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611.
基于地球敏感器和加速度计的月球车自主定向算法研究 总被引:4,自引:0,他引:4
月球车定向是月球车导航的一个重要组成部分,它是月球车定位的基础和前提。针对这一问题,提出了一种适用于月球车长时间、长距离导航的绝对定向算法。该算法利用非线性最小二乘平差原理对CCD地球敏感器成像进行处理,实现了在月球表面CCD地球敏感器的矢量观测功能。结合加速度计的测角原理,实现了航向角确定。以理论分析和实际推算描述了该定向方法的具体实现过程,最后以仿真结果验证了该方案的可行性,为未来我国月球探测中月球车的实际应用提供了技术参考。 相似文献
612.
探讨了地月系统、地日系统,并在此基础上提出了"地月日大系统"的研究思路。将地、月、日三者关联起来,从系统的角度和多时空尺度研究地、月、日三者之间的内在关联和相互影响,从中找出未来空间探索的主题和科学研究的目标,同时还要围绕这一主题和目标,用系统、整体、历史的观点筹划未来空间活动的开展。 相似文献
613.
张丹 《长沙航空职业技术学院学报》2003,3(4):61-63
人力资源管理的核心问题是员工积极性的调动,即激励管理,对激励本质的认识和理解决定了人力资源管理的基本前提和理论框架,本文围绕激励的内涵试图从不同学科的角度提示其本质特征。 相似文献
614.
D. V. Kartashov O. B. Shchuko R. Orosei 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(12):2263-2269
The structure of the pulse radar signal reflected from continuously changing layered Martian crust is investigated theoretically. As a simple model of stratigraphy, we considered one layer with electrodynamics’ parameters increasing or decreasing exponentially upon a depth laying on monolith base and covered by homogeneous layer. This exponential changing of electromagnetic properties of the layer is assumed due to exponential changing of porosity (or saturation) in the bedrocks with pores filled by seawater. The conditions of subsurface features resolution are obtained. It is shown that the sign and value for gradient of the electromagnetic properties change can be resolved from the reflection peaks trend. These results are important for subsurface detection of liquid water on Mars by orbit-based radars. 相似文献
615.
《Acta Astronautica》2014,93(2):407-416
This paper discusses a landing response control system based on the momentum exchange principle for planetary exploration spacecraft. In the past, landing gear systems with cantilever designs that incorporate honeycomb materials to dissipate shock energy through plastic deformation have been used, but once tested before launch, the system cannot be used in a real mission. The sky crane system used for the Mars Science Laboratory by NASA can achieve a safe and precise landing, but it is highly complex. This paper introduces a momentum exchange impact damper (MEID) that absorbs the controlled object׳s momentum with extra masses called damper masses. The MEID is reusable, which makes it easy to ensure the landing gear׳s reliability. In this system, only passive elements such as springs are needed. A single-axis (SA) model has already been used to verify the effectiveness of MEIDs through simulations and experiments measuring the rebound height of the spacecraft. However, the SA model cannot address the rotational motion and tipping of the spacecraft. This paper presents a two-landing-gear-system (TLGS) model in which multiple MEIDs are equipped for two-dimensional analysis. Unlike in the authors׳ previous studies, in this study each MEID is launched when the corresponding landing gear lands and the MEIDs do not contain active actuators. This mechanism can be used to realize advanced control specifications, and it is simply compared with previous mechanisms including actuators, in which all of the MEIDs are launched simultaneously. If each MEID works when the corresponding gear lands, the rebound height of each gear can be minimized, and tipping can be prevented, as demonstrated by the results of our simulations. 相似文献
616.
