Space Shuttle abort modes

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The switch for preselecting the abort mode in the shuttle cockpit

Space Shuttle abort modes ( English for space shuttle Abbruchmodi ) were emergency procedures for technical problems during the final launch preparations or the flight of a space shuttle . Most likely this could occur during the launch and ascent phases, e.g. B. if a main engine fails . When re-entering the earth's atmosphere and approaching the landing, there were fewer abort options. During the re-entry of the Columbia space shuttle at the end of the STS-107 mission, there was no way to prevent the shuttle from breaking up.

Errors that occurred during a later phase of the landing could be survived, even if this was no longer considered a termination. For example, a problem with the flight control system or multiple failures of the auxiliary engines could have made reaching the runway impossible and forced the astronauts to jump over the ocean.

Types of abortions during the ascent

There were five possible abort types during the ascent, in addition to abortions on the starting platform. These were classified as intact demolitions and demolitions with potential for damage . The decision as to which type of demolition was chosen depended on the situation and which emergency runway could be reached. The abort modes included a large number of potential problems, but the most anticipated problem was the failure of the space shuttle's main engine. Whether this made it impossible to cross the Atlantic or to reach an orbit depended on the time and number of the failed engines. Other possible non-engine-dependent failures were multiple failures of auxiliary engines, a cabin leak or a leak in the external tank.

Redundant Set Launch Sequencer (RSLS) termination

The three main engines (SSME, Space Shuttle Main Engines) could be switched off on the launch platform as long as the solid fuel boosters had not yet ignited (from T - 6.6 to T - 0.0 seconds). This is known as the Redundant Set Launch Sequencer abort and happened five times on the STS-41-D , STS-51-F , STS-51 , STS-55, and STS-68 . Each time this abort was triggered by a computer which, via sensors, detected a problem with the main engines after they had been ignited but before the solid fuel boosters (SRBs) were ignited . Once the solid fuel boosters were activated, they could no longer be turned off and the space shuttle should have started. In this case there was no way to cancel until the SRBs burned out after 123 seconds. A premature detonation of the SRBs was not intended, as the resulting dynamic stress would have destroyed the orbiter.

"Intact" termination types

There were four "intact" abort modes that caused the flight to be aborted in the actual sense (English: intact abort modes), but only one (ATO) was ever carried out. These aborts are designed to ensure a safe return of the orbiter to a previously planned runway. The respective applicable type of termination was selected by the commander using a switch with the positions “OFF”, “RTLS”, “AOA” and “ATO”.

