→Post-Challenger abort enhancements: A bit of missing grammar? Revert if necessary.
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Return to launch site (RTLS) was the first abort mode available and could be selected just after SRB jettison. The shuttle would continue [[downrange]] to burn excess propellant, as well as [[Flight dynamics|pitch up]] to maintain vertical speed in aborts with a main-engine failure. After burning sufficient propellant, the vehicle would be pitched all the way around and begin thrusting back towards the launch site. This maneuver was called the "powered pitcharound" (PPA) and was timed to ensure that less than 2% propellant remained in the external tank by the time the shuttle's trajectory brought it back to the [[Kennedy Space Center]]. Additionally, the shuttle's [[Orbital Maneuvering System|OMS]] and reaction control system (RCS) motors would continuously thrust to burn off excess OMS propellant to reduce landing weight and adjust the orbiter's center of gravity.
Just before main engine cutoff, the orbiter would be commanded to pitch nose-down to ensure proper orientation for [[Space Shuttle external tank|external tank]] jettison, since aerodynamic forces would otherwise cause the tank to collide with the orbiter. The main engines would cut off, and the tank would be jettisoned, as the orbiter used its RCS to increase separation.
Cutoff and separation would occur effectively inside the upper atmosphere at an altitude of about 230,000
Once this phase was complete, the orbiter would be about 150 nmi (278
If a second main engine failed at any point during PPA, the shuttle would not be able to reach the runway at KSC, and the crew would have to bail out. A failure of a third engine during PPA would lead to loss of control and subsequent loss of crew and vehicle (LOCV). Failure of all three engines as horizontal velocity approached zero or just before external tank jettison would also result in LOCV.<ref name = NASACA/>
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==== Transoceanic abort landing {{anchor|Transoceanic Abort Landing}} ====
A transoceanic abort landing (TAL) involved landing at a predetermined location in Africa, Western Europe or the Atlantic Ocean (at [[Lajes Field]] in the [[Azores]]) about 25 to 30 minutes after liftoff.<ref name="FS-2006-01-004-KSC">{{cite web |date=December 2006 |title=Space Shuttle Transoceanic Abort Landing (TAL) Sites |url=http://www.nasa.gov/centers/kennedy/pdf/167472main_TALsites-06.pdf
For performance issues such as engine failure(s), a TAL abort would have been declared between roughly T+2:30 (two minutes 30 seconds after liftoff) and about T+5:00 (five minutes after liftoff), after which the abort mode changed to Abort Once Around (AOA) followed by Abort To Orbit (ATO). However, in the event of a time-critical failure, or one that would jeopardize crew safety such as a cabin leak or cooling failure, TAL could be called until shortly before main engine cutoff (MECO) or even after MECO for severe underspeed conditions. The shuttle would then have landed at a predesignated airstrip across the Atlantic. The last four TAL sites were [[Istres Air Base]] in France, [[Zaragoza Air Base|Zaragoza]] and [[Morón Air Base|Morón]] air bases in Spain, and [[RAF Fairford]] in England. Prior to a shuttle launch, two sites would be selected based on the flight plan and were staffed with standby personnel in case they were used. The list of TAL sites changed over time because of geopolitical factors. The exact sites were determined from launch to launch depending on orbital inclination.<ref name="FS-2006-01-004-KSC" />
Preparations of TAL sites took four to five days and began one week before launch, with the majority of personnel from NASA, the Department of Defense and contractors arriving 48 hours before launch. Additionally, two [[C-130]] aircraft from the
This abort mode was never needed during the entire history of the Space Shuttle program.
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#RTLS resulted in the quickest landing of all abort options, but was considered the riskiest abort. Therefore, it would have been selected only in cases in which the developing emergency was so time-critical that the other aborts were not feasible, or in cases in which the vehicle had insufficient energy to perform the other aborts.
