Editing Space Shuttle external tank (section)

==Versions==
Over the years, NASA worked to reduce the weight of the ET to increase overall efficiency. The weight reduced from the ET resulted in an almost equal increase of the cargo-carrying capability of the Space Shuttle.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/et.html|title=External Tank|publisher=NASA|access-date=November 25, 2010|archive-date=August 19, 2019|archive-url=https://web.archive.org/web/20190819161653/https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/et.html|url-status=dead}}</ref>

===Orange color===
The external tank's orange color is the color of the spray-on foam insulation. The first two tanks, used for [[STS-1]] and [[STS-2]], were painted white to protect the tanks from [[ultraviolet light]] during the extended time that the shuttle spent on the launch pad prior to launch.<ref>{{cite web|title=Columbia's White External Fuel Tanks|date=April 12, 2006 |url=http://www.space.com/businesstechnology/060412_sts1_whitetank.html|publisher=Space.com}}</ref> NASA engineer Farouk Huneidi told the agency that the paint did not actually protect the foam.<ref name="vogt20110728">{{Cite news |last=Vogt |first=Tom |date=2024-04-04 |title=Local man takes first-hand pride in space program |url=https://www.columbian.com/news/2011/jul/28/salmon-creek-resident-reflects-first-hand-pride-in/ |access-date=2024-04-08 |work=The Columbian |language=en-US}}</ref> Martin Marietta (now part of [[Lockheed Martin]]) reduced weight by leaving the rust-colored spray-on insulation unpainted beginning with [[STS-3]], saving approximately {{convert|272|kg|lb|abbr=on|lk=on}}.<ref name="et_paint">National Aeronautics and Space Administration [http://www.msfc.nasa.gov/news/news/releases/1999/99-193.html "NASA Takes Delivery of 100th Space Shuttle External Tank."] {{webarchive|url=https://web.archive.org/web/20070311004932/http://www.msfc.nasa.gov/news/news/releases/1999/99-193.html |date=March 11, 2007 }} Press Release 99-193. August 16, 1999.</ref>

===Standard Weight Tank===
The original ET is informally known as the Standard Weight Tank (SWT) and was fabricated from [[2219 aluminium alloy|2219 aluminum alloy]], a high-strength aluminum-copper alloy used for many aerospace applications.

After [[STS-4]], several hundred pounds were eliminated by deleting the anti-geyser line. This line paralleled the oxygen feed line, providing a circulation path for liquid oxygen. This reduces accumulation of [[gas]]eous oxygen in the feed line during prelaunch tanking (loading of the LOX). After [[propellant]] loading data from ground tests and the first few Space Shuttle missions were assessed, the anti-geyser line was removed for subsequent missions. The total length and diameter of the ET remain unchanged. The last SWT, flown on [[STS-7]], weighed approximately {{convert|35000|kg|order=flip}} inert.

===Lightweight Tank===
[[Image:Externaltank.jpg|thumb|The [[Space Shuttle]] external tank for [[STS-114]] on its way to the [[Vehicle Assembly Building]]]]
Beginning with the [[STS-6]] mission, a lightweight ET (LWT), was introduced. This tank was used for the majority of the Shuttle flights, and was last used during the launch of the [[Space Shuttle Columbia disaster|ill-fated]] [[STS-107]] mission. Although tanks vary slightly in weight, each weighed approximately {{convert|30000|kg|lb|order=flip}} inert.

The weight reduction from the SWT was accomplished by eliminating portions of stringers (structural stiffeners running the length of the hydrogen tank), using fewer stiffener rings and by modifying major frames in the hydrogen tank. Also, significant portions of the tank were [[milling machine|mill]]ed differently so as to reduce thickness, and the weight of the ET's aft [[Space Shuttle Solid Rocket Booster|solid rocket booster]] attachments was reduced by using a stronger, yet lighter and less expensive [[titanium]] alloy.

