Space Shuttle external tank

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The Space Shuttle external tank ( ET ) is a component of the Space Shuttle launch vehicle containing liquid hydrogen fuel and liquid oxygen oxidizer. During the appointment and ascent it supplies fuel and oxidizers under the pressure of the Space Space Shuttle's three engines (SSME) in the orbiter. The ET is discarded more than 10 seconds after MECO (Main Engine Cut Off), where SSME is closed, and reentered into Earth's atmosphere. Unlike Solid Rocket Boosters, external tanks are not reused. They broke before impacting in the Indian Ocean (or the Pacific Ocean in the case of a direct insertion launch trajectory), away from the cruise line and not found.

Video Space Shuttle external tank

Overview

ET is the largest element of the spacecraft, and when it is loaded, it is also the toughest. It consists of three main components:

• liquid oxygen tank forward (LOX)
• an unpressured intertank containing most of the electrical components
• liquid hydrogen tank behind (LH ₂ ); this is the largest part, but it is relatively light, due to the very low density of liquid hydrogen.

ET is the "backbone" of the space shuttle during launch, providing structural support for attachments with the Space Shuttle Solid Rocket Boosters (SRBs) and orbiting. The tank is connected to each SRB at one point of the attachment forward (using a crossbar through the intertank) and one back bracket, and it is connected to the orbiter on one front bipod attachment and two burip beeps. In the stern attachment area, there is also an umbilical carrying liquid, gas, electrical signals and electric power between the tank and the orbiter. Electrical signals and control between the orbiter and two solid rocket boosters are also directed through the umbilical.

Although the external tank is always discarded, it may be reusable in orbit. Plans for reuse range from merging to space stations as extra living or research space, such as rocket fuel tanks for interplanetary missions (eg Mars), to feedstocks for orbiting plants.

Another concept is to use ET as a cargo carrier for large payloads. One proposal is for the main mirror of a 7-meter aperture telescope to carry with the tank. Another concept is the Aft Cargo Carrier (ACC).

Maps Space Shuttle external tank

Version

Over the years, NASA is working to reduce ET weight to improve overall efficiency. For each pound of weight reduction, the ability to carry a shuttle's space shuttle increases almost a pound.

Standard Weight Tank

Original ET is informally known as Standard Weight Tank (SWT) and is made from 2219, a high-strength aluminum-copper alloy used for many aerospace applications. The first two, used for STS-1 and STS-2, are painted white to protect the tanks from ultraviolet light for extended periods that the space shuttle uses on the launch pad before launch. As this is not a problem, Lockheed Martin (at the time, Martin Marietta) reduced his weight by leaving unpainted colorful sprayers with STS-3, saving about 272 kg (600 pounds).

After STS-4, several hundred pounds are removed by removing the anti-geyser line. This line is parallel to the oxygen feed path, providing a circulation path for liquid oxygen. This reduces the accumulation of oxygen gas in the feed channel during the pre-launch race (LOX loading). Once the propellant loading data from the ground test and some of the first space shuttle missions are assessed, the anti-geyser line has been removed for the next mission. The total length and diameter of ET remain unchanged. The last SWT, flown on STS-7, weighed about 35,000 kg (77,000 lb) inert.

Light Tank

Beginning with the STS-6 mission, lightweight ET (LWT), was introduced. This tank is used for most shuttle flights, and was last used on the disastrous shuttle disaster of Columbia (STS-107). Although the tanks vary slightly in weight, each weighs about 30,000 kg (66,000 lb) inert.

Weight reduction of SWT is done by removing parts of the stringer (a structural stiffener running the length of the hydrogen tank), using fewer rings and modifying the main frame in the hydrogen tank. Also, significant portions of the tank are milled differently so as to reduce the thickness, and the weight of the ET stern rocket reinforcement is reduced by using stronger but lighter and less expensive titanium alloys.

