algorithm for GEO SAR by means of series reversion, which realizes the focusing on large scene under the synthetic aperture time of 100 s. Finally, the simulation results at apogee and perigee prove the correction of the slant range model and imaging algorithm.     

The situation in the geostationary ring

For more than 25 years, the practice of reorbiting of a geostationary satellite at the end of its mission in order to protect the geostationary orbit (GEO) environment has been recommended and performed by a number of operators. In recent years, an internationally recognised re-orbiting altitude has been defined by the Inter-Agency Space Debris Coordination Committee (IADC). Based on orbital data contained in the DISCOS database, the situation on the geostationary ring is analysed. In January 2004, from 1036 catalogued objects passing through the geostationary region, 340 are controlled within their allocated longitude slots, 395 are drifting above, below or through GEO, and 140 are in a libration orbit. In the periods 1997–2003, 103 spacecraft reached their end of life; 34 were reorbited in compliance with the IADC recommendation, 35 were reorbited below the minimum recommended altitude, and 34 were abandoned without any end-of-life disposal manoeuvre. Apart from these catalogued objects, the ESA 1-m telescope has observed many smaller debris (down to 10–15 cm) in this orbital region representing a collision risk for GEO spacecraft which is difficult to quantify.     

Feasibility study of LEO,GEO and Molniya orbit based satellite solar power station for some identified sites in India

The analysis of satellite solar power station (SSPS) is carried out for some specified locations (Delhi, Mumbai, Kolkata and Bengaluru) in India and consequently the performance of the system is evaluated for geostationary earth orbit (GEO) based SSPS, low earth orbit (LEO) based SSPS and Molniya (quasi geostationary) orbit based SSPS for sites located at different latitudes. The analysis of power; received energy over a year and weight of the rectenna array for the same beam intensity showed varied results for Molniya orbit based SSPS, LEO based SSPS and GEO based SSPS. The power delivered by the LEO SSPS was highest which indicated that this SSPS may be efficient for the short term power requirement. However, it is observed from the results of the energy received over a year that the GEO based system is suitable for base load power plant as it is capable of delivering constant energy through out a year. Further, the weight of the rectenna and hence the space required for ground station for same power output is smallest for Molniya orbit based system for a range of rectenna array radius considered. It is thus envisaged that the Molniya orbit based system would be a better choice for commercial use of SSPS. These findings may help for judicious selection of satellite orbit and ground station location for placing the satellite for SSPS for various applications.     

Near real-time BDS GEO satellite orbit determination and maneuver analysis with reversed point positioning

The Geostationary Earth Orbit (GEO) satellite is a crucial part of the BeiDou Navigation Satellite System (BDS) constellation. However, due to various perturbation forces acting on the GEO satellite, it drifts gradually over time. Thus, frequent orbit maneuvers are required to maintain the satellite at its designed position. During the orbit maneuver and recovery periods, the orbit quality of the maneuvered satellite computed with broadcast navigation ephemeris will be significantly degraded. Furthermore, the conventional dynamic Precise Orbit Determination (POD) approach may not work well, because of a lack of publicly available satellite information for modeling the thrust forces. In this paper, a near real-time approach free of thrust forces modeling is proposed for BDS GEO satellite orbit determination and maneuver analysis based on the Reversed Point Positioning (RPP). First, the station coordinates and receiver clock offsets are estimated by GPS/BDS combined Single Point Positioning (SPP) with single-frequency phase-smoothed pseudorange observations. Then, with the fixed station coordinates and receiver clock offsets, the RPP method can be conducted to determine the GEO satellite orbits. When no orbit maneuvers occur, the proposed method can obtain orbit accuracies of 0.92, 2.74, and 8.30?m in the radial, along-track, and cross-track directions, respectively. The average orbit-only Signal-In-Space Range Error (SISRE) is 1.23?m, which is slightly poorer than that of the broadcast navigation ephemeris. Using four days of GEO maneuvered datasets, it is further demonstrated that the derived orbits can be employed to characterize the behaviors of GEO satellite maneuvers, such as the time span of the maneuver as well as the satellite thrusting accelerations. These results prove the efficiency of the proposed method for near real-time GEO satellite orbit determination during maneuvers.     

