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Space debris

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Space debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 around Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s to erosion, explosion and collision fragments. As the orbits of these objects often overlap the trajectories of newer objects, debris is a potential collision risk to operational spacecraft.

The vast majority of the estimated tens of millions of pieces of space debris are small particles, less than 1 centimetre (0.393700787401575 in). These include dust from solid rocket motors, surface degradation products such as paint flakes, and coolant released by RORSAT
RORSAT
Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar...

 nuclear powered satellites. Impacts of these particles cause erosive damage, similar to sandblasting. This damage can be partly mitigated through the use of the "meteor bumper
Whipple shield
The Whipple shield or Whipple bumper, invented by Fred Whipple, is a type of hypervelocity impact shield used to protect manned and unmanned spacecraft from collisions with micrometeoroids and orbital debris whose velocities generally range between ....

", which is widely used on spacecraft such as the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

. However, not all parts of a spacecraft may be protected in this manner, e.g. solar panels and optical devices (such as telescopes, or star trackers), and these components are subject to constant wear by debris, and to a much lesser extent, micrometeorites.

A much smaller number of the debris objects are larger, over 10 centimetres (3.9 in). Against larger debris, the only protection is to maneuver the spacecraft in order to avoid a collision. If a collision with larger debris does occur, many of the resulting fragments from the damaged spacecraft will be in the 1 kilograms (2.2 lb) mass range, and these objects become an additional collision risk. As the chance of collision is a function of the number of objects in space, there is a critical density where the creation of new debris occurs faster than the various natural forces that remove these objects from orbit. Beyond this point a runaway chain reaction
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....

 can occur that reduces all objects in orbit to debris in a period of years or months. This possibility is known as the "Kessler Syndrome
Kessler Syndrome
The Kessler syndrome , proposed by NASA scientist Donald J...

", and there is debate as to whether or not this critical density has already been reached in certain orbital bands.

A runaway Kessler Syndrome would render the useful polar-orbiting bands difficult to use, and greatly increase the cost of space launches and missions.
Measurement, growth mitigation and active removal of space debris are major activities within the space industry today.

Micrometeorites


In 1946, during the Giacobinid meteor shower, Helmut Landsberg
Helmut Landsberg
Helmut Erich Landsberg was a noted and influential climatologist. He was born in Frankfurt, Germany, February 9, 1906 and died December 6, 1985 in Geneva, Switzerland while attending a meeting of the World Meteorological Organization. Landsberg was an important figure in meteorology and...

 collected several small magnetic particles that apparently were associated with the shower. Fred Whipple was intrigued by this and wrote a paper that demonstrated that particles of this size were too small to maintain their velocity when they encountered the upper atmosphere. Instead, they quickly decelerated and then fell to Earth unmelted. In order to classify these sorts of objects, he coined the term "micro-meteorites
Micrometeoroid
A micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.-Scientific interest:...

".

Whipple, in collaboration with Fletcher Watson of the Harvard Observatory, led an effort to build an observatory to directly measure the velocity of the meteors that could be seen. At the time the source of the micro-meteorites was not known. Direct measurements at the new observatory were used to locate the source of the meteors, demonstrating that the bulk of material was leftover from comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

 tails, and that none of it could be shown to have an extra-solar origin. Today it is understood that meteors of all sorts are leftover material from the formation of the solar system, consisting of particles from the interplanetary dust cloud
Interplanetary dust cloud
The interplanetary dust cloud is cosmic dust which pervades the space between planets in the Solar System and in other planetary systems...

 or other objects made up from this material, like comets.

The early studies were based on optical measures only. In 1957 Hans Pettersson conducted one of the first direct measurements of the fall of space dust on the Earth, estimating it to be 14,300,000 tons per year. This suggested that the meteor flux in space was much higher than the number based on telescope observations. Such a high flux presented a very serious risk to missions deeper in space, specifically the high-orbiting Apollo
Project Apollo
The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...

 capsules. To determine whether the direct measure was accurate, a number of additional studies followed, including the Pegasus satellite program
Pegasus satellite program
The Pegasus satellite program was a series of three American satellites launched in 1965 to study the frequency of micrometeorite impacts on spacecraft...

. These showed that the rate of meteorites passing into the atmosphere, or flux, was in line with the optical measures, at around 10,000 to 20,000 tons per year.

Micrometeorite shielding


Whipple's work pre-dated the space race
Space Race
The Space Race was a mid-to-late 20th century competition between the Soviet Union and the United States for supremacy in space exploration. Between 1957 and 1975, Cold War rivalry between the two nations focused on attaining firsts in space exploration, which were seen as necessary for national...

 and it proved useful when space exploration started only a few years later. His studies had demonstrated that the chance of being hit by a meteor large enough to destroy a spacecraft was extremely remote. However, a spacecraft would be almost constantly struck by micrometeorites, about the size of dust grains.

Whipple had already developed a solution to this problem in 1946. Originally known as a "meteor bumper" and now termed the Whipple shield
Whipple shield
The Whipple shield or Whipple bumper, invented by Fred Whipple, is a type of hypervelocity impact shield used to protect manned and unmanned spacecraft from collisions with micrometeoroids and orbital debris whose velocities generally range between ....

, this consists of a thin foil film held a short distance away from the spacecraft's body. When a micrometeorite strikes the foil, it vaporizes into a plasma that quickly spreads. By the time this plasma crosses the gap between the shield and the spacecraft, it is so diffuse that it is unable to penetrate the structural material below. The shield allows a spacecraft body to be built to just the thickness needed for structural integrity, while the foil adds little additional weight. Such a spacecraft is lighter than one with panels designed to stop the meteors directly.

For spacecraft that spend the majority of their time in orbit, some variety of the Whipple shield has been almost universal for decades. Later research showed that ceramic fiber
Ceramic engineering
Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high purity chemical solutions...

 woven shields offer better protection to hypervelocity (~7 km/s) particles than aluminum shields of equal weight. Another modern design uses multi-layer flexible fabric, as in NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's TransHab
Transhab
TransHab was a concept pursued by NASA to develop the technology for expandable habitats inflated by air in space. Specifically, TransHab was intended as a replacement for the already existing rigid International Space Station crew Habitation Module. When deflated, inflatable modules provide an...

 expandable space habitation module.

Kessler's asteroid study


As space missions moved out from the Earth and into deep space, the question arose about the dangers posed by the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

 environment, which probes would have to pass through on voyages to the outer solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. Although Whipple had demonstrated that the near-Earth environment was not a problem for space travel, the same depth of analysis had not been applied to the belt. Starting in late 1968, Donald Kessler published a series of papers estimating the spatial density of asteroids. The main outcome of this work was the demonstration that risks in transiting the asteroid belt could be mitigated, and the maximum possible flux was about the same as the flux in near-Earth space. A few years later, the Pioneer
Pioneer program
The Pioneer program is a series of United States unmanned space missions that was designed for planetary exploration. There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system...

 and Voyager
Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...

 missions demonstrated this to be true by successfully transiting this region.

The evolution of the asteroid belt had been studied as a dynamic process since it was first considered by Ernst Öpik. Öpik's seminal paper considered the effect of gravitational influence
Perturbation (astronomy)
Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....

 of the planets on smaller objects, notably the Mars-crossing asteroids, noting that their expected lifetime was on the order of billions of years. A number of papers explored this work further, using elliptical orbits for all of the objects and introducing a number of mathematical refinements. Kessler used these methods to study Jupiter's moons, calculating expected lifetimes on the order of billions of years and demonstrating that several of the outer moons were almost certainly the result of recent collisions.

NORAD, Gabbard and Kessler


Since the earliest days of the space race
Space Race
The Space Race was a mid-to-late 20th century competition between the Soviet Union and the United States for supremacy in space exploration. Between 1957 and 1975, Cold War rivalry between the two nations focused on attaining firsts in space exploration, which were seen as necessary for national...

, the North American Aerospace Defense Command
North American Aerospace Defense Command
North American Aerospace Defense Command is a joint organization of Canada and the United States that provides aerospace warning, air sovereignty, and defense for the two countries. Headquarters NORAD is located at Peterson AFB, Colorado Springs, Colorado...