Super Light Tank

Super Lightweight Tank (SLWT) was first flown in 1998 at STS-91 and used for all subsequent missions with two exceptions (STS-99 and STS-107). SLWT basically has the same design as LWT except that it uses an aluminum-lithium alloy (Al 2195) for most of the tank structure. These alloys provide significant reductions in tank weight (~ 3.175 kg/7,000 pounds) above LWT. Manufacture also includes frictional frictional friction technology. Although all ETs generated after the introduction of SLWT are this configuration, one LWT remains in stock to be used if requested until the end of the space shuttle era. SLWT provides 50% of the required performance improvements for the space shuttle to reach the International Space Station. Weight reduction allows the Orbiter to carry more loads into the highly sloped ISS orbit.

Technical specifications

SLWT Specifications

• Length: 153.8Ã, ft (46.9 m)
• Diameter: 27.6Ã, ft (8.4 m)
• Empty Weight: 58,500 pounds (26,500 kg)
• Gross Lift Weight: 1,680,000 pounds (760,000 kg)

LOX tank

• Length: 54.6Ã, ft (16.6 m)
• Diameter: 27.6Ã, ft (8.4 m)
• Volume (at 22 psig): 19,541.66 cuÃ, ft (146,181,8Ã, USÃ, gal; 553,358Ã, l)
• LOX mass (at 22 psig): 1,387,457Ã, lb (629,340Ã, kg)
• Operation Pressure: 34.7-36.7 psi (239-253 kPa) (gauge) (absolute)

Intertank

• Length: 22.6Ã, ft (6.9 m)
• Diameter: 27.6Ã, ft (8.4 m)

LH tank ₂

• Length: 97.0 ft (29.6 m)
• Diameter: 27.6Ã, ft (8.4 m)
• Volume (at 29.3 psig): 52,881.61 cuÃ, ft (395,581.9Ã, USÃ, gal; 1,497,440Ã, l)
• LH ₂ mass (at 29.3 psig): 234,265Ã, lb (106,261Ã, kg)
• Operation Pressure: 32-34Ã, psi (220-230 kPa) (absolute)
• Operating Temperature: -423Ã, Â ° F (-252.8Ã, Â ° C)

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Contractor

Contractors for external tanks are Lockheed Martin (formerly Martin Marietta), New Orleans, Louisiana. The tank is manufactured at Michoud Assembly Facility, New Orleans, and transported to Kennedy Space Center by barge.

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Components

ET has three main structures: LOX tank, intertank, and LH tank ₂ . Both tanks are made of aluminum alloy shell with a support frame or stability as needed. The aluminum intertank structure uses a leather stringer with a stabilizer frame. The main aluminum materials used for the three structures are 2195 and 2090 alloys. AL 2195 is an Al-Li alloy designed by Lockheed Martin and Reynolds for cryogenics storage (and used for SLW versions of ET - previous versions used Al 2219). Al 2090 is a commercially available Al-Li alloy.

Liquid oxygen tank

The LOX tank is located at the top of the ET and has an ogive shape to reduce aerodynamic obstacles and aerothermodynamic heating. The ogive nose section is covered by a removable flat cover plate and the nasal cone. The nose cone consists of a removable cone assembly that serves as an aerodynamic fairing for propulsion and electrical system components. The front element of the cone of the nose serves as an antidote to aluminum lightning. The volume of the LOX tank is 19,744 cuÃ,ft (559.1 m ³ ) at 22 psig (250 kPa absolute) and -297 Â ° F (90.4 K? -182,8 Â ° C) (cryogenic).

The tank is inserted into a 17-diameter feed line at (430 mm) that delivers liquid oxygen through the intertank, then outside the ET to the right of the stern ET/umbilical disconnect orbiter. The diameter 17 (430 mm) feed line allows liquid oxygen to flow at about 2.787 lb/s (1264 kg/s) with SSME operating at 104% or allowing a maximum flow of 17.592 gal/min (1.1099 m/s/s).

All loads except aerodynamic loads are transferred from the LOX tank on the flange-joint interface interface with intertank.

The LOX tank also includes an internal slash insulator and a vortex insulator to dampen the slosh liquid. Vortex baffles are mounted on top of LOX feed boards to reduce the flow of liquid generated from the slosh and to prevent gas traps in the LOX being sent.

Intertank

Intertank is a structural connection ET that joins the LOX and LH ₂ tanks. Its main function is to receive and distribute all the thrust loads from the SRB and transfer the load between the tanks.