Guidepost-based autonomous orbit determination method for GEO satellite

Guidepost-based navigation system is a novel autonomous orbit determination method for the GEO satellite. The system is achieved by using the camera imaging function to obtain the guidepost images and the GNSS signal receiver to obtain the pseudoranges between the GEO and the navigation satellites. Due to the high altitude of GEO satellite and the time-varying sunlight condition in the space environment, it may be difficult to obtain object image points and the distance measurements of GNSS because of the weak visibility of the guideposts. To deal with the problem, a novel integrated orbit determination system is presented. The Earth landmarks, the in-orbit spacecraft and GNSS navigation satellites whose line-of-sights and the distance can be easily obtained are used at the same time as information for the GEO satellite navigation based on the observability conditions analysis. The observability of the GEO satellite navigation system is analyzed through the physical observability, the mathematical observability and the engineering observability through the observing geometry, the rank of observability matrix and the Cramer-Rao lower bound (CRLB) respectively. Besides, the maximum correntropy unscented Kalman filter (MCUKF) algorithm is applied to improve the estimation stability of the system in the presence of non-Gaussian noises. The simulation indicates the feasibility of the proposed scheme.     

地球同步轨道带动态监视光学系统样机及试验观测结果

地球同步轨道上目标数量多，运动形式多样.为了保障航天活动的安全，有必要开展地球同步轨道目标的动态监测，及时掌握发生在中国专属地球同步轨道带的空间事件.2015年12月地球同步轨道带动态监视光学系统样机正式安装在中国丽江高美古观测站.2015年12月至2016年2月，利用该样机对台站上空地球同步轨道带的样本天区开展了试验观测.结果表明，样机能够对27颗地球同步轨道目标进行连续监测，其中两颗为北美航空航天司令部未编目的目标；目标天文定位的内符精度在方位上约为4"，在俯仰上约为1".利用多圈次观测结果对轨道进行改进，在无轨控发生时，24h和48h点位预报精度在方位和俯仰上分别优于9"和2".以3颗GEO目标为例，通过实测资料对轨道变化事件进行了初步分析和验证.      

一种用于同步静止卫星监测的微型VLBI网

针对地球静止轨道（GEO）卫星全天时全天候高精度的监测需求，考虑传统甚长基线干涉（VLBI）测站高成本、高投入和GEO卫星专用观测时段有限等制约条件，研发了简易型VLBI观测系统，并组建了包括上海、都匀和乌鲁木齐三站的微型VLBI网（micro VLBI network，MVN），开展了并置站测试以及对GEO卫星亚太6C的连续监测，并评估了当前MVN的观测能力。结果表明MVN扣除系统差后的单站接收精度为2ns，各基线观测时延拟后残差约几纳秒，GEO目标实测位置精度为百米级（内外符精度分别约100m和400m）。不同于传统VLBI和其他GEO监测手段，MVN还具备全天时、全天候、低造价、易布设及易推广等特点，充分表明了其在GEO卫星监测领域的应用价值。     

The classical Laplace plane as a stable disposal orbit for geostationary satellites

The classical Laplace plane is a frozen orbit, or equilibrium solution for the averaged dynamics arising from Earth oblateness and lunisolar gravitational perturbations. The pole of the orbital plane of uncontrolled GEO satellites regress around the pole of the Laplace plane at nearly constant inclination and rate. In accordance with Friesen et al. (1993), we show how this stable plane can be used as a robust long-term disposal orbit. The current graveyard regions for end-of-life retirement of GEO payloads, which is several hundred kilometers above GEO depending on the spacecraft characteristics, cannot contain the newly discovered high area-to-mass ratio debris population. Such objects are highly susceptible to the effects of solar radiation pressure exhibiting dramatic variations in eccentricity and inclination over short periods of time. The Laplace plane graveyard, on the contrary, would trap this debris and would not allow these objects to rain down through GEO. Since placing a satellite in this inclined orbit can be expensive, we discuss some alternative disposal schemes that have acceptable cost-to-benefit ratios.     

