Space junk, or space debris, is any piece of machinery or debris left by humans in space. It can refer to big objects such as dead satellites that have failed or been left in orbit at the end of their mission. It can also refer to smaller things, like bits of debris or paint flecks that have fallen off a rocket.
Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) is a term for defunct human-made objects in space principally in Earth orbit which no longer serve a useful function. These include derelict spacecraft nonfunctional spacecraft and abandoned launch vehicle stages mission-related debris, and particularly numerous in Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-built objects left in orbit, other examples of space debris include fragments from their disintegration, erosion and collisions, or even paint flecks, solidified liquids expelled from spacecraft, and unburned particles from solid rocket motors. Space debris represents a risk to spacecraft.
Space debris is typically a negative extremely it creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit a cost that is typically not taken into account nor fully accounted for in the cost by the launcher or payload owner. Several spacecraft, both manned and unmanned, have been damaged or destroyed by space debris. The measurement, mitigation, and potential removal of debris are conducted by some participants in the space industry.
As of October 2019, the US space surveillance network reported nearly 20,000 artificial objects in orbit above the Earth, including 2,218 operational satellites. However, these are just objects large enough to be tracked. As of January 2019, more than 128 million pieces of debris smaller than 1 cm (0.4 in), about 900,000 pieces of debris 1-10 cm, and around 34,000 of pieces larger than 10 cm were estimated to be in orbit around the Earth. When the smallest objects of human-made space debris are grouped with micrometeoroids, they are together sometimes referred to by space agencies as MMOD (Micrometeoroid and Orbital Debris). Collisions with debris have become a hazard to spacecraft; the smallest objects cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic shield.
Below 2,000 km (1,200 mi) Earth-altitude, pieces of debris are denser than meteoroids; most are dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from RORSAT (nuclear-powered satellites). For comparison, the international space station orbits in the 300–400 kilometres (190–250 mi) range, while the two most recent large debris events—the 2007 Chinese antistat weapon test and the 2009 satellite collision—occurred at 800 to 900 kilometres (500 to 560 mi) altitude. The ISS has Whipple shielding to resist damage from small MMOD; however, known debris with a collision chance of over 1/10,000 are avoided by manoeuvring the station.
Debris growth
During the 1980s, NASA and other U.S. groups attempted to limit the growth of debris. One trial solution was implemented by Mcdonald Douglas for the Delta launch vehicle, by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris. Other countries were slower to adopt this measure and, due especially to a number of launches by the soviet union, the problem grew throughout the decade.
A new battery of studies followed as NASA, NORAD and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 (when Schefter's article was published) the number of objects was estimated at 5,000, new detectors in the Ground-based electro-optical deep-space surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit. By 2005 this was adjusted upward to 13,000 objects, and a 2006 study increased the number to 19,000 as a result of an ASAT test and a satellite collision. In 2011, NASA said that 22,000 objects were being tracked.
By the late 2010s, plans by multiple providers to deploy a large mega constellation of broadband internet satellites had been licensed by regulatory authorities, with operational satellites entering production by both OnWeb and SpaceX. The first deployments occurred in 2019 with six from OneWeb, followed by 60 227 kg (500 lb) satellites from SpaceX in May, the first satellites for the project Starlink. While the increased satellite density causes concerns, both licensing authorities and the manufacturers are well aware of debris problems. The vendors must have debris-reduction plans and are taking measures to actively de-orbit unneeded satellites and/or ensure their orbits will decay naturally.
Debris history in particular years
2009, 19,000 debris over 5 cm (2 in) were tracked.
2013, estimates of more than 170 million pieces of debris smaller than 1 cm (0.4 in), about 670,000 debris 1–10 cm, and approximately 29,000 larger pieces of debris are in orbit.
July 2016, nearly 18,000 artificial objects are orbiting above Earth, including 1,419 operational satellites.
October 2019, nearly 20,000 artificial objects are in orbit above the Earth, including 2,218 operational satellites.