Both SRB mounting attachments are located 180 ° apart on the intertank structure. The beams are extended throughout the structure of the intertank and are mechanically fastened to the attachment. When SRB is on, the light will bend because of the high stress load. These loads will be transferred to the fittings.

Side by side fitting attach SRB is the main ring frame. The load is transferred from the fittings to the main ring frame which then distributes the tangential load to the intertank skin. Two panels of intertank leather, called thrust panels, distribute axial axial SRB axial load to LOX and LH ₂ tanks and to adjacent intertank skin panels. These adjacent panels consist of six stinger-stiffened panels.

Intertank also serves as a protective compartment for residential operational instrumentation.

Liquid hydrogen tank

The LH tank ₂ is the bottom of the ET. The tank is built from four cylindrical parts of the cylinder, the dome to the front, and the rear dome. The halves are joined together by five main ring frames. This frame of the ring receives and distributes the load. The advanced dome-to-barrel frame distributes the load applied through the intertank structure and also the flange to install the LH ₂ tank to the intertank. The stern main ring accepts an orbited-induced load from the back-orbiting rear support strut and SRB-induced load from the SRB back support struts. The remaining three ring frames distribute the orbit thrust load and LOX feedline support load. Loads from the frame are then distributed through barrel skin panels. The LH tank ₂ has a volume of 53,488 cubic feet (1,514.6 m ³ ) at 29.3 psig (3.02 bar absolute) and -423Ã, Â ° F (20 , 4Ã, K; -252,8 Â ° C) (cryogenic).

The front and rear vaults have the same modified ellipsoidal shape. For advanced domes, installation conditions are included for LH ₂ ventilation valves, mounting of LH ₂ pressure conduits, and electrical post-installation. The rear dome has a hole fitting for access to LH feedline and support buffer for LH ₂ feedline.

The LH tank ₂ also has a baffle vortex to reduce the rotation generated from the slosh and to prevent gas traps in LHs sent ₂ . The baffle is located in a siphon outlet just above the LH <2> sub tank vault. This channel transmits liquid hydrogen from the tank through a 17-inch (430 mm) channel to the left rear umbilic. The rate of liquid hydrogen feed flow is 465 lb/s (211 kg/s) with SSMEs at 104% or a maximum flow of 47,365 US gal/min (2,988 mÃ,³/s).

Thermal protection system

The ET thermal protection system consists primarily of spray foam insulation (SOFI), plus pre-formed foam cuts and folded ablator material. This system also includes the use of phenolic heat insulators to block air liquefaction. Thermal insulators are required for the attachment of liquid hydrogen tanks to block air liquefaction of exposed metals, and to reduce heat flow into liquid hydrogen. While warmer liquid oxygen produces less thermal needs, aluminum from the liquid oxygen tank area to the front requires protection from aeroheating. Meanwhile, the isolation on the stern surface prevents the liquid air from incorporating in the intertank. The middle cylinder of the oxygen tank, and the propellant line, can withstand the accumulated depth of accumulated ice that is condensed from moisture, but the orbiter can not take damage from the liberated ice. The thermal protection system weighs 4,823 pounds (2,188 kg).

Development of ETs thermal protection system is problematic. Anomalies in foam applications are so frequent that they are treated as variance, not a safety incident. NASA had trouble preventing discarded splinter fragments during the flight for the entire program history:

• STS-1, 1981: Crew reports white matter flowing through the window during an orbiter-external-tank flight. Crew approximate size from 1/4-inch to boxed-sized. The post-landing report explains the possible loss of foam from an unknown location, and 300 tiles requiring direct replacement for various causes.
• STS-4, 1982: ramp ramp ramp; 40 tiles require immediate replacement.
• STS-5, 1982: Continued high level of tile loss.
• STS-7, 1983: 50 x 30 cm (20 times 12 years) Bipod ramp loss is photographed, dozens of spot loss.
• STS-27, 1988: One large loss of uncertain origin, causing one total loss. Hundreds of small losses.
• STS-32, 1990: Bipod ramp loss photographed; five loss points up to 70Ã, cm in diameter, plus tile damage.
• STS-50, 1992: Bipod ramp loss. 20ÃÆ' â € "10ÃÆ' â €" 1cm damage tiles.
• STS-52, 1992: Part of the beep path, the jackpad is missing. 290 total plot marks, 16 larger than an inch.
• STS-62, 1994: Part of the beep path has been lost.