 (NORAD) has maintained a database of all known rocket launches and the various objects that reach orbit as a result – not just the satellites themselves, but the aerodynamic shields that protected them during launch, upper stage booster rockets that placed them in orbit, and in some cases, the lower stages as well. This was known as the Space Object Catalog when it was created with the launch of Sputnik
Sputnik 1
Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...

 in 1957. NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 published modified versions of the database in the now common two-line element set format via mail, and starting in the early 1980s, the CelesTrak Bulletin Board System
Bulletin board system
A Bulletin Board System, or BBS, is a computer system running software that allows users to connect and log in to the system using a terminal program. Once logged in, a user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging...

 (BBS) re-published them.
The trackers that fed this database were aware of a number of other objects in orbit, many of which were the result of on-orbit explosions. Some of these were deliberately caused during the 1960s anti-satellite weapon
Anti-satellite weapon
Anti-satellite weapons are designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former Soviet Union, and the People's Republic of China are known to have developed these weapons. On September 13, 1985, the United States destroyed US...

 (ASAT) testing, while others were the result of rocket stages that had "blown up" in orbit as leftover fuel expanded into a gas and ruptured their tanks. Since these objects were only being tracked in a haphazard manner, a NORAD employee, John Gabbard, took it upon himself to keep a separate database of as many of these objects as he could. Studying the results of these explosions, Gabbard developed a new technique for predicting the orbital paths of their products. "Gabbard diagrams" (or plots) have since become widely used. Along with Preston Landry, these studies were used to dramatically improve the modelling of orbital evolution and decay.

When NORAD's database first became publicly available in the 1970s, Kessler applied the same basic technique developed for the asteroid belt study to the database of known objects. In 1978, Kessler and Burton Cour-Palais co-authored the seminal Collision Frequency of Artificial Satellites: The Creation of a Debris Belt, which showed that the same process that controlled the evolution of the asteroids would cause a similar collisional process in low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

 (LEO), but instead of billions of years, the process would take just decades. The paper concluded that by about the year 2000, the collisions from debris formed by this process would outnumber micrometeorites as the primary ablative risk to orbiting spacecraft.

At the time this did not seem like cause for major concern, as it was widely held that drag from the upper atmosphere would de-orbit the debris faster than it was being created. However, Gabbard was aware that the number of objects in space was under-represented in the NORAD data, and was familiar with the sorts of debris and their behaviour. Shortly after Kessler's paper was published, Gabbard was interviewed on the topic, and he coined the term "Kessler syndrome
Kessler syndrome
The Kessler syndrome , proposed by NASA scientist Donald J...

" to refer to the orbital regions where the debris had become a significant issue. The reporter used the term verbatim, and when it was picked up in a Popular Science
Popular Science
Popular Science is an American monthly magazine founded in 1872 carrying articles for the general reader on science and technology subjects. Popular Science has won over 58 awards, including the ASME awards for its journalistic excellence in both 2003 and 2004...

article in 1982, the term became widely used. The article won the Aviation/Space Writers Association's 1982 National Journalism Award.

Follow-up studies


A lack of good data about the debris problem prompted a series of studies to better characterize the LEO environment. In October 1979 NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 provided Kessler with additional funding for further studies of the problem. Several approaches were used by these studies.

Optical telescopes or short-wavelength radars were used to more accurately measure the number and size of objects in space. These measurements demonstrated that the published population count was too low by at least 50%. Before this it was believed that the NORAD database was essentially complete and accounted for at least the majority of large objects in orbit. These measurements demonstrated that some objects (typically U.S. military spacecraft) were deliberately eliminated from the NORAD list, while many others were not included because they were considered unimportant, and the list could not easily account for objects under 20 centimetres (7.9 in) in size. In particular, the debris left over from exploding rocket stages and several 1960s anti-satellite tests were only tracked in a haphazard way with the main database.

Spacecraft that had returned to Earth were examined with microscopes, looking for impacts that had already taken place and had gone unnoticed. Sections of Skylab
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...

 and the Apollo CSMs that had been recovered in the 1960s and '70s were shown to be heavily pitted by debris. Every study demonstrated that the debris flux was much higher than expected, and that the debris was already the primary source of collisions in space. LEO was shown to be subject to the Kessler Syndrome, as originally defined. These results were refined by scrutiny of returning spacecraft, including the Solar Maximum Mission
Solar Maximum Mission
The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....

, the Long Duration Exposure Facility
Long Duration Exposure Facility
NASA's Long Duration Exposure Facility, or LDEF, was a school bus-sized cylindrical space experiment rack that exposed various material samples to outer space for about 5.7 years, completing 32,422 Earth orbits.- Construction :...

, numerous Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

 missions, and many others.

One discovery that was particularly disconcerting was that 42% of all cataloged debris was the result of only 19 events, which were all caused by explosions of spent rocket stages, mostly from U.S. Delta rockets. Kessler made this discovery using Gabbard's methods against known debris fields, which overturned the previously held belief that most unknown debris was from formerly unknown ASAT tests. The Delta remained a workhorse of the U.S. space program, and there were numerous other Delta components in orbit that had not yet exploded.

A new Kessler Syndrome


Through the 1980s, the US Air Force ran an experimental program to determine what would happen if debris collided with satellites or other debris. The study demonstrated that the process was entirely unlike the micrometeor case, and that many large chunks of debris would be created that would themselves be a collisional threat. This leads to a worrying possibility – instead of the density of debris being a measure of the number of items launched into orbit, it was that number plus any new debris caused when they collided. If the new debris did not decay from orbit before impacting another object, the number of debris items would continue to grow even if there were no new launches.

In 1991 Kessler published a new work using the best data then available. In "Collisional cascading: The limits of population growth in low earth orbit" he mentioned the USAF's conclusions about the creation of debris. Although the vast majority of debris objects by number was lightweight, like paint flecks, the majority of the mass was in heavier debris, about 1 kilograms (2.2 lb) or heavier. This sort of mass would be enough to destroy any spacecraft on impact, creating more objects in the critical mass area. As the National Academy of Sciences put it:

A 1-kg object impacting at 10 km/s, for example, is probably capable of catastrophically breaking up a 1,000-kg spacecraft if it strikes a high-density element in the spacecraft. In such a breakup, numerous fragments larger than 1 kg would be created.


Kessler's analysis led to the conclusion that the problem could be categorized into three regimes. With a low enough density, the addition of debris through impacts is slower than their rate of decay, and the problem does not become significant. Beyond that is a critical density where additional debris lead to additional collisions. At densities greater than this critical point, the rate of production is greater than decay rates, leading to a "cascade", or chain reaction
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....

, that reduces the on-orbit population to small objects on the order of a few cm in size, making any sort of space activity very hazardous. This third condition, the chain reaction, became the new use of the term "Kessler Syndrome".

In a historical overview written in early 2009, Kessler summed up the situation bluntly:

Aggressive space activities without adequate safeguards could significantly shorten the time between collisions and produce an intolerable hazard to future spacecraft. Some of the most environmentally dangerous activities in space include large constellations such as those initially proposed by the Strategic Defense Initiative in the mid-1980s, large structures such as those considered in the late-1970s for building solar power stations in Earth orbit, and anti-satellite warfare using systems tested by the USSR, the U.S., and China over the past 30 years. Such aggressive activities could set up a situation where a single satellite failure could lead to cascading failures of many satellites in a period of time much shorter than years.

Debris growth


Faced with this scenario, as early as the 1980s NASA and other groups within the U.S. attempted to limit the growth of debris. One particularly effective solution was implemented by McDonnell Douglas
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...

 on the Delta booster, by having the booster move away from their payload and then venting any remaining fuel in the tanks. This eliminated the pressure build-up in the tanks that had caused them to explode in the past. Other countries, however, were not as quick to adopt this sort of measure, and the problem continued to grow throughout the 1980s, especially due to a large number of launches in the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

.

