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For further information about Challenger's mission and crew, see STS-51-L.
The Space Shuttle Challenger disaster occurred on the morning of January 28 1986, at 11:39 EST, when Space Shuttle ''Challenger'' disintegrated 73 seconds into its flight, owing to the failure of an O-ring seal in the right solid rocket booster (SRB). The seal failure caused a flame leak from the SRB that impinged upon the adjacent external propellant tank and aft SRB connecting strut. Within seconds the flame caused structural failure of the external tank, and the orbiter broke up abruptly due to aerodynamic forces. The crew compartment and many other vehicle fragments were eventually recovered from the ocean floor.
The Rogers Commission, appointed by President Reagan to investigate the accident, found that NASA's organizational culture and decision-making processes had been a key contributing factor to the accident. NASA managers had failed to deal with the flawed design of the O-rings, had ignored warnings from engineers about the inadvisability of launching on an unusually cold day, and had failed to adequately report these technical concerns to their superiors. The Rogers Commission offered NASA nine recommendations that were to be implemented before shuttle flights resumed.
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Crew
Mission Specialist 2: Ellison Onizuka - Air Force flight test engineer, Eagle Scout, also flew on STS-51-C on Discovery, the first space shuttle mission for the Department of Defense.
Mission Specialist 3: Dr. Ronald McNair - staff physicist at the Hughes Research Laboratories, also flew on STS-41-B
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Launch delays
Challenger's launch was originally set for 2:43pm EST on January 22. Delays with STS-61-C caused the launch date to be pushed back to the 23rd and then to the 24th. Launch was re-scheduled for the 25th due to bad weather at the Transoceanic Abort Landing (TAL) site in Dakar, Senegal. NASA decided to use Casablanca as the TAL site, but because it was not equipped for night landings the launch had to be moved to the morning (Florida time). Predictions of unacceptable weather at Kennedy Space Center (KSC) caused the launch to be re-scheduled for 9:37am EST on the 27th. Launch was then delayed 24 hours when the pad technicians could not remove a 'closing fixture' from the orbiter's hatch. When the fixture was finally sawn off, cross winds at the Shuttle Landing Facility exceeded the limits for a Return to Launch Site (RTLS) abort, and thus the launch was delayed once again.•
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Pre-launch conditions
The morning of the 28th dawned unusually cold, with temperatures having dropped into the low twenties overnight. The low temperatures had prompted concern from engineers at Morton Thiokol, the contractor responsible for the construction and maintenance of the Shuttle's solid rocket boosters. At a teleconference which took place on the evening of the 27th, Thiokol engineers and managers discussed the weather conditions with NASA managers from Kennedy Space Center and Marshall Space Flight Center. Although several engineers--most notably Roger Boisjoly--expressed concern about the effect of the temperature on the resilience of the rubber O-rings that sealed the joints of the solid rocket boosters, Morton Thiokol managers in the end decided to recommend that the launch should go ahead.•
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Liftoff
At 6.6 seconds before liftoff, the three space shuttle main engines (SSME) ignited. Until liftoff actually occurs, the SSMEs can be safely shut down and the launch aborted if necessary. At liftoff time (T=0), the three SSMEs were at 100% of rated performance and began throttling up to 104% of rated performance under computer control. At this moment, the two SRBs were ignited and hold-down bolts were released with explosives, freeing the vehicle from the pad. With the first vertical motion of the vehicle, the gaseous hydrogen vent arm retracted from the External Tank (ET) but failed to latch back. Review of film shot by pad cameras showed that the arm did not re-contact the vehicle.• The following account of the accident is derived from real time telemetry data and photographic analysis, as well as from transcripts of air-to-ground and mission control voice communications.
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Initial ascent
As the vehicle cleared the tower, the SSMEs were operating at 104% of rated performance, and control switched from the Launch Control Center (LCC) at KSC to the Mission Control Center (MCC) in Houston, Texas.
To prevent aerodynamic forces from tearing the shuttle apart, the SSMEs throttled down to limit the velocity of the shuttle in the dense lower atmosphere. The throttle down operation began at about T+28 seconds. At T+35.379, the SSMEs throttled back further to the pre-planned 65%. Five seconds later, at about 19,000 feet, Challenger passed through Mach 1. At T+51.860, the SSMEs began throttling back up to 104% as the vehicle approached Max Q, the period of maximum aerodynamic pressure on the vehicle.
