On January 28, 1986, the NASA shuttle orbiter mission STS-51-L and the tenth flight of Space Shuttle Challenger (OV-99) broke apart 73 seconds into its flight, killing all seven crew members, which consisted of five NASA astronauts, one payload specialist and a civilian school teacher. The spacecraft disintegrated over the Atlantic Ocean, off the coast of Cape Canaveral, Florida, at 11:39 a.m. EST (16:39 UTC). The disintegration of the vehicle began after a joint in its right solid rocket booster (SRB) failed at liftoff.
The failure was caused by the failure of O-ring seals used in the joint that were not designed to handle the unusually cold conditions that existed at this launch. The seals’ failure caused a breach in the SRB joint, allowing pressurized burning gas from within the solid rocket motor to reach the outside and impinge upon the adjacent SRB aft field joint attachment hardware and external fuel tank. This led to the separation of the right-hand SRB’s aft field joint attachment and the structural failure of the external tank. Aerodynamic forces broke up the orbiter.
The crew compartment and many other vehicle fragments were eventually recovered from the ocean floor after a lengthy search and recovery operation. The exact timing of the death of the crew is unknown; several crew members are known to have survived the initial breakup of the spacecraft. The shuttle had no escape system, and the impact of the crew compartment at terminal velocity with the ocean surface was too violent to be survivable.
The disaster resulted in a 32-month hiatus in the shuttle program and the formation of the Rogers Commission, a special commission appointed by United States President Ronald Reagan to investigate the accident. The Rogers Commission found NASA’s organizational culture and decision-making processes had been key contributing factors to the accident, with the agency violating its own safety rules. NASA managers had known since 1977 that contractor Morton-Thiokol’s design of the SRBs contained a potentially catastrophic flaw in the O-rings, but they had failed to address this problem properly. NASA managers also disregarded warnings from engineers about the dangers of launching posed by the low temperatures of that morning, and failed to adequately report these technical concerns to their superiors.
Approximately 17 percent of Americans witnessed the launch live because of the presence of high school teacher Christa McAuliffe, who would have been the first teacher in space. Media coverage of the accident was extensive: one study reported that 85 percent of Americans surveyed had heard the news within an hour of the accident. The Challenger disaster has been used as a case study in many discussions of engineering safety and workplace ethics.
Challenger was originally set to launch from KSC in Florida at 14:42 Eastern Standard Time (EST) on January 22, 1986. Delays in the previous mission, STS-61-C, caused the launch date to be moved to January 23 and then to January 24. The launch was then rescheduled to January 25 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 KSC on January 26, caused the launch to be rescheduled for 09:37 EST on January 27.
The launch was delayed the next day, due to problems with the exterior access hatch. First, one of the micro-switch indicators, used to verify that the hatch was safely locked, malfunctioned. Then, a stripped bolt prevented the closeout crew from removing a closing fixture from the orbiter’s hatch. By the time repair personnel had sawed the fixture off, crosswinds at the Shuttle Landing Facility exceeded the limits for a Return to Launch Site (RTLS) abort. While the crew waited for winds to die down, the launch window expired, forcing yet another scrub.
Forecasts for January 28 predicted an unusually cold morning, with temperatures close to −1 °C (30 °F), the minimum temperature permitted for launch. The Shuttle was never certified to operate in temperatures that low. The O-rings, as well as many other critical components, had no test data to support any expectation of a successful launch in such conditions.
By mid-1985 Thiokol engineers worried that others did not share their concerns about the low temperature effects on the boosters. Bob Ebeling in October 1985 wrote a memo—titled “Help!” so others would read it—of concerns regarding low temperatures and O-rings. After the weather forecast, NASA personnel remembered Thiokol’s warnings and contacted the company. When a Thiokol manager asked Ebeling about the possibility of a launch at 18 °F (−8 °C), he answered “[W]e’re only qualified to 40° [40 °F or 4 °C]… ‘what business does anyone even have thinking about 18°, we’re in no-man’s land.'” After his team agreed that a launch risked disaster, Thiokol immediately called NASA recommending a postponement until temperatures rose in the afternoon. NASA manager Jud Lovingood responded that Thiokol could not make the recommendation without providing a safe temperature. The company prepared for a teleconference two hours later during which it would have to justify a no-launch recommendation.
At the teleconference on the evening of January 27, Thiokol engineers and managers discussed the weather conditions with NASA managers from Kennedy Space Center and Marshall Space Flight Center. Several engineers (most notably Ebeling and Roger Boisjoly) reiterated their concerns about the effect of low temperatures on the resilience of the rubber O-rings that sealed the joints of the SRBs, and recommended a launch postponement. They argued that they did not have enough data to determine whether the joints would properly seal if the O-rings were colder than 54 °F (12 °C). This was an important consideration, since the SRB O-rings had been designated as a “Criticality 1” component, meaning that there was no backup if both the primary and secondary O-rings failed, and their failure could destroy the Orbiter and kill its crew.
