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.     

Benefits and risks of using electrodynamic tethers to de-orbit spacecraft

By using electrodynamic drag to greatly increase the orbital decay rate, an electrodynamic space tether can remove spent or dysfunctional spacecraft from low Earth orbit (LEO) rapidly and safely. Moreover, the low mass requirements of such tether devices make them highly advantageous compared to conventional rocket-based de-orbit systems. However, a tether system is much more vulnerable to space debris impacts than a typical spacecraft and its design must be proved to be safe up to a certain confidence level before being adopted for potential applications. To assess space debris related concerns, in March 2001 a new task (Action Item 19.1) on the “Potential Benefits and Risks of Using Electrodynamic Tethers for End-of-life De-orbit of LEO Spacecraft” was defined by the Inter-Agency Space Debris Coordination Committee (IADC). Two tests were proposed to compute the fatal impact rate of meteoroids and orbital debris on space tethers in circular orbits, at different altitudes and inclinations, as a function of the tether diameter to assess the survival probability of an electrodynamic tether system during typical de-orbiting missions. IADC members from three agencies, the Italian Space Agency (ASI), the Japan Aerospace Exploration Agency (JAXA) and the US National Aeronautics and Space Administration (NASA), participated in the study and different computational approaches were specifically developed within the framework of the IADC task. This paper summarizes the content of the IADC AI 19.1 Final Report. In particular, it introduces the potential benefits and risks of using tethers in space, it describes the assumptions made in the study plan, it compares and discusses the results obtained by ASI, JAXA and NASA for the two tests proposed. Some general conclusions and recommendations are finally extrapolated from this massive and intensive piece of research.     

Compliance of disposal orbits with the French Space Operations Act: The Good Practices and the STELA tool

Space debris mitigation is one objective of the French Space Operations Act (FSOA), in line with Inter-Agency Space Debris Coordination Committee (IADC) recommendations, through the removal of non-operational objects from populated regions. At the end of their mission, space objects are to be placed on orbits that will minimize future hazards to space objects orbiting in the same region. The FSOA, which came into force in 2010, ensures that technical risks associated with space activities are properly mitigated. The Act confers CNES a central support role in providing technical expertise to government on regulations dealing with space operations. In order to address the compliance of disposal orbits with the law technical requirements, CNES draws up Good Practices as well as a dedicated tool, Semi-analytic Tool for End of Life Analysis (STELA).     

Space debris mitigation measures applied to European launchers

In November 1986, more than 20 years ago, an H8 upper stage of Ariane 1 exploded in orbit nine months after the end of its mission. So as to avoid the generation of debris in low Earth orbit, a dedicated complementary development modified the design, introducing systematic passivation of the stage. Ever since this event, space debris mitigation has been a major concern for all launcher activities in Europe.After a short recall of the launchers currently operated by Arianespace as well as those currently developed by ESA with CNES, particularly for the safeguard authority, including the most promising future evolutions, the set of applicable regulations is described. These rules are fundamentally derived from the IADC Guidelines (hence the UNCOPUOS ones), translated into European Code of Conduct and in some more applicable Standards, such as the one prepared by ESA. The process of preparing ISO standards, mainly through the ECSS Working Group, is also described.Three major families can be identified: minimization of Mission Related Objects, Passivation of stages at the end of mission, and orbital protected zones including the so-called 25-year rule.The paper describes how European launchers do or will fulfill these applicable standards, quantifying the efficiency of the mitigation rules, and describing improvement actions currently under study.     

地球静止轨道空间碎片的处置

介绍了国际机构间碎片协调委员会提出的关于地球静止轨道（GEO）空间碎片问题的研究结果和碎片处置的建议，主要内容包括：GEO与GEO环的概念、EGO上物体现状，EGO空间碎片处置的基本原则和8条具体处置措施建议。该建议已于2000年2月提交联合国和平利用外层空间委员会科技小组委员会第37届会议。     

International Practices to Protect the Geostationary Ring

Since more than 20 years reorbiting of geostationary satellites at the end of their mission is recommended and partially performed to protect the GEO environment. Now a worldwide accepted reorbiting altitude was defined by the Inter-Agency Space Debris Coordination Committee (IADC). Still only one-third of the aging satellites follow this IADC rule. Based on orbital data in the DISCOS database, the situation in the geostationary ring is analyzed. From 878 known objects, 305 are controlled inside their longitude slots, 353 are drifting above, below or through GEO, and 125 are in a libration orbit (status of January 2001). In the last four years (1997–2000) 58 spacecraft reached end-of-life. Twenty of them were reorbited in compliance with the IADC recommendations, 16 were reorbited below this recommendation and 22 were abandoned without any end-of-life disposal manoeuvre.     

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.     

