A space based radar on a micro-satellite for in-situ detection of small orbital debris

The increase in the number of satellites in the Near Earth Orbit is exponential. The consequent increase in pollution of the orbital environment is of growing concern to the international community. There are currently only two observation systems available for measurement of orbital debris. Ground based radar and telescopes can detect objects larger than about 7 cm. Passive space based systems provide an accurate statistical estimation of flux for debris smaller than about 0.1 mm in size. Consequently, there is no way of obtaining information about debris in the millimeter-size range. Considering that the relative speed between objects in space is commonly in the km/s range, millimeter sized debris carry enough energy to be deadly to astronauts or to totally destroy the functioning of any satellite. Then National space agencies have recommended launching orbital spacecraft carrying debris detection experiments for gaining a better understanding of small debris.CNES (the French Space Agency) is developing a new family of micro-satellites, that will make possible to put into orbit a totally new system of radar that could measure in-situ flux of debris. We present results of this system analysis, which would cumulate the advantages of both ground-based radar and in orbit passive experiments.The proposed method for detection is quite original and allows the radar to act like a band-pass filter with respect to the debris diameter. The optimum frequency is shown to be in the Ka-band. Two points are critical in the definition of the radar: the average power available and the false alarm probability in the detection criterion. Therefore, we present a special receiver chain in order to optimize the signal-to-noise ratio. The estimate of the radial velocity through Doppler frequency measurement may be used to discriminate orbital debris from meteoroids. This system could be built today using an existing Continuous Wave amplifier. Several hundreds of objects per year could be detected yielding an accurate statistical estimation.The orbital debris radar would be a major contribution to our knowledge of millimeter sized debris. This experiment would contribute to making the current models more accurate at all inclinations. The micro-satellite concept would make the orbital debris radar mission cheap enough for considering a constellation of such satellites.     

基于计算机的低地球轨道航天器设计与观测的轨道碎片环境模型

文章介绍了一个半经验的基于计算机的轨道碎片模型。该模型将轨道环境简化为6个不同的倾角带,每个倾角带都有各自的半长轴和近地点分布及根据不同的碎片来源有其各自的尺寸分布。用碰撞概率方程将轨道碎片分布与航天器上的碎片通量或通过地面探测器视角的通量联系起来。经比较,碎片的半长轴、近地点和倾角分布与美国空间司令部大于10cm的碎片目录是一致的。对于较小的碎片,这些分布与地面望远镜、“干草堆”雷达的测量结果一致,同时也与LDEF卫星和航天飞机的测量结果一致。     

Study on electrodynamic tether system for space debris removal

As a countermeasure for suppressing space debris growth (P. Eighler, A. Bade, Chain Reaction of Debris Generation by Collisions in Space—A Final Threat to Spaceflight? in: 40th Congress of the International Astronautical Federation, IAA-89-628, October 1989), the National Aerospace Laboratory of Japan is investigating a satellite capture, repair and removal system for non-cooperative satellites, part of which involves assessing the viability of electrodynamic tether (EDT) technology as an orbital transfer system. In this paper, some results concerning the time required to remove existing satellites, the behavior of flexible tethers during the debris separation phase, and orbital transfer strategies of EDT systems during space debris removal operations are described. From numerical simulations, it is found that EDT systems can transfer satellites from LEO to orbits with a short lifetime within a realistic timeframe. It is also found that the stability of EDT systems is compromised when debris separation occurs both while a tether current is running and when the ratio of the end mass to that of the service satellite is high. To ensure stability, the end mass should be selected from the target debris group with due regard for the maximum possible mass that can be maneuvered safely. Moreover, it is also found that orbital elements (a, e, i) can be changed independently with an adequate current control strategy.     

The capture-cell experiment for the first LDEF mission

The Long Duration Exposure Facility (LDEF) is an experiment carrying structure, which will be transported into a near earth orbit by the Space Transportation System of the U.S.A., where it will remain for approx, one year and then be brought back to Earth. A group of experiments investigates the cosmic dust environment. This paper describes the principle of a micro-meteoroid capture-cell experiment which has been accepted for the first LDEF flight in 1984. The development of the components and the tests conducted with the prototype are discussed together with the analysis of the simulation results using a secondary ion mass spectrometer (SIMS).     

