Editing Space Shuttle Challenger (section)

===Construction===
[[File:Challenger 1A.jpg|thumb|upright|''Challenger'' being prepared in 1985 for its penultimate flight, [[STS-61-A]]]]
[[File:STS-51-L - Space Shuttle Challenger on the Crawler-Transporter.jpg|thumb|''Challenger'' atop a [[Crawler-transporter]], en route to the launch site for its final flight, [[STS-51-L]]]]
Because of the low production volume of orbiters, the Space Shuttle program decided to build a vehicle as a [[Test article (aerospace)|Structural Test Article]], STA-099, that could later be converted to a flight vehicle. The contract for STA-099 was awarded to North American Rockwell on July 26, 1972, and construction was completed in February 1978.<ref>{{cite web|title=NASA – Space Shuttle Overview: Challenger (OV-099)|url=http://www.nasa.gov/centers/kennedy/shuttleoperations/orbiters/challenger-info.html|access-date=November 7, 2012|archive-date=June 11, 2017|archive-url=https://web.archive.org/web/20170611063127/http://www.nasa.gov/centers/kennedy/shuttleoperations/orbiters/challenger-info.html|url-status=dead}}</ref> After STA-099's rollout, it was sent to a [[Lockheed Corporation|Lockheed]] test site in Palmdale, where it spent over 11 months in vibration tests designed to simulate entire shuttle flights, from launch to landing.<ref name="Lardas 2012 36">{{cite book|last=Lardas|first=Mark|title=Space Shuttle Launch System: 1972–2004|year=2012|publisher=[[Osprey Publishing]]|pages=36}}</ref> To prevent damage during structural testing, qualification tests were performed to a [[safety factor]] of 1.2 times the design limit loads. The qualification tests were used to validate computational models, and compliance with the required 1.4 factor of safety was shown by analysis.<ref>NASA Engineering and Safety Center (2007). [http://www.nasa.gov/pdf/189071main_RP-06-108_05-173_DDT%26_E_Volume_II_(MASTER)08-07-2007_Final_%5B1%5D.pdf Design Development Test and Evaluation (DDT&E) Considerations for Safe and Reliable Human Rated Spacecraft Systems, Vol. II] {{Webarchive|url=https://web.archive.org/web/20201025055455/https://www.nasa.gov/pdf/189071main_RP-06-108_05-173_DDT%26_E_Volume_II_(MASTER)08-07-2007_Final_%5B1%5D.pdf |date=October 25, 2020 }}, June 14, 2007, p. 23.</ref> STA-099 was essentially a complete airframe of a Space Shuttle orbiter, with only a mockup crew module installed and [[thermal insulation]] placed on its forward fuselage.<ref>{{cite book|last=Evans|first=Ben|title=Space Shuttle Challenger: Ten Journeys Into the Unknown|year=2007|publisher=Praxis Publishing|isbn=978-0-387-46355-1|page=8}}</ref>
[[File:STS Challenger on 747 SCA.jpg|thumb|''Challenger'' being transported by [[Shuttle Carrier Aircraft]] 905, shortly before being delivered in 1982]]

NASA planned to refit the prototype orbiter [[Space Shuttle Enterprise|''Enterprise'']] (OV-101), used for flight testing, as the second operational orbiter; but ''Enterprise'' lacked most of the systems needed for flight, including a functional propulsion system, thermal insulation, a life support system, and most of the cockpit instrumentation. Modifying it for spaceflight was considered to be too difficult, expensive, and time-consuming. Since STA-099 was not as far along in the construction of its airframe, it would be easier to upgrade to a flight article. Because STA-099's qualification testing prevented damage, NASA found that rebuilding STA-099 into a flightworthy orbiter would be less expensive than refitting ''Enterprise''. Work on converting STA-099 to operational status began in January 1979, starting with the crew module (the pressurized portion of the vehicle), as the rest of the vehicle was still being used for testing by Lockheed. STA-099 returned to the Rockwell plant in November 1979, and the original, unfinished crew module was replaced with the newly constructed model. Major parts of STA-099, including the payload bay doors, body flap, wings, and vertical stabilizer, also had to be returned to their individual subcontractors for rework. By early 1981, most of these components had returned to Palmdale to be reinstalled. Work continued on the conversion until July 1982, when the new orbiter was rolled out as ''Challenger''.<ref name="Lardas 2012 36"/>

''Challenger'', as did the orbiters built after it, had fewer tiles in its [[Space Shuttle thermal protection system|Thermal Protection System]] than ''Columbia'', though it still made heavier use of the white LRSI tiles on the cabin and main fuselage than did the later orbiters. Most of the tiles on the payload bay doors, upper wing surfaces, and rear fuselage surfaces were replaced with [[DuPont]] white [[Nomex]] felt insulation. These modifications and an overall lighter structure allowed ''Challenger'' to carry 2,500&nbsp;lb (1,100&nbsp;kg) more payload than ''Columbia.'' ''Challenger''{{'}}s fuselage and wings were stronger and lighter than ''Columbia''{{'}}s.<ref name="Lardas 2012 36"/> The hatch and vertical-stabilizer tile patterns were different from those of the other orbiters. ''Challenger'' was the first orbiter to have a [[heads-up display]] (HUD) system for use in the [[Space Shuttle#Re-entry and landing|descent]] phase of a mission, and the first to feature [[Space Shuttle Main Engine#Upgrades|Phase I main engines]] rated for 104% maximum thrust.

====Construction milestones (as STA-099)====
{| class="wikitable"
|-
! style="background:#efefef;" | Date
! style="background:#efefef;" | Milestone<ref name="NASA/KSC">{{cite web|title=Shuttle Orbiter ''Challenger'' (OV-099)|url=http://science.ksc.nasa.gov/shuttle/resources/orbiters/challenger.html|publisher=NASA/KSC|access-date=November 7, 2012|archive-date=May 23, 2019|archive-url=https://web.archive.org/web/20190523112035/https://science.ksc.nasa.gov/shuttle/resources/orbiters/challenger.html|url-status=dead}}</ref>
|-
| July 26, 1972
| Contract Award to [[Rockwell International|North American Rockwell]]
|-
| November 21, 1975
| Start structural assembly of crew module
|-
| June 14, 1976
| Start structural assembly of aft fuselage.
|-
| March 16, 1977
| Wings arrive at Palmdale from [[Grumman]]
|-
| September 30, 1977
| Start of Final Assembly
|-
| February 10, 1978
| Completed Final Assembly
|-
| February 14, 1978
| Rollout from Palmdale
|}

====Construction milestones (as OV-099)====
{| class="wikitable"
|-
! style="background:#efefef;" | Date
! style="background:#efefef;" | Milestone<ref name="NASA/KSC"/>
|-
| January 5, 1979
| Contract Award to [[Rockwell International]], Space Transportation Systems Division
|-
| January 28, 1979
| Start structural assembly of crew module
|-
| November 3, 1980
| Start of Final Assembly
|-
| October 23, 1981
| Completed Final Assembly
|-
| June 30, 1982
| Rollout from Palmdale
|-
| July 1, 1982
| Overland transport from Palmdale to Edwards
|-
| July 5, 1982
| Delivery to KSC
|-
| December 18, 1982
| Flight Readiness Firing (FRF)
|-
|January 25, 1983
|Second FRF (performed due to a hydrogen leak having occurring during the first FRF)<ref>{{cite web |date=April 6, 2013 |title=30 Years Since STS-6: The Rise of the Challenger (Part 1) |url=http://www.americaspace.com/?p=33504}}</ref>
|-
| April 4, 1983
| First Flight ([[STS-6]])
|}