制约卫星轨道寿命的另一种机制(续)

对于制约低轨人造地球卫星轨道寿命的耗散机制，人们已有足够的重视，但在深空探测中，另一种制约低轨卫星轨道寿命的引力机制同样应予重视，前文讨论了高轨卫星的情况，在第三体引力作用下，有可能导致卫星轨道偏心率产生变幅较大的长周期变化。特别是极轨卫星，其轨道偏心率在一定的时间内可增大到使其近星距rp=a(1-e)≈Re（Re是中心天体的赤道半径），从而落到中心天体上，结束其轨道寿命，目前对低轨卫星作了详尽的理论分析，研究表明，与高轨卫星有类似结果，但其力学机制却不相同，低轨卫星的轨道寿命与第三体引力无关。它取决于中心天体非球形引力位中的扁率项（即J2项）与其他带谐项之间的相对大小，这不仅是一个纯理论结果，也有实际背景，在太阳系中慢自传天体（月球和金星等）的低轨卫星就存在这一问题，还给出了有关判据，并以计算实例作了验证。     

GPS星历对LEO星载GPS精密定轨精度的影响

目前,越来越多的低轨卫星上都搭载了用于精密定轨的星载GPs接收机,星载GPS已成为低轨卫星精密定轨的主要手段之一.星载GPS精密定轨精度依赖于GPS星历及钟差精度.基于SHORDE-Ⅲ非差动力学定轨功能,以2005年8月1日至8月7日一周的GRACE卫星实测数据为例,采用事后精密轨道(igs)、快速轨道(igr)和超快速轨道(igu)三种GPS星历在同等条件下定轨,估计GPS星历精度对低轨卫星定轨精度的影响,实际计算结果表明igs和igr两类GPS星历定轨精度相当,约为9.5 cm,igu星历定轨精度略低于igs和igr星历,约为10.5cm:高频GPS卫星钟差数据对定轨精度会产生1-6cm影响.     

我国低轨道卫星定轨精度分析

针对高度在250－350km的三颗低轨道卫星,根据我国现有的卫星跟踪网和跟踪技术（雷达测距和多普勒测速）等观测条件,利用模拟方法估计和分析了各种误差源对定轨精度的影响,并对能达到的定轨精度进行了恰如其分的估计。     

探测双星轨道演变及定轨精度分析

探测双星是中国目前在轨运行的大椭圆轨道卫星.自发射以来,双星轨道不断演变,对定轨和预报精度产生了一定影响.定性定量地分析了探测双星的轨道演变规律.在当前的跟踪模式下,根据轨道演变的不同阶段分析了相应的定轨预报精度,从而为卫星应用部门调整计划模式,确保卫星有效载荷正常提供依据.最后,通过轨道演变的趋势预测了双星的轨道寿命.     

转发器式卫星测轨方法

提出了转发器式卫星测轨方法。发射信号和接收信号的不同组合,形成不同模式的转发器式卫星测轨方法,并给出了不同模式下归算转发器式卫星测轨的公式。自发自收模式下的转发器式卫星测轨方法的观测和计算结果表明,定轨观测残差小于9cm。用转发器式卫星测轨方法,不但能给出高精度时间比对结果,而且能给出高精度卫星轨道和卫星预报轨道。     

针对低轨星座的空间信号测距误差投影系数确定

随着低轨星座建设的不断推进,计算卫星空间信号测距误差(signal in space range error,SISRE)的面向对象不再局限于全球卫星导航系统(Global Navigation Satellite System, GNSS)的地面用户,还包括GNSS的低轨星载用户和低轨导航系统地面用户。为更好地支持基于低轨星座SISRE的解算,根据SISRE的计算原理,分别研究了低轨星载用户和低轨卫星地面用户的SISRE误差投影系数的特征。计算结果显示,GNSS卫星对地面用户的误差投影系数并不适用于低轨星载用户及低轨导航星座地面用户。当低轨卫星轨道高度由2 000 km降低至300 km时,GNSS卫星对低轨星载接收机的轨道径向误差投影系数由0.96增加到0.98,轨道切法平面误差投影系数由0.20降低至0.15;低轨卫星对地面用户的轨道径向误差投影系数从0.72降至0.37,轨道切法平面误差投影系数从0.49增加至0.66。上述结果可为未来低轨卫星相关的空间信号测距误差分析以及低轨完好性研究提供重要参考。     