A new battery of studies followed as NASA, NORAD and others attempted to better understand exactly what the environment was like. Every one of these studies adjusted the number of pieces of debris in this critical mass zone upward. In 1981 when Schefter's article was published it was placed at 5,000 objects, but a new battery of detectors in the Ground-based Electro-Optical Deep Space Surveillance system quickly found new objects within its resolution. By the late 1990s it was thought that the majority of 28,000 launched objects had already decayed and about 8,500 remained in orbit. By 2005 this had been adjusted upward to 13,000 objects, and a 2006 study raised this to 19,000 as a result of an ASAT
Anti-satellite weapon
Anti-satellite weapons are designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former Soviet Union, and the People's Republic of China are known to have developed these weapons. On September 13, 1985, the United States destroyed US...

 test and a satellite collision. In 2011, NASA said 22,000 different objects were being tracked.

The growth in object count as a result of these new studies has led to intense debate within the space community on the nature of the problem and earlier dire warnings. Following Kessler's 1991 derivation, and updates from 2001, the LEO environment within the 1000 kilometres (621.4 mi) altitude range should now be within the cascading region. However, only one major incident has occurred: the 2009 satellite collision
2009 satellite collision
The 2009 satellite collision was the first accidental hypervelocity collision between two intact artificial satellites in Earth orbit. The collision occurred at 16:56 UTC on February 10, 2009, at above the Taymyr Peninsula in Siberia, when Iridium 33 and Kosmos-2251 collided...

 between Iridium 33 and Cosmos 2251. The lack of any obvious cascading in the short term has led to a number of complaints that the original estimates overestimated the issue. Kessler has pointed out that the start of a cascade would not be obvious until the situation was well advanced, which might take years.

A 2006 NASA model suggested that even if no new launches took place, the environment would continue to contain the then-known population until about 2055, at which point it would increase on its own. Richard Crowther of Britain's Defence Evaluation and Research Agency
Defence Evaluation and Research Agency
The Defence Evaluation and Research Agency was a part of the UK Ministry of Defence until July 2, 2001. At the time it was the United Kingdom's largest science and technology organisation...

 stated that he believes the cascade will begin around 2015. The National Academy of Sciences, summarizing the view among professionals, noted that there was widespread agreement that two bands of LEO space, 900 to 1000 kilometres (621.4 mi) and 1500 kilometres (932.1 mi) altitudes, were already past the critical density.

In the 2009 European Air and Space Conference, University of Southampton
University of Southampton
The University of Southampton is a British public university located in the city of Southampton, England, a member of the Russell Group. The origins of the university can be dated back to the founding of the Hartley Institution in 1862 by Henry Robertson Hartley. In 1902, the Institution developed...

, UK researcher, Hugh Lewis predicted that the threat from space debris would rise 50 percent in the coming decade and quadruple in the next 50 years. Currently more than 13,000 close calls are tracked weekly.

A report in 2011 by the National Research Council in the USA warned NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 that the amount of space debris orbiting the Earth was at critical level. Some computer models revealed that the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures". The report has called for international regulations to limit debris and research into disposing of the debris.

Large vs. small


Any discussion of space debris generally categorizes large and small debris. "Large" is defined not by its size so much as the current ability to detect objects of some lower size limit. Generally, large is taken to be 10 centimetres (3.9 in) across or larger, with typical masses on the order of 1 kilograms (2.2 lb). Logically it would follow that small debris would be anything smaller than that, but in fact the cutoff is normally 1 centimetre (0.393700787401575 in) or smaller. Debris between these two limits would normally be considered "large" as well, but goes unmeasured due to our inability to track them.

The great majority of debris consists of smaller objects, 1 centimetre (0.393700787401575 in) or less. The mid-2009 update to the NASA debris FAQ
FAQ
Frequently asked questions are listed questions and answers, all supposed to be commonly asked in some context, and pertaining to a particular topic. "FAQ" is usually pronounced as an initialism rather than an acronym, but an acronym form does exist. Since the acronym FAQ originated in textual...

 places the number of large debris items over 10 centimetres (3.9 in) at 19,000, between 1 and 10 centimetres (3.9 in) approximately 500,000, and that debris items smaller than 1 centimetre (0.393700787401575 in) exceeds tens of millions. In terms of mass, the vast majority of the overall weight of the debris is concentrated in larger objects, using numbers from 2000, about 1,500 objects weighing more than 100 kilograms (220.5 lb) each account for over 98% of the 1,900 tons of debris then known in low earth orbit.

Since space debris comes from man-made objects, the total possible mass of debris is easy to calculate: it is the total mass of all spacecraft and rocket bodies that have reached orbit. The actual mass of debris will be necessarily less than that, as the orbits of some of these objects have since decayed. As debris mass tends to be dominated by larger objects, most of which have long ago been detected, the total mass has remained relatively constant in spite of the addition of many smaller objects. Using the figure of 8,500 known debris items from 2008, the total mass is estimated at 5,500 tonnes.

Debris in LEO


Every satellite, space probe and manned mission has the potential to create space debris. Any impact between two objects of sizeable mass can spall
Spall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...

 off shrapnel debris from the force of collision. Each piece of shrapnel has the potential to cause further damage, creating even more space debris. With a large enough collision (such as one between a space station and a defunct satellite), the amount of cascading debris could be enough to render Low Earth Orbit essentially unusable.

The problem in LEO is compounded by the fact that there are few "universal orbits" that keep spacecraft in particular rings, as opposed to GEO, a single widely-used orbit. The closest would be the sun-synchronous orbit
Sun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...

s that maintain a constant angle between the sun and orbital plane. But LEO satellites are in many different orbital planes providing global coverage, and the 15 orbits per day typical of LEO satellites results in frequent approaches between object pairs. Since sun-synchronous orbits are polar, the polar regions are common crossing points.

After space debris is created, orbital perturbations mean that the orbital plane's direction will change over time, and thus collisions can occur from virtually any direction. Collisions thus usually occur at very high relative velocities, typically several kilometres per second. Such a collision will normally create large numbers of objects in the critical size range, as was the case in the 2009 collision. It is for this reason that the Kessler Syndrome is most commonly applied only to the LEO region. In this region a collision will create debris that will cross other orbits and this population increase that leads to the cascade effect.

At the most commonly-used low earth orbits for manned missions, 400 kilometres (248.5 mi) and below, residual air drag helps keep the zones clear. Collisions that occur under this altitude are less of an issue, since they result in fragment orbits having perigee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

 at or below this altitude. The critical altitude also changes as a result of the space weather
Space weather
Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...

 environment, which causes the upper atmosphere to expand and contract. An expansion of the atmosphere leads to an increased drag to the fragments, resulting in a shorter orbit lifetime. An expanded atmosphere for some period of time in the 1990s is one reason the orbital debris density remained lower for some time. Another was the rapid reduction in launches by Russia, which conducted the vast majority of launches during the 1970s and 80s.

Debris at higher altitudes


At higher altitudes, where atmospheric drag is less significant, orbital decay takes much longer. Slight atmospheric drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

, lunar perturbations
Lunar theory
Lunar theory attempts to account for the motions of the Moon. There are many irregularities in the Moon's motion, and many attempts have been made over a long history to account for them. After centuries of being heavily problematic, the lunar motions are nowadays modelled to a very high degree...

, and solar radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...

 can gradually bring debris down to lower altitudes where it decays, but at very high altitudes this can take millennia. Thus while these orbits are generally less used than LEO, and the problem onset is slower as a result, the numbers progress toward the critical threshold much more quickly.

The issue is especially problematic in the valuable geostationary orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...

s (GEO), where satellites are often clustered over their primary ground "targets" and share the same orbital path. Orbital perturbations
Perturbation (astronomy)
Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....

 are significant in GEO, causing longitude drift of the spacecraft, and a precession of the orbit plane if no maneuvers are performed. Active satellites maintain their station via thrusters, but if they become inoperable they become a collision concern (as in the case of Telstar 401
Telstar 401
Telstar 401 was a communications satellite owned by AT&T which was launched in 1993 to replace Telstar 301. It was destroyed by a magnetic storm in 1997....

). There has been estimated to be one close (within 50 meters) approach per year.

On the upside, relative velocities in GEO are low, compared with those between objects in largely random low earth orbits. The impact velocities peak at about 1.5 km/s. This means that the debris field from such a collision is not the same as a LEO collision and does not pose the same sort of risks, at least over the short term. It would, however, almost certainly knock the satellite out of operation. Large-scale structures, like solar power satellites, would be almost certain to suffer major collisions over short periods of time.

