Space debris: Assessing risk and responsibility

We model the orbital debris environment by a set of differential equations with parameter values that capture many of the complexities of existing three-dimensional simulation models. We compute the probability that a spacecraft gets destroyed in a collision during its operational lifetime, and then define the sustainable risk level as the maximum of this probability over all future time. Focusing on the 900- to 1000-km altitude region, which is the most congested portion of low Earth orbit, we find that – despite the initial rise in the level of fragments – the sustainable risk remains below 10^-3${10}^{-3}$ if there is high (>98%) compliance to the existing 25-year postmission deorbiting guideline. We quantify the damage (via the number of future destroyed operational spacecraft) generated by past and future space activities. We estimate that the 2007 FengYun 1C antisatellite weapon test represents ≈1%$\approx 1\%$ of the legacy damage due to space objects having a characteristic size of ?10$?10$ cm, and causes the same damage as failing to deorbit 2.6 spacecraft after their operational life. Although the political and economic issues are daunting, these damage estimates can be used to help determine one-time legacy fees and fees on future activities (including deorbit noncompliance), which can deter future debris generation, compensate operational spacecraft that are destroyed in future collisions, and partially fund research and development into space debris mitigation technologies. Our results need to be confirmed with a high-fidelity three-dimensional model before they can provide the basis for any major decisions made by the space community.     

Propagation errors analysis of TLE data

Orbit position uncertainty is an important factor for collision avoidance issues. For a single object with high frequency historical data, we can attain its position uncertainty easily. But sometimes data is not enough for errors analysis, orbits need to be classified. In this paper error analysis is made from two-line element sets data (TLEs). The Simplified General Perturbations-4 (SGP4) propagator was used. Statistical errors of debris and R/B are given for lower-altitude orbits which are classified by perigee altitude and eccentricity. The errors results and analysis for SSO (the Sun synchronous orbit) typical orbits are obtained. At last atmospheric drag as a main cause of downrange errors in lower-altitude orbit is analyzed. BSTAR in TLEs is modified to improve prediction precision.     

Qualitative estimation of magnetic storm efficiency in producing relativistic electron flux in the Earth’s outer radiation belt using geomagnetic pulsations data

It is well known that during many but not all of the geomagnetic storms enhanced fluxes of high-energy electrons are observed in the outer radiation belt. Here we examine relativistic (>2 MeV) electron fluxes measured by GOES at the synchronous orbit and on-ground observations of two types of ULF pulsations during 30 magnetic storms occurred during 1996–2000. To characterize the effectiveness of the chosen magnetic storms in producing relativistic electron fluxes, following to (Reeves, G.D., McAdams, K.L., Friedel, R.H.W., O’Brien, T.R. Acceleration and loss of relativistic electrons during geomagnetic storms. Geophys. Res. Lett. 30, doi:10.1029/2002GL016513, 2003), we calculate a ratio of the maximum daily-averaged electron flux measured during the recovery phase, to the mean pre-storm electron flux. A storm is considered an effective one if its ratio exceeds 2. We compare behavior of Pi1 and Pc5 geomagnetic pulsations during effective and non-effective storms and find a tendency for a storm efficiency to be higher when the mid-latitude Pi1 pulsations are observed for a long time during the magnetic storm main phase. We note also that the prolonged powerful Pc5 pulsation activity during the recovery phase of a magnetic storm is the necessary condition for the storm effectiveness. To interpret the found dependences, we suggest that there are two prerequisites for generating relativistic electron populations during a storm: (1) the availability of seed electrons in the magnetosphere, and Pi1 emissions are indicators of the mid-energy electron interaction with the ionosphere and (2) acceleration of the seed electrons to MeV energies, and interaction of electrons with the MHD wave activity in the Pc5 range is one of the most probable mechanisms proposed in the literature for this purpose.     