Thiokol management initially supported its engineers’ recommendation to postpone the launch, but NASA staff opposed a delay. During the conference call, Hardy told Thiokol, “I am appalled. I am appalled by your recommendation.” Mulloy said, “My God, Thiokol, when do you want me to launch—next April?” NASA believed that Thiokol’s hastily prepared presentation’s quality was too poor to support such a statement on flight safety.
One argument by NASA personnel contesting Thiokol’s concerns was that if the primary O-ring failed, the secondary O-ring would still seal. This was unproven, and was in any case an argument that did not apply to a “Criticality 1” component. As astronaut Sally Ride stated when questioning NASA managers before the Rogers Commission, it is forbidden to rely on a backup for a “Criticality 1” component.
NASA claimed that it did not know of Thiokol’s earlier concerns about the effects of the cold on the O-rings, and did not understand that Rockwell International, the shuttle’s prime contractor, additionally viewed the large amount of ice present on the pad as a constraint to launch.
According to Ebeling, a second conference call was scheduled with only NASA & Thiokol management, excluding the engineers. For reasons that are unclear, Thiokol management disregarded its own engineers’ warnings and now recommended that the launch proceed as scheduled; NASA did not ask why. Ebeling told his wife that night that Challenger would blow up.
Ken Iliff, a former NASA Chief Scientist who had worked on the Space Shuttle Program since its first mission (and the X-15 program before that), stated in 2004, “Violating a couple of mission rules was the primary cause of the Challenger accident.”
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. All times are given in seconds after launch and correspond to the telemetry time-codes from the closest instrumented event to each described event.
The Space Shuttle main engines (SSMEs) were ignited at T -6.6 seconds. The SSMEs were liquid-fueled and could be safely shut down (and the launch aborted if necessary) until the Solid Rocket Boosters ignited at T=0 (which was at 11:38:00.010 EST) and the hold-down bolts were released with explosives, freeing the vehicle from the pad. At lift off, the three SSMEs were at 100% of their original rated performance, and began throttling up to 104% under computer control. 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, and thus it was ruled out as a contributing factor in the accident. The post-launch inspection of the pad also revealed that kick springs on four of the hold-down bolts were missing, but they were similarly ruled out as a possible cause.
Later review of launch film showed that at T+0.678, strong puffs of dark gray smoke were emitted from the right-hand SRB near the aft strut that attached the booster to the ET. The last smoke puff occurred at about T+2.733. The last view of smoke around the strut was at T+3.375. It was later determined that these smoke puffs were caused by the opening and closing of the aft field joint of the right-hand SRB. The booster’s casing had ballooned under the stress of ignition. As a result of this ballooning, the metal parts of the casing bent away from each other, opening a gap through which hot gases—above 5,000 °F (2,760 °C)—leaked. This had occurred in previous launches, but each time the primary O-ring had shifted out of its groove and formed a seal. Although the SRB was not designed to function this way, it appeared to work well enough, and Morton-Thiokol changed the design specs to accommodate this process, known as extrusion.
While extrusion was taking place, hot gases leaked past (a process called “blow-by”), damaging the O-rings until a seal was made. Investigations by Morton-Thiokol engineers determined that the amount of damage to the O-rings was directly related to the time it took for extrusion to occur, and that cold weather, by causing the O-rings to harden, lengthened the time of extrusion. (The redesigned SRB field joint used subsequent to the Challenger accident used an additional interlocking mortise and tang with a third O-ring, mitigating blow-by.)
On the morning of the disaster, the primary O-ring had become so hard due to the cold that it could not seal in time. The temperature had dropped below the glass transition temperature of the O-rings. Above the glass transition temperature, the O-rings display properties of elasticity and flexibility, while below the glass transition temperature, they become rigid and brittle. The secondary O-ring was not in its seated position due to the metal bending. There was now no barrier to the gases, and both O-rings were vaporized across 70 degrees of arc. Aluminum oxides from the burned solid propellant sealed the damaged joint, temporarily replacing the O-ring seal before flame passed through the joint.
