When spaceflight goes wrong: Space Shuttle Challenger

This entry has been adapted from a popular answer I gave on Quora.com. The question that was asked was "what happened to the crew of Space Shuttle Challenger?"

Nobody knows definitively.

On January 28, 1986, the NASA space shuttle orbiter mission STS-51-L (the tenth flight of Space Shuttle Challenger) broke apart 73 seconds into its flight, killing all seven crew members.

Joe Kerwin, an astronaut and doctor who led an investigation, reported his findings:

the cause of death of the Challenger astronauts cannot be positively determined;the forces to which the crew were exposed during Orbiter breakup were probably not sufficient to cause death or serious injury; and the crew possibly, but not certainly, lost consciousness in the seconds following Orbiter breakup due to in-flight loss of crew module pressure.

To understand these findings it’s worth understanding what happened during the accident.

The full list of events is listed here: https://science.ksc.nasa.gov/shuttle/missions/51-l/docs/events.txt

Unfortunately, with hindsight, it was obvious there was a severe problem just 0.678 seconds after launch when a strong puff of gray smoke was seen spurting from the vicinity of the aft field joint on the right solid rocket booster. The vaporized material streaming from the joint indicated there was not a complete sealing action within the joint. This dark smoke suggested that the grease, joint insulation and rubber O-rings in the joint seal were being burned and eroded by the hot propellant gases.

According to analysis of the film after, a first small flame was seen at 58.788 seconds into the flight. NASA reported:

“As the flame plume increased in size, it was deflected rearward by the aerodynamic slipstream and circumferentially by the protruding structure of the upper ring attaching the booster to the external tank. These deflections directed the flame plume onto the surface of the external tank. This sequence of flame spreading is confirmed by analysis of the recovered wreckage. The growing flame also impinged on the strut attaching the solid rocket booster to the external tank.”

By 64.44 seconds, the external tank was already breached and these flames were mixing with the leaking hydrogen.

Beginning around 72 seconds, the flight was visually terminated extremely quickly. The orbiter was engulfed in an enormous explosive reaction as the external tank failed and the hydrogen fuel was instantly ignited. At this point, the Orbiter was traveling at Mach 1.92 (almost two times the speed of sound, or around 1,400mph.) at an altitude of 46,000 feet. It was at this point that the orbiter broke up into several large pieces, however the crew cabin remained largely intact. Kerwin reports that the range of most probable maximum accelerations is from 12 to 20 G's in the vertical axis. As stated above, this not enough to kill the crew. To put this in context, the Eurofighter Typhoon military jet aircraft is capable of pulling 9G safely during combat maneuvers. These accelerations lasted less than 4 seconds.

After the Orbiter began to break up, it continued upward reaching a peak altitude of around 65,000ft approximately 25 seconds later. At this altitude, if the crew compartment lost cabin pressure, a human would have lost consciousness within seconds without a spacesuit. However, it proved impossible to definitively say whether the crew cabin became depressurised or not.

During the STS-51L, in 1986, astronauts were not required to wear pressure suits on launch as nothing of this sort had ever happened before. The separation of the crew compartment deprived the crew of orbiter-supplied oxygen, except for a few seconds that were left in supply in the lines.

Each crew member was also connected to a personal egress air pack (PEAP) wich was a device, shown below, that contains an emergency supply of breathing air (not oxygen) for ground egress emergencies - such as the orbiter beginning to burn on the run way.

Astronauts from STS-34 stand next to their PEAPs in 1989. Note: They are wearing pressurised suits here which were brought in as a result of the Challenger accident. Credit: NASA.

Three PEAP's were determined to have been activated, a process which must be done manually, indicating that at least three members of the crew were aware of their situation. Further evidence of crew consciousness was discovered when several switches were found to have been moved from their launch positions - suggesting that the pilot had tried to restore electrical power to the cabin. This process involved removing switch covers and was deemed to have been due to human action, not any forces experienced during break up or descent.

The amount of air consumed from the PEAPs is consistent with the time it took the orbiter to impact the ocean after initial breakup. However, the PEAPs were not design to supply pressurised oxygen at altitude and would not have been sufficient to prevent loss of conciousness to the crew at altitudes as high as 60,000ft - if the crew cabin suffered depressurisation during breakup.

Kervin writes that it is possible, but not certain, that the crew lost consciousness when the crew cabin lost pressure. Data to support this is:

"The accident happened at 48,000 feet, and the crew cabin was at that altitude or higher for almost a minute. At that altitude, without an oxygen supply, loss of cabin pressure would have caused rapid loss of consciousness and it would not have been regained before water impact.
PEAP activation could have been an instinctive response to unexpected loss of cabin pressure.
If a leak developed in the crew compartment as a result of structural damage during or after breakup (even if the PEAP's had been activated), the breathing air available would not have prevented rapid loss of consciousness.
The crew seats and restraint harnesses showed patterns of failure which demonstrates that all the seats were in place and occupied at water impact with all harnesses locked. This would likely be the case had rapid loss of consciousness occurred, but it does not constitute proof."

Finally, 2 minutes and 45 seconds after the initial explosion, the orbiter impacted the ocean at a velocity of over 200mph. Instantly shattering the cabin and killing all crew members.

It seems likely that the crew were alive when Challenger impacted the ocean, however, it was deemed impossible to determine whether they were unconscious or not.

A list of good sources on this incident can be found here: Challenger STS 51-L Accident January 28, 1986

To read the full accident report, known as the Rogers Commission Report click here: https://spaceflight.nasa.gov/out...

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