Orbital debris–debris collision avoidance

We focus on preventing collisions between debris and debris, for which there is no current, effective mitigation strategy. We investigate the feasibility of using a medium-powered (5 kW) ground-based laser combined with a ground-based telescope to prevent collisions between debris objects in low-Earth orbit (LEO). The scheme utilizes photon pressure alone as a means to perturb the orbit of a debris object. Applied over multiple engagements, this alters the debris orbit sufficiently to reduce the risk of an upcoming conjunction. We employ standard assumptions for atmospheric conditions and the resulting beam propagation. Using case studies designed to represent the properties (e.g. area and mass) of the current debris population, we show that one could significantly reduce the risk of nearly half of all catastrophic collisions involving debris using only one such laser/telescope facility. We speculate on whether this could mitigate the debris fragmentation rate such that it falls below the natural debris re-entry rate due to atmospheric drag, and thus whether continuous long-term operation could entirely mitigate the Kessler syndrome in LEO, without need for relatively expensive active debris removal.     

空间碎片减缓措施及其研究对策

随着人类空间技术的进步和发展 ,每年发射进入太空的人造天体越来越多。当这些人造天体失效后 ,由于目前人类对其缺乏及时有效的回收手段 ,随着时间的推移 ,堆积在太空中的废弃物将越来越多 ,总有一天人类再也不能向太空中发射任何人造天体。因此为了合理利用和保护有限的太空资源 ,则必须减少或清除太空垃圾。文章正是基于上述目的 ,在人类尚无有效回收手段的情况下 ,考虑利用现有的技术提出一些空间碎片的减缓措施 ,并在此基础上提出中国对空间碎片减缓应采取的对策     

空间碎片光谱特性获取与分析方法研究

空间碎片的反射光谱是碎片表面材料与太阳光谱共同作用的结果,能够反映碎片的材料性质,为空间碎片的光学特性研究提供依据. 将观测获得的空间碎片反射光谱进行预处理后,与已知空间材料样本的光谱进行比对,比较两者间光学特性差异,包括连续反射光谱曲线中的峰值、斜率、形态、特征窄波段、吸收谱线和多波段反射光谱间的成像差异、色指数、特征温度等,分辨碎片表面可能的材料,最终实现对空间碎片光学特性的研究.      

Apparent rotation properties of space debris extracted from photometric measurements

Knowledge about the rotation properties of space debris objects is essential for the active debris removal missions, accurate re-entry predictions and to investigate the long-term effects of the space environment on the attitude motion change. Different orbital regions and object’s physical properties lead to different attitude states and their change over time.Since 2007 the Astronomical Institute of the University of Bern (AIUB) performs photometric measurements of space debris objects. To June 2016 almost 2000 light curves of more than 400 individual objects have been acquired and processed. These objects are situated in all orbital regions, from low Earth orbit (LEO), via global navigation systems orbits and high eccentricity orbit (HEO), to geosynchronous Earth orbit (GEO). All types of objects were observed including the non-functional spacecraft, rocket bodies, fragmentation debris and uncorrelated objects discovered during dedicated surveys. For data acquisition, we used the 1-meter Zimmerwald Laser and Astrometry Telescope (ZIMLAT) at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald, Switzerland. We applied our own method of phase-diagram reconstruction to extract the apparent rotation period from the light curve. Presented is the AIUB’s light curve database and the obtained rotation properties of space debris as a function of object type and orbit.     

Practical guidelines for electro-dynamic tethers to survive from orbital debris impacts

Japan Aerospace Exploration Agency (JAXA) has proposed an active debris removal using electro-dynamic tether to reduce large space debris in the low-Earth orbit. However, a tether strand is thin but long enough to have a large area so that it is vulnerable to small particles. This vulnerability might be the weakest point of a tether system against orbital debris. In order to overcome this weakest point, a double tether system, in which two tether strands are tied together at even intervals to form equally spaced loops, has been suggested as one of the promising candidates. This paper provides a mathematical approach to estimate the survival probability of a double tether system and then apply the approach to evaluate the mission success rate of the active debris removal using electro-dynamic tether that JAXA has proposed. It can be concluded the countermeasure to get enough success rate can be obtained. The result is simulated for Advanced Earth Observing Satellite II (ADEOS-II) re-entry from 800 km sun synchronized orbit to atmosphere. The simulation shows that mission success rate over 90% can be obtained with number of loops over 1000 and 10 mm clearance between two strands.     

