基于分段连续推力的晕轨道控制方法

基于小偏差理论,推导了三体动力学模型的误差线性模型,并将此假设下的控制归纳为终端固定的有限时间调节器问题。在此基础上,进一步利用该最优控制方法推导了晕轨道周期内的连续小推力控制方案,验证了控制加速度及状态量的收敛。同时针对整周期控制方式在超调后状态量收敛速度慢的问题,通过分段连续推力控制模式(Sectional Continuous Thrust Control,SCTC)来近似瞬时脉冲推力控制模式,给出了最短分段控制时间的计算方法。实验表明,SCTC模式加快了轨道状态的收敛速度。对于km级入轨偏差,通过1次控制即可使实际轨道收敛至标称轨道。     

访问多个特定相对位置的航天器轨道设计

在航天器轨道设计问题中,将惯性空间中经典的吉布斯三矢量定轨方法拓展到相对运动空间中,给出了一种相对运动条件下的三矢量定轨方法。针对已知轨道的目标航天器,以及二个或三个给定的空间相对位置,基于相对运动方程,提出了设计跟随航天器飞行轨道的数值方法。以轨道面共面或异面,以及目标航天器轨道形状为椭圆或圆,将问题分为四种情况进行约束条件和自由变量个数的分析讨论。对于自由变量个数多于约束方程的情况,额外给定周期重访约束,将各种情况下的特定相对位置访问问题转化为一至二维的非线性方程(组)求解问题。对一维方程求解采用分段黄金分割+割线法进行快速求解;对二维方程组通过网格法搜索迭代初值并通过牛顿迭代快速求解。进一步基于线性模型的解,采用微分修正方法求解了各情况下J2摄动模型下的结果。数值算例验证了提出方法的正确性及有效性。     

Space station orbit design using dynamic programming

A space station orbit design mission is characterized by a long-duration and multi-step decision process. First, the long-duration design process is divided into multiple planning periods, each of which consists of five basic flight segments. Second, each planning period is modeled as a multi-step decision process, and the orbital altitude strategies of different flight segments have interaction effects on each other. Third, a dynamic programming method is used to optimize the total propellant consumption of a planning period while considering interaction effects. The step cost of each decision segment is the propellant for orbital-decay maintenance or lifting altitude, and is calculated by approximate analytical equations and combining a shooting iteration method. The proposed approach is demonstrated for a typical orbit design problem of a space station. The results show that the proposed approach can effectively optimize the design of altitude strategies, and can save considerable propellant consumption for the space station than previous public studies.     

Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

Low-Earth-Orbit(LEO) formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination(PROD) is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System(BDS) to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System(GPS) is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from9.71 to 21.58. Secondly, the results show that the 3-Dimensional(3 D) accuracy of PROD, based on BDS-only, GPS-only and BDS + GPS, is 0.74 mm, 0.66 mm and 0.52 mm, respectively. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit(GEO) satellites and Inclined Geosynchronous-Orbit(IGSO) satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision(ADOP), based on BDS + GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the SingleDifference(SD) ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit(MEO) satellites co-work with GEO satellites, the accuracy decreases by 17.02%.     

Forecasting the geomagnetic activity of the Dst index using multiscale radial basis function networks

The Dst index is a key parameter which characterises the disturbance of the geomagnetic field in magnetic storms. Modelling of the Dst index is thus very important for the analysis of the geomagnetic field. A data-based modelling approach, aimed at obtaining efficient models from limited input–output observational data, provides a powerful tool for analysing and forecasting geomagnetic activities including the prediction of the Dst index. In this study, the process of the Dst index is treated to be a structure-unknown system, where the solar wind parameter (VBs) and the solar wind dynamic pressure (P) are the system inputs, and the Dst index is the system output. A novel multiscale RBF (MSRBF) network is introduced to represent such a two-input and single-output system, where the Dst index is related to the solar wind parameter and the dynamic pressure, via a hybrid network model consisting of two submodels: a linear part that reflects the linear relationship between the output and the inputs, and a nonlinear part that captures the effect of the interacting contribution of past observations of the inputs and the output, on the current output. The proposed MSRBF network can easily be converted into a linear-in-the-parameters form and the training of the linear network model can easily be implemented using a forward orthogonal regression (FOR) algorithm. One advantage of the new MSRBF network, compared with traditional single scale RBF networks, is that the new network is more flexible for describing complex nonlinear dynamical systems.     

