Developing a Low-Velocity Collision Model Based on the Nasa Standard Breakup Model

We have conducted a series of low-velocity impact experiments to understand the dispersion properties of fragments newly created by low-velocity impacts possible in space, especially in geostationary Earth orbit. The test results are utilized to establish a mathematical prediction model to be used in debris generation and propagation codes. Since the expected collision velocity between catalogued objects in geostationary Earth orbit shows a peak at a few hundreds meters per second, these impact experiments were conducted at a velocity range lower than 300m/s. As a typical structure of satellites in geostationary Earth orbit, thin aluminum honeycomb sandwich panels with carbon fiber reinforced plastics face sheets were prepared, while the projectile was a stainless steel ball of 9mm diameter. The data collected through these impact experiments have been re-analyzed based on the method used in the National Aeronautics and Space Administration (NASA) standard breakup model 1998 revision. The results indicate that the NASA standard breakup model derived from hypervelocity impacts could be applied to low-velocity collision possible in geostationary Earth orbit with some modifications.     

单层及双层板的超高速碰撞试验(速度超过10km/s)的数值模拟

文章介绍了在Sandia国家实验室所进行的3个精确控制的超高速碰撞试验,使用两种复杂的流体码即多维流体动力学代码CTH和平滑粒子流体动力学代码SPH,对该试验进行数值模拟。该试验用质量为克大小的飞片及球形射弹以大约10km/s的速度撞击薄铝板及钢板(厚度小于1cm)。并分析了碎片云动力学计算预示结果及这些试验中金属板的损坏。     

Experimental and theoretical investigation of encounter of a group of particles with protecting elements of spacecraft

We present the results of comprehensive experimental and theoretical investigations of encounter with a barrier of a group of bodies thrown with a high-velocity. Throwing of a group of particles (from two to twelve bodies) was realized on a ballistic route using powder and light-gas units of different calibers in the range of velocities 500–3500 m/s. The process of particle throwing was controlled by acting aerodynamic forces. In experiments on collisions with barriers of a finite thickness (which imitates the protective shield of spacecraft) the number of particles in a homogeneous stream was varied from 2 to 7 at changing the flux density (distances between particles). Experimental data are obtained on variations of the area and mass of back-surface splinters. Numerical calculations simulated a knock of 2 to 4 particles against a barrier in the cases of normal impact and at an angle. The calculations were performed in three-dimensional formulation and applying criteria of complete destruction of material. The appearance of additional destruction centers in the barrier due to mutual influence of particles is revealed. Simple criteria are obtained for estimating the degree of interference of particles and the character of barrier destruction.     

钛合金弧板类零件冲压成型回弹仿真计算

采用板料成型仿真软件Pamstamp对钛合金Ti-15-3材料弧板零件冲压成型回弹进行仿真计算,预测了不同阴模型面圆弧尺寸冲压成型后的回弹量.依据计算结果优选的阴模型面圆弧尺寸设计了成型模具,并进行了冲压成型试验.零件试验件型面尺寸与设计型面尺寸最大相差0.15 mm,满足不大于0.2 mm的要求.结果表明：采用仿真软件Pamstamp进行回弹仿真计算对Ti-15-3材料弧板成型模具设计和零件快速制造是可行的;采用本计算结果减少了模具返修次数,降低了成本,提高了钣金成型质量和生产效率.     

微重力下热薄材料燃烧特性的窄通道实验研究

利用高度分别为10 mm,12 mm和14 mm的水平窄通道对微重力环境下热薄材料表面的火焰传     

A Study of the Destruction of Spacecraft Surfaces at Contact Interactions with Microparticles of the Space Environment

The results of studying the high-velocity impact interactions of a particle flux of space’s meteoric background with satellites have been presented. The effects that arises during the microparticle motion in the material have been described; the models of solid particle interactions with spacecraft’s onboard hardware protection have been presented. The experimental and analytical dependences have been given. The basic factors have been revealed, and their effect on the erosion wear of satellite’s surface has been estimated. The dependences for calculating the rectilinear (horizontal, inclined and vertical) sections of satellite’s surface have been given. The presented dependences represent the results of experimental and analytical studies.     