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Dead spacecraft
In 1958, the United States launched Vanguard 1 I into a Medium earth orbit (MEO). As of October 2009, it, and the upper stage of its launch rocket, are the oldest surviving human-made space objects still in orbit. In a catalogue of known launches until July 2009, the Union of Concerned Scientists listed 902 operational satellites from a known population of 19,000 large objects and about 30,000 objects launched.
An example of additional derelict satellite debris is the remains of the 1970s/80s Soviet RORSAT naval surveillance satellite program. The satellites' BES-5 nuclear reactors were cooled with a coolant loop of sodium-potassium alloy, creating a potential problem when the satellite reached the end of its life. While many satellites were nominally boosted into medium-altitude graveyard orbits, not all were. Even satellites which had been properly moved to a higher orbit had an eight-per cent probability of puncture and coolant release over a 50-year period. The coolant freezes into droplets of solid sodium-potassium alloy forming additional debris. These events continue to occur. For example, in February 2015, the USAF Defense Meteorological Satellite Program Flight 13 (DMSP-F13) exploded in orbit, creating at least 149 debris objects, which were expected to remain in orbit for decades.
Orbiting satellites have been deliberately destroyed. The United States and USSR/Russia have conducted over 30 and 27 ASAT tests, respectively, followed by 10 from China and one from India. The most recent ASATs were Chinese interception of FY-1C, trials of Russian PL-19 Nudol, American interception of USA-193 and Indian interception of the unstated live satellite.
Lost equipment
A drifting thermal blanket was photographed in 1998 during STS-88. Space debris includes a glove lost by astronaut Ed White on the first American space-walk (EVA), a camera lost by Michael Collins near Gemini 10, a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir's 15-year life, a wrench, and a toothbrush. Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag.
Boosters
In characterizing the problem of space debris, it was learned that much debris was due to rocket upper stages which end up in orbit and break up due to decomposition of unvented unburned fuel. However, a major known impact event involved an (intact) Ariane booster. Although NASA and the United States Air Force now require upper-stage passivation, other launchers do not. Lower stages, like the Space Shuttle's solid rocket boosters or the Apollo program's Saturn IB launch vehicles, do not reach orbit.
On 11 March 2000 a Chinese Long March 4 CBERS-1 upper stage exploded in orbit, creating a debris cloud. A Russian Briz-M booster stage exploded in orbit over South Australia on 19 February 2007. Launched on 28 February 2006 carrying an Arabsat-4A communications satellite, it malfunctioned before it could use up its propellant. Although the explosion was captured on film by astronomers, due to the orbit path the debris cloud has been difficult to measure with radar. By 21 February 2007, over 1,000 fragments were identified. A 14 February 2007 breakup was recorded by Celestial. Eight breakups occurred in 2006, the most since 1993. Another Briz-M broke up on 16 October 2012 after a failed 6 August Proton-M launch. The amount and size of the debris were unknown. A Long March 7 rocket booster created a fireball visible from portions of Utah, Nevada, Colorado, Idaho and California on the evening of 27 July 2016; its disintegration was widely reported on social media. In 2018–2019, three different Atlas V Centaur second stages have broken up.
Weapons
A past debris source was the testing of anti-satellite weapons (ASATs) by the U.S. and Soviet Union during the 1960s and 1970s. North American Aerospace Defense Command (NORAD) files only contained data for Soviet tests, and debris from U.S. tests was only identified later. By the time the debris problem was understood, widespread ASAT testing had ended; the U.S. Program 437 was shut down in 1975.
The U.S. restarted their ASAT programs in the 1980s with the Vought ASM-135 ASAT. A 1985 test destroyed a 1-tonne (2,200 lb) satellite orbiting at 525 km (326 mi), creating thousands of debris larger than 1 cm (0.39 in). Due to the altitude, atmospheric drag decayed the orbit of most debris within a decade. Ade facto moratorium followed the test.
