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511.
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在导弹飞行试验时,基于GPS的弹道基准系统可替代常规雷达。由于GPS弹道基准的精度高,所以可用来评定导弹惯性测量装置的性能。在两发现役的和平保卫者导弹发射前配置了GPS转发器和三波段天线。根据GPS测量的矩离、矩离增量数据,用卡尔曼滤波方法评定各个IMU误差,结果证明GPS优于雷达。 相似文献
513.
Pacôme Delva Uroš Kostić Andrej Čadež 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this article we model a Global Navigation Satellite System (GNSS) in a Schwarzschild space–time, as a first approximation of the relativistic geometry around the Earth. The closed time-like and scattering light-like geodesics are obtained analytically, describing respectively trajectories of satellites and electromagnetic signals. We implement an algorithm to calculate Schwarzschild coordinates of a GNSS user who receives proper times sent by four satellites, knowing their orbital parameters; the inverse procedure is implemented to check for consistency. The constellation of satellites therefore realizes a geocentric inertial reference system with no a priori realization of a terrestrial reference frame. We perform a simulation of position determination and show that the determination of the four coordinates with a 25–32 digit accuracy takes only around 60 ms. Effects of non-gravitational perturbations on positioning errors are assessed, and methods to reduce them are sketched. In particular, inter-links between satellites could greatly enhance stability and accuracy of the positioning system. Effects of gravitational perturbations are omitted in this paper in order to make a clearer comparison between the relativistic and non-relativistic scheme, but they will be included in subsequent work. We believe that the final algorithm will be a serious alternative to the usual post-Newtonian scheme. 相似文献
514.
Swantje Hauschild Svantje Tauber Beatrice Lauber Cora S. Thiel Liliana E. Layer Oliver Ullrich 《Acta Astronautica》2014
Dating back to the Apollo and Skylab missions, it has been reported that astronauts suffered from bacterial and viral infections during space flight or after returning to Earth. Blood analyses revealed strongly reduced capability of human lymphocytes to become active upon mitogenic stimulation. Since then, a large number of in vitro studies on human immune cells have been conducted in space, in parabolic flights, and in ground-based facilities. It became obvious that microgravity affects cell morphology and important cellular functions. Observed changes include cell proliferation, the cytoskeleton, signal transduction and gene expression. This review gives an overview of the current knowledge of T cell regulation under altered gravity conditions obtained by in vitro studies with special emphasis on the cell culture conditions used. We propose that future in vitro experiments should follow rigorous standardized cell culture conditions, which allows better comparison of the results obtained in different flight- and ground-based experiment platforms. 相似文献
515.
The GFZ real-time GNSS precise positioning service system and its adaption for COMPASS 总被引:1,自引:0,他引:1
Xingxing Li Maorong Ge Hongping Zhang Thomas Nischan Jens Wickert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Motivated by the IGS real-time Pilot Project, GFZ has been developing its own real-time precise positioning service for various applications. An operational system at GFZ is now broadcasting real-time orbits, clocks, global ionospheric model, uncalibrated phase delays and regional atmospheric corrections for standard PPP, PPP with ambiguity fixing, single-frequency PPP and regional augmented PPP. To avoid developing various algorithms for different applications, we proposed a uniform algorithm and implemented it into our real-time software. In the new processing scheme, we employed un-differenced raw observations with atmospheric delays as parameters, which are properly constrained by real-time derived global ionospheric model or regional atmospheric corrections and by the empirical characteristics of the atmospheric delay variation in time and space. The positioning performance in terms of convergence time and ambiguity fixing depends mainly on the quality of the received atmospheric information and the spatial and temporal constraints. The un-differenced raw observation model can not only integrate PPP and NRTK into a seamless positioning service, but also syncretize these two techniques into a unique model and algorithm. Furthermore, it is suitable for both dual-frequency and sing-frequency receivers. Based on the real-time data streams from IGS, EUREF and SAPOS reference networks, we can provide services of global precise point positioning (PPP) with 5–10 cm accuracy, PPP with ambiguity-fixing of 2–5 cm accuracy, PPP using single-frequency receiver with accuracy of better than 50 cm and PPP with regional augmentation for instantaneous ambiguity resolution of 1–3 cm accuracy. We adapted the system for current COMPASS to provide PPP service. COMPASS observations from a regional network of nine stations are used for precise orbit determination and clock estimation in simulated real-time mode, the orbit and clock products are applied for real-time precise point positioning. The simulated real-time PPP service confirms that real-time positioning services of accuracy at dm-level and even cm-level is achievable with COMPASS only. 相似文献
516.
超精密定位中的几项相关关键技术 总被引:3,自引:1,他引:2
通过结合自已的实际工作,分别从伺服进给机构,位置检测技术,数控及伺服控制等几个方面对超精密机床的定位系统进行了说明 相似文献
517.
基于粒子滤波和似然比的接收机自主完好性监测算法 总被引:1,自引:0,他引:1
由于粒子滤波算法在处理非线性系统非高斯噪声问题具有较大的优势,提出将粒子滤波算法与对数似然比方法有机结合应用于接收机自主完好性监测(Receiver autonomous integrity monitoring,RAIM)中。通过粒子滤波算法对状态进行精确估计,利用对数似然比建立一致性检验统计量进行故障检测。在建立全量累加对数似然比和部分累加对数似然比检验统计值的基础上,通过比较系统各状态累加对数似然比和检测阈值之间的关系,进而对卫星故障进行检测。对算法进行了数学建模,描述了RAIM算法流程。通过实测数据对提出的RAIM算法进行验证,结果表明:粒子滤波在非高斯测量噪声情况下可以对GPS接收机状态进行精确的估计,利用对数似然比建立的一致性检验统计量能有效地检测并隔离故障卫星,验证了该算法应用于接收机自主完好性监测的可行性和有效性。 相似文献
518.
双线阵立体测绘卫星定位对外方位元素的测量精度要求高,然而布设控制点成本高,缺少全世界范围内的控制点。针对这一问题,提出应用星载激光测高仪提高定位精度的方法。首先,分析了双线阵立体测绘卫星和激光测高仪的误差特性,即测绘相机定位精度受外方位角元素影响比较大,激光测高仪高程精度受角元素影响相对较小。然后,论证了用激光测高仪提高定位精度的可行性。在相同的卫星平台定向辅助数据下,激光测高仪高程精度要比测绘相机高得多,可以作为高程约束提高定位精度。最后,应用光束法平差原理对激光测高数据作为高程约束进行了仿真试验。结果表明,加入激光测高数据可将双线阵立体测绘卫星的高程精度由8.0m提高到约3.5m。此方法可为实现全球无控制点测绘提供一定参考。 相似文献
519.
结合海上高精度定位保障工程实践,描述长基线网络差分定位技术应用的技术构成、应用模式,展示了海上高精度实时动态定位技术优势和应用前景,为海上高精度定位应用提供宝贵经验。 相似文献
520.