Collision Probabilities for Keplerian Orbits

We present a new derivation of the probability of collisions between spherical satellites occupying Keplerian orbits. The equations follow from the central concept of the instantaneous collision rate, an expression that describes the occurrence of collisions by using a Dirac -function. The derivation proceeds by showing how this instantaneous collision rate can be averaged over orbital mean anomaly angles and, additionally, over orbital precession angles to generate expressions appropriate for intermediate and long time scales. Collision rates averaged over mean anomalies tend to be non-zero during relatively brief collision seasons, when the peak collision probability may exceed the long-term average by several orders of magnitude. Derived precession-angle averages have a functional form similar but not identical to the collision probability expression derived using the spatial density approach of Kessler (Icarus, 48: 39–48, 1981), and the two methods have been found to yield numerical results to within 1% for all cases examined.     

Excitation and propagation of an electromagnetic pulse in magnetized plasma in the low-hybrid frequency range

We analyze specific features of slow quasi-static waves excited in the low-hybrid frequency band by a source whose dimensions are much smaller than electromagnetic wavelength. Main attention in this paper is given to an analysis of emission of harmonic signals by a dipole source in pulsed mode. First, the issue of influence of electromagnetic, thermal, and collision corrections in the dispersion equation on the field structure has been studied. Second, the structure of electric and magnetic fields near the resonant cone has been analyzed: in particular, effects of group delay and anomalous spreading of signals are considered. Thus constructed theory explains results of the OEDIPUS-C experiment, in which, for example, already at distances of order of ten wavelengths a signal delay of approximately 10^?4 s was observed. Finally, we have studied some aspects of the inverse problem of electrodynamics: the role played in field formation by smoothness of charge distribution over antenna is demonstrated, and a class of smooth distributions of charge on antenna is found that form a preset field structure.     

铁电阴极用于小功率电推力器

分析了当前小功率电推力器对零流动无推进剂阴极的需求现状。提出铁电阴极用于小功率电推进中和器的可能性。研究了厚度为0．5mm的PLZT（锆钛镧酸铅）铁电陶瓷在低电压（1．0～1．2kV）条件下的电子发射性能。实验采用脉宽为1μs的单极性正高压脉冲作为激励源。在收集极获得了脉宽为320ns～3000ns,最高峰值为34A的发射电流。在10^-4乇的真空环境中得到了非常可靠的电子发射。     

Tether Satellite System Collision Study

A study was performed to determine the probability of collision with resident space objects and untrackable debris for the tether component of the Tethered Satellite System (TSS) after it broke away from the Space Shuttle orbiter (mission STS-75) in February 1996. Both an analytical and a numerical approach were used in this study, and the results obtained with these two methods were found to be in good agreement. These results show that the deployed tether is expected to have been impacted by several particles 0.1mm or larger in size. The probability of collision with objects 10cm in size or larger was on the order of 10^–3 per month. Since the severed tether reentered within one month after deployment, the collision hazard to other objects while in orbit was small. The analytical methods used in this study are useful for tether collision evaluations in general.     

Optimal nodal flyby with near-Earth asteroids using electric sail

The aim of this paper is to quantify the performance of an Electric Solar Wind Sail for accomplishing flyby missions toward one of the two orbital nodes of a near-Earth asteroid. Assuming a simplified, two-dimensional mission scenario, a preliminary mission analysis has been conducted involving the whole known population of those asteroids at the beginning of the 2013 year. The analysis of each mission scenario has been performed within an optimal framework, by calculating the minimum-time trajectory required to reach each orbital node of the target asteroid. A considerable amount of simulation data have been collected, using the spacecraft characteristic acceleration as a parameter to quantify the Electric Solar Wind Sail propulsive performance. The minimum time trajectory exhibits a different structure, which may or may not include a solar wind assist maneuver, depending both on the Sun-node distance and the value of the spacecraft characteristic acceleration. Simulations show that over 60% of near-Earth asteroids can be reached with a total mission time less than 100 days, whereas the entire population can be reached in less than 10 months with a spacecraft characteristic acceleration of 1 mm/s².     

