Initially the term Space debris referred to the natural debris found in the Solar System like; asteroids, comets and meteoroids. However the beginning of the NASA Orbital debris program in 1979, the term also refers to the debris (alt: space waste or Space garbage) from the mass of defunct, artificially created objects in space in the orbit of the Earth. Theseinclude old satellites and spent rocket stages as well as the fragments from their disintegration and collisions.
As of December 2016, five satellite collisions have generated space debris. Space debris is also known as Orbitaldebris, spacejunk, spacewaste, spacetrash, and space litter or space garbage. As of 5th July 2016, the United States strategic Command tracked a total of 17,852 artificial objects in orbit above the Earth, including 1,419 operational satellites. However these are just objects enough to be tracked. As of January 2019, more than 128 million bits of debris smaller than 1 cm (0.4 inch), about 9, 00,000 pieces of debris (1 -10 cm) and around 34,000 pieces larger than 10 cm were estimated to be in orbit around the Earth. Collision with debris have become a hazard to Spacecraft, causing damage akin to sandblasting, especially to Solar Panels and optics like telescopes or Star trackers that cannot be covered with a ballistic whipple shield( unless it is transparent).
Below 2,000 kms(1,200 miles)Earth-altitudes, 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 power satellites). For comparison ,the International Space Station orbits in the 300 -400 Kms( 190-250 miles) range and 2009 satellite collision and 2007 antisat test occurred at 800 to 900 kms( 500 -560 miles) altitudes. The ISS has whipple shielding,however known debris with a collision chance over 1/10,000 are avoided by maneuvering the stations.
The Kessler syndrome, a runway chain reaction of collision exponentially increasing the amount of debris, has been hypothesized to ensue beyond a critical density. This could affect useful polar –orbiting bands, increases the cost of protection for spacecraft missions and could destroy livesatellites. Whether Kessler syndrome is already underway has been debated. The measurement, mitigation and potential removal of debris are conducted by some participants in the space industry. The main sources of space debris are (i) Dead spacecraft’si.e those spacecraft’s and satellites whose life span are ended (ii)Lost equipment’s belonging to the astronauts and cosmonauts. AstronautsEd White lost a glove on the first American spacewalk (EVA); a camera lost by Michael Collins near Gemini 10; a thermal blanket lost during STS-88; garbage bags jettisoned by Soviet cosmonaut during Mir’s 15-year life, a wrench and a toothbrush; Sunita William 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, HeidermarieStefanyshyn-piper lost a briefcase sized tool bag (iii) Booster: characterizing the problem of space debris, it was learned that much debris was due to rocket upper stages which end up in orbit and breakup due to decomposition of unvented, unburned fuel(iv)Weapons: a past debris source was the testing of antisatellite weapon (ASAT) 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. test were only identified later. By the time the debris problem was understood, thus widespread ASAT testing ended; the U.S. program 437 was shut down in 1975. But on 27 March 2019, Indian Prime Minister Narendra Modi announced that India shot down one of its own LEO (Low Earth Orbit) satellite with a ground base missile. He stated that the operation ,part of Mission Shakti, would defend the country’s interest in space .The vulnerability of satellite to debris and possibility of attacking satellite 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 tons or more would heavily damage the LEO environment.
The threats of space debris aremultipronged. It is a threat to active satellite and spaceships. The Earth orbit may even become impassable as the risk of collision grows too high. Although spacecraft’s are protected by whippleshields, solar panels which are exposed to the sun, wear from low mass impacts. These produce a cloud of plasma which is an electrical risk to the panels. Satellites are believed to have been destroyed by micrometeorites and orbital debris (MMOD). The earliest suspected lost was of kosmos 1275, which disappeared on 24th 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 destruction explosion which took place. However, the case has not been proven. It is also a challenge to manned spacecraft’s to avoid collision. Although most debris burns up in the atmosphere, larger objects can reach the ground intact. In 1969 five sailors on a Japanese ship injured by space debris. In 1997an Oklahoma woman ,Lettie William, was injured when she was hit in the shoulder by a 10 cm X 13 cm (3,9 in x 5.1 in) piece of blackened ,woven metallic material confirmed as part of the propellant tank of Delta II rocket which launched by U.S Air Force satellite the year before. We may recall the original re-entry plan for SKYLAB, called for the station to remain in space for 8 to 10 years after its final mission in February 1974.On 12 January 2001, a Star 48 payload Assist Module (PAM-D) rocket upper stage re-entered the atmosphere after a catastrophic orbital decay, crashing in the Saudi Arabian desert. In the 2003, Columbia disaster, larger parts of the spacecraft reached the ground and entire equipment system remained intact. So, space debris or space garbage is a great threat to the Earth,the control of which is beyond our reach.
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