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On January 28, 1986, Space Shuttle Challenger was launched from Kennedy Space Center, Florida. It was the twenty-fifth flight of the American Space Shuttle program, the tenth mission of the Challenger Shuttle and it was the first time ever a civilian - teacher Christa McAuliffe - was among the astronauts.
Only 73 seconds after lift-off Space Shuttle Challenger exploded - an O-ring seal in its right solid rocket booster had failed, allowing a flare to damage the attachment hardware which lead to a structural failure of the external tank. It was the first time that U.S. astronauts were killed in-flight, and NASA's first ever manned mission to launch and fail to reach space.
When watching the Challenger disaster video one may think that the astronauts should have been killed instantly. But later investigations showed that this has not been the case, they were still alive and were probably only killed when they finally impacted the ocean's surface.
In fact, the shuttle and the external tank did not actually "explode", but rapidly disintegrated under tremendous aerodynamic forces. The visible massive fireball and the cloud were caused by the quick release of a huge amount of fuel and oxidizer stored within the external tank - there was no detonation or explosion, which would have instantly destroyed the entrie shuttle and killed all astronauts.
Some experts even believe that at least pilot Mike Smith should have been aware of a fatal problem for a single moment, as the flames swept up past his window and should have been visible for him at the moment the main fuel tank caught fire. Smith's last words were "Uh-oh!", just before the communications system broke down (although this could also have been responding to onboard indications of main engine performance or to falling pressures in the external fuel tank).
The Challenger then immediately broke into pieces, as the aerodynamic forces of up to 20g caused by the main tank's desintegration were well over the Shuttle's design limit. But the more robustly constructed crew cabin was detached in one piece from the Shuttle's cargo bay and survived the disaster, it continued its flight along a clean ballistic trajectory and it wasn't even spinning (this is also clearly visible on the launch videos).
NASA expects that forces of up to 20g occurred very briefly at the moment of the disaster, but within a few seconds the cabin was already in free fall. NASA states that it's unlikely that the astronauts have been killed or even injured by the Shuttle's desintegration. At least some of the astronauts survived the disaster and must have been conscious afterwards, as three of the four Personal Egress Air Packs (PEAP) had been manually activated.
Experts determined that PEAP activation could not have been caused by the water impact or other meachanical influences, they must have been activated manually by the astronauts. It could have been an instinctive response to unexpected loss of cabin pressure - if this was the case then the crew probably lost consciousness after only a few seconds at such an altitude as the PEAPs supplied only unpressurized air, and they wouldn't have regained consciousness before water impact. Later analysis showed that the remaining unused air supply was roughly consistent with the expected consumption during the 2 minute 45 second post-breakup trajectory, which indicates that the astronauts were breathing all the way down (while it remains unclear if they were conscious or not).
While the disaster had occurred at only 48,000 feet (14.6 km), the crew cabin continued on its trajectory, peaked at a height of 65,000 feet (19.8 km), began its curve earthward and then impacted on the water surface at roughly 334 km/h (207 mph), causing forces no human could ever survive. The magnitude and direction of the crush damage indicates that the module was in a nose down attitude when it hit the water.
All crew members were still in their seats, all seats were in place and all harnesses were locked, which may lead to the conclusion that they were unconscious, although this remains pure speculation. Identifiable remains of all seven astronauts had been found, but it was not possible to clearly determine the cause of death.
It may be possible that the Shuttle's cabin and windows survived the disintegration without major damages, then the air pressure would probably not have been lost. In this case, crew members could have been conscious until water impact. The exact sequence of events will probably never be known as the crew cabin wreckage was severely damaged upon impact, which makes any further analysis impossible. But the wreckage showed no evidence of heat or fire, which confirms that the cabin was not severly damaged by the external tank's fireball.
Unlike to Apollo spacecraft, the Space Shuttle does not provide a launch escape system and the astronauts are not wearing full pressure suits when the shuttle is being launched, as NASA concluded that the shuttle's expected high reliability would preclude the need for one and that is was undesirable due to "limited utility, technical complexity and excessive cost in dollars, weight or schedule delays."
Videos of the Challenger disaster are available here:
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