In response, the ITU
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...

 has placed increasingly strict requirements on the station-keeping ability of new satellites and demands that the owners guarantee their ability to safely move the satellites out of their orbital slots at the end of their lifetime. However, studies have suggested that even the existing ITU requirements are not enough to have a major effect on collision frequency. Additionally, GEO orbit is too distant to make accurate measurements of the existing debris field for objects under 1 metres (3.3 ft), so the precise nature of the existing problem is not well known. Others have suggested that these satellites be moved to empty spots within GEO, which would require less maneuvering and make it easier to predict future motions. An additional risk is presented by satellites in other orbits, especially those satellites or boosters left stranded in geostationary transfer orbit
Geostationary transfer orbit
A geosynchronous transfer orbit or geostationary transfer orbit is a Hohmann transfer orbit used to reach geosynchronous or geostationary orbit....

, which are a concern due to the typically large crossing velocities.

In spite of these efforts at risk reduction, spacecraft collisions have taken place. The ESA telecommunications satellite Olympus-1
Olympus-1
Olympus-1 was a communications satellite built by British Aerospace for the European Space Agency. At the time of its launch on 12 July 1989, it was the largest civilian telecomms satellite ever built, and sometimes known as "LargeSat" or "L-Sat"...

 was hit by a meteor on 11 August 1993 and left adrift. On 24 July 1996, Cerise
Cerise (satellite)
Cerise was a French military reconnaissance satellite. Its main purpose was to intercept HF radio signals for French intelligence services. With a mass of 50 kg, it was launched by an Ariane rocket from Kourou in French Guiana at 17:23 UT, 7 July 1995...

, a French microsatellite
Miniaturized satellite
Miniaturized satellites or small satellites are artificial satellites of unusually low weights and small sizes, usually under . While all such satellites can be referred to as small satellites, different classifications are used to categorize them based on mass .One reason for miniaturizing...

 in a sun-synchronous LEO, was hit by fragments of an Ariane-1 H-10 upper-stage booster that had exploded in November 1986. On 29 March 2006, the Russian Express-AM11
Express (satellite)
Ekspress , is a series of geostationary communications satellites owned by Russian State Company for Satellite Communications. The first satellite of this kind was launched on October 13, 1994...

 communications satellite was struck by an unknown object which rendered it inoperable. Luckily, the engineers had enough time in contact with the spacecraft to send it to a parking orbit out of GEO.

Dead spacecraft




In 1958 the United States launched Vanguard I into a medium Earth orbit
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....

 (MEO). It became one of the longest surviving pieces of space junk and remains the oldest piece of junk still in orbit.

In a catalog listing known launches up to July 2009, the Union of Concerned Scientists
Union of Concerned Scientists
The Union of Concerned Scientists is a nonprofit science advocacy group based in the United States. The UCS membership includes many private citizens in addition to professional scientists. James J...

 listed 902 operational satellites. This is out of a known population of 19,000 large objects and about 30,000 objects ever launched. Thus, operational satellites represent a small minority of the population of man-made objects in space. The rest are, by definition, debris.

One particular series of satellites presents an additional concern. During the 1970s and 80s the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 launched a number of naval surveillance satellites as part of their RORSAT
RORSAT
Radar Ocean Reconnaissance SATellite or RORSAT is the western name given to the Soviet Upravlyaemyj Sputnik Aktivnyj satellites. These satellites were launched between 1967 and 1988 to monitor NATO and merchant vessels using active radar...

 (Radar Ocean Reconnaissance SATellite) program. These satellites were equipped with a BES-5 nuclear reactor in order to provide enough energy to operate their radar systems. The satellites were normally boosted into a medium altitude graveyard orbit
Graveyard orbit
A graveyard orbit, also called a supersynchronous orbit, junk orbit or disposal orbit, is an orbit significantly above synchronous orbit, where spacecraft are intentionally placed at the end of their operational life...

, but there were several failures that resulted in radioactive material reaching the ground (see Kosmos 954 and Kosmos 1402). Even those successfully disposed of now face a debris issue of their own, with a calculated probability of 8% that one will be punctured and release its coolant over any 50 year period. The coolant self-forms into droplets up to around some centimeters in size and these represent a significant debris source of their own.

Lost equipment


According to Edward Tufte
Edward Tufte
Edward Rolf Tufte is an American statistician and professor emeritus of political science, statistics, and computer science at Yale University. He is noted for his writings on information design and as a pioneer in the field of data visualization....

's book Envisioning Information, space debris objects have included a glove lost by astronaut Ed White
Edward Higgins White
Edward Higgins White, II was an engineer, United States Air Force officer and NASA astronaut. On June 3, 1965, he became the first American to "walk" in space. White died along with fellow astronauts Gus Grissom and Roger Chaffee during a pre-launch test for the first manned Apollo mission at...

 on the first American space-walk
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...

 (EVA); a camera Michael Collins
Michael Collins (astronaut)
Michael Collins is a former American astronaut and test pilot. Selected as part of the third group of fourteen astronauts in 1963, he flew in space twice. His first spaceflight was Gemini 10, in which he and command pilot John Young performed two rendezvous with different spacecraft and Collins...

 lost near the spacecraft Gemini 10
Gemini 10
-Backup crew:-Mission parameters:*Mass: *Perigee: *Apogee: *Inclination: 28.87°*Period: 88.79 min-Docking:*Docked: July 19, 1966 - 04:15:00 UTC*Undocked: July 20, 1966 - 19:00:00 UTC-Space walk:...

; garbage bags jettisoned by the Soviet cosmonauts throughout the Mir
Mir
Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...

 space station's 15-year life; a wrench and a toothbrush. Sunita Williams
Sunita Williams
Sunita Williams is a United States Naval officer and a NASA astronaut. She was assigned to the International Space Station as a member of Expedition 14 and then joined Expedition 15...

 of STS-116
STS-116
-Crew notes:Originally this mission was to carry the Expedition 8 crew to the ISS. The original crew was to be:-Mission highlights:* The STS-116 mission delivered and attached the International Space Station's third port truss segment, the P5 truss....

 lost a camera during EVA. In an EVA to reinforce a torn solar panel during STS-120
STS-120
-Crew notes:As commander of STS-120, Pamela Melroy became the second woman to command a space shuttle mission. Additionally, the Expedition 16 crew that received STS-120 was commanded by Peggy Whitson, the first female ISS commander...

, a pair of pliers was lost and during STS-126
STS-126
-Crew notes:Originally scheduled to fly on STS-126 was Joan E. Higginbotham, who was a mission specialist on STS-116. On 21 November 2007, NASA announced a change in the crew manifest due to Higginbotham's decision to leave NASA to take a job in the private sector. Stephen G...

, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag in one of the mission's EVAs.

Boosters



Lower stages, like the solid rocket booster
Solid rocket booster
Solid rocket boosters or Solid Rocket Motors, SRM, are used to provide thrust in spacecraft launches from the launchpad up to burnout of the SRBs. Many launch vehicles include SRBs, including the Ariane 5, Atlas V , and the NASA Space Shuttle...

s of the Space Shuttle, or the Saturn IB
Saturn IB
The Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration for use in the Apollo program...

 stage of the Apollo program era, do not reach orbital velocities and do not add to the mass load in orbit. Upper stages, like the Inertial Upper Stage
Inertial Upper Stage
The Inertial Upper Stage , originally known as the Interim Upper Stage, is a two-stage solid-fueled booster rocket developed by the U.S...

, start and end their productive lives in orbit. Boosters that remain on orbit are a serious debris problem, and one of the major known impact events was due to an Ariane booster. During the initial attempts to characterize the space debris problem, it became evident that a good proportion of all debris was due to the breaking up of rocket stages. Although NASA and the USAF quickly made efforts to improve the survivability of their boosters, other launchers did not implement similar changes.

On 11 March 2000, a Chinese Long March 4's CBERS-1/SACI-1 upper stage exploded in orbit and created a debris cloud.