As the vehicle cleared the tower, the SSMEs were operating at 104% of their rated maximum thrust, and control switched from the Launch Control Center (LCC) at Kennedy to the Mission Control Center (MCC) at Johnson Space Center in Houston, Texas. To prevent aerodynamic forces from structurally overloading the orbiter, at T+28 the SSMEs began throttling down to limit the velocity of the shuttle in the dense lower atmosphere, per normal operating procedure. At T+35.379, the SSMEs throttled back further to the planned 65%. Five seconds later, at about 19,000 feet (5,800 m), Challenger passed through Mach 1. At T+51.860, the SSMEs began throttling back up to 104% as the vehicle passed beyond max q, the period of maximum aerodynamic pressure on the vehicle.
The crew cabin, made of reinforced aluminum, was a particularly robust section of the orbiter. During vehicle breakup, it detached in one piece and slowly tumbled into a ballistic arc. NASA estimated the load factor at separation to be between 12 and 20 g; within two seconds it had already dropped to below 4 g and within 10 seconds the cabin was in free fall. The forces involved at this stage were probably insufficient to cause major injury.
At least some of the crew were probably alive and at least briefly conscious after the breakup, as three of the four recovered Personal Egress Air Packs (PEAPs) on the flight deck were found to have been activated. These were those of Judith Resnik, mission specialist Ellison Onizuka, and pilot Michael J. Smith. The location of Smith’s activation switch, on the back side of his seat, likely indicated that either Resnik or Onizuka activated it for him. Mike Mullane writes: “There had been nothing in our training concerning the activation of a PEAP in the event of an in-flight emergency. The fact that Judy or El had done so for Mike Smith made them heroic in my mind.” Investigators found their remaining unused air supply consistent with the expected consumption during the 2-minute-and-45-second post-breakup trajectory.
While analyzing the wreckage, investigators discovered that several electrical system switches on Pilot Mike Smith’s right-hand panel had been moved from their usual launch positions. Fellow astronaut Richard Mullane wrote, “These switches were protected with lever locks that required them to be pulled outward against a spring force before they could be moved to a new position.” Later tests established that neither force of the explosion nor the impact with the ocean could have moved them, indicating that Smith made the switch changes, presumably in a futile attempt to restore electrical power to the cockpit after the crew cabin detached from the rest of the orbiter.
Whether the crew members remained conscious long after the breakup is unknown, and largely depends on whether the detached crew cabin maintained pressure integrity. If it did not, the 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 to retain consciousness. If, on the other hand, the cabin was not depressurized or only slowly depressurizing, they may have been conscious for the entire fall until impact. Recovery of the cabin found that the middeck floor had not suffered buckling or tearing, as would result from a rapid decompression, thus providing some evidence that the depressurization may have not happened all at once.
NASA routinely trained shuttle crews for splashdown events, but the cabin hit the ocean surface at roughly 207 mph (333 km/h), with an estimated deceleration at impact of well over 200 g, far beyond the structural limits of the crew compartment or crew survivability levels, and far greater than almost any automobile, aircraft, or train accident. The crew would have been torn from their seats and killed instantly by the extreme impact force.
On July 28, 1986, NASA’s Associate Administrator for Space Flight, former astronaut Richard H. Truly, released a report on the deaths of the crew from the director of Space and Life Sciences at the Johnson Space Center, Joseph P. Kerwin. A medical doctor and former astronaut, Kerwin was a veteran of the 1973 Skylab 2 mission. According to the Kerwin Report:
The findings are inconclusive. The impact of the crew compartment with the ocean surface was so violent that evidence of damage occurring in the seconds which followed the disintegration was masked. Our final conclusions are:
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.
Some experts believe most if not all of the crew were alive and possibly conscious during the entire descent until impact with the ocean. Astronaut and NASA lead accident investigator Robert Overmyer said, “I not only flew with Dick Scobee, we owned a plane together, and I know Scob did everything he could to save his crew. Scob fought for any and every edge to survive. He flew that ship without wings all the way down … they were alive.”
During powered flight of the space shuttle, crew escape was not possible. Launch escape systems were considered several times during shuttle development, but 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 for the two-man crews on the first four shuttle orbital missions, which were considered test flights, but they were removed for the “operational” missions that followed. (The Columbia Accident Investigation Board later declared, after the 2003 Columbia re-entry disaster, that the space shuttle system should never have been declared operational because it is experimental by nature due to the limited number of flights as compared to certified commercial aircraft.) The multi-deck design of the crew cabin precluded use of such ejection seats for larger crews. Providing some sort of launch escape system had been considered, but deemed impractical due to “limited utility, technical complexity and excessive cost in dollars, weight or schedule delays.”
After the loss of Challenger, the question was re-opened, and NASA considered several different options, including ejector seats, tractor rockets and emergency egress through the bottom of the orbiter. 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 system was designed to give the crew the option to leave the shuttle during gliding flight, but this system would not have been usable in the Challenger situation.
