Adaptation of neuromuscular activation patterns during treadmill walking after long-duration space flight

The precise neuromuscular control needed for optimal locomotion, particularly around heel strike and toe off, is known to he compromised after short duration (8- to 15-day) space flight. We hypothesized here that longer exposure to weightlessness would result in maladaptive neuromuscular activation during postflight treadmill walking. We also hypothesized that space flight would affect the ability of the sensory-motor control system to generate adaptive neuromuscular activation patterns in response to changes in visual target distance during postflight treadmill walking. Seven crewmembers, who completed 3- to 6-month missions, walked on a motorized treadmill while visually fixating on a target placed 30 cm (NEAR) or 2 m (FAR) from the subject's eyes. Electronic foot switch data and surface electromyography were collected from selected muscles of the right lower limb. Results indicate that the phasic features of neuromuscular activation were moderately affected and the relative amplitude of activity in the tibialis anterior and rectus femoris around toe off changed after space flight. Changes also were evident after space flight in how these muscles adapted to the shift in visual target distance.     

核火箭原理、发展及应用

人类在不懈地对浩瀚的宇宙进行着探索,而强劲的推力是人类探索宇宙的关键。化学火箭在人类宇宙探索活动中书写了一页又一页的华丽篇章,现今在人类新的探索使命下,出现了激光、太阳能、微波、核热能等新的推进技术。在这些技术中,核火箭推进无疑是人类继续探索太空最有希望的技术之一。对核火箭的原理、发展状况以及应用前景进行了介绍。     

Strategy for capturing of a tumbling space debris

In general space debris objects do not possess much convenient features and are non-cooperative. In such cases, since the conditions for capture are not favorable, tracking errors will lead to loading, and momentum transfer will occur during the capture process.In most cases, detailed mass and inertial characteristics of the target are unknown, either because design details are unavailable or due to changes as a result of damage sustained when failure occurred or gradual degradation over the years, and this makes impedance matching of the capture arm force control system difficult.This led to us to devise a “joint virtual depth control” algorithm for robot arm control, which brakes the rotation of a target with unknown inertia. This paper deals with a removal work strategy and control method for capturing and braking a tumbling, non-cooperative target space debris.We propose a new brush type contactor as end-effecter of a robot arm for reducing the rotational rate of the target debris. As a means for relieving the loads generated during target tapping, in addition to joint compliance control we propose a new control method that controls the arm tip force according to a contact force profile.     

追踪星跟踪空间非合作目标的相对轨道设计

对空间非合作目标跟踪飞行可以执行观测或监视等任务。首先从一般性出发对追踪星与非合作目标之间的椭圆轨道相对运动方程进行分析,给出具有任意初始条件的相对运动方程解析表达式。其次,对追踪星沿航向跟踪目标并考虑约束条件时的相对轨道设计进行分析后,给出设计追踪星轨道的方法,该方法使得追踪星在保持对地定向的同时也满足测量敏感器的约束条件。最后通过数学仿真进行了验证。     

Space radiation analysis: Radiation effects and particle interaction outside the Earth's magnetosphere using GRAS and GEANT4

In order to explore the Moon and Mars it is necessary to investigate the hazards due to the space environment and especially ionizing radiation. According to previous papers, much information has been presented in radiation analysis inside the Earth's magnetosphere, but much of this work was not directly relevant to the interplanetary medium. This work intends to explore the effect of radiation on humans inside structures such as the ISS and provide a detailed analysis of galactic cosmic rays (GCRs) and solar proton events (SPEs) using SPENVIS (Space Environment Effects and Information System) and CREME96 data files for particle flux outside the Earth's magnetosphere. The simulation was conducted using GRAS, a European Space Agency (ESA) software based on GEANT4. Dose and equivalent dose have been calculated as well as secondary particle effects and GCR energy spectrum. The calculated total dose effects and equivalent dose indicate the risk and effects that space radiation could have on the crew, these values are calculated using two different types of structures, the ISS and the TransHab modules. Final results indicate the amounts of radiation expected to be absorbed by the astronauts during long duration interplanetary flights; this denotes importance of radiation shielding and the use of proper materials to reduce the effects.     