An event of similar magnitude occurred on 19 February 2007, when a Russian Briz-M
Briz-M
The Briz-M , is a Russian orbit insertion upper stage manufactured by Khrunichev State Research and Production Space Center and used on the Proton-M rocket.- Characteristics :...

 booster stage exploded in orbit over South Australia. The booster had been launched on 28 February 2006 carrying an Arabsat-4A communication satellite but malfunctioned before it could use all of its fuel. The explosion was captured on film by several astronomers, but due to the path of the orbit the debris cloud has been hard to quantify using radar. As of 21 February 2007, over 1,000 fragments had been identified. A third break-up event occurred on 14 February 2007 as recorded by Celes Trak. Eight break-ups occurred in 2006, the most break-ups since 1993.

Debris from and as a weapon


One major source of debris in the past was the testing of anti-satellite weapon
Anti-satellite weapon
Anti-satellite weapons are designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former Soviet Union, and the People's Republic of China are known to have developed these weapons. On September 13, 1985, the United States destroyed US...

s carried out by both the U.S. and Soviet Union in the 1960s and '70s. The NORAD element files only contained data for Soviet tests, and it was not until much later that debris from U.S. tests was identified. By the time the problem with debris was understood, widespread ASAT testing had ended. The U.S.'s only active weapon, Program 437
Program 437
Program 437 was the second anti-satellite weapons program of the U.S. military. The US anti-satellite weapons program began development in the early 1960s and was officially discontinued on 1 April 1975. Program 437 was approved for development by U.S. Secretary of Defense Robert McNamara on...

, was shut down in 1975.

The U.S. re-started their ASAT programs in the 1980s with the Vought ASM-135 ASAT
ASM-135 ASAT
The ASM-135 ASAT is an air-launched anti-satellite multi stage missile that was developed by Ling-Temco-Vought'sLTV Aerospace division. The ASM-135 was carried exclusively by the United States Air Force 's F-15 Eagle fighter aircraft.-Development:...

. A 1985 test destroyed a 1 tonnes (2,204.6 lb) satellite orbiting at 525 kilometres (326.2 mi) altitude, creating thousands of pieces of space debris larger than 1 centimetre (0.393700787401575 in). Because it took place at relatively low altitude, atmospheric drag caused the vast majority of the large debris to decay from orbit within a decade. Following the U.S. test in 1985, there was a de-facto moratorium on such tests.

China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 was widely condemned after their 2007 anti-satellite missile test
2007 Chinese anti-satellite missile test
The 2007 Chinese anti-satellite missile test was conducted by China on January 11, 2007. A Chinese weather satellite—the FY-1C polar orbit satellite of the Fengyun series, at an altitude of , with a mass of 750 kg—was destroyed by a kinetic kill vehicle traveling with a speed of 8 km/s in...

, both for the military implications as well as the huge amount of debris it created. This is the largest single space debris incident in history in terms of new objects, estimated to have created more than 2,300 pieces (updated 13 December 2007) of trackable debris (approximately golf ball size or larger), over 35,000 pieces 1 cm (0.393700787401575 in) or larger, and 1 million pieces 1 mm (0.0393700787401575 in) or larger. The test took place in the part of near Earth space most densely populated with satellites, as the target satellite orbited between 850 kilometres (528.2 mi) and 882 kilometres (548.1 mi). Since the atmospheric drag is quite low at that altitude, the debris will persist for decades. In June 2007, NASA's Terra environmental spacecraft
Terra (satellite)
Terra is a multi-national NASA scientific research satellite in a sun-synchronous orbit around the Earth. It is the flagship of the Earth Observing System...

 was the first to perform a maneuver in order to prevent impacts from this debris.

On 20 February 2008, the U.S. launched an SM-3 Missile
RIM-161 Standard Missile 3
The RIM-161 Standard Missile 3 is a ship-based missile system used by the US Navy to intercept short-to intermediate-range ballistic missiles as a part of Aegis Ballistic Missile Defense System. Although primarily designed as an anti-ballistic missile, the SM-3 has also been employed in an...

 from the USS Lake Erie
USS Lake Erie (CG-70)
USS Lake Erie is a Ticonderoga-class guided-missile cruiser in the United States Navy. She is named for the decisive USN victory in the Battle of Lake Erie during the War of 1812....

 specially to destroy a defective U.S. spy satellite thought to be carrying 1000 pounds (453.6 kg) of toxic hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

 fuel. Since this event occurred at about 250 km (155 mi) altitude, all of the resulting debris have a perigee of 250 km (155 mi) or lower. The missile was aimed to deliberately reduce the amount of debris as much as possible, and they had decayed by early 2008.

The vulnerability of satellites to a collision with larger debris and the ease of launching such an attack against a low-flying satellite, has led some to speculate that such an attack would be within the capabilities of countries unable to make a precision attack like former U.S. or Soviet systems. Such an attack against a large satellite of 10 tonnes or more would cause enormous damage to the LEO environment.

Operational aspects



Threat to unmanned spacecraft


Spacecraft in a debris field are subject to constant wear as a result of impacts with small debris. Critical areas of a spacecraft are normally protected by Whipple shields, eliminating most damage. However, low-mass impacts have a direct impact on the lifetime of a space mission, if the spacecraft is powered by solar panels. These panels are difficult to protect because their front face has to be directly exposed to the sun. As a result, they are often punctured by debris. When hit, panels tend to produce a cloud of gas-sized particles that, compared to debris, does not present as much of a risk to other spacecraft. This gas is generally a plasma when created and consequently presents an electrical risk to the panels themselves.

The effect of the many impacts with smaller debris was particularly notable on Mir
Mir
Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...

, the Soviet space station, as it remained in space for long periods of time with the panels originally launched on its various modules.

Impacts with larger debris normally destroy the spacecraft. To date there have been several known and suspected impact events. The earliest on record was the loss of Kosmos 1275, which disappeared on 24 July 1981 only a month after launch. Tracking showed it had suffered some sort of breakup with the creation of 300 new objects. Kosmos did not contain any volatiles and is widely assumed to have suffered a collision with a small object. However, proof is lacking, and an electrical battery explosion has been offered as a possible alternative. Kosmos 1484 suffered a similar mysterious breakup on 18 October 1993.

Several confirmed impact events have taken place since then. Olympus-1 was hit by a meteor on 11 August 1993 and left adrift. On 24 July 1996, the French microsatellite
Miniaturized satellite
Miniaturized satellites or small satellites are artificial satellites of unusually low weights and small sizes, usually under . While all such satellites can be referred to as small satellites, different classifications are used to categorize them based on mass .One reason for miniaturizing...

 Cerise
Cerise (satellite)
Cerise was a French military reconnaissance satellite. Its main purpose was to intercept HF radio signals for French intelligence services. With a mass of 50 kg, it was launched by an Ariane rocket from Kourou in French Guiana at 17:23 UT, 7 July 1995...

 was hit by fragments of an Ariane-1 H-10 upper-stage booster that had exploded in November 1986. On 29 March 2006 the Russian Express-AM11 communications satellite was struck by an unknown object which rendered it inoperable. Luckily, the engineers had enough time in contact with the spacecraft to send it to a parking orbit out of GEO.

The first major space debris collision
2009 satellite collision
The 2009 satellite collision was the first accidental hypervelocity collision between two intact artificial satellites in Earth orbit. The collision occurred at 16:56 UTC on February 10, 2009, at above the Taymyr Peninsula in Siberia, when Iridium 33 and Kosmos-2251 collided...

 was on 10 February 2009 at 16:56 UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

. The deactivated 950 kilograms (2,094.4 lb) Kosmos 2251 and an operational 560 kilograms (1,234.6 lb) Iridium 33
Iridium 33
Iridium 33 was a U.S. Iridium communications satellite. It was launched into low Earth orbit from Site 81/23 at the Baikonur Cosmodrome at 01:36 GMT on 14 September 1997, by a Proton-K carrier rocket with a Block DM2 upper stage...

 collided 500 miles (804.7 km) over northern Siberia. The relative speed of impact was about 11.7 km/s, or approximately 42120 kilometres per hour (26,172.2 mph). Both satellites were destroyed and the collision scattered considerable debris, which poses an elevated risk to spacecraft. The collision created a debris cloud, although accurate estimates of the number of pieces of debris is not yet available.

