精确星光大气折射导航观测模型的研究

高精度星光折射间接敏感地平的自主导航方法,目前被国内外广泛关注,由于大气参数变化的不确定性,国内外现用星光折射模型有一定局限性,使得利用星光折射导航定位精度大打折扣.根据大气密度随高度、纬度、季节等变化规律,有效改进现有固定高度(25km)的观测模型,可从整体上提高自主导航精度及可靠性.并通过对大气折射原理、平流层大气数据、大气模型以及影响星光折射观测模型的诸多因素的深入研究,建立了自适应连续高度(20~50km)的星光折射观测模型,同时建立带摄动的系统方程,利用Unscented卡尔曼滤波算法进行了计算机仿真研究,并对仿真结果进行了误差分析.      

近圆轨道控制的分析方法

应用卫星绝大部分都是近圆轨道的卫星 ,其中又有很多是需要进行轨道控制的。在航天工程的实践中由于各种误差影响 ,实际的轨道控制过程并不是而且也没有必要基于精确的轨道动力学方程来执行。对于近圆轨道控制所用的动力学模型可以按圆轨道进行近似 ,得到一种非常简单的形式 ,基于这种简化的模型可以获得非常有用的分析解。为了从理论上证明这种简化的有效性 ,文中对动力学模型简化过程中所产生的各项误差进行了理论估计。     

星载圆柱阵电子消旋天线研究

对同步轨道自旋稳定卫星提出了一种 32列圆柱阵的电子消旋天线。该天线每列有 4个辐射单元 ,通过开关矩阵和数字可变功分器 ,对相邻五列阵顺序馈电形成覆球波束 ,在 0°～ 360°范围内周向扫描。利用星载地球敏感器输出脉冲作为角度参考 ,通过控制软件实现自主消旋 ,并获得了周向约 1 6°的波束跃度和电平起伏小于 1dB的平稳消旋结果     

地球同步轨道卫星混合推进转移轨道特性分析

以地球同步轨道卫星转移轨道设计为背景,针对全化学推进燃料消耗大和全电推进转移时间长的问题,开展了化学-电混合推进转移轨道优化设计与特性分析。首先,讨论了轨道倾角和近地点幅角变化对混合推进转移轨道的影响。研究表明,在混合推进优化设计中需要将轨道倾角作为优化变量之一。然后,以近地点半径、远地点半径、轨道倾角为优化变量生成搜索网格,得到过渡轨道集。针对每条过渡轨道,构建化学推进转移段和电推进转移段。其中化学推进段采用单圈兰伯特转移解算,电推进段采用混合法优化。最后,以燃料消耗和转移时间为指标,在搜索域内开展解算分析,研究了混合推进轨道在整个搜索域内的变化趋势。该方法可以提供具有不同燃料消耗和转移时间的混合推进转移解集,拓宽了解空间,可供轨道设计人员根据任务约束灵活选用。     

Analysis of laser ranges and angular measurements data fusion for space debris orbit determination

In the framework of space debris, the orbit determination process is a fundamental step, both, for researchers and for satellite operators. The accurate knowledge of the orbit of space debris objects is needed to allow space debris characterization studies and to avoid unnecessary collision avoidance maneuvers.The accuracy of the results of an orbit determination process depends on several factors as the number, the accuracy, the kind of processed measurements, their distribution along the orbit, and the object-observer relative geometry. When the observation coverage of the target orbit is not homogeneous, the accuracy of the orbit determination can be improved processing different kind of observables. Recent studies showed that the satellite laser ranging technique can be successfully applied to space debris.In this paper, we will investigate the benefits of using laser ranges and angular measurements for the orbit determination process. We will analyze the influence of the number of used observations, of the covered arc of orbit, of each observable, and of the observation geometry on the estimated parameters. Finally, using data acquired on short observation arcs, we analyze the achievable accuracies for the orbital regimes with the highest space debris density, and to the consequences of the data fusion on catalog maintenance operations. The results shown are obtained using only real data (both angular and laser measurements) provided by sensors of the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald owned by the Astronomical Institute of the University of Bern (AIUB) and for some studies also using ranges provided from other stations of the International Laser Ranging Service (ILRS).     