Safety implications of unscheduled situations in the operation of tethered satellite systems from the international space station

Space based experiments involving the use of tethers were examined with a view to identifying the implications of unscheduled events such as tether severance and interference between the tether and other hardware. It is the authors opinion that these type of events, which have important consequences for the operation of tethers in space, have received insufficient consideration in the extensive literature on the subject. In particular, the investigation of the interference event appears to be completely new. The examination focussed on tether experiments planned for the forthcoming International Space Station (ISS). Results were obtained through the use of a highspeed, non-linear, computer simulation model specifically designed for use with tethered satellite systems. Simulations showed that both severance and interference were possible during retrieval of the tether, particularly if ‘skip-rope’ motion is initiated. The motion following each of these incidents is predicted and shows that these unscheduled events are potentially very hazardous for the ISS. While the results of these simulations are not directly applicable to specific operations on the ISS, they fulfill the primary purpose of this paper which is the demonstration of this new technology.     

Configuration studies for active electrostatic space radiation shielding

Developing successful and optimal solutions to mitigating the hazards of severe space radiation in deep space long duration missions is critical for the success of deep-space explorations. Space crews traveling aboard interplanetary spacecraft will be exposed to a constant flux of galactic cosmic rays (GCR), as well as intense fluxes of charged particles during solar particle events (SPEs). A recent report (Tripathi et al., Adv. Space Res. 42 (2008) 1043–1049), had explored the feasibility of using electrostatic shielding in concert with the state-of-the-art materials shielding technologies. Here we continue to extend the electrostatic shielding strategy and quantitatively examine a different configuration based on multiple toroidal rings. Our results show that SPE radiation can almost be eliminated by these electrostatic configurations. Also, penetration probabilities for novel structures such as toroidal rings are shown to be substantially reduced as compared to the simpler all-sphere geometries. More interestingly, the dimensions and aspect ratio of the toroidal rings could be altered and optimized to achieve an even higher degree of radiation protection.     

Experimental hypervelocity impacts: Implication for the analysis of material retrieved after exposure to space environment: Part I. Impacts on aluminium targets

During the last three decades a wide variety of surfaces have been brought back to Earth after being exposed to space environment. The impact features found on these surfaces are used to evaluate the damages caused to spacecraft and can give clues to the characteristics of the orbital debris and meteoroids that created them. In order to derive more precisely the particle parameters and to improve the analysis of projectile remnants, we have performed an extensive analysis of craters caused by the impact of high velocity particles on thick ductile targets, using a micro-particle accelerator. We show that from the geometry of the craters and from the analysis of the remnants it is possible to derive the main characteristics of the projectiles. In particular, using up-to-date instrumentation, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) spectrometer, we found that even small residues inside craters can be identified. However, this study shows that a velocity resolution better than 1 km/s would be appropriate to obtain a fair calibration of the impact processes on a ductile target. This would allow to decipher with precision impact features on ductile surfaces exposed to space environment.     

含共因事件航天系统的通用动态故障树方法

为了表示航天复杂系统中组件依赖关系和输入次序等动态事件与共因事件,动态故障树的求解过程通常会面临很高的计算复杂度与时间开销。基于系统定义假设,由基本事件的概率分布入手,根据动态门的时序逻辑定义和关联方式,给出系统故障事件的准确通用计算方法GDFTA (Generic Dynamic Fault Tree Algorithm)。GDFTA方法实现了通用的动态树求解,避免了Markov方法的状态空间爆炸问题,并取得了较理想的计算准确性。通过对动态树实例的可靠性评估证明该方法可行。在标准动态故障树测试集中,四类不同系统的可靠性结果精度优于Monte Carlo方法,计算效率也有显著提高。     

Malfunction of satellite navigation systems GPS and GLONASS caused by powerful radio emission of the Sun during solar flares on December 6 and 13, 2006, and October 28, 2003

Poor quality of functioning of GPS during solar flares on December 6 and 13, 2006 is analyzed in this paper. These flares were accompanied by extremely high (unexampled) level of the solar radio emission flux. A comparison is made of these events with the solar flare on October 28, 2003. Statistically reliable experimental evidence is obtained that GPS positioning was partially paralyzed on the sunlit side of the Earth during the strongest bursts of solar radio emission. The obtained results give a serious ground to revise the role played by space weather factors in operation of modern satellite systems and to take these factors into account more carefully, when such systems are designed and exploited.     

Optical methods for non-contact measurements of membranes

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes.The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements).Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles.     