热控涂层搭载飞行试验进展综述

文章对国内外航天器热控涂层在轨搭载飞行试验进行了调研,综述了利用和平号空间站、＂国际空间站＂、美国航天飞机、＂长期暴露装置＂等航天器进行的相关试验工作及主要的研究成果等。在此基础上提出了我国开展热控涂层搭载飞行试验的建议。     

Investigation of Hypervelocity Impacts on Retrieved Surfaces by Direct Simulation Monte Carlo

Hypervelocity impacts on the retrieved Hubble Space Telescope (HST) solar array was investigated by our extended Direct Simulation Monte Carlo (DSMC) model and the result matches well with the measured data in most of the particle mass range. The revelation of the altitude dependence of particles flux onto the retrieved surfaces provides some insight in understanding the observed higher flux onto Mir space station relative to that onto Long Duration Exposure Facility (LDEF). Our analysis suggests that a slightly higher primary flux onto Mir space station would be possible even without taking into account the secondary impacts, as a result of the existence of the highly eccentric orbits of small-sized debris. It is, furthermore, predicted that 43% of the measured impact flux onto Mir station in PIE experiment may be from secondary impacts, and a corresponding 7% for the detectors in Echantillions experiment.     

Enhancement and Validation of the IDES Orbital Debris Environment Model

Orbital debris environment models are essential in predicting the characteristics of the entire debris environment, especially for altitude and size regimes where measurement data is sparse. Most models are also used to assess mission collision risk. The IDES (Integrated Debris Evolution Suite) simulation model has recently been upgraded by including a new sodium–potassium liquid coolant droplet source model and a new historical launch database. These and other features of IDES are described in detail. The accuracy of the IDES model is evaluated over a wide range of debris sizes by comparing model predictions to three major types of debris measurement data in low Earth orbit. For the large-size debris population, the model is compared with the spatial density distribution of the United States (US) Space Command Catalog. A radar simulation model is employed to predict the detection rates of mid-size debris in the field of view of the US Haystack radar. Finally, the small-size impact flux relative to a surface of the retrieved Long Duration Exposure Facility (LDEF) spacecraft is predicted. At sub-millimetre sizes, the model currently under-predicts the debris environment encountered at low altitudes by approximately an order of magnitude. This is because other small-size debris sources, such as paint flakes have not yet been characterised. Due to the model enhancements, IDES exhibits good accuracy when predicting the debris environment at decimetre and centimetre sizes. Therefore, the validated initial conditions and the high fidelity future traffic model enables IDES to make long-term debris environment projections with more confidence.     

Evaluation of a satellite constellation for active debris removal

This paper analyzes an example of a three-dimensional constellation of debris removal satellites and proposes an effective constellation using a delta-V analysis that discusses the advisability of rendezvousing satellites with space debris. Lambert?s Equation was used to establish a means of analysis to construct a constellation of debris removal satellites, which has a limit of delta-V injection by evaluating the amount of space debris that can be rendezvoused by a certain number of removal satellite. Consequently, we determine a constellation of up to 38 removal satellites for debris removal, where the number of space debris rendezvoused by a single removal satellite is not more than 25, removing up to 584 pieces of debris total. Even if we prepare 38 removal satellites in their respective orbits, it is impossible to remove all of the space debris. Although many removal satellites, over 100 for example, can remove most of the space debris, this method is economically disproportionate. However, we can also see the removal satellites are distributed nearly evenly. Accordingly, we propose a practical two-stage strategy. The first stage is to implement emergent debris removal with the 38 removal satellites. When we find a very high probability of collision between a working satellite and space debris, one of the removal satellites in the constellation previously constructed in orbit initiates a maneuver of emergent debris removal. The second stage is a long-term space debris removal strategy to suppress the increase of space debris derived from collisions among the pieces of space debris. The constellation analyzed in this paper, which consists of the first 38 removal satellites, can remove half of the over 1000 dangerous space debris among others, and then the constellation increases the number of the following removal satellites in steps. At any rate, an adequate orbital configuration and constellation form is very important for both space debris removal and economic efficiency. Though the size of constellation of debris removal satellites would be small originally, such a constellation of satellites should be one of the initial constellations of removal satellites to ensure the safety of the future orbital environment.     

