Space Shuttle abort modes: Difference between revisions

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  ft (70,000 m), high enough to avoid subjecting the external tank to excessive aerodynamic stress and heating. The cutoff velocity would depend on the distance still to be traveled to reach the landing site and would increase based on the distance of the orbiter at cutoff. In any case, the orbiter would be flying too slowly to glide gently at such high altitude, and would start descending rapidly. A series of maneuvers in quick succession would pitch the orbiter's nose up to level off the orbiter once it reached thicker air, while at the same time ensuring that the structural limits of the vehicle were not exceeded (the operational load limit was set to 2.5 Gs, and at 4.4 Gs the OMS pods were expected to be torn off the orbiter).

Once this phase was complete, the orbiter would be about 150 nmi (278 &nbsp;km) from the landing site and in a stable glide, proceeding to make a normal landing about 25 minutes after liftoff.<ref>{{Cite web|title=NASA Intact Ascent Aborts Workbook, chapter 6 RETURN TO LAUNCH SITE|url=https://www.nasa.gov/centers/johnson/pdf/383447main_intact_ascent_aborts_workbook_21002.pdf|access-date=2021-03-28|archive-date=2021-03-21|archive-url=https://web.archive.org/web/20210321153202/https://www.nasa.gov/centers/johnson/pdf/383447main_intact_ascent_aborts_workbook_21002.pdf|url-status=live}}</ref>

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|title=Space Shuttle Transoceanic Abort Landing (TAL) Sites|dateurl-status=Decemberdead 2006|publisher=National Aeronautics and Space Administration|access-date=2009-07-01|archive-date=2010-02-25|archive-url=https://web.archive.org/web/20100225085509/http://www.nasa.gov/centers/kennedy/pdf/167472main_TALsites-06.pdf |urlarchive-statusdate=live2010-02-25 |access-date=2009-07-01 |publisher=National Aeronautics and Space Administration}}</ref> It was to be used when velocity, altitude, and distance downrange did not allow return to the launch point by Return To Launch Site (RTLS). It was also to be used when a less time-critical failure did not require the faster but more dangerous RTLS abort.

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 manned space flight support office from the adjacent [[Patrick Space Force Base]] (then known as Patrick Air Force Base) would deliver eight crew members, nine [[pararescue|pararescuemen]]rs, two [[flight surgeon]]s, a nurse and medical technician, and {{convert|2500|lb}} of medical equipment to Zaragoza, Istres, or both. One or more [[Learjet C-21|C-21S]] or [[C-12 Huron|C-12S]] aircraft would also be deployed to provide weather reconnaissance in the event of an abort with a [[TALCOM]], or astronaut flight controller aboard for communications with the shuttle pilot and commander.<ref name="FS-2006-01-004-KSC" />

Unlike with all other United States orbit-capable crewed vehicles (both previous and subsequent, as of 20212024), the shuttle was never flown without astronauts aboard. To provide an incremental non-orbital test, NASA considered making the first mission an RTLS abort. However, [[STS-1]] commander [[John Young (astronaut)|John Young]] declined, saying, "let's not practice [[Russian roulette]]"<ref name="popmech">{{cite web

}}</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=live dead}}</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.

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. mannedcrewed space vehicles have launch escape systems, although {{as of|20212024|lc=on}} none have ever been used for an American mannedcrewed flight.

The first two shuttles, ''[[Space Shuttle Enterprise|Enterprise]]'' and ''[[Space Shuttle Columbia|Columbia]]'', were built with [[ejection seat]]s. It was only theseThese two thatvehicles were plannedintended to be flown with a crewpartoftwo.the Subsequentshuttle shuttlestest wereprogram builtand onlywould for missionsfly with a crew of more than two, includingtest seatspilots inor theastronauts. lowerSubsequent deck, and ejection seat options were deemed to be infeasible, soshuttles ''[[Space Shuttle Challenger|Challenger]]'', ''[[Space Shuttle Discovery|Discovery]]'', ''[[Space Shuttle Atlantis|Atlantis]]'', and ''[[Space Shuttle Endeavour|Endeavour]]'' were built withoutfor ejectionoperational missions with a crew of more than two, including seats in the lower deck, and ejection seat options were deemed to be infeasible. The type used on the first two shuttles were modified versions of the seats used in the [[Lockheed SR-71]] seat. The [[approach and landing tests]] flown by ''Enterprise'' had these as an escape option, and the first four flights of ''Columbia'' had this as a crew abort option as well.<ref>{{Cite journal |last=Henderson |first=Edward |date=29 September 2011 |title=Space Shuttle Abort Evolution |url=https://ntrs.nasa.gov/api/citations/20110015564/downloads/20110015564.pdf |journal=AIAA SPACE 2011 Conference & Exposition |volume=1 |issue=1 |pages=2 |via=NASA, Johnson Space Center}}</ref> ButWith [[STS-5]] wasmarking the firstend missionof toColumbia's havetest aflight crewprogram, ofand moreas thanan two,operational andmission thewith commanderfour decidedcrew thatmembers, flyingthe withtwo thecockpit ejection seats disabledhad wastheir therocket moremotors ethicalremoved option.{{Citationfor needed|date=Octoberthe flight. 2020}} ''Columbia'''s next flight ([[STS-9]]) was likewise flown with the seats disabled in this manner. By the time ''Columbia'' flew again ([[STS-61-C]], launched on January 12, 1986), it had been through a full maintenance overhaul at [[Palmdale, California|Palmdale]] and the ejection seats (along with the explosive hatches) had been fully removed. Ejection seats were not further developed for the shuttle for several reasons:

* Astronauts were skeptical of the ejection seats' usefulness. [[STS-1]] pilot [[Robert Crippen]] stated:{{quoteblockquote|...in truth, if you had to use them while the solids were there, I don’t believe you would [survive]—if you popped out and then went down through the fire trail that’s behind the solids, that you would have ever survived, or if you did, you wouldn't have a parachute, because it would have been burned up in the process. But by the time the solids had burned out, you were up to too high an altitude to use it. ... So I personally didn't feel that the ejection seats were really going to help us out if we really ran into a contingency.<ref name="numbering-crippenoh">[http://www.jsc.nasa.gov/history/oral_histories/CrippenRL/CrippenRL_5-26-06.pdf "Robert L. Crippen"] {{Webarchive|url=https://web.archive.org/web/20160303183030/http://www.jsc.nasa.gov/history/oral_histories/CrippenRL/CrippenRL_5-26-06.pdf |date=2016-03-03 }}, NASA Johnson Space Center Oral History Project, 26 May 2006.</ref>}}

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 |m}} and speeds up to Mach three.<ref>{{cite web|url=http://www.zvezda-npp.ru/english/05.htm|title=Emergency escape systems of RD&PE Zvezda|url-status=dead|archive-url=https://web.archive.org/web/20130115034951/http://www.zvezda-npp.ru/english/05.htm|archive-date=2013-01-15}}</ref> Buran flew only once in fully automated mode without a crew, thus the seats were never installed and were never tested in real human space flight.

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 }}</ref>

| [[STS-51-F]]

| Sensor problem shutdownshut SSME No. 1 down. Mission continued in lower than planned orbit.

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>Sites in which an orbiter has landed are listed in bold, but none have been emergency landings.</small>

*[[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 }} Alberta Online Encyclopedia - Alberta's Aviation Heritage. Retrieved: 2011-03-01</ref>