China's government was condemned for the military implications and the amount of debris from the 2007 anti-satellite missile test, the largest single space debris incident in history (creating over 2,300 pieces golf-ball-size or larger, over 35,000 1 cm (0.4 in) or larger, and one million pieces 1 mm (0.04 in) or larger). The target satellite orbited between 850 km (530 mi) and 882 km (548 mi), the portion of near-Earth space most densely populated with satellites. Since atmospheric drag is low at that altitude the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft manoeuvred to avoid impact from the debris. Dr Brian Weeden, U.S. Air Force officer and Secure World Foundation staff member, noted that the 2007 Chinese satellite explosion created orbital debris of more than 3,000 separate objects that then required tracking. On 20 February 2008, the U.S. launched an SM-3 missile from the USS e ErieLak to destroy a defective U.S. spy satellite thought to be carrying 450 kg (1,000 lb) of toxic hydrazine propellant. The event occurred at about 250 km (155 mi), and the resulting debris has a perigee of 250 km (155 mi) or lower. The missile was aimed to minimize the amount of debris, which (according to Pentagon Strategic Command chief Kevin Chilton) had decayed by early 2009. On 27 March 2019, Indian Prime Minister Narendra Modi announced that India shot down one of its own LEO satellites with a ground-based missile. He stated that the operation, part of Mission Shakti, would defend the country's interests in space. Afterwards, US Air Force Space Command announced they were tracking 270 new pieces of debris but expected the number to grow as data collection continues.
The vulnerability of satellites to debris and the possibility of attacking LEO satellites to create debris clouds has triggered speculation that it is possible for countries unable to make a precision attack. An attack on a satellite of 10 tonnes or more would heavily damage the LEO environment.
Hazards:-
To spacecraft
Space junk can be a hazard to active satellites and spacecraft. It has been theorized that Earth's orbit could even become impassable if the risk of collision grows too high.
However, since the risk to spacecraft increases with the time of exposure to high debris densities, it is more accurate to say that LEO would be rendered unusable by orbiting craft. The threat to craft passing through LEO to reach higher orbit would be much lower owing to the very short time span of the crossing.
Uncrewed spacecraft
Although spacecraft are typically protected by Whipple shields, solar panels, which are exposed to the Sun, wear from low-mass impacts. Even small impacts can produce a cloud of plasma which is an electrical risk to the panels.
Satellites are believed to have been destroyed by micrometeorites and (small) orbital debris (MMOD). The earliest suspected loss was of Kosmos 1275, which disappeared on 24 July 1981 (a month after launch). Kosmos contained no volatile propellant, therefore, there appeared to be nothing internal to the satellite which could have caused the destructive explosion which took place. However, the case has not been proven and another hypothesis forwarded is that the battery exploded. Tracking showed it broke up, into 300 new objects.
Many impacts have been confirmed since. For example, on 24 July 1996, the French microsatellite Cerise was hit by fragments of an Ariane-1 H-10 upper-stage booster which exploded in November 1986. On 29 March 2006, the Russian Ekspress AM11 communications satellite was struck by an unknown object and rendered inoperable. On 13 October 2009, Terra suffered a single battery cell failure anomaly and a battery heater control anomaly which were subsequently considered likely the result of an MMOD strike. On 12 March 2010, Aura lost power from one-half of one of its 11 solar panels and this was also attributed to an MMOD strike. On 22 May 2013, GOES-13 was hit by an MMOD which caused it to lose track of the stars that is used to maintain an operational attitude.
It took nearly a month for the spacecraft to return to operation.[ The first major satellite collision occurred on 10 February 2009. The 950 kg (2,090 lb) derelict satellite Kosmos 2251 and the operational 560 kg (1,230 lb) Iridium 33 collided, 500 mi (800 km) over northern Siberia. The relative speed of impact was about 11.7 km/s (7.3 mi/s), or about 42,120 km/h (26,170 mph). Both satellites were destroyed, creating thousands of pieces of new smaller debris, with legal and political liability issues unresolved even years later. On 22 January 2013 BLITS (a Russian laser-ranging satellite) was struck by debris suspected to be from the 2007 Chinese anti-satellite missile test, changing both its orbit and rotation rate. Satellites sometimes perform Collision Avoidance Maneuvers and satellite operators may monitor space debris as part of manoeuvre planning. For example, in January 2017, the European Space Agency made the decision to alter the orbit of one of its three Swarm mission spacecraft, based on data from the US Joint Space Operations Center, to lower the risk of collision from Cosmos-375, a derelict Russian satellite.