SDEEM2015空间碎片环境工程模型

文章介绍了哈尔滨工业大学空间碎片高速撞击研究中心"十二五"期间发布的空间碎片环境工程模型(SDEEM 2015)。该模型可实现LEO空间碎片环境描述,空间碎片撞击风险评估以及地基探测结果仿真,还可输出LEO航天器不同轨道位置处空间碎片撞击通量随撞击方位角、撞击速度及碎片尺寸的分布规律,地基探测设备探测区域内空间碎片空间密度及通量的分布情况等信息。SDEEM 2015适用轨道高度范围为200~2000 km,时间范围为1959年—2050年,所考虑的空间碎片来源包括解体碎片、Na K液滴、固体火箭发动机喷射物、溅射物和剥落物。     

Active debris removal: Recent progress and current trends

According to all available findings at international level, the Kessler syndrome, increase of the number of space debris in Low Earth Orbits due to mutual collisions, appears now to be a fact, triggered mainly by several major break-ups in orbit which occurred since 2007. The time may have come to study how to clean this fundamentally useful orbital region in an active way.CNES has studied potential solutions for more than 12 years! The paper aims at reviewing the current status of these activities.The high level requirements are fundamental, and have to be properly justified. The working basis, as confirmed through IADC studies consists in the removal of 5–10 integer objects from the overcrowded orbits, spent upper stages or old satellites, as identified by NASA.The logic of CNES activities consider a stepped approach aiming at progressively gaining the required Technological Readiness Level on the features required for Active Debris Removal which have not yet been demonstrated in orbit. The rendezvous with a non-cooperative, un-prepared, tumbling debris is essential. Following maturation gained with Research and Technology programs, a set of small orbital demonstrators could enable a confidence high enough to perform a full end to end demonstration performing the de-orbiting of a large debris and paving the way for the development of a first generation operational de-orbiter.The internal CNES studies, led together by the Toulouse Space Centre and the Paris Launcher Directorate, have started in 2008 and led to a detailed System Requirements Document used for the Industrial studies.Three industrial teams did work under CNES contract during 2011, led by Thales Alenia Space, Bertin Technologies and Astrium Space Transportation, with numerous sub-contractors. Their approaches were very rich, complementary, and innovative. The second phase of studies began mid-2012. Some key questions nevertheless have to be resolved, and correspond generally to current IADC actions:The casualty risk associated to a “passive” de-orbitation is of paramount importance, major driver between passive and active re-entry,The residual movement of debris is crucial for the interfacing phase, whichever the solution is,The debris physical state in orbit is a major question,Some solutions increase the collision risk, but for a limited time period; we may not have yet the appropriate tools.The paper gives a status of where we stand, of the cooperation with the international partners, and raises the questions which remain open and have to be dealt with in the coming months.     

Investigation of national policy shifts to impact orbital debris environments

Low earth orbit has become increasingly congested as the satellite population has grown over the past few decades, making orbital debris a major concern for the operational stability of space assets. This congestion was highlighted by the collision of the Iridium 33 and Cosmos 2251 satellites in 2009. This paper addresses the current state of orbital debris regulation in the United States and asks what might be done through policy change to mitigate risks in the orbital debris environment. A brief discussion of the nature of orbital debris addresses the major contributing factors including size classes, locations of population concentrations, projected satellite populations, and current challenges presented in using post-mission active debris removal to mitigate orbital debris. An overview of the current orbital debris regulatory structure of the United States reveals the fragmented nature of having six regulating bodies providing varying levels of oversight to their markets. A closer look into the regulatory policy of these agencies shows that, while they all take direction from The U.S. Government Orbital Debris Mitigation Standard Practices, this policy is a guideline with no real penalty for non-compliance. Various policy solutions to the orbital debris problem are presented, ranging from a business as usual approach to a consolidated regulation system which would encourage spacecraft operator compliance. The positive aspects of these options are presented as themes that would comprise an effective policy shift towards successful LEO conservation. Potential economic and physical limitations to this policy approach are also addressed.     