In a Kessler Syndrome cascade, satellite lifetimes would be measured on the order of years or months. New satellites could be launched through the debris field into higher orbits or placed in lower ones where natural decay processes remove the debris, but it is precisely because of the utility of the orbits between 800 and 1500 kilometres (932.1 mi) that this region is so filled with debris.

Threat to manned spacecraft


From the earliest days of the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

 missions, NASA has turned to NORAD's database to constantly monitor the orbital path in front of the Shuttle to find and avoid any known debris. During the 1980s, these simulations used up a considerable amount of the NORAD tracking system's capacity. The first official Space Shuttle collision avoidance maneuver was during STS-48
STS-48
-Mission parameters:*Mass:**Orbiter landing with payload: **Payload: *Perigee: *Apogee: *Inclination: 57.0°*Period: 96.2 min-Mission highlights:...

 in September 1991. A 7-second reaction control system
Reaction control system
A reaction control system is a subsystem of a spacecraft whose purpose is attitude control and steering by the use of thrusters. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow...

 burn was performed to avoid debris from the Cosmos satellite
Cosmos (satellite)
Kosmos is a designation given to a large number of satellites operated by the Soviet Union and subsequently Russia. Kosmos 1, the first spacecraft to be given a Kosmos designation, was launched on March 16, 1962....

 955. Similar maneuvers followed on missions 53, 72 and 82.

One of the first events to widely publicize the debris problem was Space Shuttle Challenger
Space Shuttle Challenger
Space Shuttle Challenger was NASA's second Space Shuttle orbiter to be put into service, Columbia having been the first. The shuttle was built by Rockwell International's Space Transportation Systems Division in Downey, California...

's first flight on STS-7
STS-7
STS-7 was a NASA Space Shuttle mission, during which Space Shuttle Challenger deployed several satellites into orbit. The shuttle launched from Kennedy Space Center on 18 June 1983, and landed at Edwards Air Force Base on 24 June. STS-7 was the seventh shuttle mission, and was Challengers second...

. A small fleck of paint impacted Challenger's front window and created a pit over 1 millimetre (0.0393700787401575 in) wide. Endeavour
Space Shuttle Endeavour
Space Shuttle Endeavour is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States. Endeavour was the fifth and final spaceworthy NASA space shuttle to be built, constructed as a replacement for Challenger...

 suffered a similar impact on STS-59
STS-59
-Mission parameters:*Mass: payload*Perigee: *Apogee: *Inclination: 57°*Period: 88.4 min-9 April:Endeavour began its sixth mission on the morning of 9 April 1994 with an on-time launch at 7:05 am Eastern time...

 in 1994, but this one pitted the window for about half its depth: a cause for much greater concern. Post-flight examinations have noted a marked increase in the number of minor debris impacts since 1998.

The damage due to smaller debris has now grown to become a significant problem in its own right. Chipping of the windows became common by the 1990s, along with minor damage to the thermal protection system tiles
Space Shuttle thermal protection system
The Space Shuttle thermal protection system is the barrier that protects the Space Shuttle Orbiter during the searing heat of atmospheric reentry...

 (TPS). To mitigate the impact of these events, once the Shuttle reached orbit it was deliberately flown tail first in an attempt to intercept as much of the debris load as possible on the engines and rear cargo bay. These were not used on orbit or during descent and thus were less critical to operations after launch. When flown to the ISS, the Shuttle was placed where the station provided as much protection as possible.

The sudden increase in debris load led to a re-evaluation of the debris issue and a catastrophic impact with large debris was considered to be the primary threat to Shuttle operations on every mission. Mission planning required a thorough discussion of debris risk, with an executive level decision to proceed if the risk is greater than 1 in 200 of destroying the Shuttle. On a normal low-orbit mission to the ISS the risks were estimated to be 1 in 300, but the STS-125
STS-125
STS-125, or HST-SM4 , was the fifth and final space shuttle servicing mission to the Hubble Space Telescope .Launch occurred on 11 May 2009 at 2:01 pm EDT...

 mission to repair the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 at 350 miles (563.3 km) was initially calculated at 1 in 185 due to the 2009 satellite collision, and threatened to cancel the mission. However, a re-analysis as better debris numbers became available reduced this to 1 in 221, and the mission was allowed to proceed.
In spite of their best efforts, however, there have been two serious debris incidents on more recent Shuttle missions. In 2006, Atlantis
Space Shuttle Atlantis
The Space Shuttle Atlantis is a retired Space Shuttle orbiter in the Space Shuttle fleet belonging to the National Aeronautics and Space Administration , the spaceflight and space exploration agency of the United States...

 was hit by a small fragment of a circuit board during STS-115
STS-115
Note:The P3/P4 Truss segment and batteries were so heavy that the crew count was reduced from seven to six.-Crew notes:...

, which bored a small hole through the radiator panels in the cargo bay (the large gold colored objects visible when the doors are open). A similar incident followed on STS-118
STS-118
- Crew notes :Astronaut Clayton Anderson originally was slated to be launched to the ISS on this mission, but was moved to STS-117. His replacement was Alvin Drew....

 in 2007, when Endeavour was hit in a similar location by unknown debris which blew a hole several centimetres in diameter through the panel.

The International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

 (ISS) uses extensive Whipple shielding to protect itself from minor debris threats. However, large portions of the ISS cannot be protected, notably its large solar panels. In 1989 it was predicted that the International Space Station's panels would suffer about 0.23% degradation over four years, which was dealt with by overdesigning the panel by 1%. New figures based on the increase in collisions since 1998 are not available.

Like the Shuttle, the only protection against larger debris is avoidance. On two occasions the crew have been forced to abandon work and take refuge in the Soyuz
Soyuz spacecraft
Soyuz , Union) is a series of spacecraft initially designed for the Soviet space programme by the Korolyov Design Bureau in the 1960s, and still in service today...

 capsule while the threat passed. This close call is a good example of the potential Kessler Syndrome; the debris is believed to be a small 10 centimetres (3.9 in) portion of the former Cosmos 1275, which is the satellite that is considered to be the first example of an on-orbit impact with debris.

If the Kessler Syndrome comes to pass, the threat to manned missions may be too great to contemplate operations in LEO. Although the majority of manned space activities take place at altitudes below the critical 800 to 1,500 kilometres (310.7 mi) regions, a cascade within these areas would result in a constant rain down into the lower altitudes as well. The time scale of their decay is such that "the resulting debris environment is likely to be too hostile for future space use."

Hazard on Earth


Although most debris will burn up in the atmosphere, larger objects can reach the ground intact and present a risk.

The original re-entry plan for Skylab
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...

 called for the station to remain in space for 8 to 10 years after its final mission in February 1974. Unexpectedly high solar activity expanded the upper atmosphere resulting in higher than expected drag on space station bringing its orbit closer to Earth than planned. On 11 July 1979, Skylab re-entered the Earth's atmosphere and disintegrated, raining debris harmlessly along a path extending over the southern Indian Ocean and sparsely populated areas of Western Australia.

On 12 January 2001, a Star 48
Star 48
The Star 48 is a type of solid rocket motor used by many space propulsion and launch vehicle stages, including the Space Shuttle and the New Horizons probe. It is used almost exclusively as an upper stage...

 Payload Assist Module
Payload Assist Module
frame|PAM-D with the [[Phoenix |Phoenix]] spacecraft. The [[Star 48|Star 48-B]] engine is shown being spun, fired, [[Yo-yo de-spin|yo-yo de-spun]] and jettisoned.thumb|SBS-3 satellite with PAM-D stage inside the space shuttle...

 (PAM-D) rocket upper stage re-entered the atmosphere after a "catastrophic orbital decay". The PAM-D stage crashed in the sparsely populated Saudi Arabian desert. It was positively identified as the upper-stage rocket for NAVSTAR 32, a GPS satellite launched in 1993.

The Columbia disaster in 2003 demonstrated this risk, as large portions of the spacecraft reached the ground. In some cases entire equipment systems were left intact. NASA continues to warn people to avoid contact with the debris due to the possible presence of hazardous chemicals.

On 27 March 2007, wreckage from a Russian spy satellite
Spy satellite
A spy satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications....

 was spotted by Lan Chile (LAN Airlines
LAN Airlines
LAN Airlines S.A. is an airline based in Santiago, Chile. LAN is currently positioned amongst the largest airlines in Latin America, serving Latin America, United States, the Caribbean, Oceania, and Europe. It is a member of the Oneworld airline alliance...