变刚度连续型机械臂设计与控制

针对空间机械臂碰撞过程中产生的冲击和破坏问题,提出一种能被动适应碰撞且能保证操作精度的可变刚度丝驱动连续型机械臂。在以超弹镍钛合金丝为支撑脊椎和驱动部件的基础结构上,设计了一种利用温控记忆合金改变关节内摩擦力的变刚度方法。通过运动学分析得到机械臂驱动空间、构型空间和工作空间之间的坐标映射及速度雅克比矩阵,并结合末端位置反馈设计了一个稳定的闭环运动控制器。在检测丝驱动力的基础上提出了一种碰撞识别方法和相应的变刚度控制策略。运动控制和变刚度控制的实验结果表明该连续型机械臂具有良好的运动控制精度和刚度调节能力。     

Results of impact simulation for the GIOTTO mission

The European Space Agency (ESA) has decided to carry out a fly-by mission to the comet Halley. The spacecraft will be launched by an ARIANE II and intercept the retrograde Halley orbit on 13 March, 1986. One group of experiments is designed to obtain data on size, mass and composition of the dust in the cometary tail. Because of the very high relative velocity during fly-by (69 km/s) laboratory experiments are necessary to develop and calibrate the experiments. These experiments are presently under way in the laboratory of the Lehrstuhl für Raumfahrttechnik of the Technische Universität München. First results have been obtained for both the Dust Impact Detection System (DIDSY) and the P?articulate Impact Analyzer (PIA). These results are compared with the theoretical models for hypervelocity impact craters. The agreement is good at impact velocities around 15 km/s.     

Hypervelocity impact testing of advanced materials and structures for micrometeoroid and orbital debris shielding

A series of 66 hypervelocity impact experiments have been performed to assess the potential of various materials (aluminium, titanium, copper, stainless steel, nickel, nickel/chromium, reticulated vitreous carbon, silver, ceramic, aramid, ceramic glass, and carbon fibre) and structures (monolithic plates, open-cell foam, flexible fabrics, rigid meshes) for micrometeoroid and orbital debris (MMOD) shielding. Arranged in various single-, double-, and triple-bumper configurations, screening tests were performed with 0.3175 cm diameter Al2017-T4 spherical projectiles at nominally 6.8 km/s and normal incidence. The top performing shields were identified through target damage assessments and their respective weight. The top performing candidate shield at the screening test condition was found to be a double-bumper configuration with a 0.25 mm thick Al3003 outer bumper, 6.35 mm thick 40 PPI aluminium foam inner bumper, and 1.016 mm thick Al2024-T3 rear wall (equal spacing between bumpers and rear wall). In general, double-bumper candidates with aluminium plate outer bumpers and foam inner bumpers were consistently found to be amongst the top performers. For this impact condition, potential weight savings of at least 47% over conventional all-aluminium Whipple shields are possible by utilizing the investigated materials and structures. The results of this study identify materials and structures of interest for further, more in-depth, impact investigations.     

Modelling of Spall in an Anisotropic Aluminium Alloy

Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using a number of spall models. The Hugoniot elastic limit and spall strength have been studied as a function of orientation, and compared to experimental results.     