Space Materials Science in China: II. Ground-based Researches and Academic Activities

Activities of space materials science research in China have been continuously supported by two main national programs. One is the China Space Station (CSS) program since 1992, and the other is the Strategic Priority Program (SPP) on Space Science since 2011. In CSS plan in 2019, eleven space materials science experimental projects were officially approved for execution during the construction of the space station. In the SPP Phase II launched in 2018, seven pre-research projects are deployed as the first batch in 2018, and one concept study project in 2019. These pre-research projects will be cultivated as candidates for future selection as space experiment projects on the recovery of scientific experimental satellites in the future. A new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the National Natural Science Foundation of China. In order to promote domestic academic activities and to enhance the advancement of space materials science in China, the Space Materials Science and Technology Division belong to the Chinese Materials Research Society was established in 2019. We also organized scientists to write five review papers on space materials science as a special topic published in the journal Scientia Sinica to provide valuable scientific and technical references for Chinese researchers.      

Improved orbit predictions using two-line elements

The density of orbital space debris constitutes an increasing environmental challenge. There are two ways to alleviate the problem: debris mitigation and debris removal. This paper addresses collision avoidance, a key aspect of debris mitigation. We describe a method that contributes to achieving a requisite increase in orbit prediction accuracy for objects in the publicly available two-line element (TLE) catalog. Batch least-squares differential correction is applied to the TLEs. Using a high-precision numerical propagator, we fit an orbit to state vectors derived from successive TLEs. We then propagate the fitted orbit further forward in time. These predictions are validated against precision ephemeris data derived from the international laser ranging service (ILRS) for several satellites, including objects in the congested sun-synchronous orbital region. The method leads to a predicted range error that increases at a typical rate of 100 m per day, approximately a 10-fold improvement over individual TLE’s propagated with their associated analytic propagator (SGP4). Corresponding improvements for debris trajectories could potentially provide conjunction analysis sufficiently accurate for an operationally viable collision avoidance system based on TLEs only.     

An adaptive strategy for active debris removal

Many parameters influence the evolution of the near-Earth debris population, including launch, solar, explosion and mitigation activities, as well as other future uncertainties such as advances in space technology or changes in social and economic drivers that effect the utilisation of space activities. These factors lead to uncertainty in the long-term debris population. This uncertainty makes it difficult to identify potential remediation strategies, involving active debris removal (ADR), that will perform effectively in all possible future cases. Strategies that cannot perform effectively, because of this uncertainty, risk either not achieving their intended purpose, or becoming a hindrance to the efforts of spacecraft manufactures and operators to address the challenges posed by space debris.     

Pulsed laser interactions with space debris: Target shape effects

Among the approaches to the proposed mitigation and remediation of the space debris problem is the de-orbiting of objects in low Earth orbit through irradiation by ground-based high-intensity pulsed lasers. Laser ablation of a thin surface layer causes target recoil, resulting in the depletion of orbital angular momentum and accelerated atmospheric re-entry. However, both the magnitude and direction of the recoil are shape dependent, a feature of the laser-based remediation concept that has received little attention. Since the development of a predictive capability is desirable, we have investigated the dynamical response to ablation of objects comprising a variety of shapes. We derive and demonstrate a simple analytical technique for calculating the ablation-driven transfer of linear momentum, emphasizing cases for which the recoil is not exclusively parallel to the incident beam. For the purposes of comparison and contrast, we examine one case of momentum transfer in the low-intensity regime, where photon pressure is the dominant momentum transfer mechanism, showing that shape and orientation effects influence the target response in a similar, but not identical, manner. We address the related problem of target spin and, by way of a few simple examples, show how ablation can alter the spin state of a target, which often has a pronounced effect on the recoil dynamics.     

Space Debris Research Progress of China

The rapid increase of space debris population has posed serious threaten to the safety of human space activities and became a global issue. How to enhance the technical capabilities of space debris threat coping ability is of great significance to the sustainable development of space activities, the further development, and utilization of outer space. In this paper, we describe space debris research progress of China on observation, collision avoidance, protection, mitigation, regulation, and standard during the last twenty years, and look forward to the future development direction of space debris.      