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Plume
At about T+58.788, a tracking film camera captured the beginnings of a plume near the aft attach strut on the right SRB. Unknown to those on Challenger or in Houston, ignited gas had begun to leak through a growing hole in one of the right-hand SRB's joints. Within a second, the plume became well defined and intense. Internal pressure in the right-side SRB began to drop because of the rapidly enlarging hole in the failed joint, and at T+60.238 seconds there was evidence of flame through the rupture impinging on the external tank.
At T+64.660 seconds, the plume suddenly changed shape, indicating that a leak had begun in the liquid hydrogen tank, the aft portion of the external tank. Main engine nozzles pivoted under computer control to compensate for the unbalanced thrust produced by the booster burn-through. Pressure in the shuttle's external liquid hydrogen tank began to drop at T+66.764 seconds, indicating the effect of the leak.
At this stage the situation still seemed normal both to the astronauts and to flight controllers. At T+68 seconds, the Capcom informed the crew that they were "go at throttle up," and Commander Dick Scobee confirmed the call. His response, "Roger, go at throttle up," was the last communication from Challenger on the air-to-ground loop.
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Vehicle breakup
At T+72.284 seconds, the right SRB apparently pulled away from the aft strut attaching it to the external tank. Later analysis of telemetry data showed a sudden lateral acceleration to the right at T+72.525 seconds, which may have been felt by the crew. The last statement captured by the crew cabin recorder came just half a second after this acceleration; Pilot Michael J. Smith said "Uh oh". Smith may also have been responding to indications on main engine performance or falling pressures in the external fuel tank.
At T+73.124 seconds, the aft dome of the liquid hydrogen tank failed, producing a propulsive force pushing the tank into the liquid oxygen tank in the forward external tank. At the same time, the right SRB rotated about the forward attach strut and struck the intertank structure.
At about T+73.162 seconds, and at 48,000 feet (15 km) in altitude, the vehicle breakup began.•
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Post-breakup flight controller dialog
In Mission Control, there was silence for some seconds after the accident. Television screens showed a cloud of smoke and vapor where Challenger had been, with pieces of debris falling toward the ocean. At about T+89 seconds, flight director Jay Greene prompted his flight dynamics officer for information. The response was that "filters radar got discreting sources," a further indication that Challenger had broken into multiple pieces. The ground controller reported "negative contact, loss of downlink" of radio and telemetry data from Challenger.
At T+110.250 the Range Safety Officer (RSO) at the Cape Canaveral Air Force Station sent radio signals that activated the range destruct packages on board both solid rocket boosters. This was a normal contingency procedure, undertaken because the RSO judged the free-flying SRBs a possible threat to land or sea. The same destruct signal would have destroyed the External Tank had it not already disintegrated.•
"Flight controllers here are looking very carefully at the situation," reported the public affairs officer. "Obviously a major malfunction." Shortly afterwards, the flight dynamics officer relayed the range safety officer's report that the vehicle had exploded. Flight director Jay Greene then ordered that contingency procedures be put into effect at Mission Control; these procedures included locking the doors of the control center, shutting down telephone communications with the outside world, and following checklists that ensured that the relevant data was correctly recorded and preserved.
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No "explosion"
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The shuttle and external tank did not actually "explode"; there was no detonation. Instead they rapidly disintegrated under tremendous aerodynamic forces, since the shuttle was near "Max Q", or maximum aerodynamic pressure. When the external tank disintegrated, the fuel and oxidizer stored within it was released, producing the appearance of a massive fireball. However, according to the NASA team that analyzed imagery after the accident, there was only "localized combustion" of propellant.
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Cause and time of death
At vehicle breakup, the robustly constructed crew cabin detached in one piece and slowly tumbled. NASA estimated separation forces at about 12 to 20 times the force of gravity (''g'') very briefly; within two seconds forces were below 4 g, and within ten seconds the cabin was in free fall. These forces were likely insufficient to cause major injury. At least some of the astronauts were likely alive and briefly conscious after the breakup, because three of the four personal egress air packs (PEAPs) on the flight deck were found to have been activated. Investigators found their remaining unused air supply roughly consistent with the expected consumption during the 2 minute 45 second post-breakup trajectory. Whether the astronauts remained conscious long after the breakup is unknown, and largely depends on whether the detached crew cabin maintained pressure integrity. If it did not, time of useful consciousness at that altitude is just a few seconds; the PEAPs supplied only unpressurized air, and hence would not have helped the crew retain consciousness. The crew cabin impacted the ocean surface at roughly 207 miles per hour (333 km/hour), causing deceleration of over 200 g, far beyond the structural limits of the crew compartment or crew survivability levels.