In 1995, 11 (CFC-11) chlorofluorocarbons began being withdrawn from large foams sprayed on the machine in accordance with the Environmental Protection Agency's prohibition on CFCs under section 610 of the Clean Air Act. Instead, hydrochlorofluorocarbons known as HCFC-141b have been certified for use and incorporated into the shuttle program. The remaining foam, especially hand-sprayed detail pieces, continues to use CFC-11 to this day. These areas include troubled bipod and PAL ramp, as well as some fittings and interfaces. For bipod roads in particular, "the process of applying the foam to the tank parts has not changed since 1993." The "new" foam containing HCFC 141b was first used in the stern dome portion of the ET-82 during the STS-79 flight in 1996. The use of HCFC 141b was extended to the ET area, or larger section of the tank, beginning with ET-88, which flew on STS-86 in 1997.

During the appointment of STS-107 on January 16, 2003, a piece of foam insulation escaped one of the bipod lines in the tank and hit the front of the Space Shuttle Columbia at several hundred miles per hour. The impact is believed to have damaged one comparatively compensated carbon panel on the left wing front edge, which is believed to be the size of a basketball which then allows super hot gas to enter the wing superstructure a few days later during re-entry. This resulted in the destruction of Columbia and the loss of its crew. The report specifies that the external fuel tank, ET-93, "has been built with BX-250", the fuel-cover foam is the CFC-11 and not the newer HCFC 141b.

In 2005, the problem of foam foam has not fully healed; on STS-114, an auxiliary camera mounted in the tank records a piece of foam separated from one of the Protuberance Air Load (PAL) slopes, designed to prevent unstable airflow under the tray of the tank and pressure lines during the climb. The PAL path consists of layers of sprayed foam manually, and is more likely to be a source of debris. That piece of foam has no impact on the orbiter.

Reports published in conjunction with the STS-114 mission indicate that excessive ET handling during modifications and upgrades may have contributed to the loss of foam on the Discovery 's Return to Flight mission. However, three repeat missions (STS-121, STS-115, and STS-116) have been performed, all with an "acceptable" foam level. However, on an STS-118 piece of foam (and/or ice) with a diameter of about 10 cm separated from the feedline mounting bracket on the tank, bouncing one of the rear struts and hitting the underside of the wing, damaging two tiles. The damage is not considered dangerous.

Hardware

External hardware, ET-orbiter complementary fittings, umbilical fittings, and electrical security systems and a weighing range of 9,100 pounds (4.1 Â ° t).

Ventilation and release valve

Each propellant tank has a ventilation valve and assistance at the front end. This dual function valve can be opened by ground support equipment for ventilation function during prelaunch and can be opened during flight when the ullage pressure of liquid hydrogen tank reaches 38 psig (262 kPa) or liquid oxygen tank ullage pressure reaches 25 psig (172 kPa ).

In the initial flight, the liquid oxygen tank contains a separate ventilated valve which is removed by pyrotechnic and operates on the front end. At separation, the liquid oxygen ventilation valve is opened, providing an impetus to assist in the more positive separation and control maneuvers of aerodynamics entering ET. The last flight with the active fall valve is STS-36.

Each of the two external umbilical tank plates paired with the corresponding plate on the orbiter. Plates help maintain alignment between umbilicals. The physical strength of the umbilical plate is provided by bending the corresponding umbilical plate. When the GPC orbiter orders the separation of the external tank, the bolt is disconnected by the pyrotechnic device.

ET has five umbilical propellant valves that interact with orbiter umbilicals: two for liquid oxygen tanks and three for liquid hydrogen tanks. One of the umbilical valves of the liquid oxygen tank is for liquid oxygen, the other for gas oxygen. The umbilical liquid hydrogen tank has two valves for liquid and one for gas. The diameter of the hydrogen fluid of the umbilical intermediates is the recirculation umbilical used only during the sequence of liquid hydrogen cooling during prelaunch.

