page_title: Space Shuttle abort modes
section_title: Post-Challenger abort enhancements
hierarchical_section_title: Space Shuttle abort modes / Post-Challenger abort enhancements
caption_attribution_description: English: Space Shuttle abort options after STS-51L
context_page_description: Space Shuttle abort modes were procedures by which the nominal launch of the NASA Space Shuttle could be terminated. A pad abort occurred after ignition of the shuttle's main engines but prior to liftoff. An abort during ascent that would result in the orbiter returning to a runway or to a lower than planned orbit was called an "intact abort", while an abort in which the orbiter would be unable to reach a runway, or any abort involving the failure of more than one main engine, was called a "contingency abort". Crew bailout was still possible in some situations where the orbiter could not land on a runway.
context_section_description: Before the Challenger disaster during STS-51-L, ascent abort options involving failure of more than one SSME were very limited.  While failure of a single SSME was survivable throughout ascent, failure of a second SSME prior to about 350 seconds (the point at which the orbiter would have sufficient downrange velocity to reach a TAL site on just one engine) would mean an LOCV, since no bailout option existed.  Studies showed that an ocean ditching was not survivable.  Furthermore, the loss of a second SSME during an RTLS abort would have caused an LOCV except for the period of time just prior to MECO (during which the orbiter would be able to reach KSC by prolonging the burn time of the remaining engine), as would a triple SSME failure at any point during an RTLS abort.
  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 due to design loads being exceeded on the forward orbiter/ET and SRB/ET attach points, and still problematic at any time during SRB flight due to controllability during staging.
  A particularly  significant enhancement was bailout capability.  Unlike the ejection seat in a fighter plane, the shuttle had an inflight crew escape system (ICES).  The vehicle was put in a stable glide on autopilot, the hatch was blown, and the crew slid out 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 due to 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).
  An ECAL/BDA abort was similar to RTLS, but instead of landing at the Kennedy Space Center, the orbiter would attempt to land at another site along the east coast of North America (in the case of ECAL) or Bermuda (in the case of BDA).  Various potential ECAL landing sites extended from South Carolina into Newfoundland, Canada. The designated landing site in Bermuda was Naval Air Station Bermuda (a United States Navy facility). ECAL/BDA was a contingency abort that was less desirable than an intact abort, primarily because there was so little time to choose the landing site and prepare for the orbiter's arrival. All of the pre-designated sites were either
caption: Abort options after STS-51-L.  Grey zones indicate failures in which the orbiter could remain intact until crew bailout.
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