On July 28, 1986, Rear Admiral Richard H. Truly, NASA's Associate Administrator for Space Flight and a former astronaut, released a report from Joseph P. Kerwin, biomedical specialist from the Johnson Space Center in Houston, Texas, relating to the deaths of the astronauts in the accident. Dr. Kerwin, a veteran of the Skylab 2 mission, had been commissioned to undertake the study soon after the accident. According to the Kerwin Report:
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Crew escape was not possible
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During powered flight of the space shuttle, crew escape was not possible. While launch escape systems were considered several times during shuttle development, NASA's conclusion was that the shuttle's expected high reliability would preclude the need for one. Modified SR-71 Blackbird ejection seats and full pressure suits were used on the first four shuttle orbital missions, considered test flights, but they were removed for the operational missions that followed. Providing a launch escape system for larger crews was considered undesirable due to "limited utility, technical complexity and excessive cost in dollars, weight or schedule delays."•
After the Challenger loss, the question was re-opened, and NASA considered several different options, including ejector seats, tractor rockets and bailing out through the bottom of the orbiter. However, NASA once again concluded that all of the launch escape systems considered would be impractical due to the sweeping vehicle modifications that would have been necessary and the resultant limitations on crew size. A bail-out system was designed to give the crew the option to leave the shuttle during gliding flight; however, this system would not have been available in the Challenger scenario.•
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Tributes
On the night of the disaster, President Ronald Reagan had been scheduled to give his annual State of the Union address. He initially announced that the address would go on as scheduled, but under mounting pressure he postponed the State of the Union address for a week and gave a national address on the Challenger disaster from the Oval Office of the White House. The speech was written by Peggy Noonan. At its end, he made the following statement, quoting from the poem "High Flight" by John Gillespie Magee, Jr.: "We will never forget them, nor the last time we saw them, this morning, as they prepared for their journey and waved goodbye and 'slipped the surly bonds of earth' to 'touch the face of God.'" Three days later, he and his wife Nancy traveled to the Johnson Space Center for a memorial service to honor the astronauts.
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Funeral ceremonies
The remains of the crew that were identifiable were returned to their families on April 29, 1986. Two of the crewmembers, Dick Scobee and Michael Smith, were buried by their families at Arlington National Cemetery at individual grave sites. Other crew remains were buried at the Space Shuttle Challenger Memorial in Arlington on May 20, 1986.
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Recovery of debris
On board Challenger was an American flag that was sponsored by Boy Scout Troop 514 of Monument, Colorado. It was recovered intact, still sealed in its cargo bag.
Debris from Challenger washed up on Florida beaches for years after the incident. On December 17, 1996, ten years after the incident, two large pieces of the shuttle washed up at Cocoa Beach. The USS ''Simpson'' was among the naval ships that assisted in the recovery with the United States Coast Guard.
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Investigation
In the aftermath of the accident, NASA was criticized for its lack of openness with the press. The New York Times noted on the day after the accident that "neither Jay Greene, flight director for the ascent, nor any other person in the control room, was made available to the press by the space agency".•
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Rogers Commission
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The Presidential Commission on the Space Shuttle Challenger Accident, also known as the Rogers Commission (after its chairman), was formed to investigate the disaster. The commission members were Chairman William P. Rogers, Vice Chairman Neil Armstrong, David Acheson, Eugene Covert, Richard Feynman, Robert Hotz, Donald Kutyna, Sally Ride, Robert Rummel, Joseph Sutter, Arthur Walker, Albert Wheelon, and Chuck Yeager. The commission worked for several months and published a report of its findings. It found that the Challenger accident was caused by a failure in the O-rings sealing a joint on the right solid rocket booster, which allowed pressurized hot gasses and eventually flame to "blow by" the O-ring and make contact with the adjacent external tank, causing structural failure. The failure of the O-rings was attributed to a faulty design, whose performance could be too easily compromised by factors including the low temperature on the day of launch.•
More broadly, the report also considered the contributing causes of the accident. Most salient was the failure of both NASA and its contractor Morton Thiokol to respond adequately to the danger posed by the deficient joint design; rather than redesigning the joint, they came to define the problem as an acceptable flight risk.• The report also strongly criticised the decision making process that led to the launch of Challenger, saying that it was seriously flawed.•
One of the commission's most well-known members was theoretical physicist Richard Feynman. During a televised hearing, he famously demonstrated how the O-rings became less resilient and subject to seal failures at ice-cold temperatures by immersing a sample of the material in a glass of ice water. He was so critical of flaws in NASA's "safety culture" that he threatened to remove his name from the report unless it included his personal observations on the reliability of the shuttle, which appeared as Appendix F. In the appendix, he argued that the estimates of reliability offered by NASA management were wildly unrealistic, differing as much as a thousandfold from the estimates of working engineers. "For a successful technology," he concluded, "reality must take precedence over public relations, for nature cannot be fooled."