Sporadic plasma streams and their sources in the period of extraordinary solar activity from October 26 to November 6, 2003

Based on the results of investigations made by various authors applying different semiempirical models, we have formulated the principles of a complex method that allows one to associate sporadic streams of the solar wind (SW) at the Earths orbit with coronal mass ejections (CMEs), which are their sources on the Sun. This method is applied to an analysis of the events in the interval from October 26 to November 6, 2003. It is shown that, in the period under consideration, which is close to the maximum of solar activity, the majority of CMEs (up to 80% of their total number) turn out to be at the base of a chain of streamers. It is also shown that the component of the interplanetary magnetic field is the main factor of geoeffectiveness for six sporadic SW streams. At the same time, an unusually low value of the index minD_st< -300 nT for two streams with the velocities V_max > 1000 km/s is a consequence of the fact that they are not isolated; i.e., the subsequent stream moves through the medium disturbed by the preceding stream.Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 595–607.Original Russian Text Copyright © 2004 by M. Eselevich, V. Eselevich.     

低轨对地凝视卫星姿态控制

研究了低轨航天器执行对地观测任务时对地凝视观测的姿态控制。根据刚体动力学导出基于误差四元数和误差角速度的动力学与运动学方程,设计了一变结构控制律。仿真结果表明:在对地凝视的姿态控制过程中,设计的控制方法响应速度快于传统控制方法,对卫星转动惯量摄动及外部干扰的鲁棒性较佳。     

嫦娥三号月面巡视器机械臂就位探测规划

提出了一种基于SA *算法的嫦娥三号月面巡视器机械臂就位探测规划方法。建立了机械臂的正逆运动学模型,满足机械臂与环境不存在干涉的约束条件,并通过碰撞检测避免机械臂与环境和巡视器本体发生干涉;利用SA *算法在机械臂的工作空间进行搜索,在机械臂位形切换次数最少的优化条件下,实现了月面巡视器机械臂就位探测规划;通过月面巡视器在轨任务执行数据验证了基于SA *算法的月面巡视器机械臂就位探测任务的可行性。     

A procedure for three-dimensional angular velocity determination using a star sensor in high-rate rotation modes

This paper presents an application for modern star trackers aimed at the estimation of the spacecraft angular velocity vector on the basis of the star field images acquired during fast rotations, when star identification and tracking are not possible. Angular rates in the range 2–8°/s are considered, which strongly affect the characteristics of the acquirable images, in particular for shape and brightness. The procedure consists in the exploitation of the rigid motion equations to identify the rotation that best fits the observed star trajectories in the sensor field of view. Its coverage capability is analysed with reference to the sensitivity of state-of-the-art photodetectors. The probability of an adequate acquisition is shown to be 0.80 with random pointing and rotation axis over the celestial sphere. Firstly, the accuracy of the procedure is discussed in numerical tests. Then, end-to-end tests are reported, which have been operated by implementing the procedure in a hardware sensor model that acquires simulated star field scenes in a laboratory facility. Both the validations point out that the accuracy of 1°/s, suggested by the European Space Agency for this kind of application, has been achieved. Moreover, the rate of rotation about axes perpendicular to the boresight can be computed with accuracy one order of magnitude better.     

微重力环境模拟作业训练机器人碰撞力反馈控制

针对航天员在地球表面进行微重力环境中操作训练时微重力环境模拟作业训练机器人存在的碰撞力反馈控制问题,建立碰撞力反馈模型、提出单个柔索驱动单元控制策略和机器人系统碰撞力反馈控制策略。利用Matlab/Simulink软件对碰撞力反馈模型和控制策略进行仿真验证,该模型和控制策略可以实现机器人碰撞力反馈,且具有计算量小、实时性好、不需要额外增加传感器等优势;结合提出的柔索驱动单元复合控制策略和机器人系统碰撞力反馈控制策略进行机器人碰撞力反馈控制实验,提高机器人控制的准确性和实时性。结果表明,基于干扰观测器的柔索驱动单元复合控制策略将柔索驱动单元主动控制精度提升11%,被动控制多余力消除率达到81.82%;机器人碰撞力反馈控制策略可以有效提升航天员作业训练时碰撞力临场感体验。