Editing Space Shuttle Columbia disaster (section)

== Background ==

=== Space Shuttle ===
{{Main|Space Shuttle}}

[[File:STS-107 launchpad circled.jpg|thumb|upright|alt=The Space Shuttle stack standing vertically on the launchpad, with a red circle around the bipod foam.|''Columbia'' prior to launch. The circled area on the [[external tank]] (ET) is the left bipod foam ramp, and the circled area on the orbiter is the location that was damaged.]]

The [[Space Shuttle]] was a partially reusable spacecraft operated by the U.S. [[NASA|National Aeronautics and Space Administration]] (NASA).<ref name="rogers_com">{{cite report |url=https://sma.nasa.gov/SignificantIncidents/assets/rogers_commission_report.pdf |title=Report of the Presidential Commission on the Space Shuttle Challenger Accident |last1=Rogers |first1=William P. |last2=Armstrong |first2=Neil A. |date=June 6, 1986 |publisher=NASA |volume=1 |last3=Acheson |first3=David C. |last4=Covert |first4=Eugene E. |last5=Feynman |first5=Richard P. |last6=Hotz |first6=Robert B. |last7=Kutyna |first7=Donald J. |last8=Ride |first8=Sally K |last9=Rummel |first9=Robert W. |last10=Sutter |first10=Joseph F. |last11=Walker |first11=Arthur B.C. |last12=Wheelon |first12=Albert D. |last13=Yeager |first13=Charles E. |author-link1=William P. Rogers |author-link2=Neil Armstrong |access-date=July 13, 2021 |archive-url=https://web.archive.org/web/20201018005636/https://sma.nasa.gov/SignificantIncidents/assets/rogers_commission_report.pdf |archive-date=October 18, 2020 |author-link3=David Campion Acheson |author-link4=Eugene E. Covert |author-link5=Richard Feynman |author-link7=Donald Kutyna |author-link8=Sally Ride |author-link10=Joe Sutter |author-link11=Arthur B. C. Walker Jr. |author-link13=Chuck Yeager |url-status=live}}</ref>{{Reference page|pages=5, 195}} It [[STS-1|flew in space for the first time]] in April{{nbsp}}1981,{{r|jenkins2016}}{{Reference page|page=III-24}} and was used to conduct in-orbit research,<ref name="jenkins2016">{{cite book |last= Jenkins |first= Dennis R. |title= Space Shuttle: Developing an Icon – 1972–2013|isbn=978-1580072496|location=[[Forest Lake, Minnesota|Forest Lake]] |publisher= Specialty Press |date= 2016}}</ref>{{Reference page|III-188}} and deploy commercial, military, and scientific payloads.{{r|jenkins2016}}{{Reference page|pages=III-66, 68, 148}} At launch, it consisted of the [[Space Shuttle orbiter|orbiter]], which contained the [[List of Space Shuttle crews|crew]] and payload, the [[Space Shuttle external tank|external tank]] (ET), and the two [[Space Shuttle Solid Rocket Booster|solid rocket boosters]] (SRBs).<ref name="jenkins">{{cite book |last=Jenkins |first=Dennis R. |title=Space Shuttle: The History of the National Space Transportation System|location=[[Stillwater, Minnesota|Stillwater]] |publisher=Voyageur Press |year=2001 |isbn=978-0963397454 }}</ref>{{Reference page|page=363}} The orbiter was a reusable, winged vehicle that launched vertically and landed as a glider.{{r|jenkins2016}}{{Reference page|II-1}} Five operational orbiters were built during the [[Space Shuttle program]].{{r|rogers_com|p=5}} {{OV|102|full=no}} was the first space-rated orbiter constructed, following the atmospheric test vehicle {{OV|101|full=no}}. The orbiter contained the crew compartment, where the crew predominantly lived and worked throughout a mission.{{r|jenkins2016}}{{Reference page|II-5}} Three [[Space Shuttle main engines]] (SSMEs) were mounted at the aft end of the orbiter and provided thrust during launch.{{r|jenkins}}{{Reference page|II-170}} Once in space, the crew maneuvered using the two smaller, aft-mounted [[Orbital Maneuvering System]] (OMS) engines.{{r|jenkins}}{{Reference page|page=II-79}}