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U.S. House Committee hearings
The U.S. House Committee on Science and Technology also conducted hearings, and on October 29, 1986 released its own report on the Challenger accident.• The committee reviewed the findings of the Rogers Commission as part of its investigation, and agreed with the Rogers Commission as to the technical causes of the accident. However, it differed from the committee in its assessment of the accident's contributing causes.
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NASA response
After the Challenger accident, further shuttle flights were suspended, pending the results of the Rogers Commission investigation. Whereas NASA had held an internal inquiry into the Apollo 1 fire, its actions after Challenger were more constrained by the judgments of outside bodies. The Rogers Commission offered nine recommendations on improving safety in the space shuttle program, and NASA was directed by President Ronald Reagan to report back within thirty days as to how it planned to implement those recommendations.• NASA's contract with Morton Thiokol, the contractor responsible for the solid rocket boosters, included a clause stating that in the event of a failure leading to "loss of life or mission," Thiokol would forfeit $10 million of its incentive fee and formally accept legal liability for the failure. After the Challenger accident, Thiokol agreed to "voluntarily accept" the monetary penalty in exchange for not being forced to accept liability.
NASA also created a new Office of Safety, Reliability and Quality Assurance, headed as the commission had specified by a NASA associate administrator who reported directly to the NASA administrator. George Martin, formerly of Martin Marietta, was appointed to this position.• Former Challenger flight director Jay Greene became chief of the Safety Division of the directorate.
The unrealistically optimistic launch schedule pursued by NASA had been criticised by the Rogers Commission as a possible contributing cause to the accident. After the accident, NASA attempted to aim at a more realistic shuttle flight rate: it added another orbiter, ''Endeavour'', to the space shuttle fleet in order to replace Challenger, and worked with the Department of Defense in order to put more satellites in orbit using expendable launch vehicles rather than the shuttle.• In August 1986, President Reagan also announced that the shuttle would no longer carry commercial satellite payloads. After a thirty-two month hiatus, the next shuttle mission, STS-26, was launched on September 29, 1988.
Although significant changes were made by NASA after the Challenger accident, many commentators have argued that the changes in its management structure and organizational culture were neither deep nor long-lasting. After the Space Shuttle Columbia disaster in 2003, attention once again focused on the attitude of NASA management towards safety issues. The Columbia Accident Investigation Board (CAIB) concluded that NASA had failed to learn many of the lessons of Challenger. In particular, the agency had not set up a truly independent office for safety oversight; the CAIB felt that in this area, "NASA's response to the Rogers Commission did not meet the Commission's intent".• The CAIB believed that "the causes of the institutional failure responsible for Challenger have not been fixed," saying that the same "flawed decision making process" that had resulted in the Challenger accident was responsible for Columbias destruction seventeen years later.•
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See also
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Further reading
Harry Collins and Trevor Pinch. The Golem at Large: What you should know about technology. Includes chapter on the Challenger disaster.
Claus Jensen. (1996) No Downlink: A Dramatic Narrative about the Challenger Accident and Our Time. ISBN 0-374-12036-6
Joseph Trento. (1988) Prescription for Disaster, ISBN 0-245-54615-4.
Edward Tufte. (1997) Visual Explanations, ISBN 0-9613921-2-6, Chapter 2.
Diane Vaughan. (1996) The Challenger Launch Decision: Risky Technology, Culture and Deviance at NASA ISBN 0-226-85176-1
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