) in an Airbus A340
Airbus A340
The Airbus A340 is a long-range four-engine wide-body commercial passenger jet airliner. Developed by Airbus Industrie,A consortium of European aerospace companies, Airbus is now fully owned by EADS and since 2001 has been known as Airbus SAS. a consortium of European aerospace companies, which is...

, which was travelling between Santiago, Chile
Santiago, Chile
Santiago , also known as Santiago de Chile, is the capital and largest city of Chile, and the center of its largest conurbation . It is located in the country's central valley, at an elevation of above mean sea level...

, and Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...

, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 carrying 270 passengers. The pilot estimated the debris was within 8 km of the aircraft, and he reported hearing the sonic boom
Sonic boom
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion...

 as it passed. The aircraft was flying over the Pacific Ocean, which is considered one of the safest places in the world for a satellite to come down because of its large areas of uninhabited water.

In 1969, five sailors on a Japanese ship were injured by space debris, probably of Russian origin; see p. 11 (p. 3 in the document's numbering system) of In 1997 an Oklahoma woman named Lottie Williams was hit in the shoulder by a 10 x 13 centimetres (5.1 in) piece of blackened, woven metallic material that was later confirmed to be part of the fuel tank of a Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...

 rocket which had launched a U.S. Air Force
United States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

 satellite in 1996. She was not injured.

Tracking from the ground


Radar and optical detectors such as lidar
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...

 are the main tools used for tracking space debris. However, determining orbits to allow reliable re-acquisition is problematic. Tracking objects smaller than 10 cm (4 in) is difficult due to their small cross-section and reduced orbital stability, though debris as small as 1 cm (0.393700787401575 in) can be tracked. NASA Orbital Debris Observatory
NASA Orbital Debris Observatory
NASA Orbital Debris Observatory or NODO was an observatory that hosted NASA-LMT, a 3 meter diameter aperture liquid metal telescope and astronomical survey funded and operated by NASA from 1995 to 2002 in New Mexico, USA. It was a zenith or transit telescope pointed straight up, that used 20...

 tracked space debris using a 3 m (10 ft) liquid mirror transit telescope.

The U.S. Strategic Command
United States Strategic Command
United States Strategic Command is one of nine Unified Combatant Commands of the United States Department of Defense . The Command, including components, employs more than 2,700 people, representing all four services, including DoD civilians and contractors, who oversee the command's operationally...

 maintains a catalogue containing known orbital objects. The list was initially compiled in part to prevent misinterpretation as hostile missiles. The version compiled in 2009 listed about 19,000 objects. Observation data gathered by a number of ground-based radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 facilities and telescopes as well as by a space-based telescope is used to maintain this catalogue. Nevertheless, the majority of expected debris objects remain unobserved – there are more than 600,000 objects larger than 1 cm (0.393700787401575 in) in orbit (according to the ESA Meteoroid and Space Debris Terrestrial Environment Reference, the MASTER-2005 model).

Other sources of knowledge on the actual space debris environment include measurement campaigns by the ESA Space Debris Telescope
ESA Space Debris Telescope
The ESA Space Debris Telescope is located at the Teide Observatory on the island of Tenerife, Spain. The telescope is ESA's Optical Ground Station forming a part of the Artemis experiment...

, TIRA (System)
TIRA (System)
The Tracking & Imaging Radar system serves as the central experimental facility for the development and investigation of radar techniques for the detection and reconnaissance of objects in space, and to a certain degree also of air targets. The TIRA system gains radar data at 22.5 cm and 1.8 cm ...

, Goldstone radar
Goldstone Deep Space Communications Complex
The Goldstone Deep Space Communications Complex  — commonly called the Goldstone Observatory — is located in California's Mojave Desert. Operated by ITT Corporation for the Jet Propulsion Laboratory, its main purpose is to track and communicate with space missions. It includes the Pioneer...

, Haystack radar
Haystack Observatory
Haystack Observatory is a group of astronomical observatories owned and operated by Massachusetts Institute of Technology. It is located in Westford, Massachusetts . It is the home of the Millstone Hill Observatory....

,, the EISCAT radars
EISCAT
EISCAT is an acronym for the European Incoherent Scatter Scientific Association. It operates three incoherent scatter radar systems, at 224 MHz, 931 MHz in Northern Scandinavia and one at 500 MHz on Svalbard, used to study the interaction between the Sun and the Earth as revealed by disturbances in...

, and the Cobra Dane
Cobra Dane
The AN/FPS-108 COBRA DANE radar is an active electronically scanned array installation operated by the United States Air Force at Eareckson Air Station on the island of Shemya, Alaska. This radar system was built in 1976 and brought on-line in 1977 for the primary mission of intelligence gathering...

 phased array radar. The data gathered during these campaigns is used to validate models of the debris environment like ESA-MASTER. Such models are the only means of assessing the impact risk caused by space debris, as only larger objects can be regularly tracked.

Measurement in space


Returned space debris hardware is a valuable source of information on the (sub-millimetre) space debris environment. The LDEF satellite deployed by STS-41-C
STS-41-C
STS-41-C was NASA's 11th Space Shuttle mission, and the fifth mission of Space Shuttle Challenger. The launch on 6 April 1984 was the first direct ascent trajectory for a shuttle mission...

 Challenger
Space Shuttle Challenger
Space Shuttle Challenger was NASA's second Space Shuttle orbiter to be put into service, Columbia having been the first. The shuttle was built by Rockwell International's Space Transportation Systems Division in Downey, California...

 and retrieved by STS-32
STS-32
STS-32 was the 33rd mission of NASA's Space Shuttle program, and the 9th launch of Space Shuttle Columbia. Launching on 9 January 1990, it marked the first time since STS-61-C that Pad A at Kennedy Space Center's Complex 39 was used for a launch; it also marked the first use of Mobile Launcher...

 Columbia
Space Shuttle Columbia
Space Shuttle Columbia was the first spaceworthy Space Shuttle in NASA's orbital fleet. First launched on the STS-1 mission, the first of the Space Shuttle program, it completed 27 missions before being destroyed during re-entry on February 1, 2003 near the end of its 28th, STS-107. All seven crew...

 spent 68 months in orbit. Close examination of its surfaces allowed an analysis of the directional distribution and composition of the debris flux. The EURECA satellite deployed by STS-46
STS-46
STS-46 was a NASA space shuttle mission using orbiter Atlantis and launched on 31 July 1992 at 9:56:48 am EDT.-Crew:-Mission parameters:*Mass:**Orbiter landing with payload: **Payload: *Perigee: *Apogee:...

 Atlantis
Space Shuttle Atlantis
The Space Shuttle Atlantis is a retired Space Shuttle orbiter in the Space Shuttle fleet belonging to the National Aeronautics and Space Administration , the spaceflight and space exploration agency of the United States...

 in 1992 and retrieved by STS-57
STS-57
STS-57 was a Shuttle-Spacehab mission of that launched 21 June 1993 from Kennedy Space Center, Florida.-Crew:-Mission parameters:**Mass:**Orbiter landing with payload: **Payload: *Perigee: *Apogee:...

 Endeavour
Space Shuttle Endeavour
Space Shuttle Endeavour is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States. Endeavour was the fifth and final spaceworthy NASA space shuttle to be built, constructed as a replacement for Challenger...

 in 1993 was similarly used for debris studies.

The solar arrays of the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 returned during missions STS-61
STS-61
STS-61 was the first Hubble Space Telescope servicing mission, and the fifth flight of the Space Shuttle Endeavour. The mission launched on 2 December 1993 from Kennedy Space Center in Florida. The mission restored the spaceborne observatory's vision, marred by spherical aberration, with the...

 Endeavour and STS-109
STS-109
STS-109 was a Space Shuttle mission that launched from the Kennedy Space Center on 1 March 2002. It was the 108th mission of the Space Shuttle program, the 27th flight of the orbiter Columbia and the fourth servicing of the Hubble Space Telescope...