Satellite end of life constraints: Technical and organisational solutions

Since 1974 with the radiocommunication satellite Symphony1, CNES launched and operated 11 GEO and 20 LEO satellites. During those 36 years, both flight segment and ground segment dramatically evolved and operational organisations and techniques equally improved. At the present time, CNES operates 1 GEO satellite and 17 LEO satellites with not much more people and costs than in 1986 when its first Satellite Operation Direction in Toulouse was only in charge of Telecom1A, Telecom1B and Spot1. This fantastic technical evolution combined with the huge increase of services to citizens and governments given by Space systems was unfortunately also associated with an enormous growth of space pollution by debris of all sizes. From the beginning, CNES was a major actor of the international effort to promote regulations in order to try to reduce or at least control this problematic situation. Internally, CNES, not only set up an operational on-call service to deal with collision risks, but decided to do its best to apply the new guidelines to the end of life of satellites under its responsibility even for those developed and launched a very long time ago. For instance, that was the case in 2009 for the reorbitation of the GEO satellite Telecom 2C (launched in 1995) and for the deorbitation of the LEO satellite Spot2 (launched in 1990). In addition, CNES prepares procedures to be able to be as exemplary as possible for its other spacecrafts whose end of life approaches. The constraints and challenges to face in order to cope with these new requirements are multiple: choice of final orbit, realistic calculation of re-entry duration, estimation of residual propellant, electric passivation, management of explosion risks… All these studies and operational experience gained will be helpful for the new role of CNES, which recently became in charge of controlling space operators in the frame of the new French space law on space operations.     

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.     

Assuring the sustainability of space activities

The growth of new space systems and the continued creation of orbital debris could in a few years make activities in Earth orbit unsustainable, so finding cost-effective ways to sustain space activities in Earth orbit is essential. Because outer space activities serve the needs of the military–intelligence, civil, and commercial communities, each with their own requirements, creating the necessary international agreements for reaching and maintaining a condition of sustainability will not be easy. This paper summarizes the primary issues for the international space community regarding our future ability to reap the benefit of space systems in Earth orbit. It explores several of the efforts to develop international agreements that would lead to or support the sustainability of space activities and examines the benefits and drawbacks of each approach. In particular, it reviews progress within the UN COPUOS, and examines the EU's proposal for an international Code of Conduct for Outer Space Activities. It also notes the need for states to establish or expand their own space legal infrastructure to conform to the UN treaties and guidelines for space activities.     

Assessing the Risk of Orbital Debris Impact

A Space Debris Impact Risk Analysis Tool (SDIRAT) was developed and implemented to assess the orbital debris impact risk on a specified target in Earth orbit, in terms of flux, relative velocity, impact velocity, direction of the incoming particles, debris mass and diameter. Based on a deterministic approach, SDIRAT uses a realistic orbital debris population where each representative particle is identified by its rectangular coordinates (position and velocity) at a reference epoch. Using this information, some geometrical algorithms were developed and implemented to evaluate the contribution of each particle to the incoming flux. The position of the particle with respect to a specified target drives the selection criteria to reject, or select, it as a possible projectile. On the other hand, the relative velocity vector can be used to estimate the impact direction of the incoming flux. SDIRAT was conceived as a general tool for a variety of scenarios, such as low circular and elliptical orbits, up to the geosynchronous ring. This paper presents some examples of possible applications, including the computation of the incoming debris flux on SAX (low Earth orbit), SIRIO (geosynchronous orbit) and the IRIS upper stage (elliptical orbit). Other applications assess the impact risk for the Soviet Radar Ocean Reconnaissance Satellites Cosmos 1900 and Cosmos 1932.     

GEO卫星寿命末期离轨控制策略

根据机构间空间碎片协调委员会(IADC)1997年的建议,提出了一种采用多次两脉冲霍曼变轨对寿命末期地球同步轨道(GEO)卫星实施离轨控制的策略。分析了剩余燃料充足时变轨中燃料消耗的计算,以及剩余燃料不足时应采用一次两脉冲霍曼变轨使卫星尽可能离开GEO的对策。仿真结果表明,该离轨控制策略可行。     

The french educational satellite arsene

ARSENE (Ariane, Radio-amateur, Satellite pour l'ENseignement de l'Espace) is a telecommunications satellite for Amateur Space Service. Its main feature is that more than 100 students from French engineering schools and universities have been working since 1979 for definition phase and satellite development. The highest IAF awards has been obtained by “ARSENE students” in Tokyo (1980) and Rome (1981). The French space agency, CNES and French aerospace industries are supporting the program. The European Space Agency offered to place ARSENE in orbit on the first Ariane mark IV launch late 1985.     