Crewed spacecraft
Crewed flights are naturally particularly sensitive to the hazards that could be presented by space debris conjunctions in the orbital path of the spacecraft. Examples of occasional avoidance manoeuvres, or longer-term space debris wear, have occurred in Space Shuttle missions, the MIR space station, and the International Space Station.
Space Shuttle missions
From the early Space Shuttle missions, NASA used NORAD space monitoring capabilities to assess the Shuttle's orbital path for debris. In the 1980s, this used a large proportion of NORAD capacity. The first collision-avoidance manoeuvre occurred during STS-48 in September 1991, a seven-second thruster burn to avoid debris from the derelict satellite Kosmos 955. Similar manoeuvres were initiated on missions 53, 72 and 82.
One of the earliest events to publicize the debris problem occurred on Space Shuttle Challenger's second flight, STS-7. A fleck of paint struck its front window, creating a pit over 1 mm (0.04 in) wide. On STS-59 in 1994, Endeavour's front window was pitted about half its depth. Minor debris impacts increased from 1998.
Window chipping and minor damage to thermal protection system tiles (TPS) were already common by the 1990s. The Shuttle was later flown tail-first to take a greater proportion of the debris load on the engines and rear cargo bay, which are not used in orbit or during descent, and thus are less critical for post-launch operation. When flying attached to the ISS, the two connected spacecraft were flipped around so the better-armoured station shielded the orbiter.
A NASA 2009 study concluded that debris accounted for approximately half of the overall risk to the Shuttle. Executive-level decision to proceed was required if the catastrophic impact was likelier than 1 in 200. On a normal (low-orbit) mission to the ISS, the risk was approximately 1 in 300, but the Hubble telescope repair mission was flown at the higher orbital altitude of 560 km (350 mi) where the risk was initially calculated at a 1-in-185 (due in part to the 2009 satellite collision). A re-analysis with better debris numbers reduced the estimated risk to 1 in 221, and the mission went ahead.
Debris incidents continued on later Shuttle missions. During STS-115 in 2006, a fragment of circuit board bored a small hole through the radiator panels in Atlantis's cargo bay. On STS-118 in 2007 debris blew a bullet-like hole through Endeavour's radiator panel.
Mir
Impact wear was notable on Mir, the Soviet space station since it remained in space for long periods with its original solar module panels. Debris impacts onMir's solar panels degraded their performance. The damage is most noticeable on the panel on the right, which is facing the camera with a high degree of contrast. Extensive damage to the smaller panel below is due to an impact with a Progress spacecraft.
International Space Station
The ISS also uses Whipple shielding to protect its interior from minor debris. However, exterior portions (notably its solar panels) cannot be protected easily. In 1989, the ISS panels were predicted to degrade approximately 0.23% in four years due to the "sandblasting" effect of impacts with small orbital debris. An avoidance manoeuvre is typically performed for the ISS if "there is a greater than one-in-10,000 chance of a debris strike". As of January 2014, there have been sixteen manoeuvres in the fifteen years the ISS had been in orbit.
As another method to reduce the risk to humans on board, ISS operational management asked the crew to shelter in the Soyuz on three occasions due to late debris-proximity warnings. In addition to the sixteen thruster firings and three Soyuz-capsule shelter orders, one attempted manoeuvre was not completed due to not having the several days' warning necessary to upload the manoeuvre timeline to the station's computer. A March 2009 event involved debris believed to be a 10 cm (3.9 in) piece of the Kosmos 1275 satellite. In 2013, the ISS operations management did not make a manoeuvre to avoid any debris, after making a record four debris manoeuvres the previous year.
