Accurate orbit predictions for debris orbit manoeuvre using ground-based lasers

Orbit manoeuvre of low Earth orbiting (LEO) debris using ground-based lasers has been proposed as a cost-effective means to avoid debris collisions. This requires the orbit of the debris object to be determined and predicted accurately so that the laser beam can be locked on the debris without the loss of valuable laser operation time. This paper presents the method and results of a short-term accurate LEO (<900 km in altitude) debris orbit prediction study using sparse laser ranging data collected by the EOS Space Debris Tracking System (SDTS). A main development is the estimation of the ballistic coefficients of the LEO objects from their archived long-term two line elements (TLE). When an object is laser tracked for two passes over about 24 h, orbit prediction (OP) accuracy of 10–20 arc seconds for the next 24–48 h can be achieved – the accuracy required for laser debris manoeuvre. The improvements in debris OP accuracy are significant in other applications such as debris conjunction analyses and the realisation of daytime debris laser tracking.     

航天器交会飞行设计方法研究

针对半自主飞行追踪星,阐述航天器交会总体设计方法。根据对接点的地理位置范围、共面轨道倾角以及目标星轨道周期与追踪星入轨点地理位置,确定交会飞行时间和两星初始相位差范围。考虑最小轨道机动动力要求与飞行轨迹安全性等因素,并兼顾地面测控条件,设计追踪星远程导引段与相对导航段的轨道机动与飞行轨迹,特别是选择与比较不同的初始轨道、调相轨道与漂移轨道以及保持点停泊时间与最终逼近段飞行时间等交会飞行要素,调整飞行时间、相位差与对接点位置,确定最佳交会飞行方案,完成空间交会任务。     

相邻两航天器相对运动近似方程的解析解及比动能方程

给出了地心引力场中受控航天器相对目标航天器运动的推力加速度随时间线性变化时Hill方程的解析解，根据Hill方程导出了受控航天器相对目标航天器运动的比动能方程，并讨论了比动能方程在上述两天器轨道相遇和轨道交会问题中的应用。     

目标分速度的遥、外测数据融合估计算法

建立了发射坐标系和惯性坐标系之间的转换关系，讨论了利用遥测数据计算引力加速度的具体方法，并给出了计算公式；最后建立了利用遥、外数据融合估计目标外测分速度的算法。文中给出的仿真结果说明，利用遥测数据融合计算目标分速度可极大提高计算精度，并为合理利用遥测数据解决外测数据处理中遇到的有关问题提供方法基础。     

航星座自主运行平行系统的轨道计算方法

构建一个能够与实际卫星导航系统长期保持时空一致的平行系统,可为导航星座自主运行提供一个监视与评估平台。针对建设该平行系统所需的高逼真轨道计算问题,引入平行系统理论的思想,在分析历史精密轨道的基础上,提出高精度轨道计算与预报方法。该方法以不断更新的精密轨道作为输入,利用PID增量式算法或时变加权法进行数据平滑,使得轨道计算结果始终与实际系统保持高度一致性。试验结果表明,该方法可使卫星轨道计算的结果与实际卫星轨道长期保持在分米量级。     

Use of two-line element data for thermosphere neutral density model calibration

Traditional empirical thermospheric density models are widely used in orbit determination and prediction of low-Earth satellites. Unfortunately, these models often exhibit large density errors of up to around 30% RMS. Density errors translate into orbit errors, adversely affecting applications such as re-entry operations, manoeuvre planning, collision avoidance and precise orbit determination for geodetic missions. The extensive database of two-line element (TLE) orbit data contains a wealth of information on satellite drag, at a sufficiently high spatial and temporal resolution to allow a calibration of existing neutral density models with a latency of one to two days. In our calibration software, new TLE data for selected objects is converted to satellite drag data on a daily basis. The resulting drag data is then used in a daily adjustment of density model calibration parameters, which modify the output of an existing empirical density model with the aim of increasing its accuracy. Two different calibration schemes have been tested using TLE data for about 50 objects during the year 2000. The schemes involve either height-dependent scale factors to the density or corrections to CIRA-72 model temperatures, which affect the density output based on a physical model. Both schemes have been applied with different spherical harmonic expansions of the parameters in latitude and local solar time. Five TLE objects, varying in perigee altitude between 280 and 530 km, were deliberately not used during calibration, in order to provide independent validation. Even with a single daily parameter, the RMS density model error along their tracks can already be reduced from the 30% to the 15% level. Adding additional parameters results in RMS errors lower than 12%.     