When ET is filled, excess hydrogen gas is released through the umbilical connection through a large diameter tube in the extended arm of the fixed service structure. The connection for this pipe between the ET and the service structure is made on the ground umbilical carrier plate (GUCP). Sensors are also installed in GUCP to measure Hydrogen levels. Countdown STS-80, STS-119, STS-127 and STS-133 have been discontinued and resulted in a delay of several weeks in later cases due to hydrogen leakage in this relationship. It requires complete tank drying and removal of all hydrogen through helium gas cleaning, a 20 hour process, before the technician can check and fix the problem.

The lid mounted on the swing arm on the service structure still covers the oxygen tank vent above the ET for a countdown and is drawn approximately two minutes before lifting. The chiffon cap from oxygen vapor threatens to form a large ice accumulation on the ET, thus protecting the orbiter's heat protection system during launch.

Sensor

There are eight propellant discharge sensors, each four for fuel and oxidizer. The fuel thinning sensor is located at the bottom of the fuel tank. The oxidizing sensor is installed in the liquid oxygen feed lane of the manifold orbiter at the downstream portion of the feed line termination. During SSME thrusts, the orbiter's general-purpose computer continues to count the momentary mass of the vehicle due to the use of propellants. Typically, the main machine cutoff is based on a predetermined rate; however, if there are two fuel sensors or oxidizers that feel dry conditions, the engine will be turned off.

The location of the liquid oxygen sensor allows the maximum amount of oxidizer to be consumed in the machine, while allowing sufficient time to turn off the engine before the hollow oxidation pump (run dry). In addition, 1,100 lb (500 × kg) of liquid hydrogen is loaded above and above that required by the 6-1/ratio ratio of the fuel combustion engine. This ensures that the cutoff of the fuel depletion sensor is rich; The oxidation-rich engine shutdown can cause severe combustion and erosion of the engine components, potentially leading to the loss of vehicles and flight crews.

The erroneous and false readings of the fuel thinning sensors have delayed some of the shuttle launch efforts, notably STS-122. In 2007-12-18, the tanking test determined the cause of the error to be an error in the cable connector, rather than the sensor failure itself.

Four pressure transducers located at the top of the oxygen liquid and liquid hydrogen tank monitor the ullage pressure.

ET also has two electric umbilicals that carry electrical power from the orbiter to the tank and two SRBs and provide information from SRB and ET to the orbiter.

ET has an external camera mounted inside the built-in brackets on the shuttle along with the transmitter that can continue to send video data long after the space shuttle and ET have split up.

System security range

Previous tanks use a range safety system to disperse tank propellants if needed. This includes battery power, receiver/decoder, antenna and weaponry. Starting with STS-79 the system is disabled, and completely removed for STS-88 and all subsequent flights.

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Future use

In 1990, it was suggested that the external tank be used as a moon habitat or as an orbital station. This proposal did not work.

As a base for Ares in Constellation

With the retirement of the space shuttle in 2011, NASA, with its planned Project Constellation, featuring the Orion spacecraft from Apollo, will also feature the debut of two launch vehicles derived from space shuttle, Ares I aircraft crew. and heavy-lift cargo vehicles belonging to Ares V.

While Ares I and Ares V will use a five-segment Solid-Rocket Booster modification for the first stage, the ET will now serve as the basic technology for the first phase of Ares V and the second stage of Ares I; For comparison, the second Ares I stage will have about 26,000 US gal (98,000 l) LOX, versus ET holding 146,000 US gal (550,000 l), more than 5 times that amount.

The first Ares V, which will be equipped with five RS-68 rocket engines (the same engine used on Delta IV rockets), will be 33 feet (10 m) in diameter, as wide as S-IC and S Stage II in Saturn V rockets. This will use the same internal ET configuration (separate LH ₂ and LOX tanks separated by intertank structure), but will be configured to directly receive LH ₂ and LOX fill and drain , along with LOX ventilation on the retractable arm as used on Shuttle for LH ₂ (as "beanie cap" will not be useful because of the in-line design of the three-stage vehicles).