卫星轨道偏心率的变化特征及其对轨道寿命的影响

轨道偏心率的变化极其重要,它是制约各类(不同高度)空间飞行体轨道寿命的关键因素之一.对于地球低轨卫星,主要受大气耗散作用的影响,而对环月(或环火星)低轨卫星,主要受非球形引力位中奇次带谐项的影响,会出现变幅较大的长周期变化,从而导致近星点高度hp在一段时间内有明显的下降趋势.对大偏心率轨道和高轨道,第三体的引力作用也会使e出现变幅较大的长周期变化,近星点高度hp也会有明显下降的现象,这都会影响卫星的轨道寿命,但这一动力学机制与大气耗散机制和非球形引力机制都不相同.即对轨道偏心率的变化特征及其对轨道寿命的影响作一综述.     

双星定位系统在中低轨卫星定轨中的应用

对双星定位系统在中低轨卫星轨道确定中的应用做了详细的分析，给出了在该系统的测量模式中低轨卫星定轨的几种方法。通过对这些方法进行的大量模拟计算和分析，结果表明作为双星定位系统的一种潜在功能，用其对中低轨卫星定轨是可行的。     

GEO卫星定轨可视化软件设计

介绍了基于Windows系统开发的GEO卫星定轨可视化软件,该软件是采用Microsoft Visual Studio 2005软件平台,利用Visual Basic.NET编程技术开发设计的,具有预处理观测数据资料、解算GEO卫星精密轨道、分析和图形化轨道解算结果等功能。该软件界面友好、可操作性强、方便省时,有效地提高了GEO卫星定轨工作效率。     

月球重力场对绕月低轨卫星的长期影响

从解析形式出发,利用月球重力场模型JGL165P1,分析了月球重力场(带谐项)对绕月低轨卫星的长期影响。为了减少计算误差,保证计算精度,在分析解中使用循环公式来计算倾角函数。结果指出对于一个高度为100km的极月轨道卫星,冻结轨道存在的可能性不大,但是当轨道倾角在i=90°附近或者高度再高一些,则有可能存在冻结轨道;对于100km高的初始圆轨道,卫星在无控的情况下半年内将会坠落到月球表面,如果高度增加到200km,则不进行轨道控制也不会坠落到月面上。利用仿真软件GEODYN解算出来的结果证实了上述结论。     

A Study on the Relationship between the Orbital Lifetime and Inclination of Low Lunar Satellites

A detailed theoretical analysis on the orbital lifetime and orbital inclination of a Low Moon-Orbiting satellite (LMOs) and the 'stable areas' of long orbital lifetime are given. Numerical simulations under the real force model were carried out, which not only validate the theoretical analysis and also give some valuable results for the orbit design of the LMOs.     

Two problems about the motion of low-moon-orbit satellites

A detailed theoretical analysis on the orbital lifetime and frozen orbit of low-moon-orbit satellites (LMOS) is carried out, and their relationships with the orbital inclination, as well as some mutual relationships are presented. Taking account of the main perturbing sources of low-orbit satellites, we carried out numerical simulations under a comprehensive force model, and the results not only confirm the correctness of the theoretical analysis, but also provide some valuable insights on the orbital design of LMOS.     

A method of astronomical autonomous orbit and attitude determinations for satellites

A method of realtime autonomous orbit determination for earth satellites using the extended Kalman filtering is proposed. The observed quantities are: the satellite-sun direction vector measured by a sun sensor, the satellite-earth and satellite-moon direction vectors measured by an ultraviolet sensor, and the geocentric distance measured by a radar altimeter. At the same time the satellite attitude to the earth is also determined. Results of our simulation of the autonomous orbit determination show that the precision of the orbit determinations is better than 200 m. The effects of the sampling period, orbital inclination, orbital eccentricity and orbital altitude on the precision of orbit determination are analyzed and compared, and certain principles helpful for improving the precision of orbit determination are suggested.     

The orbital evolution of NEA 30825 1900 TG1

The orbital evolution of the near-Earth asteroid (NEA) 30825 1990 TG1 has been studied by numerical integration of the equations of its motion over the 100 000-year time interval with allowance for perturbations from eight major planets and Pluto, and the variations in its osculating orbit over this time interval were determined. The numerical integrations were performed using two methods: the Bulirsch-Stoer method and the Everhart method. The comparative analysis of the two resulting orbital evolutions of motion is presented for the time interval examined. The evolution of the asteroid motion is qualitatively the same for both variants, but the rate of evolution of the orbital elements is different. Our research confirms the known fact that the application of different integrators to the study of the long-term evolution of the NEA orbit may lead to different evolution tracks.     