The orbiter was protected from heat during reentry by the [[thermal protection system]] (TPS), a [[Atmospheric entry#Thermal soak|thermal soaking]] protective layer around the orbiter. In contrast with previous US spacecraft, which had used ablative heat shields, the reusability of the orbiter required a multi-use heat shield.<ref name="shuttle_manual">{{cite book |last=Baker |first=David |author-link=David Baker (author) |title=NASA Space Shuttle: Owners' Workshop Manual |publisher=[[Zenith Press]] |year= 2011 |location=Somerset, UK |isbn=978-1844258666}}</ref>{{Reference page|72–73}} During reentry, the TPS experienced temperatures up to {{convert|3000|F|C|sigfig=2|abbr=on|order=flip}}, but had to keep the orbiter vehicle's aluminum skin temperature below {{convert|350|F|C|sigfig=2|abbr=on|order=flip}}. The TPS primarily consisted of four sub-systems. The nose cone and leading edges of the wings experienced temperatures above {{convert|2300|F|C|sigfig=2|abbr=on|order=flip}}, and were protected by the composite material [[reinforced carbon–carbon]] (RCC). Thicker RCC was developed and installed in 1998 to prevent damage from [[space debris|micrometeoroid and orbital debris]].<ref name="jenkins2016" />{{Reference page|pages=II-112–113}} The entire underside of the orbiter vehicle, as well as the other hottest surfaces, were protected with black high-temperature reusable surface insulation. Areas on the upper parts of the orbiter vehicle were covered with white low-temperature reusable surface insulation, which provided protection at temperatures below {{convert|1200|F|C|sigfig=2|abbr=on|order=flip}}. The payload bay doors and parts of the upper wing surfaces were covered with reusable felt surface insulation, as the temperature there remained below {{convert|700|F|C|sigfig=2|abbr=on|order=flip}}.<ref name="jenkins" />{{Reference page|page=395}}

Two solid rocket boosters (SRBs) were connected to the ET, and burned for the first two minutes of flight.{{r|jenkins}}{{Reference page|page=II-222}} The SRBs separated from the ET once they had expended their fuel and fell into the Atlantic Ocean under a parachute.{{r|jenkins}}{{Reference page|II-289}} NASA retrieval teams recovered the SRBs and returned them to the [[Kennedy Space Center]] (KSC), where they were disassembled and their components were reused on future flights.{{r|jenkins}}{{Reference page|page=II-292}}

When the Space Shuttle launched, the orbiter and SRBs were connected to the ET, which held the fuel for the SSMEs.{{r|jenkins}}{{Reference page|page=II-222}} The ET consisted of a tank for liquid hydrogen (LH2), stored at {{convert|-423|F|C|order=flip|sigfig=3}} and a smaller tank for liquid oxygen (LOX), stored at {{convert|-297|F|C|order=flip|sigfig=3}}. It was covered in insulating foam to keep the liquids cold and prevent ice forming on the tank's exterior. The orbiter connected to the ET via two umbilicals near its bottom and a bipod near its top section.<ref name="caib_report">{{cite report |url=https://ntrs.nasa.gov/api/citations/20030066167/downloads/20030066167.pdf |title=Report of Columbia Accident Investigation Board |last1=Gehman |first1=Harold |last2=Barry |first2=John |date=August 26, 2003 |publisher=NASA |volume=1 |last3=Deal |first3=Duane |last4=Hallock |first4=James |last5=Hess |first5=Kenneth |last6=Hubbard |first6=G. Scott |last7=Logsdon |first7=John |last8=Osheroff |first8=Douglas D. |last9=Ride |first9=Sally |author-link1=Harold W. Gehman Jr. |access-date=August 15, 2022 |archive-url=https://web.archive.org/web/20210505113049/https://ntrs.nasa.gov/api/citations/20030066167/downloads/20030066167.pdf |archive-date=May 5, 2021 |author-link4=James N. Hallock |author-link6=G. Scott Hubbard |author-link7=John Logsdon |author-link8=Douglas Osheroff |author-link9=Sally Ride |url-status=live |last10=Tetrault |first10=Roger |last11=Turcotte |first11=Stephen |author-link11=Stephen A. Turcotte |last12=Wallace |first12=Steven |last13=Widnall |first13=Sheila |author-link13=Sheila Widnall}}</ref>{{Reference page|pages=50–51}}
After its fuel had been expended, the ET separated from the orbiter and reentered the atmosphere, where it would break apart during reentry and its pieces would land in the [[Indian Ocean|Indian]] or [[Pacific Ocean]].{{r|jenkins}}{{Reference page|page=II-238}}