===Super Lightweight Tank===
The Super Lightweight Tank (SLWT) was first flown in 1998 on [[STS-91]] and was used for all subsequent missions with two exceptions ([[STS-99]] and [[STS-107]]).<ref name=LMFS07>*[http://www.lockheedmartin.com/data/assets/12742.pdf "FACT SHEET SPACE SHUTTLE EXTERNAL TANK"]{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }} April 2007 [[Lockheed Martin]]{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes }}
*http://www.nasa-klass.com/Curriculum/Get_Training%201/ET/RDG_ET-Additional/ETFactSheet.pdf
*https://www.nasa.gov/returntoflight/system/system_ET.html</ref> The SLWT had basically the same design as the LWT except that it used an [[aluminium-lithium alloy]] ([[2195 aluminium alloy|Al 2195]]) for a large part of the tank structure. This alloy provided a significant reduction in tank weight (about {{convert|3,175|kg|order=flip|disp=or|abbr=out}}) over the LWT. Manufacture also included [[Friction stir welding#Aerospace|friction stir welding]] technology. Although all ETs produced after the introduction of the SLWT were of this configuration, one LWT remained in inventory to be used if requested until the end of the shuttle era. The SLWT provided 50% of the performance increase required for the shuttle to reach the [[International Space Station]].<ref name="by the numbers">{{cite web|url=http://www.lockheedmartin.com/ssc/michoud/ExternalTank/ByNumbers.html|title=External Fuel Tank by the Numbers|publisher=Lockheed Martin|archive-url = https://web.archive.org/web/20080103111431/http://www.lockheedmartin.com/ssc/michoud/ExternalTank/ByNumbers.html|archive-date=January 3, 2008 }}</ref> The reduction in weight allowed the Orbiter to carry more payload to the [[International Space Station#Orbit|highly inclined orbit of the ISS]].

[[Image:Pegasus barge being moved by Freedom Star and towboat American 2.jpg|right|thumb|300px|The Pegasus barge<ref>{{Cite web |last=Harbaugh |first=Jennifer |date=February 4, 2020 |title=NASA's Barge Pegasus – Transportation for the Space Launch System Core Stage |url=http://www.nasa.gov/exploration/systems/sls/fs/pegasus-barge.html |access-date=October 25, 2022 |website=NASA}}</ref> carrying ET-119 (which will be used on [[STS-121]]) is towed to Port Canaveral.]]<!-- There is no other mention of "the Pegasus barge" in this article; yet a [[WP:REDIRECT]] points to it. Needs to be mentioned/cited in the article prose. -->

=== Technical specifications ===
'''SLWT specifications'''<ref name=LMFS07/>
*Length: {{convert|153.8|ft|m|abbr=on}}
*Diameter: {{convert|27.6|ft|m|abbr=on}}
*Empty weight: {{convert|58500|lb|kg|abbr=on}}
*Gross liftoff weight: {{convert|1680000|lb|kg|abbr=on}}

'''LOX tank'''
*Length: {{convert|54.6|ft|m|abbr=on}}
*Diameter: {{convert|27.6|ft|m|abbr=on}}
*Volume (at 22 [[pounds per square inch|psig]]): {{convert|19541.66|cuft|USgal l|abbr=on|lk=on}}
*LOX mass (at 22 psig): {{convert|1387457|lb|kg|abbr=on}}
*Operation pressure: {{convert|34.7|-|36.7|psi|abbr=on|kPa}} (absolute)

'''Intertank'''
*Length: {{convert|22.6|ft|m|abbr=on}}
*Diameter: {{convert|27.6|ft|m|abbr=on}}

'''LH<sub>2</sub> tank'''
*Length: {{convert|97.0|ft|m|abbr=on}}
*Diameter: {{convert|27.6|ft|m|abbr=on}}
*Volume (at 29.3 psig): {{convert|52881.61|cuft|USgal l|abbr=on}}
*LH<sub>2</sub> mass (at 29.3 psig): {{convert|234265|lb|kg|abbr=on}}
*Operation pressure: {{convert|32|-|34|psi|kPa|abbr=on}} (absolute)<!--32-34 psia (221-235 kPa (absolute)) -->
*Operation temperature: {{convert|-423|F|C|0}}<ref name="by the numbers"/>