The second stage of Ares I, on the other hand, will only use the spray-on insulation foam that is currently used on current ET. Originally configured like that of Ares V and Shuttle ET, NASA, after completing its design review in 2006, decided, to save weight and cost, to reconfigure the second stage internal structure by using a combined LH ₂ /tank LOX with propellant separated by a common bulkhead, the configuration is successfully used in the S-II and S-IVB stages of the Saturn V rocket. Unlike the Ares V, which will use the same air/contents/air/hose configurations used on Shuttle, the Ares system I will use the traditional filling/exhaust/ventilation system used on Saturn IB and Saturn V rockets, but quickly-holding the arms as the jumping frog accelerates the Ares I would expect during SRB ignition.

As originally envisaged, both Ares I and Ares V will use the "throw" version of SSME, but in time, due to the need to keep R & D down and to maintain the schedule set by NASA Administration Michael D. Griffin to launch Ares and Orion in 2011, NASA decided (after the 2006 review) to switch to a cheaper RS-68 engine for the Ares V and J-2 engines that improved for Ares I. Due to the less efficient switch to RS-68, the Ares V extends from 28.6 to 33 feet (8.72 to 10.06 m) to accommodate extra propellants, while Ares I is reconfigured to combine solid rotor segments fifth with the J-2X upper stage, because the new engine has less thrust than the original SSME. Due to the trade-off, NASA will save approximately USD $ 35 million using a simplified and higher RS-68 thrust engine (reconfigured to be enabled and working like SSME), while at the same time eliminating the expensive tests needed for SSME air -startable for Ares I (as J-2X and its predecessors are designed to start in both the air and in the near hollow).

Proposed for DIRECT

The DIRECT project, an alternate shuttle-derived vehicle, will use a modified external tank of standard diameter, with three SSMEs, with two standard SRBMs, as the Crew Launch Vehicle. The same vehicle, with one extra SSME, and top level EDS, will serve as the Cargo Launch Vehicle. It is planned to save $ 16 billion, eliminate the loss of NASA jobs, and reduce post-space space gap, manned space from five years to two or less.

No hardware

MPTA-ET is displayed alongside the Space Shuttle Pathfinder in the U.S. Space & amp; Rocket Center in Huntsville, Alabama.

ET-94 (old version of LWT) is in Los Angeles and in 2019 will be shown with the Space Shuttle Endeavor at California Science Center when Samuel Oschin Air and Space Center is opened.

Three other external tanks are being prepared, when manufacturing stops. ET-139 is at an advanced stage of manufacturing; ET-140 and ET-141 are in the early stages of manufacturing.

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See also

• Space Launch System (heavy launcher under development in 2010)
• DIRECT (the proposed heavy launch system)
• MPTA-ET (external tank test for STS)
• List of large re-entry debris
• List of the heaviest spacecraft

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References

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Further reading

• "External Tank Protection System" NASA Facts Return to Aviation Focus Area , National Aeronautics and Space Agency, Marshall Space Flight Center, Huntsville, Alabama (Pub 8-40392, FS2005- 4-10-MSFC, April 2005)
• National Aviation and Space Agency. Booster Systems Briefs . Basic, Rev F, PCN 1. April 27, 2005.
• National Aviation and Space Agency. Shuttle System Design Criteria. Volume I: Document on the Performance of Shuttle Review . NSTS 08209, Volume I, Revised B. March 16, 1999.

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External links

• Aircraft Propulsion and External Tank Photo Gallery
• STS-115 launch as seen from ET Camera Video
• Report of Columbia Investigation Board Investigation Vol. 1, Chp. 3, "Accident Analysis" August 2003
• STS-125 External Jettisoned Tank View and in decaying orbit as seen from Shuttle Atlantis Video
• Round panorama from the bottom of ET-122 on its scaffold at Michoud Assembly Facility
• Round panorama from the top of ET-122 on its scaffold at Michoud Assembly Facility
• Round panorama from the top of ET-138 on its scaffold at the Michoud Assembly Facility. This is the last tank scheduled to fly.
• Round panorama along the bottom line of ET-138 near the feedlines on its scaffold at the Michoud Assembly Facility. This is the last tank scheduled to fly.
• "Space Shuttle External Tank Used as Space Station - Study Project Perun" An award-winning student paper started in 1979 about building a space station from the External Tank.
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Source of the article : Wikipedia