Return To Launch Site (RTLS)
The shuttle would have continued its flight until the solid fuel boosters burned out and dropped. Then the space shuttle would have turned around so that the main engines could have fired against the horizontal flight direction. This maneuver would have been performed out of atmosphere and was conceptually very similar to firing the OMS to exit orbit. The main engines would have reduced horizontal speed and brought the shuttle back westward at a speed sufficient to reach the runway. Then the main engines would stop, the external tank dropped, and the orbiter could make a normal landing on the Kennedy Space Center runway. Should a return to the KSC not be possible, other airfields on the east coast of the USA could have been approached, which is what the name East Coast Abort Landing (ECAL) stood for. For this purpose, some previously selected airfields were on alert during the start of the shuttle.
The RTLS maneuver was by far the riskiest type of termination, and it was controversial how high the chances of success would be. NASA had originally considered performing an RTLS demolition on the shuttle's first test flight . John Young, the commander of the flight, had rejected these considerations and warned against playing "Russian roulette".
Transoceanic Abort Landing (TAL)
A previously defined runway in Africa or Western Europe would have been approached (or, if Vandenberg AFB took off, Easter Island ). The maneuver would have been used if the speed, altitude and distance of the horizontal flight had not allowed it to return to the launch site via RTLS (communicated via radio with the message: "negative return"). It would also have been executed if a less time critical error did not require a return via RTLS. The latter would have meant a greater burden for the shuttle and the crew. A TAL termination was only possible after reaching a certain height and speed. As a rule, depending on the orbit and charge, the shuttle reached an altitude and speed after approx. 150 to 180 seconds at which a TAL could be carried out even if an engine failed. This point in time was called "2 engine TAL" or "2 engine <target runway>" B. "2 engine Moron", if the Moron Airforce Base in Spain could be reached. In a later part of the ascent, depending on the orbit and charge, one engine (i.e. if two engines fail) was enough to carry out a TAL. This point in time was called “single engine <target runway> 104”, where 104 means that the remaining engine for a TAL should have been operated at 104% of its rated power at this point in time (which is the case during the ascent anyway). The required altitude and speed were reached after 360 to 400 seconds of flight time.
Abort Once Around (AOA)
Would have been possible if the shuttle could not reach a stable orbit but had enough speed to orbit the earth once and then land either in California or Florida, possibly using the OMS engines. The time window to carry out AOA was very small and was only a few seconds between the TAL and ATO cancellation option. Therefore, this option was very unlikely to run.
Abort to Orbit (ATO)
Was carried out when the intended orbit could not be reached, but a lower stable orbit was possible. This happened during the STS-51-F mission , which was carried out to a lower orbit despite the abortion. A leak in the hydrogen tank made the STS-93 orbit slightly lower than expected. However, this was not counted as an ATO. However, if a major leak had occurred, an ATO, RTLS or TAL termination might have been necessary. The moment at which an ATO was possible in the event of an engine failure was referred to as “press to ATO”. The shuttle reached the required height and speed after a flight time of approx. 240 to 330 seconds, depending on the orbit and charge.
No breakdown despite engine failure
From a certain altitude and airspeed, the shuttle was able to reach its target orbit even in the event of an engine failure. The point in time from which this was possible is referred to as “press to MECO” (Main Engine Cut Off). The shuttle reached the required height and speed after about 315 to 390 seconds of flight time, depending on the orbit and charge. After approx. 390 to 420 seconds of flight time, depending on orbit and charge, the shuttle reached an altitude and speed at which a single engine was sufficient to reach the target orbit. This point in time was known as the “single engine press 104”, whereby the 104, as with TAL, meant that the remaining engine had to be operated at 104% of its rated power in order to reach the target orbit.

Terminations with the possibility of damage

If an intact termination was no longer possible due to serious errors, ensuring the survival of the crew had the highest priority; Any (irreparable) damage to the ferry was also accepted.

If the orbiter could not reach a safe maneuvering area, an emergency landing on a suitable surface or a ditching would have had to be carried out - but with such maneuvers the survival chances of the crew members decreased. If an emergency landing / ditching had not been possible either, the crew would have been able to jump off a guide pole with parachutes, provided the space shuttle had switched to a controlled glide flight.

In the Challenger disaster (1986) and the Columbia crash (2003), there were no more options to cancel, as in both cases the space shuttles were destroyed within a very short time.

During the ascent of the space shuttle Challenger, a defective sealing ring in the right solid fuel booster triggered a fire, which burned through the insulation and the jacket of the outer tank and caused the liquid hydrogen and oxygen in it to explode.

The Columbia broke on re-entry into the earth's atmosphere due to a faulty heat shield in the area of ​​the left wing root. At the time of the accident, the ferry was moving at high supersonic speed, so that the crew would not have survived an exit from the orbiter under any circumstances due to the great heat generated by air friction. In addition, when the damage was discovered, there was no longer any radio contact with the shuttle crew; NASA's final report from 2005 assumes that the crew members were still alive at this point, but unconscious.

Emergency landing sites

The shuttle flights usually ended at the Shuttle Landing Facility at Kennedy Space Center or at Edwards Air Force Base in California . The only mission that had to move to another landing site was STS-3 , which touched down on the White Sands Missile Range in New Mexico . In addition, emergency landing sites were defined for each mission, but they were never needed.