Kessler syndrome
The Kessler syndrome, proposed by NASA scientist Donald J. Kessler in 1978, is a theoretical scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade effect where each collision generates space debris that increases the likelihood of further collisions, He further theorized that one implication if this were to occur, is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges economically impractical for many generations.
The growth in the number of objects as a result of the late-1990s studies sparked debate in the space community on the nature of the problem and the earlier dire warnings. According to Kessler's 1991 derivation and 2001 updates, the LEO environment in the 1,000 km (620 mi) altitude range should be cascading. However, only one major satellite collision incident occurred: the 2009 satellite collision between Iridium 33 and Cosmos 2251. The lack of obvious short-term cascading has led to speculation that the original estimates overstated the problem. According to Kessler 2010 however, a cascade may not be obvious until it is well advanced, which might take years.
Dealing with debris
The problem
NASA estimates that there are more than 100 million pieces of human-produced space debris in orbit. Only 21,000 or so of those objects are big enough to be tracked by space surveillance sensors. Circling around at speeds upwards of five miles per second, even tiny pieces of space junk can pack a wallop, endangering current and future space missions. Here are a few solutions that have been proposed to clean up the mess in orbit.
Use a Giant net
JAXA, the Japanese space agency, is experimenting with giant magnetic nets developed in consultation with a fishing net manufacturer.
JAXA hopes to put the first space nets into service by 2019. The European Space Agency is working on its own version, set for a 2021 launch. Space nets are becoming a fashionable idea for catching more than just space junk: NASA's Innovative Advanced Concepts program funded a study for a net called the WRANGLER that would capture asteroids and large space objects.
The Clean Space One is a test satellite built by the Swiss Space Center and the École Polytechnique Fédérale de Lausanne to de-orbit dead satellites by locating, capturing, and throwing debris into the atmosphere, where it will burn up in the intense pressure and friction of reentry. It's set for a 2018 launch into low Earth orbit from an unmanned spaceplane. Its first two targets will be small, Cubesat-like satellites owned by the agency.
Tow it
You can net it, you can grab it, but you can also tow it. The idea of using a space tug to grab old satellites has been around since the beginning of the space race—Lockheed Martin has been batting around tug concepts since at least 1958. It recently introduced the CRS-2, a planned space tug that, along with its intended goal of ISS resupplies, could refurbish satellites, de-orbit nonfunctioning spacecraft, and haul broken satellites to a space station or craft for repair or safe cargo return, to Earth or otherwise.
Kill it with (laser)fire
One of the more (seemingly) crazy proposals to tackle the space junk problem involves firing lasers from the ground at objects we want to bring down. Lasers could reduce the expensive need to send new technology up into orbit for cleanup.
Instead, firing a laser pulse at a piece of space junk could perturb its orbit enough to drag it back to Earth. However, shooting stuff down from the ground could make for some scary accusations of aggression, depending on who takes out whose trash.
Grab on and hold tight
The American space program takes its best cues from the animal kingdom. Take, for instance, NASA JPL's Gecko Grippers, tested here on a "Vomit Comet" microgravity test aeroplane. The grippers are designed to grab onto an orbiting object using microscopic "hairs" that enable a firm grip, just like a gecko's sticky toes. The direction of the hairs determines its "stickiness," and they make it easy to ungrip as well.
Reduce, Reuse, Recycle
In the above still, Andy Griffith stars in the pilot of a television show called "Salvage," in which a scrappy salesman builds a lunar rocket out of salvaged parts in order to grab artefacts from an Apollo landing site worth millions of dollars. The show may have had a ridiculous conceit, but DARPA has a less ridiculous idea: use a robotic handyman to salvage old satellites, in orbit, for usable parts to create entirely new ones. It could also upgrade satellites still in space, as well as return other parts to the ground.
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