Metallic and Oxidized Aluminum Debris Impacting the Trailing Edge of the Long Duration Exposure Facility (LDEF)

A total of 87 microcraters >30 m in diameter that were found in gold substrates exposed on the trailing edge of the non-spinning Long Duration Exposure Facility (LDEF) yielded analyzable projectile residues in their interiors. Using qualitative SEM-EDS analysis methods, some 60 of these craters were formed by natural cosmic-dust particles, while 27 residues (31%) were assigned to orbital debris (Hörz et al., 1993). The far majority of the orbital-debris impacts, 24 (89%) of the 27 events, contained only aluminum in their X-ray spectra. The present study evaluates these aluminum-rich residues in detail and employs a windowless X-ray detector, which permits for the analysis of low-Z elements and specifically of oxygen. This makes it possible to discriminate between oxidized (Al₂O₃) and metallic (Al) projectiles from dramatically different sources, the former produced during solid-fuel rocket firings, the latter resulting from explosively or collisionally disrupted spacecraft.Of the 24 craters analyzed with the windowless detector, 13 (54%) contained Al₂O₃ and 11 (46%) yielded structurally disintegrated Al metal. The oxidized residues preferentially occur in the smaller craters, all <60 m in diameter. Corresponding particles on LDEF's trailing edge are <35 m in diameter. Some 70% of this particle population is composed of Al₂O₃. Although solid-fuel rocket exhaust products are typically <5 m in size, they tend to coagulate into crusts at the rocket nozzle to be shed occasionally as relatively large, aggregate particles. Structurally disintegrated, metallic fragments compose one-third of all particles <35 m, but they dominate all particles >35 m, and thus all craters >60 m. These findings clearly establish that solid-rocket exhaust particles, as well as explosively or collisionally produced debris, exist in low-inclination, high-eccentricity orbits in sufficient quantities that they must be accounted for in models describing the present and future orbital-debris population at typical Shuttle and Space Station altitudes.     

The Investigation of Possible Approaches of Cataloged Space Objects to Manned Spacecraft

Initial orbital parameter errors are used to examine the miss distance between a spacecraft and an ensemble of tracked objects by a Monte Carlo-type analysis. The radial separation between orbits is evaluated and a keep-out zone is determined, which reduces the risk of collision to an acceptable level.An operational prediction methodology is suggested based on a catalog database, which identifies potentially hazardous approaches and computes the probability of collision for selected spacecraft. An example for the Mir Space Station is presented, which estimates the collision probability and the cross-sectional flux of cataloged objects for the time frame of interest. The results appear to be in good agreement with those of other space debris models.     

Conceptualizing an economically,legally, and politically viable active debris removal option

It has become increasingly clear in recent years that the issue of space debris, particularly in low-Earth orbit, can no longer be ignored or simply mitigated. Orbital debris currently threatens safe space flight for both satellites and humans aboard the International Space Station. Additionally, orbital debris might impact Earth upon re-entry, endangering human lives and damaging the environment with toxic materials. In summary, orbital debris seriously jeopardizes the future not only of human presence in space, but also of human safety on Earth. While international efforts to mitigate the current situation and limit the creation of new debris are useful, recent studies predicting debris evolution have indicated that these will not be enough to ensure humanity?s access to and use of the near-Earth environment in the long-term. Rather, active debris removal (ADR) must be pursued if we are to continue benefiting from and conducting space activities. While the concept of ADR is not new, it has not yet been implemented. This is not just because of the technical feasibility of such a scheme, but also because of the host of economic, legal/regulatory, and political issues associated with debris remediation. The costs of ADR are not insignificant and, in today?s restrictive fiscal climate, are unlikely/to be covered by any single actor. Similarly, ADR concepts bring up many unresolved questions about liability, the protection of proprietary information, safety, and standards. In addition, because of the dual use nature of ADR technologies, any venture will necessarily require political considerations. Despite the many unanswered questions surrounding ADR, it is an endeavor worth pursuing if we are to continue relying on space activities for a variety of critical daily needs and services. Moreover, we cannot ignore the environmental implications that an unsustainable use of space will imply for life on Earth in the long run. This paper aims to explore some of these challenges and propose an economically, politically, and legally viable ADR option. Much like waste management on Earth, cleaning up space junk will likely lie somewhere between a public good and a private sector service. An international, cooperative, public-private partnership concept can address many of these issues and be economically sustainable, while also driving the creation of a proper set of regulations, standards and best practices.     