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.” In the absence of reliable sources, the press turned to speculation; both The New York Times and United Press International ran stories suggesting that a fault with the space shuttle external tank had caused the accident, despite the fact that NASA’s internal investigation had quickly focused in on the solid rocket boosters. “The space agency,” wrote space reporter William Harwood, “stuck to its policy of strict secrecy about the details of the investigation, an uncharacteristic stance for an agency that long prided itself on openness.”
After the accident, NASA’s Space Shuttle fleet was grounded for almost three years while the investigation, hearings, engineering redesign of the SRBs, and other behind-the-scenes technical and management reviews, changes, and preparations were taking place. At 11:37 on September 29, 1988, Space Shuttle Discovery lifted off with a crew of five from Kennedy Space Center pad 39-B. It carried a Tracking and Data Relay Satellite, TDRS-C (named TDRS-3 after deployment), which replaced TDRS-B, the satellite that was launched and lost on Challenger. The “Return to Flight” launch of Discovery also represented a test of the redesigned boosters, a shift to a more conservative stance on safety (e.g., it was the first time the crew had launched in pressure suits since STS-4, the last of the four initial Shuttle test flights), and a chance to restore national pride in the American space program, especially manned space flight. The mission, STS-26, was a success (with only two minor system failures, one of a cabin cooling system and one of a Ku-band antenna), and a regular schedule of STS flights followed, continuing without extended interruption until the 2003 Columbia disaster.
Barbara Morgan, the backup for McAuliffe who trained with her in the Teacher in Space program and was at KSC watching her launch on January 28, 1986, flew on STS-118 as a Mission Specialist in August 2007.
Seven asteroids were named after the crew members: 3350 Scobee, 3351 Smith, 3352 McAuliffe, 3353 Jarvis, 3354 McNair, 3355 Onizuka, and 3356 Resnik. The approved naming citation was published by the Minor Planet Center on March 26, 1986 (M.P.C. 10550).
On the evening of April 5, 1986, the Rendez-vous Houston concert commemorated and celebrated the crew of the Challenger. It featured a live performance by musician Jean Michel Jarre, a friend of crew member Ron McNair. McNair was supposed to play the saxophone from space during the track “Last Rendez-Vous”. It was to have become the first musical piece professionally recorded in space. His substitute for the concert was Houston native Kirk Whalum.
In June 1986, singer-songwriter John Denver, a pilot with a deep interest in going to space himself, released the album One World which included the song Flying For Me, a tribute to the Challenger crew.
Star Trek IV: The Voyage Home was dedicated to the crew of the Challenger. Principal photography for The Voyage Home began four weeks after Challenger and her crew were lost.
Until 2010, the live broadcast of the launch and subsequent disaster by CNN was the only known on-location video footage from within range of the launch site. As of March 15, 2014, eight other motion picture recordings of the event have become publicly available:
a professional black-and-white NASA video recording closely showing the breakup and the subsequent remote detonation of one of the booster rockets, a video recording by Jack Moss from the front yard of his house in Winter Haven, Florida, 80 miles (130 km) from Cape Canaveral a video recording by Ishbel and Hugh Searle on a plane leaving from Orlando International Airport, 50 miles (80 km) from Cape Canaveral, was posted by their daughter Victoria Searle on January 30, 2011 along with an interview taken on the couple two days earlier, a Super 8 mm film recorded by then-19-year-old Jeffrey Ault of Orange City, Florida, at the Kennedy Space Center, 10 miles (16 km) from the launch, a video recording by Lawrence Hebert of Electric Sky Films, filmed at the Kennedy Space Center 10 miles from the launch, uncovered in March 2012. a video recording by Steven Virostek uncovered in May 2012, a video recording by Michael and Frances VanKulick of Melbourne, Florida was made public in 2014.
An ABC television movie titled Challenger was broadcast on February 24, 1990. It starred Barry Bostwick as Scobee, Brian Kerwin as Smith, Joe Morton as McNair, Keone Young as Onizuka, Julie Fulton as Resnik, Richard Jenkins as Jarvis and Karen Allen as McAuliffe.
A BBC docudrama titled The Challenger was broadcast on March 18, 2013, based on the last of Richard Feynman’s autobiographical works, What Do You Care What Other People Think?. It stars William Hurt as Feynman.
In the Sega Saturn version of the video game The House of the Dead, the words “Challenger, go at throttle up”, spoken by Richard O. Covey from the mission control room only seconds before the explosion, can be heard in the soundtrack of Stage 2, several times. History Channel released a documentary titled Days That Shaped America; the first episode was about the disaster and it was aired on January 28, 2018.