Natural killer cells after ALTAIR mission

Reduced in vitro NK cytotoxic activity have routinely been observed after both prolonged and short-term space flights. This study investigated the effects of space flight on NK cell functions, NK cell counts and the production of IL-2 and TNF by lymphocytes of French-Russian crew members. In the French cosmonaut, after 21 days space flight, the cytotoxic activity of NK cells, the capacity the NK cells to bind and lyse the individual target cells and the percentage of NK cells were decreased. In this cosmonaut a twofold reduction TNF production in cultures of lymphocytes stimulated with PMA and with the mixture of PHA and PMA was observed on the first day after landing. However, the activity of the production of TNF in 48-hour PHA-cultures of lymphocytes was unchanged and the biological activity of IL-2 was not reduced. The immunological examination did not detecte any substantial deviations from the norm in both russian cosmonauts after 197 days space flight. Various explanations for decreased cytotoxicity in cosmonauts after space flight can be proposed, and these include the defective function of NK cells and reduced numbers of circulating effector cells.     

Vestibular function in the space environment

Adaptation to the weightless state and readaptation after space flight to the 1-G environment on the ground are accompanied by various transitory symptoms of vestibular instability, kinetosis, and illusory sensations. Aside from the problem of how to treat and if possible prevent such symptoms, they offer a clue to a better understanding of normal vestibular functions. Weightlessness is a powerful new "tool" of vestibular research. Graybiel reported as early as 1952 that human subjects observed the illusion that a real target and the visual afterimage seemed to raise in the visual field during centrifugation when the subjects were looking toward the axis of rotation (oculogravic illusion). In aircraft parabolic-flight weightlessness, human subjects observed that fixed real targets appeared to have moved downward while visual afterimages appeared to have moved upward (oculoagravic illusion). It can be shown by electronystagmography as well as by a method employing double afterimages that part of this illusion is caused by eye movements that are triggered by the changing input from the otolith system. Another part of the illusion is based on a change of the subjective horizontal and must be caused by convergence of vestibular and visual impulses "behind" the eyes. This part was measured independently of the first one by using a new method. Eye movements could be prevented during these experiments by optical fixation with the right eye on a target at the end of a 24-in. long tube which was rigidly attached parallel to the longitudinal axis of an aircraft. At the same time the subject tried to line up a shorter tube, which was pivoting around his left eye, with the subjective horizon.     

空间失稳目标线阵雷达成像机理及三维重建

利用线阵激光雷达载荷小、抗干扰能力强等优势,研究空间失稳目标动态测量技术。探究线阵激光雷达成像机理,建立空间失稳目标运动模型,提出基于双切片法的目标可测区域提取机制,实现线阵激光雷达对空间失稳目标的驻留观测扫描;以ICP(Iterative closest point)配准结果为先验信息,提出逆序重建方案,建立重建点云精度以及平均密度评价机制,分析数据冗余对重建精度的影响,采用采样降维的方法进行配准重建计算,提高重建结果精度;最后进行仿真实验检验分析,实验结果表明空间目标可测部位数据提取合理准确,数据输出频率可达 1 Hz ,重建结果满足任务指标要求,重建点云平均密度达到19 mm,重建点云精度达到90 mm,为地面验证及在轨应用提供数据支撑和参考。     

空间特定目标表面的双波段红外辐射特性调控方法

红外诱饵等空间特定目标是对抗红外探测的主要手段之一。随着双色制导技术的发展,红外探测灵敏度不断提升,目标识别能力不断增强,这对空间特定目标表面的双波段红外辐射的逼真性提出了要求。通过改变空间特定目标表面发射率控制其红外辐射强度的大小,使用数值仿真的方法进行计算,从而提出了对空间特定目标表面红外辐射特性的调控方法。此外根据所确定的表面发射率、可见光吸收及红外发射比例以及内热源功率,选择合适的表面材料以及热功率施加方法,在保证空间特定目标表面机械性能的同时,使空间特定目标满足光照及阴影区的双波段红外辐射特性要求,并进行模型的制作以及热真空实验,证明了理论计算的准确性。     

主导概率数据关联及算法

本文给出主导概率数据关联（ＤＰＤＡ）及算法，定义主导联合事件和主导概率，考虑实际目标环境可行联合事件出现为非等概率，导出主导概率数据关联计算方法，它无需计算所有行联合事件的联合率，从而克服了联合概率数据关联（ＪＰＤＡ）的组合问题，本文证明了ＤＰＤＡ性能上限不低于ＪＰＤＡ，下限低于ＰＤＡ，而下限出现的概率极小。本文给出了ＭｏｎｔｅＣａｒｌｏ仿真表明ＤＰＤＡ算法具有很好的性能和较高的实用价值。     