 Columbia are an important source of information on the debris environment. The impact craters found on the surface were counted and classified by ESA to provide a means for validating debris environment models. Similar materials returned from Mir were extensively studied, notably the Mir Environmental Effects Payload
Mir Environmental Effects Payload
The Mir Environmental Effects Payload was a set of four experiments installed on the Russian space station Mir from 1996 to 1997 to study the effects of space debris impacts and exposure to the space environment on a variety of materials...

 which studied the environment in the Mir area.

Gabbard diagrams


Space debris groups resulting from satellite breakups are often studied using scatter plots known as Gabbard diagrams. In a Gabbard diagram, the perigee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

 and apogee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

 altitudes of the individual debris fragments resulting from a collision are plotted with respect to the orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...

 of each fragment. The distribution can be used to infer information such as direction and point of impact.

Growth mitigation


In order to mitigate the generation of additional space debris, a number of measures have been proposed. The passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 of spent upper stages by the release of residual fuels is aimed at reducing the risk of on-orbit explosions that could generate thousands of additional debris objects. The modification of the Delta boosters, at a time when the debris problem was first becoming apparent, essentially eliminated their further contribution to the problem.

There is no international treaty mandating behavior to minimize space debris, but the United Nations Committee on the Peaceful Uses of Outer Space
United Nations Committee on the Peaceful Uses of Outer Space
The United Nations Committee on the Peaceful Uses of Outer Space was established in 1958 as an ad hoc committee...

 (COPUOS) did publish voluntary guidelines in 2007. As of 2008, the committee is discussing international "rules of the road" to prevent collisions between satellites. NASA has implemented its own procedures for limiting debris production as have some other space agencies, such as the European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

. Starting in 2007, the ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 has been preparing a new standard dealing with space debris mitigation.

One alternative that has been envisioned to ensure launch vehicle operators absorb the cost of debris mitigation is to implement a "one-up/one-down" launch license policy to Earth orbits. In this conception, launch operators would need to build the capability into their launch vehicle-robotic capture, navigation, mission duration extension, and substantial additional fuel – to be able to rendezvous with, capture and deorbit an existing derelict satellite from approximately the same orbital plane.

Self-removal


It is an ITU requirement that geostationary satellites be able to remove themselves to a "graveyard orbit" at the end of their lives. It has been demonstrated that the selected orbital areas do not sufficiently protect GEO lanes from debris, although a response has not yet been formulated.

Rocket stages or satellites that retain enough fuel can allow power themselves into a decaying orbit. In cases when a direct (and controlled) de-orbit would require too much fuel, a satellite can be brought to an orbit where atmospheric drag would cause it to de-orbit after some years. Such a maneuver was successfully performed with the French Spot-1 satellite
SPOT (satellites)
SPOT is a high-resolution, optical imaging Earth observation satellite system operating from space. It is run by Spot Image based in Toulouse, France...

, bringing its time to atmospheric re-entry down from a projected 200 years to about 15 years by lowering its perigee from 830 km (516 mi) to about 550 km (342 mi).

Instead of using rockets, an electrodynamic tether
Electrodynamic tether
Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy...

 can be attached to the spacecraft on launch. At the end of its lifetime it is rolled out and slows down the spacecraft. Although tethers of up to 30 km have been successfully deployed in orbit the technology has not yet reached maturity. It has been proposed that booster stages include a sail-like attachment to the same end.

External removal


A well-studied solution is to use a remotely controlled vehicle to rendezvous with debris, capture it, and return to a central station. The commercially-developed
Private spaceflight
Private spaceflight is flight above Earth altitude conducted by and paid for by an entity other than a government. In the early decades of the Space Age, the government space agencies of the Soviet Union and United States pioneered space technology augmented by collaboration with affiliated design...

 MDA Space Infrastructure Servicing vehicle is a refueling depot and service spacecraft for communication satellites in geosynchronous orbit
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...

, slated for launch in 2015. The SIS includes the vehicle capability to "push dead satellites into graveyard orbit
Graveyard orbit
A graveyard orbit, also called a supersynchronous orbit, junk orbit or disposal orbit, is an orbit significantly above synchronous orbit, where spacecraft are intentionally placed at the end of their operational life...

s." The Advanced Common Evolved Stage
Advanced Common Evolved Stage
The Advanced Common Evolved Stage, or ACES, is a proposed upper stage rocket for use on space launch vehicles. The design concept is from the U.S. company United Launch Alliance . ACES is intended to boost satellite payloads to geosynchronous orbit or, in the case of an interplanetary space...

 family of upper-stages is being explicitly designed to have the potential for high leftover fuel margins so that derelict capture/deorbit might be accomplished, as well as with in-space refueling
Propellant depot
An orbital propellant depot is a cache of propellant that is placed on an orbit about the Earth or another body to allow spacecraft to be fuelled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads...

 capability that could provide the high delta-V
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....

 required to deorbit even heavy objects from geosynchronous orbit
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...

s.

The laser broom
Laser broom
A laser broom is a proposed ground-based laser beam-powered propulsion system whose purpose is to sweep space debris out of the path of other artificial satellites such as the International Space Station.-Technical description:...

 uses a powerful ground-based laser to ablate the front surface off of debris and thereby produce a rocket-like thrust that slows the object. With a continued application the debris will eventually decrease their altitude enough to become subject to atmospheric drag. In the late 1990s, US Air Force worked on a ground-based laser broom design under the name "Project Orion". Although a test-bed device was scheduled to launch on a 2003 Space Shuttle, numerous international agreements, forbidding the testing of powerful lasers in orbit, caused the program to be limited to using the laser as a measurement device. In the end, the Space Shuttle Columbia disaster
Space Shuttle Columbia disaster
The Space Shuttle Columbia disaster occurred on February 1, 2003, when shortly before it was scheduled to conclude its 28th mission, STS-107, the Space Shuttle Columbia disintegrated over Texas and Louisiana during re-entry into the Earth's atmosphere, resulting in the death of all seven crew members...

 led to the project being postponed and, as Nicholas Johnson, Chief Scientist and Program Manager for NASA's Orbital Debris Program Office, later noted, "There are lots of little gotchas in the Orion final report. There's a reason why it's been sitting on the shelf for more than a decade."

Additionally, the momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 of the photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s in the laser beam could be used to impart thrust on the debris directly. Although this thrust would be tiny, it may be enough to move small debris into new orbits that do not intersect those of working satellites. NASA research from 2011 indicates that firing a laser beam at a piece of space junk could impart an impulse of 0.04 inch (0.1016 cm) per second. Keeping the laser on the debris for a few hours per day could alter its course by 650 feet (198.1 m) per day. A similar proposal replaces the laser with a beam of ions
Ion Beam Shepherd
An Ion Beam Shepherd is a concept in which the orbit and/or attitude of a spacecarft or a generic orbiting body is modified by having a beam of quasi-neutral plasma impinging against its surface to create a force and/or a torque on the target...

.

A number of other proposals use more novel solutions to the problem, from foamy ball of aerogel
Aerogel
Aerogel is a synthetic porous material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and thermal conductivity...

 or spray of water,
inflatable balloons,
electrodynamic tethers,
boom electroadhesion,
or dedicated "interceptor satellites".
On January 7, 2010 Star Inc. announced that it had won a contract from Navy/SPAWAR for a feasibility study of the application of the ElectroDynamic Debris Eliminator (EDDE).

, the cost of launching any of these solutions is about the same as launching any spacecraft. Johnson stated that none of the existing solutions are currently cost-effective.

See also


  • Near-Earth object
    Near-Earth object
    A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...

  • Liability Convention
    Liability Convention
    The Convention on International Liability for Damage Caused by Space Objects, also known as the Space Liability Convention, is a treaty that expands on the liability rules created in the Outer Space Treaty of 1967. Because relatively few accidents have occurred resulting from space objects, the...

  • Orbital Debris Co-ordination Working Group
  • Spacecraft cemetery
    Spacecraft cemetery
    The so-called Spacecraft Cemetery is an area in the southern Pacific Ocean 3900 km southeast of Wellington, New Zealand,where spacecraft, notably the defunct Mir space station and waste-filled Progress cargo ships are and have been routinely deposited. It has been chosen for its remoteness, as...


Further reading




External links