Ariane 5 ECA's upper stage perigee reduction via passivation manoeuvre

When Ariane 5 ECA development has been decided by Europe to increase Ariane 5 performance, the rule of 25 years in GTO orbit for the upper stage has been anticipated. This was 14 years ago and this rule was known to be satisfied with a perigee lower than 250 km. Even when lowering slightly Ariane 5 ECA performance, this maximum perigee altitude has been held and the whole Launch System has been developed under CNES responsibility with this GTO perigee. In the meantime, more precise calculations demonstrated that such a GTO perigee was giving for the ESCA a mean lifetime higher than 25 years. So studies are in progress inside CNES to decrease the perigee and re-enter inside the 25 years lifetime domain. This paper presents a CNES study to reduce the orbital lifetime of Ariane 5's upper stage that last in GTO after each commercial mission. Usually the aimed orbit has a perigee altitude of 250 km, an apogee altitude near to the geostationary position and an inclination between 2° and 7°. These conditions make stage's mean lifetime superior to 90 years. The CNES study is to expose the possibility to decrease this lifetime by reducing the perigee altitude of the final upper stage orbit through a passivation process optimised to produce orbit modification. It is shown that taking into account material and functional stage constraints the optimised passivation process is able to decrease the perigee by a few tenths of kilometres.     

美国DMSP-F13卫星解体事件对空间碎片环境影响分析

2015 年2 月3 日,美国DMSP-F13 卫星发生爆炸解体,产生了百余块编目空间碎片。该卫星解体碎片主要分布在轨道高度600～1200 km 范围内,其中近50%的编目碎片在轨寿命将超过20 年,会对未来空间碎片环境构成长期影响。结合我国空间碎片环境工程模型SDEEM 对DMSP-F13 解体事件的分析结果显示,此次解体事件造成邻近轨道区域内空间碎片空间密度增加,对该区域航天器安全运行产生影响。     

Flight demonstration of formation flying capabilities for future missions (NEAT pathfinder)

PRISMA is a demonstration mission for formation-flying and on-orbit-servicing critical technologies that involves two spacecraft launched in low Earth orbit in June 2010 and still in operation. Funded by the Swedish National Space Board, PRISMA mission has been developed by OHB-Sweden (formerly Swedish Space Corporation) with important contributions from the German Aerospace Centre (DLR/GSOC), the French Space Agency (CNES), and the Technical University of Denmark (DTU). The paper focuses on the last CNES experiment achieved in September 2012 that was devoted to the preparation of future astrometry missions illustrated by the NEAT and µ-NEAT mission concepts. The experiment consisted of performing the type of formation maneuvers required to point the two-satellite axis to a celestial target and maintain it fixed during the observation period. Achieving inertial pointing for a LEO formation represented a new challenge given the numerous constraints from propellant usage to star tracker blinding. The paper presents the experiment objectives in relation with the NEAT/µ-NEAT mission concept, describes its main design features along with the guidance and control algorithms evolutions and discusses the results in terms of performances achieved during the two rehearsals.     

The origins of the “Long-term Sustainability of Outer Space Activities” initiative at UN COPUOS

The success of space-based systems worldwide, providing services to society and satisfying defence and security needs, has led to a situation where outer space is increasingly crowded. In addition, the rapid proliferation of space debris threatens the safe utilization of outer space on the most commonly used orbits. Beyond the mitigation of the orbital debris threat, additional measures will be needed to ensure the safety and security of activities in outer space for the long-term. This article describes the initiative to introduce a new agenda item in the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), first presented to COPUOS delegations in 2007, which led to a formal decision in 2009. This in turn led to the establishment of a dedicated Working Group of the Scientific and Technical Sub-Committee in 2010, with a work plan leading to a report and associated recommendations in 2014. Some references are made to other initiatives affecting space security, such as the Russia–China draft treaty (PPWT) tabled at the Conference on Disarmament and the EU-proposed Code of Conduct.     

空间碎片减缓策略效果仿真

根据机构间空间碎片协调委员会(IADC)和欧空局(ESA)的空间碎片减缓要求,在建立航天发射、爆炸和碰撞模型,以及碎片演化机制的基础上,对常规发射(BAU)、禁止在轨爆炸(NO-EX)和全面减缓(MIT)三种空间碎片减缓策略条件下,对2000~2100年空间碎片环境进行了仿真计算。结果表明,禁止航天器在轨爆炸、对失效的卫星和火箭上面级实施离轨操作,以及在航天器的发射和运行中不产生或抛弃分离物等减缓措施是限制空间碎片数量增长的有效方法。     

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.     

Effect of Multi-wall System Composition on Survivability for Spacecraft Impacted by Orbital Debris

Long-duration spacecraft in low earth orbit such as the International Space Station (ISS) are highly susceptible to high-speed impacts by pieces of debris from past earth-orbiting missions. Among the hazards that accompany the penetration of a pressurized manned spacecraft are critical crack propagation in the module wall, crew hypoxia, and uncontrolled thrust due to air rushing out of the module wall hole. A Monte Carlo simulation tool was used to determine the effect of spacecraft wall construction on the survivability of ISS modules and crew following an orbital debris penetration. The simulation results indicate that enhanced shield wall designs (i.e., multi-wall systems with heavier inner bumpers) always lead to higher overall survivability of the station and crew due to an overwhelming decrease in likelihood of module penetration. The results of the simulations also indicate that changes in crew operations, equipment locations, and operation procedures can significantly reduce the likelihood of crew or station loss following an orbital debris penetration.