New Definition of Discovery for Solar System Objects

We propose a new formal definition of discovery for a Solar System object. It is based on an objective and mathematically rigorous algorithm to assess when a set of observations is enough to constitute a discovery. When this definition is satisfied, in almost all cases the orbit is defined well enough to establish the nature of the object discovered (Main Belt vs. Near Earth Asteroid, Trans-Neptunian vs. long period comet). The frequency of occurrence of exceptions is estimated by a set of numerical experiments. The availability of a non-subjective definition of discovery allows some rules to be adopted for the assignment of discovery credit with a minimum risk of dispute. Such rules should be fair, encourage good practice by the observers and acknowledge the contribution of the orbit computers providing the identifications and the orbits, as well as the one of all the contributing observers.     

Approximate analysis for relative motion of satellite formation flying in elliptical orbits

This paper studies the relative motion of satellite formation flying in arbitrary elliptical orbits with no perturbation. The trajectories of the leader and follower satellites are projected onto the celestial sphere. These two projections and celestial equator intersect each other to form a spherical triangle, in which the vertex angles and arc-distances are used to describe the relative motion equations. This method is entitled the reference orbital element approach. Here the dimensionless distance is defined as the ratio of the maximal distance between the leader and follower satellites to the semi-major axis of the leader satellite. In close formations, this dimensionless distance, as well as some vertex angles and arc-distances of this spherical triangle, and the orbital element differences are small quantities. A series of order-of-magnitude analyses about these quantities are conducted. Consequently, the relative motion equations are approximated by expansions truncated to the second order, i.e. square of the dimensionless distance. In order to study the problem of periodicity of relative motion, the semi-major axis of the follower is expanded as Taylor series around that of the leader, by regarding relative position and velocity as small quantities. Using this expansion, it is proved that the periodicity condition derived from Lawden’s equations is equivalent to the condition that the Taylor series of order one is zero. The first-order relative motion equations, simplified from the second-order ones, possess the same forms as the periodic solutions of Lawden’s equations. It is presented that the latter are further first-order approximations to the former; and moreover, compared with the latter more suitable to research spacecraft rendezvous and docking, the former are more suitable to research relative orbit configurations. The first-order relative motion equations are expanded as trigonometric series with eccentric anomaly as the angle variable. Except the terms of order one, the trigonometric series’ amplitudes are geometric series, and corresponding phases are constant both in the radial and in-track directions. When the trajectory of the in-plane relative motion is similar to an ellipse, a method to seek this ellipse is presented. The advantage of this method is shown by an example.     

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On the motion around the centre of mass of a viscously elastic sphere in the restricted elliptic three-body problem

In the restricted three-body problem we consider the motion of a viscously elastic sphere (planet) with its centre of mass moving in a conditionally-periodic orbit. The approximate equations describing the rotational motion of the sphere in terms of the Andoyer variables are obtained by the method of the separation of motion and averaging; the evolution of the motion is also analysed.     

新太阳光压模型在GNSS定轨中的应用

太阳光压摄动是影响卫星定轨中重要的误差源,在GNSS导航卫星精密定轨过程中使用最为广泛的光压模型为ECOM模型。为了探究几种ECOM模型及其适用性,该文以超快速星历为起算轨道,分析对比经典ECOM-1模型与最新13参数ECOMC模型对GPS/BDS卫星轨道的影响。结果显示:相较于ECOM-1模型,ECOMC模型在GPS定轨中精度有所提升,特别体现在径向精度提升,单天与三天弧段在径向的解算精度分别提升了12.73%和24.74%;在BDS定轨中,采用ECOMC模型,部分GEO卫星在径向方向单天精度有12.38%的提升,而对于IGSO与MEO卫星二者精度差异不大;分析可得,由于星体结构不对称引起卫星在沿太阳-卫星方向作用的偶数阶短周期谐波扰动,引入卫星-太阳方向偶数阶项的参数估计可提升卫星径向精度。     

基于CEI的飞船交会对接远程导引段的轨道确定方案

探讨了CEI技术在飞船交会对接远程导引段的高精度定轨与实时监控的能力。仿真结果表明:精密定轨中采用可视弧段较长的单站可使相对位置精度达百米以内,速度达厘米/秒级。采用单一绝对扩展卡尔曼滤波器的方案进行实时轨道计算,采用滤波稳定后固定模糊度的方法可以使相对轨道位置精度达十米级,速度精度达厘米/秒级,事后及实时的轨道精度均满足远程导引段的精度指标。     

利用IGS星历预报GPS卫星轨道

在动力学轨道拟合以及轨道积分的基础上,提出了基于IGS精密星历的GPS卫星轨道预报方法。该方法首先利用已知的IGS精密星历作为虚拟观测值,采用动力学方法拟合出GPS卫星的初始轨道和动力学参数,然后再通过积分来预报GPS卫星的轨道。主要讨论了基于不同弧段的IGS星历时,该方法对GPS卫星轨道的拟合和预报情况。研究结果显示:对于6 d弧段以内的IGS精密星历,其拟合轨道与IGS精密星历差值的三维RMS值均优于4 cm,随着拟合弧段的增加,拟合残差变大;当利用2～6 d弧段的IGS星历来预报GPS轨道时,大部分卫星第1天、第7天和第30天的三维预报精度可优于0.1 m、3 m和100 m。其中,2d弧段的IGS星历对GPS卫星第1天和第7天的预报结果最好,5 d弧段的IGS星历对GPS卫星第30天的预报结果最好。     

卫星定轨软件的移植与测试分析

为改变卫星定轨软件对Unix平台的依赖性和Unix平台命令式操作等因素制约后续的开发和应用的状况,进行了将精密定轨软件从Unix平台移植到Windows平台下的工作。阐述了卫星定轨软件移植的步骤,主要包括根据2个平台下软件的差异,对卫星定轨软件程序进行删除、追加、修改等。对卫星定轨软件移植前、后得到的有关数据进行了比较,结果表明移植工作是成功的。     

南海神狐海域水合物三相混合层测井评价方法研究

天然气水合物降压试采过程中,水合物、游离气和水的三相混合层中的游离气首先被采出,从而提高降压效率,促进水合物分解;因此利用岩心刻度测井的方法开展南海神狐海域水合物三相混合层测井评价方法研究,对水合物矿体储量计算以及产业化开采具有重要意义.三相混合层与水合物层相比,其密度和中子孔隙度值均减小,纵波速度明显下降;与气层相比...     

顾及系统误差的GEO卫星几何法定轨PDOP值分析

针对GEO卫星几何法定轨中系统误差对PDOP值的影响进行研究,首先回顾了经典几何法定轨的基本原理,然后根据顾及系统误差的几何法定轨原理推导出PDOP值计算公式,并利用5个跟踪站的模拟数据,计算了多种系统误差情况下PDOP值。结果表明：系统误差对GEO卫星几何法定轨的PDOP值影响很大;采用顾及系统误差的几何法定轨方法可以较好地削弱系统误差对PDOP值的影响;国外布设跟踪站比仅在中国布设跟踪站能更好地削弱系统误差对PDOP值的影响。