Unlike with all other United States orbit-capable crewed vehicles (both previous and subsequent, as of
| url = http://www.popularmechanics.com/science/air_space/1282596.html?page=4
| title = Astronauts in Danger
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| archive-url = https://web.archive.org/web/20080208195129/http://www.popularmechanics.com/science/air_space/1282596.html?page=4
| url-status = live
}}</ref> and "RTLS requires continuous miracles interspersed with acts of God to be successful."<ref name="dunn20140226">{{Cite web |url=http://www.tested.com/science/space/460233-space-shuttles-controversial-launch-abort-plan/ |title=The Space Shuttle's Controversial Launch Abort Plan |last=Dunn |first=Terry |date=2014-02-26 |website=Tested |language=en |access-date=2017-12-11 |archive-date=2017-12-08 |archive-url=https://web.archive.org/web/20171208090538/http://www.tested.com/science/space/460233-space-shuttles-controversial-launch-abort-plan/ |url-status=
===Contingency aborts===
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After the loss of ''Challenger'' in STS-51-L, numerous abort enhancements were added. With those enhancements, the loss of two SSMEs was now survivable for the crew throughout the entire ascent, and the vehicle could survive and land for large portions of the ascent. The struts attaching the orbiter to the external tank were strengthened to better endure a multiple SSME failure during SRB flight. Loss of three SSMEs was survivable for the crew for most of the ascent, although survival in the event of three failed SSMEs before T+90 seconds was unlikely because of design loads that would be exceeded on the forward orbiter/ET and SRB/ET attach points, and still problematic at any time during SRB flight because of controllability during staging.<ref name = NASACA>{{cite web|title=Contingency Aborts|url=http://www.nasa.gov/centers/johnson/pdf/383441main_contingency_aborts_21007_31007.pdf|website=NASA.gov|access-date=February 1, 2015|archive-date=February 26, 2015|archive-url=https://web.archive.org/web/20150226074439/http://www.nasa.gov/centers/johnson/pdf/383441main_contingency_aborts_21007_31007.pdf|url-status=live}}</ref>
A particularly significant enhancement was bailout capability. Unlike the ejection seat in a fighter plane, the shuttle had an inflight crew escape system<ref>[https://web.archive.org/web/20000817130106/http://spaceflight.nasa.gov/shuttle/reference/shutref/escape/inflight.html spaceflight.nasa.gov]</ref> (ICES). The vehicle was put in a stable glide on autopilot, the hatch was blown, and the crew slid outon a pole to clear the orbiter's left wing. They would then parachute to earth or the sea. While this at first appeared only usable under rare conditions, there were many failure modes where reaching an emergency landing site was not possible yet the vehicle was still intact and under control. Before the ''Challenger'' disaster, this almost happened on [[STS-51-F]], when a single SSME failed at about T+345 seconds. The orbiter in that case was also ''Challenger''. A second SSME almost failed because of a spurious temperature reading; however, the engine shutdown was inhibited by a quick-thinking flight controller. If the second SSME had failed within about 69 seconds of the first, there would have been insufficient energy to cross the Atlantic. Without bailout capability, the entire crew would have been killed. After the loss of ''Challenger'', those types of failures were made survivable. To facilitate high-altitude bailouts, the crew began wearing the [[Launch Entry Suit]] and later the [[Advanced Crew Escape Suit]] during ascent and descent. Before the ''Challenger'' disaster, crews for operational missions wore only fabric flight suits.
Another post-''Challenger'' enhancement was the addition of East Coast/Bermuda abort landings (ECAL/BDA). High-inclination launches (including all [[ISS]] missions) would have been able to reach an emergency runway on the East Coast of North America under certain conditions. Most lower-inclination launches would have landed in Bermuda (although this option was ''not'' available for the very lowest-inclination launches—those to an orbital inclination of 28.5°—which launched due east from KSC and passed far to the south of Bermuda).
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==Ejection escape systems==
An ejection escape system, sometimes called a "[[launch escape system]]", had been discussed many times for the shuttle. After the ''Challenger'' and ''Columbia'' losses, great interest was expressed in this. All previous and subsequent U.S.
===Ejection seat===
The first two shuttles, ''[[Space Shuttle Enterprise|Enterprise]]'' and ''[[Space Shuttle Columbia|Columbia]]'', were built with [[ejection seat]]s.
