Editing Space Shuttle Columbia (section)

===Thermal protection system===
[[File:STS-3 infrared on reentry.jpg|right|thumb|upright=1.2|alt=The underside of the orbiter shows a temperature gradient from relatively cool at the edges of the wing to hottest in the middle of each wing and towards the back.|The [[Space Shuttle thermal protection system]] in the underside of ''Columbia'' as seen in a visible (left side) and infrared (right side) image which was taken by the [[Kuiper Airborne Observatory]] on [[STS-3]]]]

Externally, ''Columbia'' was the first orbiter in the fleet whose surface was mostly covered with High & Low Temperature Reusable Surface Insulation (HRSI/LRSI) tiles as its main [[Space Shuttle thermal protection system|thermal protection system]] (TPS), with white silicone rubber-painted [[Nomex]] – known as Felt Reusable Surface Insulation (FRSI) blankets – in some areas on the wings, fuselage, and payload bay doors. FRSI once covered almost 25% of the orbiter; the first upgrade resulted in its removal from many areas, and in later flights, it was only used on the upper section of the payload bay doors and inboard sections of the upper wing surfaces.<ref name="OTPS">{{cite web |url=http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/TPS-06rev.pdf |title=Orbiter Thermal Protection System (PDF) |publisher=NASA's [[Kennedy Space Center]] Public Affairs Office |year=2006 |access-date=June 7, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110610021002/http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/TPS-06rev.pdf |archive-date=June 10, 2011 }}</ref> The upgrade also involved replacing many of the white LRSI tiles on the upper surfaces with Advanced Flexible Reusable Surface Insulation (AFRSI) blankets (also known as Fibrous Insulation Blankets, or FIBs) that had been used on ''Discovery'' and ''Atlantis''.<ref>{{cite web|url=http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/tps/blankets.html |archive-url=https://web.archive.org/web/20010210011912/http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/tps/blankets.html |url-status=dead |archive-date=February 10, 2001 |title=Advanced Flexible Reusable Surface Insulation Blankets |publisher=NASA |date=April 7, 2002 |access-date=June 7, 2011}}</ref>

[[File:STS-4 landing.jpg|thumb|right|''Columbia'' landing on July 4, 1982, concluding [[STS-4]], accompanied by a [[Northrop T-38 Talon|T-38 Talon]] flying in formation.]]

Originally, ''Columbia'' had 32,000 tiles – the upgrade reduced this to 24,300. The AFRSI blankets consisted of layers of pure silica felt sandwiched between a layer of silica fabric on the outside and S-Glass fabric on the inside, stitched together using pure silica thread in a 1-inch grid, then coated with a high-purity silica coating. The blankets were semi-rigid and could be made as large as 30" by 30". Each blanket replaced as many as 25 tiles and was bonded directly to the orbiter.<ref name="OTPS" /> The direct application of the blankets to the orbiter resulted in weight reduction, improved durability, reduced fabrication, and installation cost, and reduced installation schedule time.<ref>{{cite web|url=http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/tps/blankets.html |archive-url=https://web.archive.org/web/20010210011912/http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/tps/blankets.html |url-status=dead |archive-date=February 10, 2001 |title=Advanced Flexible Reusable Surface Insulation Blankets |publisher=NASA |date=April 7, 2002 |access-date=June 7, 2011}}</ref> All of this work was performed during ''Columbia's'' first retrofitting and the post-''Challenger'' stand-down.

Though the orbiter's thermal protection system and other enhancements had been refined, ''Columbia'' would never weigh as little unloaded as the other orbiters in the fleet. The next-oldest shuttle, [[Space Shuttle Challenger|''Challenger'']], was also relatively heavy, although {{convert|2200|lb|abbr=on}} lighter than ''Columbia''.