Proceedings of the Workshop - United Nations Office for Outer ...

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198 MAINTAINING THE SPACE ENVIRONMENTcomposed mainly of silicate minerals or iron andnickel, or both, minerals and metals. Their total massentering the atmosphere has been estimated at 170thousand tons per year, including 10 thousand tons ofmetalsThe space environmentFor the purposes of this paper we shall understand asspace environment those regions around the Earthwhere artificial satellites can survive for at least oneorbit. The lower limit is at approximately 100 kmaltitude. That value is a reasonably goodapproximation for most existing satellites. The precisevalue o f the limiting altitude depends on theconstruction o f a satellite, being lower for heavycompact objects and higher for lightweight objectswith a small mass per area, such as inflated balloons.The limiting altitude depends also on the actual solaractivity. If the activity is high, the temperature of theatmosphere gets higher than normal and so does thebraking force on satellites. Consequently, satellitestend to de-orbit at a higher altitude than at times witha normal solar activity.The outer limit o f the region where Earth satellitescan exist is far beyond the orbit of the Moon, atapproximately 1 million kilometres from the Earth.Objects beyond that distance do not orbit around theEarth, they orbit around the Sun.Orbits o f most satellites, including mannedspacecraft, lie in Low Earth Orbit, LEO, between 200-2000 km altitude. In High Earth Orbits, HEO, beyond2000 km altitude, the number of objects isconsiderably less. There are, however, two regionswhich are more populated than others. One is a beltfavoured by navigation satellite systems at around20,000 km, the other is the geostationary orbital belt,GEO, at around 36,000 km. GEO is mostly populatedby telecommunication satellite systems and bymeteorological satellites. Beyond the GEO there areonly the apogees of satellites of the Molniyacommunication system at around 40,000 km, orbits ofa few scientific satellites, and from time to time apassing interplanetary probe.The total number o f active satellites is around 600.Out of that number about 240 are in the GEO. Thesenumbers are in a strong contrast with the total numberof objects. There are at present in orbit over 9,000objects larger than 10 cm, over 100,000 o f objectsbetween 1-10 cm, and tens of millions o f objectssmaller than 1 cm.The lifetimes o f satellites are determined mainly bythe drag o f the rarefied atmosphere. The drag makesthe satellites to spiral down and eventually to decay.The stronger the drag, the steeper is the spiral and theshorter is the remaining lifetime. De-orbiting objectsget heated by friction with atmospheric gases and mostof their mass evaporates. Only the most compactfragments reach the ground, their shapes disfigured bythe high temperature and by the impact.At 200 km altitude the lifetimes are o f a few days,at 600 km up to 30 years and at the highest altitude ofLEO, at 2000 km the lifetimes attain 20,000 years.Satellites at the geostationary orbit are permanentfeatures, their lifetimes exceeding several millionyears.Space debrisDetails on the measurements, on modelling of thespace debris population and on space debris mitigationmeasures appeared in the Technical Report1 of theScientific and Technical Subcommittee. The Reportwas prepared with the assistance o f the Inter-AgencySpace Debris Coordination Committee, IADC,consisting of representatives of space agencies of mostactive space faring countries. It lists measures forreducing the risk posed by space debris. Thesemeasures have to remain within technical as well asfinancial possibilities o f the agencies. Otherwise theywould make future activities prohibitively difficult andcostly.The final version of the report, as adopted by theScientific and Technical Subcommittee in 1999, was1 Technical report on space debris of the Scientific andTechnical Subcommittee, A/AC. 105/720.