* Very difficult to eject seven crew members when three or four were on the middeck (roughly the center of the forward [[fuselage]]), surrounded by substantial vehicle structure.
* Limited ejection envelope. Ejection seats only work up to about {{convert|3400|mph|kn kph}} and {{convert|130,000|ft|m}}. That constituted a very limited portion of the shuttle's operating envelope, about the first 100 seconds of the 510 seconds powered ascent.
* No help during a ''Columbia''-type [[Atmospheric reentry|reentry]] accident. Ejecting during an atmospheric reentry accident would have been fatal because of the high temperatures and wind blast at high Mach speeds.
* Astronauts were skeptical of the ejection seats' usefulness. [[STS-1]] pilot [[Robert Crippen]] stated:{{
The Soviet shuttle ''[[Buran (spacecraft)|Buran]]'' was planned to be fitted with the crew emergency escape system, which would have included [[K-36RB]] (K-36M-11F35) seats and the [[Strizh]] full-pressure suit, qualified for altitudes up to {{convert|30,000
===Ejection capsule===
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== Space Shuttle abort history ==
Source:<ref>{{Cite web |url=http://www.nasa.gov/pdf/566071main_STS-135_Press_Kit.pdf |title=nasa.gov |access-date=2011-07-09 |archive-date=2012-01-11 |archive-url=https://web.archive.org/web/20120111235727/http://www.nasa.gov/pdf/566071main_STS-135_Press_Kit.pdf |url-status=live
{| class="wikitable sortable"
|-
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| 1985-07-29
| ''Challenger''
| [[STS-51-F]]
| ATO
| T+5 minutes, 45 seconds
| Sensor problem
|-
| 1993-03-22
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== Emergency landing sites ==
Predetermined emergency landing sites for the orbiter were chosen on a mission-by-mission basis according to the mission profile, weather and regional political situations. Emergency landing sites during the shuttle program included:<ref>{{cite book|title=Space shuttle: the history of the National Space Transportation System : the first 100 missions|isbn=9780963397454|url=https://archive.org/details/spaceshuttlehist0000jenk_f6n1|url-access=registration|author=Dennis R. Jenkins|year=2001}}</ref><ref>{{Cite web |url=http://space.balettie.com/LandingSiteInfo/index.html |title=Worldwide Shuttle Landing Site information<!-- Bot generated title --> |access-date=2008-05-11 |archive-date=2014-06-25 |archive-url=https://web.archive.org/web/20140625101825/http://space.balettie.com/LandingSiteInfo/index.html |url-status=live }}</ref><br
<small>An orbiter has landed at three sites that are also designated as emergency landing sites: [[Edwards Air Force Base]], [[Kennedy Space Center]], and [[White Sands Space Harbor]]. However, none of the landings at these three sites have been emergency landings. These sites are listed in '''bold''' below.</small>
'''Algeria'''
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'''Canada'''<ref>{{cite web|url=http://www.tc.gc.ca/publications/EN/TP12952/PDF%5CHR/TP12952E.PDF|title=NASA SPACE SHUTTLE EMERGENCY LANDING SITE CONTINGENCY PLAN|publisher=Transport Canada|url-status=dead|archive-url=https://web.archive.org/web/20130517012846/http://www.tc.gc.ca/Publications/EN/TP12952/PDF/HR/TP12952E.PDF|archive-date=2013-05-17}}</ref>
*[[CFB Goose Bay]], Goose Bay, Labrador
*[[CFB Namao]], Edmonton, Alberta (until 1994)<ref name="heritage2">[http://www.abheritage.ca/aviation/history/military_namao.html CFB Namao] {{Webarchive|url=https://web.archive.org/web/20081009210917/http://www.abheritage.ca/aviation/history/military_namao.html |date=2008-10-09
*[[Gander International Airport]], Gander, Newfoundland
*[[Stephenville International Airport]], Stephenville, Newfoundland
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[[Category:Space Shuttle program|Abort modes]]
[[Category:Abort modes]]
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