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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
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《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
604.
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
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深空探测领域对实时性要求较高,在较短时间内找到规划解是深空探测自主任务规划中的一个要求,运用启发式规划算法是达到该要求的方法之一。而深空探测自主任务规划的另外一个特点是需要处理持续动作和数值信息。针对深空探测任务特点,采用规划领域定义语言PDDL,建立深空探测领域中知识模型,描述操作中遇到的时间与资源约束;随后应用以条件数为代价的启发式搜索方法对深空探测规划问题进行求解,并将其与TFD规划器中以动作时间为代价的上下文增强累加启发式搜索方法得到的结果进行对比,得出以条件数为代价的启发式搜索方法在搜索速度方面效果更佳,满足深空探测自主规划任务实时性要求。 相似文献
609.
表层采样技术是获取地外天体土壤样品的重要手段,为在月表复杂地形、不确定着陆姿态、不规则器表包络约束下,快速获取安全的表层采样动态轨迹,文章根据四自由度表层采样装置设计,分析了工作过程中的正逆运动学关系;根据表层采样装置动、静态目标点运动要求,将约束空间分解为有效障碍检测区与不可达集,进行表层采样避障规划;为加快规划速度,针对表层采样装置瞬态构型构建了动态障碍检测区、动态不可达集;结合人工势场法提出了避障规划算法。对典型姿态下表层采样过程的避障规划仿真表明,该算法可实现约束条件下的表层采样轨迹规划,并对表层采样装置适应性设计提供支持。 相似文献
610.
开展深空探测对人类研究宇宙起源与发展、生命存在与进化等重大科学问题具有重要的意义。深空探测有很多关键技术有待突破,先进推进技术是其中最为重要的一个。而可用于深空探测的无需携带推进剂的磁动力推进技术,是利用太阳系和宇宙中广泛存在的等离子体流,使探测器所携带的低密度超导材料制作的线圈通电,在探测器周围形成一个磁场区域,通过该磁场与太阳风等离子流相互作用产生推动力的一种先进技术。文章介绍了磁动力技术的国内外发展现状、磁帆与等离子体流增强型磁帆的基本原理、技术特点以及在未来深空探测中的潜在应用,为我国未来深空探测任务的工程实施提供一种新的方法。 相似文献