Space patrol: Variants of the optical barrier scheme

Different variants of the space patrol system to be designed for discovering and cataloging space objects hazardous for the Earth have been investigated. The basic idea of this system is to create an optical barrier using the telescopes deployed in a heliocentric orbit. Difficulties (as well as ways of overcoming them) of this program are analyzed, associated with form and position of the orbit of a space object relative to the patrol spacecraft, determination of orbit parameters, and mutual motion of space objects and the telescopes on spacecraft. The barrier’s schemes with scanning vertical or horizontal belts are considered. Some examples of observational conditions are presented for space objects crossing the barrier region: angular positions, velocities, distances, and numbers of days during which they are observed in the barrier region. The barrier’s characteristics are given for telescopes deployed in the orbits of the Earth and Venus.     

视觉导引受限下空间绳系机器人最优逼近控制

针对空间绳系机器人对目标逼近过程中单目视觉视线角约束和导航信息不全问题,首先建立空间绳系机器人系统动力学模型。然后考虑抓捕器视线角约束,采用高斯伪谱法对空间绳系机器人逼近任务姿轨轨迹进行一体规划。同时设计无需相对目标距离的闭环控制器实现对空间绳系机器人最优姿轨轨迹进行跟踪控制。仿真结果表明,该方案能够克服视觉导引受限的影响,实现空间绳系机器人对位姿最优轨迹的精确跟踪。     

Combining solar science and asteroid science with the space weather observation network (SWON)

The peculiarity of space weather for Earth orbiting satellites, air traffic and power grids on Earth and especially the financial and operational risks posed by damage due to space weather, underline the necessity of space weather observation. The importance of such observations is even more increasing due to the impending solar maximum. In recognition of this importance we propose a mission architecture for solar observation as an alternative to already published mission plans like Solar Probe (NASA) or Solar Orbiter (ESA). Based upon a Concurrent Evaluation session in the Concurrent Engineering Facility of the German Aerospace Center, we suggest using several spacecraft in an observation network. Instead of placing such spacecraft in a solar orbit, we propose landing on several asteroids, which are in opposition to Earth during the course of the mission and thus allow observation of the Sun's far side. Observation of the far side is especially advantageous as it improves the warning time with regard to solar events by about 2 weeks. Landing on Inner Earth Object (IEO) asteroids for observation of the Sun has several benefits over traditional mission architectures. Exploiting shadowing effects of the asteroids reduces thermal stress on the spacecraft, while it is possible to approach the Sun closer than with an orbiter. The closeness to the Sun improves observation quality and solar power generation, which is intended to be achieved with a solar dynamic system. Furthermore landers can execute experiments and measurements with regard to asteroid science, further increasing the scientific output of such a mission. Placing the spacecraft in a network would also benefit the communication contact times of the network and Earth. Concluding we present a first draft of a spacecraft layout, mission objectives and requirements as well as an initial mission analysis calculation.     

空间交会相对状态测定与控制

阐述航天器交会对接最终逼近段相对状态测定与控制算法。测定算法适用于计算机视觉系统,根据标志点构型几何特征,建立非线性测距方程组并构造加权目标函数。对非共面标志点构型（如3点T型与5点锥型）和共面标志点构型（如正方形、矩形、菱形）,目标函数均含标志点间距比率关系项;对共面构型,目标函数还包含共面条件项。按最小二乘法,采用Gauaa-Newton数值迭代法求解测距最佳值;对共面标志点四边形构型,利用对角线交点的虚影像坐标确定测距求解迭代初值。获得测距后即可应用四元数估算法确定相对姿态与相对位置。对相对姿态控制算法,给出相对姿态运动学与动力学方程,讨论相平面法与四元数反馈法的控制设计方法。相平面控制法应用常值推力,针对小姿态角机动的特点,将相对姿态通道解耦为三个独立的二阶子系统,设计相平面推力方向切换函数;四元数反馈法应用本征轴旋转的线性二阶系统瞬态响应特性,选择相对四元数与相对角速率反馈增益系数,确定控制力矩。对相对位置控制算法,将实际位移对标称位移之差作为控制变量,阐述所需速度增量最小的双冲量机动。大量模拟计算结果表明相对状态测定与控制算法是有效的。