卫星对空间目标悬停的轨道动力学与控制方法研究

首先,给出了卫星悬停的轨道动力学模型,然后提出了悬停轨道的一种"持续式"的开路轨道控制策略,即通过在一段时间对轨道实施连续有限推力控制,使得在这段时间内卫星运行在新的悬停轨道上,而非开普勒轨道。最后,以地球静止轨道卫星为目标星,研究了悬停轨道的实施途径,并进行了数学仿真。仿真结果表明,在一段时间内对空间目标实施轨道悬停是可行的。     

Automatic extraction of lineaments based on wavelet edge detection and aided tracking by hillshade

Lineaments refer to the linear or curvilinear textures on remote sensing image, whose general spatial distribution characteristics are often the response of deep geological sturcture at the surface. Firstly, we use wavelet modulus maximum transformation to detect the edges with 4 scales on Landsat – 8 OLI B5 image and analyze their multi-scale characteristics. As the result, it is determined that the optimal scale of edge detection is 4, and the outline that consist of the edge pixels is roughly corresponding to the geological structure of mine area. Thus the incomplete lineaments have been extracted by using the 2D otsu algorithm. Secondly, the hillshade map generated based on DEM is processed to generate binarized linear shadow. Finally, the linear shadow is superimposed on the lineaments preliminarily extracted to obtain the optimized lineaments. Experiment results show that, based on the method, there are some deformation and displacement between the lineaments extracted and the actual geological structure, and it fail to effectively extract Qilinchang Fault, but lineaments are in good correspondence with Kuangshanchang Fault, Dongtou Fault and Niulan River Fault, which are basically in accord with the geological structure framework of the mine area.     

Integral inversion of GRAIL inter-satellite gravitational accelerations for regional recovery of the lunar gravitational field

We present an integral-based approach for high-resolution regional recovery of the gravitational field in this article. We derive rigorous remove-compute-restore integral estimators relating the line-of-sight gravitational acceleration to an arbitrary order radial derivative of the gravitational potential. The integral estimators are composed of three terms, i.e., the truncated integration, the low-frequency line-of-sight gravitational acceleration, and the high-frequency truncation error (effect of the distant zones). We test the accuracy of the integral transformations and of the integral estimators in a closed-loop simulation over the Montes Jura region on the nearside of the Moon. In this way, we determine optimal sizes of integration radii and grid discretisation. In addition, we investigate the performance of the regional integral inversion with synthetic and realistic GRAIL observations. We demonstrate that the regional inversion results of the disturbing gravitational potential and its first order radial derivative in the Montes Jura mountain range are less contaminated by high-frequency noise than the global spherical harmonic models.     

任意轮廓线图形的快速扫描线转换

多边形的扫描线转换和区域填充是光栅图形面着色的两种主要方法。前者速度快，但对多边形轮廓线的形状有一定要求；后者无此限制，但须访问区域内的所有象素点，填充速度慢。本文基于对轮廓形状信息的分析，提出了一种任意封闭轮廓线图形的快速扫描线转换方法，它无需访问映象内存即可完成任意封闭轮廓线图形的扫描线转换，保持了多边形的扫描线转换与区域种子填充两种方法的优点，避免了各自的不足，因此具有更一般的应用适应性及更高的转换效率。