Challenger 1986: Frozen O-Rings, Thiokol's Management Hat and 73 Seconds

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On January 28, 1986, schoolchildren across the country watched as the space shuttle Challenger, carrying teacher Christa McAuliffe, broke apart 73 seconds after liftoff. The failure traced to the solid rocket boosters built by Morton Thiokol, assembled in segments and sealed at tang and clevis joints by two 20-foot rubber O-rings rated criticality one, meaning no backup. Engineers had known since the 1970s about joint rotation, and O-ring erosion appeared as early as the second shuttle flight in 1981. In January 1985, at 53 degrees, the coldest launch to that point, hot gas blew past a primary O-ring. Mission STS-51-L, with a Halley's Comet study and the Teacher in Space project, slipped from July 1985 through a Senegal dust storm and a stuck hatch bolt that Dan Rather called high-tech low comedy.

With an overnight forecast of 18 degrees, Thiokol engineers argued against launching in a teleconference the night before, and booster manager Lawrence Mulloy asked whether they wanted him to launch next April. During a 30-minute offline caucus, an executive told a colleague to take off his engineering hat and put on his management hat, and Thiokol faxed a launch recommendation. Puffs of black smoke appeared in the first seconds, an aluminum oxide plug held until wind shear broke it near 58 seconds, and the stack came apart. The Rogers Commission, with Richard Feynman, Neil Armstrong and Sally Ride, blamed management culture and the normalization of deviance, a pattern the Columbia board found again in 2003.

• Rockwell International engineers warned that ice encasing the launch tower could damage the orbiter, and they were overruled.
• The crew cabin separated largely intact, and at least three personal egress air packs had been activated.
• The pilot Michael Smith's air pack switch sat behind his seat, so Ellison Onizuka or Judith Resnik had to turn it on for him.
• Feynman showed the O-ring's stiffness with a C-clamp and a glass of ice water.
• The fleet was grounded for 32 months, and flights resumed with Discovery in the fall of 1988 after a joint redesign.