Space Debris at the United Nations

Rules for activities in outer space are agreed upon in the Committee on the Peaceful Uses of Outer Space of the United Nations. Several international treaties have been adopted in the 1970s, that is, at a time before space debris became a concern for the international community. In the years 1979–1988 numerous documents were prepared by the UN Secretariat on space debris, but no official discussions of the problem were initiated by states members of the COPUOS. First proposals for introducing the matter to the UN appeared around 1988, after important studies on the subject were published by states and leading intergovernmental organizations. Also the International Telecommunication Union became concerned about the proliferation of space debris in the geostationary orbit and adopted in 1993 a recommendation to restrict the generation of debris and to re-orbit satellites approaching the end of their active lives into disposal orbits beyond the belt populated by active satellites. In 1994, the UN started discussing scientific and technical aspects of space debris. In the following years, with the assistance of experts from prominent space agencies, it elaborated a Technical Report on space debris. Legal aspects of the problem have not yet begun being discussed because the necessary consensus among states members of the COPUOS has not yet been achieved. Very recently, the UN received first information on a wider subject, space traffic management.     

现代小卫星的发展及轨道垃圾问题

文章首先综述半个多世纪以来传统和现代小卫星的技术发展,特别是现代小卫星在对地观测、通信导航、空间技术实验与演示、深空探测、军事等方面的应用取得很多成就,尤其是对地观测高分辨率成像系统取得了突破性技术成就;其次讨论小卫星所产生的轨道垃圾及其影响和处理;最后提出未来小卫星技术发展十个原则,对未来小卫星的应用作了展望。     

Density and mass distributions of orbital debris

Area-to-mass ratios for orbital debris tracked by the U.S. Space Command were calculated from observed changes in apogee and perigee altitude due to atmospheric drag. The area-to-masses observed for the orbital debris were similar to those found for debris from laboratory breakups, and suggest that much of the debris is composed of crumpled thin plates or of insulation material with low effective density. Areas for the debris objects were derived from radar cross-section data. Object masses were calculated from the ratio of the RCS-derived area to the area-to-mass ratio. Analysis of the distributions of fragment masses from the breakups suggests that in many cases, only a portion of the initial object breaks up into small fragments.     

Biobjective planning of an active debris removal mission

The growth of the orbital debris population has been a concern to the international space community for several years. Recent studies have shown that the debris environment in Low Earth Orbit (LEO, defined as the region up to 2000 km altitude) has reached a point where the debris population will continue to increase even if all future launches are suspended. As the orbits of these objects often overlap the trajectories of satellites, debris create a potential collision risk. However, several studies show that about 5 objects per year should be removed in order to keep the future LEO environment stable. In this article, we propose a biobjective time dependent traveling salesman problem (BiTDTSP) model for the problem of optimally removing debris and use a branch and bound approach to deal with it.     

Analysis on coverage ability of BeiDou navigation satellite system for manned spacecraft

To investigate the service ability of the BeiDou Navigation Satellite System (BDS) for manned spacecraft, both the current regional and the future-planned global constellations of BDS are introduced and simulated. The orbital parameters of the International Space Station and China׳s Tiangong-1 spacelab are used to create the simulation scenario and evaluate the performance of the BDS constellations. The number of visible satellites and the position dilution (PDOP) of precision at the spacecraft-based receiver are evaluated. Simulation and analysis show quantitative results on the coverage ability and time percentages of both the current BDS regional and future global constellations for manned-space orbits which can be a guideline to the applications and mission design of BDS receivers on manned spacecraft.     

Transparency and confidence-building measures for space security

Transparency and confidence-building measures (TCBMs) are a set of tools designed to display, predict and discipline states’ behaviour with respect to maintaining the security of space. With intentional and unintentional threats to the peaceful use of space on the rise, there is a growing international consensus on the need for greater transparency in space-related activities as well as confidence-building measures to reduce the prospects of disruption to the ever-expanding role of space in our day-to-day lives. Terrestrial TCBMs can serve as a guide to understanding what political arrangements are possible in space, including certain precedents in the areas of arms control, non-proliferation and disarmament. At the same time, current and emerging challenges in space - including orbital space debris, risk of collisions, growing saturation of the radiofrequency spectrum, the crowding of satellites in geostationary (GEO) orbit and threat of purposeful disruption - need to be evaluated in the context of unilateral, bilateral, multilateral and private initiatives to increase space situational awareness and security. This paper describes and evaluates various prospective TCBMs alongside current proposals to advance safety and security in space, including the EU Draft Code of Conduct for Outer Space Activities. It offers specific recommendations, arguing that Europe is uniquely qualified to negotiate a 21st century TCBM architecture thanks to its history of diplomacy and ability to identify common ground among disparate parties. This will only happen, however, with a more defined institutional design and the EU’s emergence as a global civilian leader.