The Space Shuttle Challenger’s tenth mission — designated STS-51-L — was scheduled to launch on the morning of 28 January 1986 from Launch Complex 39B at the Kennedy Space Center. The crew of seven included the schoolteacher Christa McAuliffe of Concord, New Hampshire, the first participant in NASA’s “Teacher in Space” programme. The launch was widely watched live on broadcast television, particularly by US elementary and middle-school students — many of whom were watching at school as part of educational programming built around McAuliffe’s mission.
The launch had been delayed four times since the original 22 January date. The principal cause of the delays had been a sequence of minor mechanical and weather issues. The 28 January launch was the fifth attempt.
The night before
The overnight low at Kennedy Space Center on 27-28 January 1986 was approximately minus 1°C (about 30°F) — the coldest pre-launch temperature in the Space Shuttle programme’s history. Ice formed on the launch pad structure overnight. The pad was inspected by the Ice Team in the early morning hours and was approved.
The crucial concern raised that night was about the solid rocket booster (SRB) O-rings. The Shuttle’s two solid rocket boosters — each a five-segment cylinder approximately 45 metres tall — were sealed at each segment joint by a pair of rubber O-rings between the segment-to-segment metal interfaces. The O-rings were designed to maintain a hot-gas seal across the joints during the boosters’ 124 seconds of burn time.
Engineers at the SRB manufacturer Morton Thiokol in Brigham City, Utah — particularly the senior seal engineer Roger Boisjoly — had concerns about O-ring performance at low temperatures. The O-rings were Viton rubber. Below approximately 12°C the rubber loses elasticity. The seal at low temperature might fail to close fast enough during the brief milliseconds of segment-joint flexing at ignition.
Boisjoly and his Morton Thiokol engineering colleagues had identified the O-ring temperature dependence in extensive review work through 1985. The concern was already on file at NASA in writing. The 27 January 1986 evening teleconference between Morton Thiokol management at Brigham City and NASA’s Marshall Space Flight Center engineering management at Huntsville, Alabama, was an unscheduled additional review specifically requested because the next morning’s launch temperature was forecast below the lowest temperature for which O-ring performance had ever been verified.
Morton Thiokol’s engineers — Boisjoly and Arnie Thompson principally — formally recommended against launch at the predicted morning temperature. The Marshall Space Flight Center managers (Lawrence Mulloy and George Hardy in particular) pushed back. Hardy said on the call that he was “appalled” at the no-launch recommendation. Mulloy asked the famous question: “My God, Thiokol, when do you want me to launch, next April?”
The Morton Thiokol management — under vice-presidents Joseph Kilminster, Calvin Wiggins, and Jerald Mason — caucused privately, off the conference line, for approximately 30 minutes. They reversed the engineering recommendation. The launch was approved.
73 seconds
The Challenger lifted off at 11:38 a.m. EST on 28 January 1986. The video recordings of the launch — particularly the high-resolution pad-tracking cameras — show that a small puff of dark smoke escaped from the aft segment-to-segment joint of the right SRB at the moment of ignition (T+0.678 seconds). Approximately eight further small smoke puffs followed over the first 2.5 seconds. The puffs stopped. The O-ring had not maintained the cold-temperature seal; the gap had been temporarily sealed by aluminium-oxide combustion debris from the propellant.
The Challenger continued climbing for the next 58 seconds without further visible anomaly. The launch sequence was nominal.
At approximately T+58 seconds the aluminium-oxide seal at the right SRB joint failed under the buffeting loads of the upper-atmosphere wind shear that the Shuttle had encountered between 30,000 and 35,000 feet. Hot exhaust gas from inside the SRB began jetting laterally out of the failed joint. The jet was directed at the lower right side of the external fuel tank — the large orange tank carrying the Shuttle’s liquid oxygen and liquid hydrogen.
Over the next 14 seconds the lateral jet progressively burned through the external tank’s structural attachment to the SRB and burned through the external tank’s aft dome. The external tank’s structural integrity failed at T+73 seconds.
The Challenger broke apart. The crew compartment separated from the rest of the orbiter and continued in ballistic trajectory for approximately 2 minutes 45 seconds, falling from approximately 14,000 metres to the Atlantic Ocean surface, where it impacted at approximately 333 km/h. Cabin pressure-suit oxygen indicators showed that at least three of the seven crew members survived the breakup and activated their personal egress oxygen packs. None survived the impact with the ocean.
The complete loss of vehicle took 73 seconds. The complete loss of crew took 2 minutes 45 seconds.
The Rogers Commission
The Rogers Commission — chaired by former Secretary of State William Rogers, with members including the astronauts Neil Armstrong and Sally Ride, the test pilot Chuck Yeager, and the Caltech physicist Richard Feynman — was appointed by President Reagan on 3 February 1986 and reported on 6 June 1986.
The commission’s principal finding was the technical cause: cold-temperature O-ring failure. The commission’s deeper finding, in the report’s chapters on NASA culture and decision-making, was institutional: NASA had progressively normalised an engineering anomaly (the O-ring erosion, which had occurred on multiple previous flights without complete failure) into “acceptable risk” without conducting the kind of formal flight-readiness reviews that the original Apollo-era NASA procedure would have required.
Richard Feynman’s separately-appended Appendix F — published over the strenuous objection of the rest of the commission, who had not wanted his individual conclusions to overshadow the consensus report — included his physical demonstration of O-ring temperature dependence on national television during the public hearings (the Feynman ice-water demonstration is the most-remembered single image from the commission) and his quietly devastating final sentence:
For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.
Roger Boisjoly
The Morton Thiokol engineer Roger Boisjoly testified to the Rogers Commission about his 27 January 1986 no-launch recommendation and the decision to reverse it. His testimony was the principal source of the public understanding of the night-before decision.
His testimony also ended his career. Morton Thiokol reassigned him after the Commission hearings and progressively isolated him from his previous engineering responsibilities. He left the company in 1988 with a stress-related medical retirement. He spent the rest of his career as an independent engineering-ethics consultant and lecturer, repeatedly visiting US engineering schools to discuss the Challenger decision and its consequences for the engineering profession.
He died of cancer on 6 January 2012, aged 73. The American Association for the Advancement of Science had given him its Scientific Freedom and Responsibility Award in 1988.
What followed
The Space Shuttle programme was suspended for 32 months. The next Shuttle mission — STS-26, Discovery — launched on 29 September 1988 with extensively redesigned SRB joints. The SRB joints were redesigned to use three O-rings instead of two, a tang capture feature, and heaters to maintain temperature.
The Shuttle programme continued until 2011. The second loss-of-crew-and-vehicle was Columbia on 1 February 2003 — a 17-year gap. The Columbia loss had a different proximate cause (foam impact damage to the left wing during ascent) but similar institutional characteristics (normalised acceptance of foam-strike anomalies).
The Challenger crew remains are interred at multiple cemeteries. A common memorial — including the unidentifiable common remains — is at Arlington National Cemetery, where a granite monument lists all seven names. The pieces of the Challenger that were recovered from the Atlantic Ocean in 1986 are stored in the abandoned Minuteman missile silos at the Cape Canaveral Air Force Station, on a NASA decision that the parts should neither be displayed nor scrapped.
Christa McAuliffe’s hometown of Concord, New Hampshire, named the elementary school that her own children had attended after her in May 1986. The school is still operating.