ECAL landing sites

In addition to the Shuttle Landing Facility, which was to be used for the RTLS case, there were several airfields on the North American east coast that were available for an emergency landing shortly after take-off (ECAL = East Coast Abort Landing). Depending on the mission profile, some of them were put on standby during the shuttle launch, but did not have shuttle-specific facilities or NASA personnel. This affected the following airports:

TAL landing sites

Certain airfields in Europe and Africa have been equipped with shuttle-specific facilities and designated as "augmented landing sites". For each shuttle launch, one or more of these airfields was selected as the TAL landing site and provided with NASA personnel. During the space shuttle's operating time, the following landing sites were active for TAL approaches:

For the planned shuttle launch from the Vandenberg Air Force Base in California was Easter Island provided as TAL-landing site.

Extended emergency landing sites

In the event that an unscheduled landing did not have to be carried out during take-off, and that this landing could not take place on the preferred runways in the USA, some airfields were equipped with shuttle-specific facilities and NASA personnel. These were known as "Augmented Emergency Landing Sites". These were:

More emergency landing sites

In addition, the space shuttle could land on any runway that was long enough and that was in the area overflown by the shuttle. NASA kept a list of 25 to 30 airfields that could be landed in an emergency. This list included:

Web links

Individual evidence

  1. ^ A b c Justine Whitman: Space Shuttle Abort Modes., June 25, 2006, accessed September 14, 2011 .
  2. ^ Space Shuttle Landing at Wilmington's ILM. Carolina Beach Today, October 23, 2008, accessed September 15, 2011 (source cites January 2001 AP report to: NASA Names North Carolina Airport Emergency Landing Site for Shuttle).
  3. a b c d e f DOD Support to manned space operations for STS-127. (No longer available online.) US Northern Command, July 9, 2009, archived from the original on September 15, 2012 ; accessed on September 15, 2011 .
  4. ^ Space Shuttle Transoceanic Abort Landing (TAL) Sites. (PDF; 3.4 MB) NASA, December 2006, accessed on September 13, 2011 (English).
  5. ^ Banjul, The Gambia. (No longer available online.) NASA January 11, 2006, archived from the original on June 10, 2011 ; accessed on September 13, 2011 : "It was selected in September 1987, replacing a TAL site at Dakar, Senegal, that NASA concluded was unsatisfactory due to runway deficiencies and geographic hazards"
  6. Chris Kridler: French base named emergency shuttle landing site. USA Today, June 8, 2005, accessed September 13, 2011 .
  7. STS-49 Press Kit. NASA, May 1992, accessed on September 14, 2011 (English): “Loss of one or more main engines midway through powered flight would force a landing at either Ben Guerir, Morroco; Moron, Spain; or Rota, Spain "
  8. ^ Zaragoza Air Base, Spain. (No longer available online.) NASA January 18, 2006, archived from the original on October 29, 2011 ; accessed on September 13, 2011 .
  9. Anthony Boadle: Lonely Easter Island Will Be Emergency Shuttle Landing Site. Los Angeles Times, June 30, 1985, accessed September 15, 2011 .
  10. ^ Ask The Mission Team - Question and Answer Session. NASA, November 23, 2007, accessed on September 14, 2011 (English): "We have probably 25 or 30 emergency landing sites around the world that the orbiter can land at."
  11. ^ Space Shuttle Emergency Landing Sites., accessed September 14, 2011 .
  12. Sam Savage: NASA Puts BIA on Shuttle Landing List. Red Orbit, August 9, 2005, accessed February 8, 2017 .
  13. Fort Huachuca, AZ - Visitors - Welcome :. (No longer available online.) Fort Huachuca, archived from the original on September 3, 2011 ; accessed on September 15, 2011 (English): "Libby Army Airfield ... is on the list of alternate landing locations for the space shuttle, though it has never been used as such"