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1.
Yongliao Zou Yan Zhu Yunfei Bai Lianguo Wang Yingzhuo Jia Weihua Shen Yu Fan Yang Liu Chi Wang Aibing Zhang Guobin Yu Jihong Dong Rong Shu Zhiping He Tielong Zhang Aimin Du Mingyi Fan Jianfeng Yang Yongqing Peng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):812-823
This paper describes the scientific objectives and payloads of Tianwen-1, China’s first exploration mission to Mars. An orbiter, carrying a lander and a rover, lifted-off in July 2020 for a journey to Mars where it should arrive in February 2021. A suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of Mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. The mission will also investigate Mars climate history. It is expected that Tianwen-1 will contribute significantly to advance our scientific knowledge of Mars. 相似文献
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Shi Qian Liu James F. Whidborne Lei He 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(3):1174-1187
In the presence of unknown disturbances and model parameter uncertainties, this paper develop a nonlinear backstepping sliding-mode controller (BSMC) for trajectory tracking control of a stratospheric airship using a disturbance-observer (DO). Compared with the conventional sliding mode surface (SMS) constructed by a linear combination of the errors, the new SMS manifold is selected as the last back-step error to improve independence of the adjustment of the controller gains. Furthermore, a nonlinear disturbance-observer is designed to process unknown disturbance inputs and improve the BSMC performances. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and SMC design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission, even in the presence of unknown disturbances, and aerodynamic coefficient uncertainties. 相似文献
4.
为解决在实际航天任务中利用连线干涉测量(CEI)技术进行高精度GEO卫星定轨以及共位GEO卫星相对定位时面临的载波相位整周模糊度难题,提出了一种基于卫星下行信号的多弧段融合相位模糊度解算方法,它通过相邻多弧段载波相位值和窄带信号群时延值的融合处理可精确获得无模糊载波相时延观测量。对提出的方法进行了性能仿真和实际外场试验验证,结果表明:在20 km基线上,利用北斗GEO卫星的伪码测距信号和天链卫星的测控信号均成功实现了S频段解载波整周相位模糊,相时延测量精度优于0.1ns,对应GEO卫星定轨精度优于54 m。该方法在国内首次实现了在几十km基线量级上利用几百kHz窄带测控信号获得无模糊载波相时延,具有较好的工程应用前景。 相似文献
6.
针对翼型后缘连续变弯度运动中后缘边界精确数值模拟的问题,提出了基于二维多项式的时空曲面拟合方法,实现了对后缘边界时空位置的精确模拟。在此基础上,基于OpenFOAM发展了翼型后缘连续变弯度与大幅度俯仰运动耦合的运动边界数值模拟,并计算了翼型耦合运动的气动力,讨论了后缘线性/非线性变形对翼型大迎角动态气动特性的影响规律。结果表明:后缘运动对翼型俯仰运动的升阻特性影响显著,特别在翼型大幅度俯仰时后缘非线性变形对升阻特性改善效果比线性变形大6%~10%。同时还研究了翼型俯仰与后缘变形运动相位差对气动特性的影响。特别地,当相位差为180°时,后缘运动使动态失速时的最大升力提高50.3%,平均升力提高34.6%;当2种运动相位差为0°时,后缘运动使动态失速时的最大阻力降低39.7%,平均阻力降低30.2%,最大升阻比提高22.3%,平均升阻比提高16.8%;同时,翼型在动态俯仰过程中出现负阻力现象,对产生负阻力的原因进行了分析。这些结果可用于指导连续变弯度后缘控制律的设计。 相似文献
7.
针对椭圆轨道卫星近/远地点的星下点对全球或特定纬度区域的访问问题,提出一种连续小推力下的对地覆盖控制策略。首先,推导了自然摄动对卫星拱线变化的影响,并探讨了进行小推力覆盖控制的必要性。然后,针对燃料消耗的优化问题,将控制方程展开成含傅里叶级数的形式,用以获得便于星上计算的解析形式的次优解,同时探讨了截取阶数与优化程度的关系。在进行拱线控制的同时,通过合理设置约束,对椭圆轨道的近地点高度进行保护,确保卫星安全运行。仿真结果表明,提出的方法能够以适当的燃料消耗代价实现椭圆轨道的近/远地点的全球覆盖控制或特定纬度区域的反复推扫,且控制力在可接受的范围内。 相似文献
8.
Palanisamy Shanmugam Xianqiang He Rakesh Kumar Singh Theenathayalan Varunan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(10):2491-2509
The chlorophyll concentration of a water body is an important proxy for representing the phytoplankton biomass. Its estimation from multi or hyper-spectral remote sensing data in natural waters is generally achieved by using (i) the waveband ratioing in two or more bands in the blue-green or (ii) by using a combination of the radiance peak position and magnitude in the red-near-infrared (NIR) spectrum. The blue-green ratio algorithms have been extensively used with satellite ocean color data to investigate chlorophyll distributions in open ocean and clear waters and the application of red-NIR algorithms is often restricted to turbid productive water bodies. These issues present the greatest obstacles to our ability to formulate a modern robust method suitable for quantitative assessments of the chlorophyll concentration in a diverse range of water types. The present study is focused to investigate the normalized water-leaving radiance spectra in the visible and NIR region and propose a robust algorithm (Generalized ABI, GABI algorithm) for chlorophyll concentration retrieval based on Algal Bloom index (ABI) which separates phytoplankton signals from other constituents in the water column. The GABI algorithm is validated using independent in-situ data from various regional to global waters and its performance is further evaluated by comparison with the blue-green waveband ratios and red-NIR algorithms. The results revealed that GABI yields significantly more accurate chlorophyll concentrations (with uncertainties less than 13.5%) and remains more stable in different waters types when compared with the blue-green waveband ratios and red-NIR algorithms. The performance of GABI is further demonstrated using HICO images from nearshore turbid productive waters and MERIS and MODIS-Aqua images from coastal and offshore waters of the Arabian Sea, Bay of Bengal and East China Sea. 相似文献
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10.
在中国空气动力研究与发展中心(CARDC)超高速碰撞中心(HIRC)7.6 mm超高速碰撞设备的基础上,搭建纳秒级脉冲激光数字全息系统。提出滤波片和衰减片组合布置,减弱超高速碰撞等离子体自发光、提高信噪比的方法。实验获得了2.25 mm铝球弹丸以4.0 km/s的速度撞击0.5 mm厚铝板形成碎片云的全息图。采用小波变换算法对碎片云全息图进行重建,得到超高速撞击碎片云的三维结构和碎片大小。碎片云的轮廓呈椭球型,分为碎片云的前端、核心和外壳,碎片主要分布在弹丸破碎形成的碎片云核心,存在大碎片,且分布较集中,对后板的损伤也严重 相似文献