载人月球极地探测定点返回轨道设计

针对载人月球极地探测任务,对定点返回轨道优化设计问题进行了研究。根据月球极地轨道的特性,介绍了三种返回轨道机动方案。结合三脉冲变轨方案,采用了从初步计算到精确计算的串行求解策略,对定点返回轨道进行优化设计。初步计算阶段,建立了基于近月点伪参数的三段二体拼接模型,将三脉冲机动段与月球逃逸段解耦,求解轨道初值;精确计算阶段,提出了两段拼接方法,分别进行逆向和正向高精度数值积分。经过仿真测试,验证了该策略求解的有效性和准确性。最后,通过大量的仿真计算,分析了定点返回轨道的特性。研究结论对未来载人月球极地探测定点返回轨道方案的设计具有重要的参考价值。     

基于GLONASS星历的预报轨道的误差分析

推导了协议地球坐标系下的卫星运动方程.通过分析由GLONASS(Global Navigation Satellite System)广播星历参数确定的卫星预报轨道的拟合精度,指出了摄动力模型的简化、积分器的选择,以及忽略了极移影响等因素是引起拟合误差的主要因素,其中摄动力模型的简化起最主要的作用.通过对卫星轨道运动方程积分30?min,可知由摄动力模型的简化、积分器和忽略极移影响等因素引起的拟合误差分别为0.827?m,0.224?m和0.025?m.要提高预报轨道拟合的精度,关键是要对摄动力简化特别是地球引力摄动高阶项的截断以及日月引力场简化造成的轨道预报精度损失加以控制.     

带电卫星寿命问题的讨论

本文利用能量观点,研究了带有电荷的人造卫星在地球引力场和磁场中运行时,在大气阻力作用下的寿命问题。文中推出了带电卫星在圆形轨道上决定生存时间的理论公式,并用理论公式对卫星带电后,对其寿命的影响做了数值估计。     

Performance of GPS-based accelerometry: A simulation experiment

Recent studies have shown that with the availability of high-quality CHAMP and GRACE gravity field models, it is feasible to determine accurate non-gravitational accelerations for low Earth orbiting satellites indirectly from precise GPS satellite-to-satellite observations. Possible applications of this so-called GPS-based accelerometry approach consist of accelerometer calibration and atmospheric density and wind computations. With the growing number of high-quality space-borne GPS receivers, this method could be applied to a large range of satellites. In this paper an extensive simulation study has been carried out, based on real accelerometer data from the GRACE mission, in order to determine the optimal processing strategy and the resulting accuracy of the estimated non-gravitational accelerations. It is shown that the optimal processing strategy consists of a piecewise linear parameterization of the estimated empirical accelerations, together with short 6-h orbit arcs. The GPS-based accelerometry approach makes use of triple-differenced GPS observations and the impact of considering the correlated observation noise was found to be marginal in the presence of other error sources such as GPS ephemeris errors. Using a priori non-gravitational force models improves the recovery of low temporal resolution accelerations, except during huge geomagnetic storms. With this strategy, non-gravitational accelerations can be recovered during high solar activity with an accuracy of better than 10% of the total signal in along-track direction and around 25–40% in cross-track direction, at time resolutions of around 8–20 min. During solar minimum conditions, the relative recovery error will increase to approximately 50% in along-track direction and around 60–70% in cross-track direction, due to the reduced atmospheric drag signal. Unfortunately, GPS-based accelerometry is hardly sensitive in the radial direction.     

Towards development of a consistent orbit series for TOPEX,Jason-1, and Jason-2

The TOPEX/Poseidon, Jason-1 and Jason-2 set of altimeter data now provide a time series of synoptic observations of the ocean that span nearly 17 years from the launch of TOPEX in 1992. The analysis of the altimeter data including the use of altimetry to monitor the global change in mean sea level requires a stable, accurate, and consistent orbit reference over the entire time span. In this paper, we describe the recomputation of a time series of orbits that rely on a consistent set of reference frames and geophysical models. The recomputed orbits adhere to the IERS 2003 standards for ocean and earth tides, use updates to the ITRF2005 reference frame for both the SLR and DORIS stations, apply GRACE-derived models for modeling of the static and time-variable gravity, implement the University College London (UCL) radiation pressure model for Jason-1, use improved troposphere modeling for the DORIS data, and apply the GOT4.7 ocean tide model for both dynamical ocean tide modeling and for ocean loading. The new TOPEX orbits have a mean SLR fit of 1.79 cm compared to 2.21 cm for the MGDR-B orbits. These new TOPEX orbits agree radially with independent SLR/crossover orbits at 0.70 cm RMS, and the orbit accuracy is estimated at 1.5–2.0 cm RMS over the entire TOPEX time series. The recomputed Jason-1 orbits agree radially with the Jason-1 GDR-C orbits at 1.08 cm RMS. The GSFC SLR/DORIS dynamic and reduced-dynamic orbits for Jason-2 agree radially with independent orbits from the CNES and JPL at 0.70–1.06 cm RMS. Applying these new orbits, and using the latest altimeter corrections for TOPEX, Jason-1, and Jason-2 from September 1992 to May 2009, we find a global rate in mean sea level of 3.0 ± 0.4 mm/yr.