Properties of the high area-to-mass ratio space debris population at high altitudes

In the framework of its space debris research activities ESA established an optical survey program to study the space debris environment at high altitudes, in particular in the geostationary ring and in the geostationary transfer orbit region. The Astronomical Institute of the University of Bern (AIUB) performs these surveys on behalf of ESA using ESA’s 1-m telescope in Tenerife. Regular observations were started in 1999 and are continued during about 120–140 nights per year. Results from these surveys revealed a substantial amount of space debris at high altitudes in the size range from 0.1 to 1 m. Several space debris populations with different dynamical properties were identified in the geostationary ring. During the searches for debris in the geostationary transfer orbit region a new population of objects in unexpected orbits, where no potential progenitors exist, was found. The orbital periods of these objects are clustered around one revolution per day; the eccentricities, however, are scattered between 0 and 0.6. By following-up some of these objects using the ESA telescope and AIUB’s 1-m telescope in Zimmerwald, Switzerland, it was possible to study the properties of this new population. One spectacular finding from monitoring the orbits over time spans of days to months is the fact that these objects must have extreme area-to-mass ratios, which are by several orders of magnitudes higher than for ‘normal-type’ debris. This in turn supports the hypothesis that the new population actually is debris generated in or near the geostationary ring and which is in orbits with periodically varying eccentricity and inclination due to perturbations by solar radiation pressure. In order to further study the nature of these debris, multi-color and temporal photometry (light curves) were acquired with the Zimmerwald telescope. The light curves show strong variations over short time intervals, including signals typical for specular reflections. Some objects exhibit distinct periodic variations with periods ranging from 10 to several 100 s. All this is indicative for objects with complicated shapes and some highly reflective surfaces.     

采样时间序列的滑动递推容错预报算法

在导出线性模型系数递推最优辨识算法的基础上，探讨了滑动线性预报器的容错改进，建立了简洁、实用的滑动递推容错预报算法。通过仿真计算验证了算法的有效性。     

Navigation message designing with high accuracy for NAV

Navigation message designing with high accuracy guarantee is the key to efficient navigation message distribution in the global navigation satellite system（GNSS）. Developing high accuracy-aware navigation message designing algorithms is an important topic. This paper investigates the high-accuracy navigation message designing problem with the message structure unchanged.The contributions made in this paper include a heuristic that employs the concept of the estimated range deviation（ERD） to improve the existing well-known navigation message on L1 frequency（NAV） of global positioning system（GPS） for good accuracy service; a numerical analysis approximation method（NAAM） to evaluate the range error due to truncation（RET） of different navigation messages; and a basic positioning parameters designing algorithm in the limited space allocation. Based on the predicted ultra-rapid data from the ultra-rapid data from the international GPS service for geodynamic（IGU）, ERDs are generated in real time for error correction.Simulations show that the algorithms developed in this paper are general and flexible, and thus are applicable to NAV improvement and other navigation message designs.     

中间轨道方法的奇点处理问题

利用既有的Ｂａｒｒｏｒ中间轨道计算方法中的奇点处理方法，对有些特殊轨道不能处理，用本文所述方法不但能处理各种卫星轨道问题，也能处理各种导弹轨道的特殊计算问题。     

利用升交点经度进行轨道设计的方法

以升交点经度的范围来描述所有能覆盖到目标的轨道。利用球面三角方法详细讨论了在考虑地球形状Ｊ２项的摄动影响时，各种情况下能覆盖目标点的轨道的升交点经度范围，并将其推广到对区域目标的覆盖，给出了完整的解析表达式。结合实例给出了利用该表达式进行有连续覆盖、覆盖次数及过顶时间要求时的轨道设计方法。该方法的优点是无需进行轨道读物计算，仅用解析表达式即可快速地设计出满足覆盖要求的轨道。