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Vaios Lappas Nasir Adeli Lourens Visagie Juan Fernandez Theodoros Theodorou Willem Steyn Matthew Perren 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
CubeSail is a nano-solar sail mission based on the 3U CubeSat standard, which is currently being designed and built at the Surrey Space Centre, University of Surrey. CubeSail will have a total mass of around 3 kg and will deploy a 5 × 5 m sail in low Earth orbit. The primary aim of the mission is to demonstrate the concept of solar sailing and end-of-life de-orbiting using the sail membrane as a drag-sail. The spacecraft will have a compact 3-axis stabilised attitude control system, which uses three magnetic torquers aligned with the spacecraft principle axis as well as a novel two-dimensional translation stage separating the spacecraft bus from the sail. CubeSail’s deployment mechanism consists of four novel booms and four-quadrant sail membranes. The proposed booms are made from tape-spring blades and will deploy the sail membrane from a 2U CubeSat standard structure. This paper presents a systems level overview of the CubeSat mission, focusing on the mission orbit and de-orbiting, in addition to the deployment, attitude control and the satellite bus. 相似文献
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采用一种具有广义内模控制结构的反馈控制器,研究一类线性时滞系统的主动容错H∞控制问题。针对可由外系统描述其动态行为的故障,设计基于观测器的故障估计器,并将故障估计用于反馈控制的故障补偿。采用一种新的时滞分解方法选取Lyapunov-Krasovskii泛函,推导并证明问题可解的充分条件,最后给出主动容错控制系统的设计算法。最后通过算例验证了提出方法的有效性,并且利用时滞分解方法,保守性减小。 相似文献
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考虑复杂社会技术系统的特点,运用自适应神经模糊推理模型对提高公益科研机构的组织效率进行了实例研究。建立了针对公益科研机构员工激励决策的自适应模糊推理完整模型,利用调研数据及其处理结果验证了模型的有效性。该模型融合了神经网络的学习机制和模糊系统的语言推理能力,弥补了神经网络和模糊逻辑系统各自的不足。研究结果表明,自适应神经模糊推理模型适用于复杂社会技术系统,在解决管理领域的预测、评估和决策问题中有广阔的应用前景。 相似文献
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针对航天控制产品精密复杂零件的工艺难点,以该类零件的工艺设计过程为主线,分别论述了材料定额编制、工艺路线设计以及工序设计过程中的注意事项和工艺方案设计方法,并以实例进行了简要说明。 相似文献
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Periodic relative orbits of two spacecraft subject to differential gravity and electrostatic forcing
Coulomb forces between charged close-flying satellites can be used for formation control, and constant electric potentials enable static equilibria solutions. In this work, open-loop time-varying potential functions, which produce periodic, two-craft, Coulomb formation motions are demonstrated for the first time. This is done in the rotating Hill-Frame, with linearized gravity, and craft position components assumed in the form of simple harmonic oscillators. Substitution of the oscillatory functions into the dynamics, further constrains these functions, and yields necessary potential histories, to produce the periodic flow. The assumed position functions, however, are not arbitrary, since the dynamical model restricts what oscillatory trajectories are allowed. Specifically, a Hill-Frame integral of motion is derived, and this is used to show certain candidate periodic functions to be inadmissible. The system dynamics are then linearized to expose stability properties of the solutions, and it is established that asymptotic stability is impossible for all orbit families. Finally, the degree of instability in the assumed motions, over free parameter ranges, is determined numerically via the Floquet multipliers of the associated full-cycle state-transition matrices. 相似文献
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Remote sensing scientists work under assumptions that should not be taken for granted and should, therefore, be challenged. These assumptions include the following:1. Space, especially Low Earth Orbit (LEO), will always be available to governmental and commercial space entities that launch Earth remote sensing missions.2. Space launches are benign with respect to environmental impacts.3. Minimization of Type 1 error, which provides increased confidence in the experimental outcome, is the best way to assess the significance of environmental change.4. Large-area remote sensing investigations, i.e. national, continental, global studies, are best done from space.5. National space missions should trump international, cooperative space missions to ensure national control and distribution of the data products.At best, all of these points are arguable, and in some cases, they're wrong. Development of observational space systems that are compatible with sustainability principles should be a primary concern when Earth remote sensing space systems are envisioned, designed, and launched. The discussion is based on the hypothesis that reducing the environmental impacts of the data acquisition step, which is at the very beginning of the information stream leading to decision and action, will enhance coherence in the information stream and strengthen the capacity of measurement processes to meet their stated functional goal, i.e. sustainable management of Earth resources. We suggest that unconventional points of view should be adopted and when appropriate, remedial measures considered that could help to reduce the environmental footprint of space remote sensing and of Earth observation and monitoring systems in general. This article discusses these five assumptions in the context of sustainable management of Earth's resources. Taking each assumption in turn, we find the following:(1) Space debris may limit access to Low Earth Orbit over the next decades.(2) Relatively speaking, given that they're rare event, space launches may be benign, but study is merited on upper stratospheric and exospheric layers given the chemical activity associated with rocket combustion by-products.(3) Minimization of Type II error should be considered in situations where minimization of Type I error greatly hampers or precludes our ability to correct the environmental condition being studied.(4) In certain situations, airborne collects may be less expensive and more environmentally benign, and comparative studies should be done to determine which path is wisest.(5) International cooperation and data sharing will reduce instrument and launch costs and mission redundancy. Given fiscal concerns of most of the major space agencies – e.g. NASA, ESA, CNES – it seems prudent to combine resources. 相似文献
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文章针对无星际链路的低轨卫星通信系统,利用OPNET软件设计了低轨卫星通信系统在透明转发模式下的核心网构成,并进行了性能仿真。首先介绍核心网的构成、功能和拓扑,在此基础上实现了呼叫处理和切换的仿真,统计了呼叫时延、切换时延等性能指标,分析了仿真结果,为低轨道卫星通信系统的设计奠定了一定的参考价值。 相似文献
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