=== Debris strike concerns ===
[[File:Left bipod foam ramp.jpg|thumb|alt=Zoomed in image with arrows that label the bipod foam on the external tank.|Close-up of the left bipod foam ramp that broke off and damaged the orbiter wing]]

During the design process of the Space Shuttle, a requirement of the ET was that it would not release any debris that could potentially damage the orbiter and its TPS. The integrity of the TPS components was necessary for the survival of the crew during reentry, and the tiles and panels were only built to withstand relatively minor impacts. On STS-1, the first flight of the Space Shuttle, the orbiter ''Columbia'' was damaged during its launch from a foam strike. Foam strikes occurred regularly during Space Shuttle launches; of the 79 missions with available imagery during launch, foam strikes occurred on 65.{{r|caib_report}}{{Reference page|pages=121–122}}

The bipod connected the ET near the top to the front underside of the orbiter via two struts with a ramp at the tank end of each strut; the ramps were covered in foam to prevent ice from forming that could damage the orbiter. The foam on each bipod ramp was approximately {{convert|30|by|14|by|12|in|cm}}, and was carved by hand from the original foam application.<ref name="bipod">{{cite web|url=https://www.nasa.gov/pdf/63908main_Bipod_Fact_Sheet.pdf|title=External Tank Return to Flight Focus Area:Forward Bipod Fitting|publisher=NASA|date=August 2004|access-date=January 19, 2022|archive-date=November 4, 2021|archive-url=https://web.archive.org/web/20211104234744/https://www.nasa.gov/pdf/63908main_Bipod_Fact_Sheet.pdf|url-status=live}}</ref> Bipod ramp foam from the left strut had been observed falling off the ET on six flights prior to [[STS-107]], and had created some of the largest foam strikes that the orbiter experienced.{{NoteTag|No foam shedding was ever observed from the right bipod ramp. In its report, the CAIB hypothesized that this is because of the ET's liquid oxygen line, which partially shielded the right strut from aerodynamic forces.}} The first bipod ramp foam strike occurred during [[STS-7]]; the orbiter's TPS was repaired after the mission but no changes were made to address the cause of the bipod foam loss.{{r|caib_report}}{{Reference page|page=123}} After bipod foam loss on [[STS-32]], NASA engineers, under the assumption that the foam loss was due to pressure buildup within the insulation, added vent holes to the foam to allow gas to escape. After a bipod foam strike damaged the TPS on [[STS-50]], internal NASA investigations concluded it was an "accepted flight risk" and that it should not be treated as a flight safety issue. Bipod foam loss occurred on [[STS-52]] and [[STS-62]], but neither event was noticed until the investigation following ''Columbia'''s destruction.{{r|caib_report}}{{Reference page|page=124}}

During [[STS-112]], which flew in October 2002, a {{convert|4|by|5|by|12|in|cm|adj=on}} chunk of bipod ramp foam broke away from the ET bipod ramp and hit the SRB-ET attachment ring near the bottom of the left SRB, creating a dent {{convert|4|in|cm|sigfig=1}} wide and {{convert|3|in|cm|sigfig=1}} deep.{{r|caib_report}}{{Reference page|page=124}} Following the mission, the Program Requirements Control Board declined to categorize the bipod ramp foam loss as an in-flight anomaly. The foam loss was briefed at the [[STS-113]] Flight Readiness Brief, but the Program Requirements Control Board decided that the ET was safe to fly.{{r|caib_report}}{{Reference page|page=125}}

A debris strike from the [[ablative material]] on the right SRB caused significant damage to{{OV|104|full=no}} during the [[STS-27]] launch on December 2, 1988. On the second day of the flight the crew inspected the damage using a camera on the [[remote manipulator system]]. The debris strike had removed a tile; the exposed orbiter skin was a reinforced section, and a burn-through might have occurred had the damage been in a different location. After the mission, the NASA Program Requirements Control Board designated the issue as an in-flight anomaly that was corrected with the planned improvement for the SRB ablator.{{r|caib_report}}{{Reference page|page=127}}