气动辅助异面变轨在多碎片清除中的应用分析

碎片清除飞行器异面变轨需要消耗大量燃料.从气动辅助异面变轨优化设计及被清除碎片轨道高度差值、倾角差值等参数对变轨性能的影响出发,比较分析了优化气动辅助异面变轨与双脉冲霍曼轨道转移的燃料节约量,研究了不同轨道高度差对于实施气动辅助变轨燃料节约量的影响.当地球静止轨道（GEO）与低地轨道（LEO）间气动辅助变轨优化速度增量约为1.55km·s-1、质量面积比172kg·m-2、比冲310s、轨道倾角变化16°时,燃料节约率约为45%.对比研究了不同轨道高度差LEO轨道间实施气动辅助变轨的燃料节约情况.结果表明:随着轨道高度的增加,气动辅助优化效率逐渐降低;在相同高度轨道间实施异面变轨,随着轨道倾角的增加,气动辅助变轨燃料节约率先增大后减小,倾角改变量约为20°时,燃料节约率最大;当轨道倾角为5°时,采用气动辅助变轨和双脉冲变轨的燃料消耗量相同.      

Analysis on navigation accuracy of high orbit spacecraft based on BDS GEO and IGSO satellites

To make up for the insufficiency of earth-based TT&C systems, the use of GNSS technology for high-orbit spacecraft navigation and orbit determination has become a new technology. It is of great value to applying Geosynchronous Earth Orbit (GEO) and Inclined GeoStationary Orbit (IGSO) navigation satellites for supporting the navigation of high-orbit spacecraft since there are three different types of navigation satellites in BeiDou Navigation Satellite System (BDS): Medium Earth Orbit (MEO), GEO and IGSO. This paper conducts simulation experiments based on Two-Line Orbital Element (TLE) data to analyze and demonstrate the role of these satellites in the navigation of high-orbit spacecraft. Firstly, the spacecraft in GEO was used as the target satellite to conduct navigation experiments. Experiments show that for the spacecraft on the GEO orbit, after adding GEO and IGSO respectively on the basis of receiving MEO navigation satellite signals, the accuracies were improved by 7.22 % and 6.06 % respectively. When adding both GEO and IGSO navigation satellites at the same time, the accuracy can reach 16 m. In the second place, navigation and positioning experiments were carried out on three high elliptical orbit (HEO) satellites with different semimajor axis (32037.2 km, 42385.9 km, 67509.6 km). The experiments show that the number of visible satellites has been improved significantly after adding GEO and IGSO navigation satellites at the same time. The visible satellites in these three orbits were improved by 32.84 %, 41.12 % and 37.68 %, respectively compared with only observing MEO satellites.The RMS values of the navigation positioning errors of these three orbits are 25.59 m, 87.58 m and 712.48 m, respectively.     

Instantaneous BeiDou–GPS attitude determination: A performance analysis

The advent of modernized and new global navigation satellite systems (GNSS) has enhanced the availability of satellite based positioning, navigation, and timing (PNT) solutions. Specifically, it increases redundancy and yields operational back-up or independence in case of failure or unavailability of one system. Among existing GNSS, the Chinese BeiDou system (BDS) is being developed and will consist of geostationary (GEO) satellites, inclined geosynchronous orbit (IGSO) satellites, and medium-Earth-orbit (MEO) satellites. In this contribution, a BeiDou–GPS robustness analysis is carried out for instantaneous, unaided attitude determination.     