R.M. Wheeler C.L. Mackowiak G.W. Stutte N.C. Yorio L.M. Ruffe J.C. Sager R.P. Prince W.M. Knott 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):706-713
NASA’s Biomass Production Chamber (BPC) at Kennedy Space Center was decommissioned in 1998, but several crop tests were conducted that have not been reported in the open literature. These include several monoculture studies with wheat, soybean, potato, lettuce, and tomato. For all of these studies, either 10 or 20 m2 of plants were grown in an atmospherically closed chamber (113 m3 vol.) using a hydroponic nutrient film technique along with elevated CO2 (1000 or 1200 μmol mol−1). Canopy light (PAR) levels ranged from 17 to 85 mol m−2 d−1 depending on the species and photoperiod. Total biomass (DM) productivities reached 39.6 g m−2 d−1 for wheat, 27.2 g m−2 d−1 for potato, 19.6 g m−2 d−1 for tomato, 15.7 g m−2 d−1 for soybean, and 7.7 g m−2 d−1 for lettuce. Edible biomass (DM) productivities reached 18.4 g m−2 d−1 for potato, 11.3 g m−2 d−1 for wheat, 9.8 g m−2 d−1 for tomato, 7.1 g m−2 d−1 for lettuce, and 6.0 g m−2 d−1 for soybean. The corresponding radiation (light) use efficiencies for total biomass were 0.64 g mol−1 PAR for potato, 0.59 g DM mol−1 for wheat, 0.51 g mol−1 for tomato, 0.46 g mol−1 for lettuce, and 0.43 g mol−1 for soybean. Radiation use efficiencies for edible biomass were 0.44 g mol−1 for potato, 0.42 g mol−1 for lettuce, 0.25 g mol−1 for tomato, 0.17 g DM mol−1 for wheat, and 0.16 g mol−1 for soybean. By initially growing seedlings at a dense spacing and then transplanting them to the final production area could have saved about 12 d in each production cycle, and hence improved edible biomass productivities and radiation use efficiencies by 66% for lettuce (to 11.8 g m−2 d−1 and 0.70 g mol−1), 16% for tomato (to 11.4 g m−2 d−1and 0.29 g mol−1), 13% for soybean (to 6.9 g m−2 d−1 and 0.19 g mol−1), and 13% for potato (to 20.8 g m−2 d−1 and 0.50 g mol−1). Since wheat was grown at higher densities, transplanting seedlings would not have improved yields. Tests with wheat resulted in a relatively low harvest index of 29%, which may have been caused by ethylene or other organic volatile compounds (VOCs) accumulating in the chamber. Assuming a higher harvest index of 40% could be achieved by scrubbing VOCs, productivity of wheat seed could have been improved nearly 40% to 15.8 g m−2 d−1 and edible biomass radiation use efficiency to 0.30 g mol−1. 相似文献
617.
618.
Dynamics in the Phobos environment 总被引:2,自引:1,他引:1
D.J. Scheeres S. Van wal Z. Olikara N. Baresi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):476-495
The dynamical environment on and about the Martian moon Phobos is explored. This planetary moon provides a unique dynamical environment in the solar system, being subject to extreme tidal forces and having a characteristically non-spherical shape. Further, it is not in a fully circular orbit, meaning that it has librations that arise from its eccentricity, contributing to a periodic forcing environment. Thus, to plan and implement missions in the vicinity of and on Phobos will require these considerations be taken into account. In this paper the latest published models of the Phobos shape and dynamics are used to characterize its dynamical environment in close proximity orbit about the body, for motion across its surface and for controlled hovering motion in its vicinity. It is found that surface motion is subject to a number of “speed limits” that can cause a moving vehicle to leave the surface and to possibly escape the moon and enter orbit about Mars. In terms of orbital stability, the existence of libration orbit families are characterized down to the surface using an exact potential, and the known stable QSO orbits are shown to be associated with families of stable quasi-periodic orbits. 相似文献
619.
620.
In this paper,technological progress for China's microwave remote sensing is intro-duced.New developments of the microwave remote sensing instruments for meteorological satellite FY-3,ocean dynamic measurement satellite(HY-2),environment small SAR satellite(HJ-1C) and China's lunar exploration satellite(Chang'E-1),geostationary orbit meteorological satellite FY-4M,are reported. 相似文献