深空环境下热防护材料的研究及应用进展

随着对太空探索的深入,空间飞行器所面临的环境也越趋恶劣:太空飞行过程中的高温羽流防护,高速返回再入过程中高温气动加热;长时间日光下飞行会使飞行器表面温度越来越高;一些星球上高温的大气环境导致人类现有制造飞行器的材料无法抵挡。本文搜集国内外先进热防护系统研究资料,了解重点发展方向,介绍了我国神舟飞船热防护材料以及已经开发出的新型轻质高效热防护材料,为我国今后用于恶劣环境下的飞行器材料提供一些信息和材料基础。     

空间碎片能量转化利用技术

针对目前空间碎片问题，提出空间碎片发动机概念，立足于使用捕获到的空间碎片，转化为发动机可用的推进剂。在完成碎片清理目标的同时，获得可持续的动力来源，延长清理器的工作寿命。针对空间碎片制粉的方法进行研究，提出使用球磨仪对金属样本进行研磨。使用转刀式粉碎机对非金属材料进行粉碎。通过实验发现，多数粉末粒径达到微米量级。针对空间碎片粉末推进方式进行研究，提出使用静电加速推进方式对粉末进行加速。空间碎片发动机虽然起源于空间碎片清理任务，但是可持续的推进剂供应，也将为小行星探测等任务提供更好的思路。     

Space debris mitigation strategies and practices in geosynchronous transfer orbits

Missions to geosynchronous orbits remain one of the most important elements of space launch traffic, accounting for 40% of all missions to Earth orbit and beyond during the four-year period 2000–2003. The vast majority of these missions leave one or more objects in geosynchronous transfer orbits (GTOs), contributing on a short-term or long-term basis to the space debris population. National and international space debris mitigation guidelines seek to curtail the accumulation of debris in orbits which penetrate the regions of low Earth orbit and of geosynchronous orbit. The orbital lifetime of objects in GTO can be greatly influenced by the initial values of perigee, inclination, and right ascension of the orbital plane, leading to orbital lifetimes of from less than one month to more than 100 years. An examination of the characteristic GTOs employed by launch vehicles from around the world has been conducted. The consequences of using perigees above 300 km and super-synchronous apogees, typically above 40,000 km, have been identified. In addition, the differences in orbital behavior of launch vehicle stages and mission-related debris in GTOs have been investigated. Greater coordination and cooperation between space launch service providers and spacecraft designers and owners could significantly improve overall compliance with guidelines to mitigate the accumulation of debris in Earth orbit.     

Materials selection for electronic enclosures in space environment considering electromagnetic interference effect

Using low power electronic devices for space applications to reduce the mass and energy consumption has lead to electromagnetic interference (EMI) problem. Electronic enclosures are used to shield electronic devices against EMI. In the past, electromagnetic shielding has been mainly the only criteria considered in electronic enclosure design. However, there are several structural and thermal requirements for selection of shielding materials which should also be taken into account. In this research work, three quantitative materials selection methods, i.e. Digital Logic (DL), Modified Digital Logic (MDL), and Z-transformation, are employed to select the best material from among a list of candidate materials. Composite and metallic electronic enclosures are explored and the best material is selected. Z-transformation method is applicable to both of the considered case studies while DL and MDL can only be used for solving one of them. Z-transformation method ranks aluminum as the first choice among various metallic materials. The wide range of Z-transformation application and its practical results confirm the superiority of Z-transformation method over DL and MDL methods.     

载人深空探测任务的空间环境工程关键问题

对载人深空探测过程中将遭受的太阳宇宙射线、银河宇宙射线、微重力、尘与尘暴、深空微生物等环境进行分析。对不同深空环境给航天员带来的威胁进行了探讨。从物理屏蔽防护、辐射风险的监测和预警、辐射防护药物、航天员选拨等角度对采取的措施进行了阐述。从空间辐射对航天员的损伤机理、抗辐射和微重力药物开发、空间辐射屏蔽防护结构与材料、航天服自清洁、抗微生物侵蚀材料的研发等多个角度对需要进一步开展的工作进行了讨论。     

Materials trade study for lunar/gateway missions.

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a 'must solve' problem for space missions. The Moon and two Earth-Moon Lagrange points near Moon are being proposed as hubs for deep space missions. The focus of this study is to identify approaches to protecting astronauts and habitats from adverse effects from space radiation both for single missions and multiple missions for career astronauts to these destinations. As the great cost of added radiation shielding is a potential limiting factor in deep space missions, reduction of mass, without compromising safety, is of paramount importance. The choice of material and selection of the crew profile play major roles in design and mission operations. Material trade studies in shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space mission's to two Earth-Moon co-linear Lagrange points (L1) between Earth and the Moon and (L2) on back side of the moon as seen from Earth, and to the Moon have been studied. It is found that, for single missions, current state-of-the-art knowledge of material provides adequate shielding. On the other hand, the choice of shield material is absolutely critical for career astronauts and revolutionary materials need to be developed for these missions. This study also provides a guide to the effectiveness of multifunctional materials in preparation for more detailed geometry studies in progress.     