MAINTAINING THE SPACE ENVIRONMENT 199considered, besides the IADC, also by the InternationalAcademy o f Astronautics, IAA, representing thescientific community. The Report will be furtherconsidered by the Committee on the Peaceful Uses ofOuter Space, COPUOS. That committee will decidewhat further steps should be taken in dealing with theproblem o f space debris.The Report concludes2: "Space objects withdiameters larger than 10 cm in LEO and larger than1 m in GEO can be observed and tracked. More than8,500 catalogued objects are in Earth orbit. Thenumber o f in-orbit catalogued objects has beenincreasing at a relatively linear rate fo r the pastseveral decades. ... The trends and tendenciespredicted fo r the future orbital debris environmentare qualitatively in agreement ... The limitation o fmission-related debris and the prevention o faccidental explosions have been found effective andhave already been introduced to some extent. Also,the transfer o f GEO spacecraft into disposal orbits atthe end o f their active life is already customarypractice. ... For some satellites on long lifetime LEOorbits, a transfer to shorter lifetime orbits is plannedat the end o f their active life. Such procedures, ingeneral, could be most effective. ... Since most o f themitigation measures introduce some burden tomissions, it would be beneficial i f the same mitigationprocedures are considered globally. ”“In most cases, man-made space debris todayposes little risk to the successful operations o fapproximately 600 active spacecraft now in Earthorbit. However, the known and assessed population o fdebris is growing, and the probabilities o f potentiallydamaging collisions will consequently increase.Because o f the difficulty o f improving the spaceenvironment with existing technologies, theimplementation o f some debris mitigation measurestoday is a prudent step towards preserving space fo rfuture generations .... ”Questions arising from the growing number ofsatellites in orbit have been also considered by theFifth International Space Cooperation Workshop“Solving Global Problems”, organized by theAmerican Institute of Aeronautics and Astronautics,AIAA, was held at Bermuda, 11-15 April 19993. Theworkshop adopted several recommendations whichhave been presented recently to the Technical Forum.This session can either express its support to some ofthe recommendations or it can formulate its ownrecommendations. For the convenience o f this session,selected recommendations o f the AIAA workshopfollow:1. On the work of the COPUOS done withassistance o f the IADC and the IAA:"The Workshop participants strongly supportwork being done by the UN, the IADC, the IAA, andothers to develop guidelines designed to minimize thecreation o f new debris objects. ”“The Workshop recommends that existing andfu ture debris minimization guidelines be applieduniformly and consistently by the entire internationalspace faring community. In addition, governmentlicensing agencies are encouraged to promote suchcompliance among the space community in theirrespective countries. ”“In addition to minimizing the creation o f newdebris, the problem o f on-orbit debris must beaddressed Mitigation o f debris on orbit can beaddressed in at least two ways. First, by moving largedebris, such as satellites at the end o f operationallifetime, out o f the way o f active satellite orbits andsecond, by the active removal o f visible, butuntracked smaller debris. Some aerospace companiesare not including de-orbit capabilities on theirspacecraft, and hence these spacecraft will contributeto the problems o f orbital congestion and debris wellpast their operational lifetimes. ”2. On de-orbiting of spacecraft:“Governments and the commercial sector areencouraged to promote the application o f technical2 For a verbatim version and for details, the reader is referredto the original document.3 For details and justification see the Report on the workshoppublished by the AIAA and presented in the Technical Forumon 20 July 1999.
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ST/SPACE/2Office for Outer Space Af
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IntroductionThe Workshop on Space L
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CONCLUSIONS AND PROPOSALS OF THEWOR
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3between public and private law and
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6provide for the application of int
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8obstacles that impede ratification
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SESSION ONEExisting United Nations
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EXISTING UNITED NATIONS TREATIES: S
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EXPANDING GLOBAL LAUNCH SERVICESSES
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48low earth orbit. This commercial
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EXPANDING GLOBAL COMMUNICATIONS SER
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SESSION FOURExpanding Global Remote
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EXPANDING GLOBAL REMOTE SENSING SER
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THE ROLES OF INTERNATIONAL ORGANIZA
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Page 226 and 227: 220Session 3: Wednesday. 21 July. 1
Page 229 and 230: 223Annex IITHIRD UNITED NATIONS CON
Page 231 and 232: 225No Name Address E-Mail27. Ersfel
Page 233 and 234: 227No Name Address E-Mail57. Koloso
Page 235 and 236: 229No Name Address E-Mail86. Noack,
Page 237 and 238: 231No Name Address E-Mail117. Steph
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