The Orbital Evolution of Two Sounding Satellites and Analysis of the Accuracy of Orbit Determination

The satellites TC-1 and TC-2 are the two Chinese satellites with great elliptical orbits which are still in orbit around the earth at present. Since the launch the orbits of the two satellites have continuously evolved, which has a certain effect on the orbit determination and prediction precision. The regularities of the orbital evolution of the two sounding satellites are qualitatively and quantitatively analyzed. Under the current tracking mode the corresponding prediction precision of orbit determination is analyzed based on the different stages of the orbital evolution, thereby providing the basis for the adjustment of planning mode by the satellite application departments and the guarantee of normal satellite payload. Finally, the orbital lifetimes of the two satellites are predicted through the trend of the orbital evolution.     

The spectroscopic orbits of three double-lined eclipsing binaries: I. BG Ind,IM Mon,RS Sgr

We present the spectroscopic orbit solutions of three double-lines eclipsing binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs) of the components were determined using high resolution echelle spectra obtained at Mt. John University Observatory in New Zealand. The RVs of the components of BG Ind and RS Sgr were measured using Gaussian fittings to the selected spectral lines, whereas two-dimensional cross-correlation technique was preferred to determine the RVs of IM Mon since it has relatively short orbital period among the other targets and so blending of the lines is more effective. For all systems, the Keplerian orbital solution was used during the analysis and also circular orbit was adopted because the eccentricities for all targets were found to be negligible. The first precise orbit analysis of these systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325, respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio values, orbital sizes and minimum masses of the components of the systems indicates that all systems should have different physical, dynamical and probable evolutionary status.     

Motion near frozen orbits as a means for mitigating satellite relative drift

Generally, any initially-close satellites—chief and deputy—moving on orbits with slightly different orbital elements, will depart each other on locally unbounded relative trajectories. Thus, constraints on the initial conditions must be imposed to mitigate the chief-deputy mutual departure. In this paper, it is analytically proven that choosing the chief’s orbit to be a frozen orbit can mitigate the natural relative drift of the satellites. Using mean orbital element variations, it is proven that if the chief’s orbit is frozen, then the mean differential eccentricity is periodic, leading to a periodic variation of the differential mean argument of latitude. On the other hand, if the chief’s orbit is non-frozen, a secular growth in the differential mean argument of latitude leads to a concomitant along-track separation of the deputy from the chief, thereby considerably increasing the relative distance evolution over time. Long-term orbital simulation results indicate that the effect of choosing a frozen orbit vis-à-vis a non-frozen orbit can reduce the relative distance drift by hundreds of meters per day.     

Quasi-Tangency Points on the Orbits of a Small Body and a Planet at the Low-Velocity Encounter

We propose a method for selecting a low-velocity encounter of a small body with a planet from the evolution of the orbital elements. Polar orbital coordinates of the quasi-tangency point on the orbit of a small body are determined. Rectangular heliocentric coordinates of the quasi-tangency point on the orbit of a planet are determined. An algorithm to search for low-velocity encounters in the evolution of the orbital elements of small bodies is described. The low-velocity encounter of comet 39P/Oterma with Jupiter is considered as an example.     

Analysis of the orbit of 1970-97b (cosmos 378 rocket)

Cosmos 378 rocket, 1970-97B, entered orbit on 17 November 1970, with orbital inclination 74.0°, period 105 min and perigee height 230 km, and decayed on 30 September 1972 after 683 days in orbit. The RAE computer program PROP was used, with more than 1900 observations from 64 stations, to determine the orbit at 39 epochs between February 1971 and September 1972.The main aim of the analysis was to determine the atmospheric rotation rate from the decrease in orbital inclination, which was determined with a mean standard deviation of 0.0010° and a best standard deviation of 0.0003°. After removal of relevant perturbations, analysis of the variation in inclination between July 1971 and April 1972 yields the surprisingly low average atmospheric rotation rate of 0.75 ± 0.05 rev/day, at a mean height of 250 km. The local time at perigee is however strongly biassed towards daytime values (07–16 hr), so the results lend support to the picture of east-to-west winds by day and west-to-east winds by night.Values of scale height are obtained by analysis of the change in perigee height.