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931.
综述了Godunov型显式大时间步长格式的研究进展。首先介绍了显式大时间步长格式的概念、分类和优势。然后重点阐述了Godunov型显式大时间步长格式的构造方法、高阶精度推广方法、多维问题推广方法和收敛特性、分辨率及计算效率等性能,展示了其在典型问题中的应用和验证。最后给出了Godunov型显式大时间步长格式研究进一步可能的发展方向。 相似文献
932.
针对地球静止轨道(GEO)卫星全天时全天候高精度的监测需求,考虑传统甚长基线干涉(VLBI)测站高成本、高投入和GEO卫星专用观测时段有限等制约条件,研发了简易型VLBI观测系统,并组建了包括上海、都匀和乌鲁木齐三站的微型VLBI网(micro VLBI network,MVN),开展了并置站测试以及对GEO卫星亚太6C的连续监测,并评估了当前MVN的观测能力。结果表明MVN扣除系统差后的单站接收精度为2ns,各基线观测时延拟后残差约几纳秒,GEO目标实测位置精度为百米级(内外符精度分别约100m和400m)。不同于传统VLBI和其他GEO监测手段,MVN还具备全天时、全天候、低造价、易布设及易推广等特点,充分表明了其在GEO卫星监测领域的应用价值。 相似文献
933.
Ningbo Wang Zishen Li Yunbin Yuan Min Li Xingliang Huo Chao Yuan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(2):886-896
We proposed an ionospheric correction approach called NKlob to mitigate the ionospheric delay errors. NKlob is a modification of the original GPS Ionospheric Correction Algorithm (ICA), which uses an empirical night-time model depending on the time, geomagnetic location and periodicities of the ionospheric behavior to replace the night-time constant delay in GPS ICA. Performance of NKlob was evaluated by the independent total electron contents (TECs) derived from Global Ionospheric Maps (GIMs) of the International GNSS Services (IGS) and Jason-2 altimetry satellite during 2013–2017. Compared to GIM TECs, NKlob corrects 51.5% of the ionospheric delay errors, which outperforms GPS ICA by 6.3%. Compared to Jason-2 TECs, NKlob mitigates the ionospheric errors by 58.1%, which is approximately 3.7% better than that of GPS ICA. NKlob shows significant improvement in low-latitude and equatorial regions with respect to GPS ICA, meanwhile exhibiting comparable performance at middle and high latitudes. Since NKlob only requires slight technical changes at the processing level of GPS receivers, we suppose that it can be easily implemented for better ionospheric delay corrections of real-time GPS single-frequency applications. 相似文献
934.
连线端站干涉测量(connected element interferometry,CEI)是高精度测角技术,在中高轨卫星、月球及深空航天器定轨定位中有良好的应用前景。基于CEI技术特点,提出了一种新的测量方法,即在相干测距模式下利用测距音和载波信号作为信号源进行连线端站干涉测量。构建了CEI试验系统对北斗GEO卫星进行观测,利用相干测距模式下的下行信号解算群时延、相时延。利用北斗GEO卫星精密星历计算的时延理论值,对北斗GEO卫星CEI群时延和相时延结果进行评估。结果表明,相干测距模式下CEI群时延和相时延残差均值分别为0.47ns、0.08ns,标准差(3σ)分别4.2ns、0.13ns。该项研究验证了相干测距模式下CEI相时延解算的可行性,可为共位地球同步卫星精密相对定位、月球探测器CEI测量提供技术参考。 相似文献
935.
In this paper, the attitude control algorithm of flexible spacecraft with unknown measurement delay and input delay based on disturbance observer is designed. The influence of measurement delay and input delay on the attitude control system and disturbance observer is analyzed. The disturbance estimation error equation is transformed into a differential system with a pure delay. Then, the observer gain is chosen based on the 3/2 stability theorem to ensure the stability and disturbance attenuation performance of the pure delay system. Next, the controller gain is designed based on the Linear Matrix Inequality(LMI) approach to guarantee the stability of the composite system and achieve H_∞ performance with two additive delays. The simulation results show that the proposed method can improve the anti-disturbance ability of the attitude control system. 相似文献
936.
为了满足飞行器协同飞行任务需求,本文研究了带有时间约束的再入滑翔轨迹设计方法。首先,建立了合理假设条件下的再入滑翔运动模型,并且提出了一种再入滑翔轨迹分段方法。其次,针对不同飞行段特点及任务需求,分别设计了各段导引律。其中,重点推导了滑翔段飞行剩余时间和剩余航程的解析解,将剩余飞行时间与末制导交班点速度建立对应关系,运用解析预测-校正思想,通过在时间调整段和能量调整段调节倾侧角翻转时机和幅值,同时满足末端能量和时间约束。最后,通过理论分析与仿真校验说明了本方法的有效性及鲁棒性。 相似文献
937.
《中国航空学报》2020,33(3):990-1005
Cooperative guidance strategy for multiple hypersonic gliding vehicles system with flight constraints and cooperative constraints is investigated. This paper mainly cares about the coordination of the entry glide flight phase and driving-down phase. Different from the existing results, both the attack time and the attack angle constraints are considered simultaneously. Firstly, for the entry glide flight phase, a two-stage method is proposed to achieve the rapid cooperative trajectories planning, where the control signal corridors are designed based on the quasi-equilibrium gliding conditions. In the first stage, the bank angle curve is optimized to achieve the attack angle coordination. In the second stage, the angle of attack curve is optimized to achieve the attack time coordination. The optimized parameters can be obtained by the secant method. Secondly, for the driving-down phase, the cooperative terminal guidance law is designed where the terminal attack time and attack angle are considered. The guidance law is then transformed into the bank angle and angle of attack commands. The cooperative guidance strategy is summarized as an algorithm. Finally, a numerical simulation example with three hypersonic gliding vehicles is provided for revealing the effectiveness of the acquired strategy and algorithm. 相似文献
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