Spot 1 end of life disposition manoeuvres

The Earth observation satellites of the SPOT family are on a Sun-synchronous orbit at 822 km altitude. The on-orbit lifetime of objects at this altitude is about two centuries, which represents an important risk to the other satellites.The space debris issue has caused the main Agencies to adopt mitigation guidelines with the objective to reduce the population of objects orbiting the Earth. In 1999, CNES published its own standard presenting the management, design and operation rules. This document is fully compliant with the Inter Agency Space Debris Coordination Committee (IADC) mitigation guidelines approved in 2002 by 11 Space Agencies and submitted to United Nations – Committee on Peaceful Uses of Outer Space in February 2003.The space debris mitigation requirements expressed in the CNES standard and in the IADC mitigation guidelines limit the orbital lifetime in LEO to less than 25 years. Although not applicable to Spot 1, launched earlier in 1986, this rule was voluntarily applied and the decision to deorbit Spot 1 was taken.The corresponding operations, performed in November 2003, were complex due to a large number of constraints such as the unusual flight domain, the on-board sensors, the short ground station visibilities or the uncertainties in the estimation of the remaining fuel in the tanks. In the preliminary phase, the orbit was lowered 15 km below the operational orbit to avoid any collision risk with the other Spot satellites. Then, in a second phase, a series of eight apogee boosts lowered progressively the perigee altitude to 619 km. Finally, a large last manoeuvre was performed to empty the tanks and to reduce the perigee altitude the maximum amount. A succession of four ground stations visibilities allowed a real time monitoring of this manoeuvre. In particular the effect of gas bubbles in the propulsion system was observed through telemetry confirming the fuel depletion. The batteries were then disconnected and the telemetry emitter was switched off. According to the obtained perigee altitude, the on-orbit lifetime of Spot 1 should be about 18 years, which meets the space debris mitigation requirements.     

An adaptive threshold method for improving astrometry of space debris CCD images

Optical survey is a main technique for observing space debris, and precisely measuring the positions of space debris is of great importance. Due to several factors, e.g. the angle object normal to the observer, the shape as well as the attitude of the object, the variations of observed characteristics for low earth orbital space debris are distinct. When we look at optical CCD images of observed objects, the size and brightness are varying, hence it’s difficult to decide the threshold during centroid measurement and precise astrometry. Traditionally the threshold is given empirically and constantly in data reduction, and obviously it’s not suitable for data reduction of space debris. Here we offer a solution to provide the threshold. Our method assumes that the PSF (point spread function) is Gaussian and estimates the signal flux by a directly two-dimensional Gaussian fit, then a cubic spline interpolation is performed to divide each initial pixel into several sub-pixels, at last the threshold is determined by the estimation of signal flux and the sub-pixels above threshold are separated to estimate the centroid. A trail observation of the fast spinning satellite Ajisai is made and the CCD frames are obtained to test our algorithm. The calibration precision of various threshold is obtained through the comparison between the observed equatorial position and the reference one, the latter are obtained from the precise ephemeris of the satellite. The results indicate that our method reduces the total errors of measurements, it works effectively in improving the centering precision of space debris images.     

柱状弹丸撞击防护屏形成碎片云材料状态特性研究

微流星体及空间碎片的高速撞击威胁着长寿命、大尺寸航天器的安全运行，导致其严重的损伤和灾难性的失效。为精确估计微流星体及空间碎片高速撞击防护屏所产生碎片云对舱壁的损伤，必须确定碎片云中三种状态材料的特性，建立了碎片云特性分析模型，分别计算了柱状弹丸撞击防护屏所产生碎片云以及碎片云中弹丸和防护屏材料三种状态物质的质量分布。通过计算分析可见，弹丸以不同速度撞击防护屏所产生碎片云三种状态物质的质量分布是不同的，速度增大，液化和气化增强，对靶件的损伤小。而在速度小于7km/s时，碎片云以固体碎片的形式存在，对靶件的损伤大。