椭圆轨道卫星编队燃料最优机动实时算法

文章针对椭圆轨道编队卫星最优燃料机动的实时计算问题进行研究。利用LGL伪谱法对问题进行快速求解。由于最优燃料控制为非连续控制,如直接采用伪谱法则只有当离散点数目很大时,才能实现较高精度的编队机动控制,而这会影响算法的实时计算效率。为了克服这方面的不足,文章提出了一种时间尺度变换策略,并结合模型预测的滚动优化方法,设计了一种编队实时机动控制算法。该算法在兼顾解的全局最优性的同时改善了解的局部精确性,最后通过数值仿真验证了所设计算法的有效性。     

一种无角速度信息的挠性航天器姿态控制方法

研究了一种无角速度信息挠性航天器的姿态稳定控制方法。针对挠性航天器陀螺故障或无陀螺配置中无角速度测量信息情形下的姿态控制问题,基于姿态四元数设计了姿态定点调节的无速率控制器,利用Lyapunov方法和LaSalle不变原理证明了闭环系统的全局渐近稳定性,并对控制方案进行了改进。仿真验证了控制律的有效性。     

基于二次方程组的邻近圆轨道四冲量最优交会

研究了一种基于二次方程组的邻近圆轨道四冲量最优交会的求解方法．给出邻近圆轨道交会的无量纲化动力学方程及相应的基向量方程,介绍由Carter提出的一种基于二次方程组的四冲量最优交会的求解方法,在提出邻近圆轨道最优冲量交会的原始解、相反解、对偶解、对偶相反解概念的基础上,分析基于二次方程组的四冲量最优交会的求解方法存在的问题,并给出修正方法．仿真结果表明,该方法是对Carter提出的基于二次方程组的四冲量最优交会求解方法的有效补充．     

利用GPS接收机的精确轨道确定技术

利用GPS接收机的导航信息精确确定接收机载体航天器的轨道根数.给出了为确保10 m量级的定轨精度所必需的精确坐标系变换与时间系统变换公式,提出了采用GPS接收机的导航信息与摄动运动方程式外推的组合导航方法,以保证接收机天线被短期遮挡时导航仍能正常运行.     

飞行器在轨服务

定义了在轨服务（OOS）的概念。介绍了OOS可实现的在轨检查、组装、更换修理、补给,以及轨道转移等功能,讨论了可扩展公共卫星平台、精确测量系统与控制软件、先进对接机构、燃料传输系统、先进机械臂系统,自主运行与管理等关键技术。阐述了OOS发展的需求与驱动因素,以及对飞行器设计中通用化与标准化、理念调整,以及可靠性与技术分配重构等的影响。     

航天器姿态跟踪系统的非线性鲁棒自适应控制

研究有未知惯量矩阵和干扰力矩的刚体航天器姿态跟踪。对此类多输入多输出、不确定非线性系统,提出了一种非线性鲁棒自适应控制策略,用Lyapunov直接法分析了闭环系统稳定性。理论分析表明,该控制器不仅保证闭环系统一致最终有界稳定,航天器姿态跟踪误差收敛至系统平衡点的一个较小领域,而且使闭环系统对航天器惯量参数有自适应能力,对有界干扰力矩具鲁棒性。仿真结果表明：所设计的非线性鲁棒自适应控制器有效。     

某地球静止轨道卫星成像辐射计热控设计

对某地球静止轨道卫星成像辐射计的热控设计进行了研究。根据辐射计热特点,考虑一般温度、温度梯度和日温度变化等热控需求,给出了成像辐射计中光学基板等温化、阳光直射时扫描镜等光学部件散热,以及次镜支持材料选择等关键热控设计原则。用NEVADA、SINDNG软件对冬至、春秋分、夏至,以及阳光与卫星轨道面夹角α=-8.8°,8.8°的5种条件的初期和末期10个工况进行了仿真分析。结果表明：设计的热控方案可行,基本满足成像辐射计的使用要求。