Long term dynamics and optimal control of nano-satellite deorbit using a short electrodynamic tether

This paper studies the long term dynamics and optimal control of a nano-satellite deorbit by a short electrodynamic tether. The long term deorbit process is discretized into intervals and within each interval a two-phase optimal control law is proposed to achieve libration stability and fast deorbit simultaneously. The first-phase formulates an open-loop fast-deorbit control trajectory by a simplified model that assumes the slow-varying orbital elements of electrodynamic tethered system as constant and ignores perturbation forces other than the electrodynamic force. The second phase tracks the optimal trajectory derived in the first phase by a finite receding horizon control method while considering a full dynamic model of electrodynamic tether system. Both optimal control problems are solved by direct collocation method base on the Hermite–Simpson discretization schemes with coincident nodes. The resulting piecewise nonlinear programing problems in the sequential intervals reduces the problem size and improve the computational efficiency, which enable an on-orbit control application. Numerical results for deorbit control of a short electrodynamic tethered nano-satellite system in both equatorial and highly inclined orbits demonstrate the efficiency of the proposed control method. An optimal balance between the libration stability and a fast deorbit of satellite with minimum control efforts is achieved.     

快速成形技术概述及当前研究热点

介绍了快速成形技术的特点、应用范围、存在的问题和研究热点,综述了软件处理方法、应用领域扩充、新工艺探索以及反求和快速成形一体化技术。     

Project Galileo: completing Europa, preparing for Io.

Galileo has completed the Europa leg of the Galileo Europa Mission, and is now pumping down the apojove in each succeeding orbit in preparation for the Io phase. Including three encounters earlier in the primary mission, the total of ten close passes by Europa have provided a wealth of interesting and provocative information about this intriguing body. The results presented include new and exciting information about Europa's interactions with Jupiter's magnetosphere, its interior structure, and its tantalizing surface features, which strongly hint at a watery subsurface layer. Additional data concerning Callisto, and its own outlook for a subsurface ocean are also presented. In addition the engineering aspects of operating the spacecraft during the past year are explored, as well as a brief examination of what will be the challenges to prepare for the Io encounters. The steadily increasing radiation dosage that the spacecraft is experiencing is well beyond the original design parameters, and is contributing to a number of spacecraft problems and concerns. The ability of the flight team to analyze and solve these problems, even at the reduced staffing levels of an extended mission, is a testament to their tenacity and loyalty to the mission. The engineering data being generated by these continuing radiation-induced anomalies will prove invaluable to designers of future spacecraft to Jupiter and its satellites. The lessons learned during this arduous process are presented.     

Signal Processors and Accuracy of Three-Beam Monopulse Tracking Radar

The problem of implementing a monopulse tracking radar is considered when three beams are used rather than the customary four. Signal processors are developed for both amplitude and phase comparison radar cases and the functional form is given for the general case (a combination or hybrid case). Accuracy is investigated by applying the Cramer-Rao inequality. General results are given for the maximum theoretical accuracy of estimating target amplitude, phase, and position angles when the radar is of the amplitude comparison type. Equations sufficient for obtaining accuracies in the phase comparison and combination cases are included.     

资源一号卫星X波段IR—MSS数传天线

一种北射双线螺旋天线在中巴合作研制的地球资源卫星上首次用作x波段IR－MSS（红外遥感）数传天线，替代了国际上惯用的赋形反射面天线。飞行试验表明，天线在轨工作正常，具有与赋形反射面天线相当的性能与功能。本文简要地介绍了该天线的设计和性能。     

导弹垂直发射装置对燃气流压强周期性振荡的响应

本文对舰载导弹垂直发射装置中的燃气流周期性振荡特性进行了分析与实验测量，对装置产生的响应特性也进行了实验研究和有限元分析。实验测量结果与理论计算在规律上有定性的一致     

先进复合材料制造成本分析技术

低成本复合材料技术是复合材料发展研究领域的一个核心问题,建立成本估算模型是定量评价复合材料制造工艺成本的基础和降低复合材料制造工艺成本的重要技术手段.本文对国内外先进复合材料制造成本估算模型的现状进行了总结,研究开发以复合材料制造工艺时间的理论估算方法建立了以一阶速度动力学为基础的基于工艺的估算模型,给出模型中参数的确定方法.     

An endogenous growth pattern of roots is revealed in seedlings grown in microgravity

In plants, sensitive and selective mechanisms have evolved to perceive and respond to light and gravity. We investigated the effects of microgravity on the growth and development of Arabidopsis thaliana (ecotype Landsberg) in a spaceflight experiment. These studies were performed with the Biological Research in Canisters (BRIC) hardware system in the middeck region of the space shuttle during mission STS-131 in April 2010. Seedlings were grown on nutrient agar in Petri dishes in BRIC hardware under dark conditions and then fixed in flight with paraformaldehyde, glutaraldehyde, or RNAlater. Although the long-term objective was to study the role of the actin cytoskeleton in gravity perception, in this article we focus on the analysis of morphology of seedlings that developed in microgravity. While previous spaceflight studies noted deleterious morphological effects due to the accumulation of ethylene gas, no such effects were observed in seedlings grown with the BRIC system. Seed germination was 89% in the spaceflight experiment and 91% in the ground control, and seedlings grew equally well in both conditions. However, roots of space-grown seedlings exhibited a significant difference (compared to the ground controls) in overall growth patterns in that they skewed to one direction. In addition, a greater number of adventitious roots formed from the axis of the hypocotyls in the flight-grown plants. Our hypothesis is that an endogenous response in plants causes the roots to skew and that this default growth response is largely masked by the normal 1?g conditions on Earth.     

Graviresponses of osteocytes under altered gravity

Single cell was capable of sensing and responding to alterations of gravity. Osteocytes, as the most abundant cells of the bone tissue playing an important role in the bone mechanotransduction, are very sensitive to mechanical stimuli. However, the effect of altered gravity on osteocytes so far is less known according to the public papers. Further study on this issue will help to verify and develop the theory of how cells perceive and respond to gravity. It also brings new ideas to the study of space bone loss. In our study, Osteocyte-like MLO-Y4 cells were exposed to 30 parabolic flights three times on ZERO-G airbus A300 to investigate the comprehensive effect on osteocytes stimulated by hyper- and hypo-gravity forces. It showed that the cell morphology, as well as cell area and height, was not changed significantly by hyper-gravity and hypo-gravity. However, the cytoskeleton was reorganized. In flight cells, F-actin polymerization was enhanced at the cell periphery and microtubule organizing center disappeared, but no apoptotic feathers were detected. The results of western blot showed that connexin 43 (Cx43) expression was down-regulated, indicating an decrease of gap-junction. In conclusion, hyper- and hypo-gravity stimulation altered the cytoskeleton architecture and suppressed gap-junction of osteocyte-like MLO-Y4 cells.     

基于Web技术的设备管理信息系统

设备管理信息系统(PMIS)是为企业现代化工作提供的一个先进实用的软件，而Web技术又是全球化电子信息共享的基础。基于Web技术的PMIS充分利用洪都航空工业集团公司内部网络资源，实现设备管理的网络化。这就可以在企业内部增强信息的沟通，提高信息的质量和快速反应能力，从而树立起企业形象。