Editing Space Shuttle Columbia disaster (section)

=== Second Return to Flight mission (STS-121) ===
{{Main|STS-121}}

To address the problem of foam loss for the second Return to Flight mission ([[STS-121]]), NASA engineers removed the foam ramp from the protuberance air load (PAL) on the ET, which was the source of the largest piece of debris on STS-114.<ref name="malik_sts121">{{cite news
  | last = Malik
  | first = Tariq
  | title = NASA Nixes Foam Ramp for Next Space Shuttle Flight
  | work = Space
  | date = December 15, 2005
| url = https://www.space.com/1871-nasa-nixes-foam-ramp-space-shuttle-flight.html
  | accessdate = August 21, 2022
| archive-date = March 24, 2022
| archive-url = https://web.archive.org/web/20220324002648/https://www.space.com/1871-nasa-nixes-foam-ramp-space-shuttle-flight.html
  | url-status = live
  }}</ref> The launch was postponed from its scheduled launch of July 1, 2006, and again on July 2 due to inclement weather at KSC.<ref name="sts121_mission_accomplished">{{cite web
  | last = Marconi
  | first = Elaine M.
  | title = Mission Accomplished!
  | publisher = NASA
  | date = July 26, 2006
| url = https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/multimedia/121-overview.html
  | accessdate = August 21, 2022
| archive-date = June 8, 2017
| archive-url = https://web.archive.org/web/20170608063436/https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/multimedia/121-overview.html
  | url-status = live
  }}</ref> On July 3 a piece of foam approximately {{convert|3|by|.25|in|cm}} and weighing {{convert|0.0057|lbs|g}} broke off from the ET.<ref name="malik_foam_loss">{{cite news
  | last = Malik
  | first = Tariq
  | title = Impact of Foam Crack On Shuttle Launch Still Uncertain
  | work = Space
  | date = July 3, 2006
| url = https://www.space.com/2581-impact-foam-crack-shuttle-launch-uncertain.html
  | accessdate = August 21, 2022
| archive-date = January 23, 2021
| archive-url = https://web.archive.org/web/20210123055116/https://www.space.com/2581-impact-foam-crack-shuttle-launch-uncertain.html
  | url-status = live
  }}</ref><ref name="nasa_foam_sts121">{{cite web
  | last = Ryba
  | first = Jeanne
  | title = Space Shuttle Discovery: ET Foam
  | publisher = NASA
  | date = July 3, 2006
| url = https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/multimedia/foam_gallery.html
  | accessdate = August 21, 2022
| archive-date = June 28, 2017
| archive-url = https://web.archive.org/web/20170628062748/https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/multimedia/foam_gallery.html
  | url-status = live
  }}</ref> The mission still launched as scheduled at 2:38{{spaces}}pm (EDT) on July 4.<ref name="sts121_overview">{{cite web
  | last = Wilson
  | first = Jim
  | title = Overview
  | publisher = NASA
  | date = November 24, 2007
| url = https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/launch/index.html
  | accessdate = August 21, 2022
| archive-date = October 22, 2021
| archive-url = https://web.archive.org/web/20211022193719/https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts121/launch/index.html
  | url-status = live
  }}</ref> After reaching orbit, ''Discovery'' performed post-launch inspections of its TPS and docked with the ISS on July 6.{{r|sts121_mission_accomplished}} The orbiter carried a {{convert|28|ft|m}} remote control orbiter in-flight maintenance cable that could connect the flight deck systems to the avionics system in the mid-deck; it would allow the spacecraft to be landed remotely, to include controlling the [[landing gear]] and deploying the [[Drogue parachute|parachute]].<ref name="sts121_cord_npr">{{cite web
  | last = Kestenbaum
  | first = David
  | title = Emergency Rescue Plans in Place for Astronauts
  | publisher = NPR
  | date = June 29, 2006
| url = https://www.npr.org/2006/06/29/5521668/emergency-rescue-plans-in-place-for-astronauts
  | accessdate = August 21, 2022
| archive-date = August 21, 2022
| archive-url = https://web.archive.org/web/20220821191123/https://www.npr.org/2006/06/29/5521668/emergency-rescue-plans-in-place-for-astronauts
  | url-status = live
  }}</ref><ref name="sts121_cord">{{cite news
  | last = Malik
  | first = Tariq
  | title = Shuttle to Carry Tools for Repair and Remote-Control Landing
  | work = Space
  | date = June 29, 2006
| url = https://www.space.com/2560-shuttle-carry-tools-repair-remote-control-landing.html
  | accessdate = August 21, 2022
| archive-date = November 22, 2021
| archive-url = https://web.archive.org/web/20211122160320/https://www.space.com/2560-shuttle-carry-tools-repair-remote-control-landing.html
  | url-status = live
  }}</ref> On July 12 astronauts [[Piers Sellers]] and [[Michael Fossum]] performed an EVA to test the NonOxide Adhesive eXperiment (NOAX), which applied protective sealant to samples of damaged TPS tiles.{{r|olympus|p=70}} ''Discovery'' undocked from the ISS on July 14 and safely landed at 9:14{{spaces}}am on July 17 at KSC.{{r|sts121_mission_accomplished}} Had the crew been stranded in orbit, NASA planned to launch ''Atlantis'' to rescue them from the ISS.<ref name=sts-121_presskit>{{cite web |url=http://mynasa.nasa.gov/pdf/149873main_sts121_press_kit.pdf |title=Space Shuttle Mission STS-121: The Second Step |publisher=NASA |date=May 2006|url-status=dead |archive-url=https://web.archive.org/web/20060723042544/http://mynasa.nasa.gov/pdf/149873main_sts121_press_kit.pdf |archive-date=July 23, 2006|access-date=November 28, 2022}}</ref><ref name="sts-115">{{cite web
  | last = Dunbar
  | first = Brian
  | title = STS-115
  | publisher = NASA
  | date = April 2, 2008
| url = https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts115/main/index.html
  | accessdate = November 28, 2022
| archive-date = April 3, 2022
| archive-url = https://web.archive.org/web/20220403205134/https://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts115/main/index.html
  | url-status = live
  }}</ref>