利用摆动地球敏感器两个探测器输出的姿态确定

摆动地球敏感器是地球同步通信卫星控制系统的重要部件。这种敏感器主要用于卫星的姿态测量,测量量作为控制系统的输入信号计算控制输出量。摆动地球敏感器有4个探测器,目前在轨卫星的基本使用方法均为至少使用3个探测器的测量信息进行姿态确定。本文给出了使用2个探测器测量确定卫星姿态的计算方法,并结合实际情况给出了使用策略。这种姿态确定方法大大拓宽了地球敏感器的使用范围,增加了地球敏感器的冗余性,延长了部件的使用寿命。     

基于分段常值的全电推进GEO卫星制导策略

电推进技术因其比冲高的技术特点在GEO轨道转移中应用可大大减少燃料质量，提高有效载荷质量比，延长任务寿命等。针对全电推进GEO卫星入轨的轨迹优化和制导问题，首先利用间接法获得小推力燃料最优GEO轨道转移的数值解，提出一种多项式曲线拟合最优轨迹的方法，多项式曲线形式简单，可作为参考轨道在星上存储和使用。在多项式参考轨道的基础上，建立了一种分段常值推力跟踪参考轨道的闭环制导策略，在常值推力条件下，轨道要素控制量与控制力有解析关系，简化了制导律设计；将多圈轨道转移问题分解为多个单圈轨道优化问题。结果显示，本文提出的分段常值跟踪制导策略跟踪精度高，和最优轨道相比多消耗7%的燃料。本制导策略控制结构简单，易于工程实施。     

Orbit improvement for GTO objects using follow-up observations

The Astronomical Institute of the University of Bern was and is conducting several search campaigns for space debris in the geostationary ring (GEO) and the geostationary transfer orbit (GTO). First tests to build up a catalogue of satellites and space debris were performed recently. As the discovery observations of an object usually cover a time interval of a few minutes only, the first orbits determined are assumed to be circular. For GEO objects a circular orbit is a rather good approximation. This is certainly not the case for GTO objects. Nevertheless, a circular orbit seems to be an acceptable approximation for a short time interval around the observations. The first orbits can be used to acquire follow-up observations, which allow the determination of elliptical orbits. The maximum allowed time span between the detection and the follow-up for a successful recovery is found using simulated GTO orbits and observations. Further follow-up observations are simulated in order to study the orbit improvement process and the required force model. The accuracy of orbits needed to build up a catalogue is studied. The simulations are compared to the results achieved with observations acquired by the 1 m telescope on Tenerife.     

GEO螺旋巡游轨道的相对运动分析和螺旋环设计

摘要： GEO螺旋巡游轨道采用螺旋巡游方式，以不同的构型“上下浮动”在GEO轨道附近，可实现对该轨道上空间目标和空间环境的高精度探测.本文在分析GEO轨道航天器运动规律的基础上，应用小偏差理论分析螺旋巡游轨道与GEO目标之间的相对运动，给出平面螺旋环和三维螺旋环的设计方法，为GEO螺旋巡游轨道的设计奠定基础.     

Bayesian linking of geosynchronous orbital debris tracks as seen by the Large Synoptic Survey Telescope

We describe a Bayesian sampling model for linking and constraining orbit models from angular observations of “streaks” in optical telescope images. Our algorithm is particularly suited to situations where the observation times are small fractions of the orbital periods of the observed objects or when there is significant confusion of objects in the observation field. We use Markov Chain Monte Carlo to sample from the joint posterior distribution of the parameters of multiple orbit models (up to the number of observed tracks) and parameters describing which tracks are linked with which orbit models. Using this algorithm, we forecast the constraints on geosynchronous (GEO) debris orbits achievable with the planned Large Synoptic Survey Telescope (LSST). Because of the short 15 s exposure times, preliminary orbit determinations of GEO objects from LSST will have large and degenerate errors on the orbital elements. Combined with the expected crowded fields of GEO debris it will be challenging to reliably link orbital tracks in LSST observations given the currently planned observing cadence.