The Challenger crew embodied NASA's vision of diverse spaceflight. Commander Francis 'Dick' Scobee and Pilot Michael Smith were veterans. Mission specialists Judith Resnik, Ronald McNair, and Ellison Onizuka represented NASA's increasing diversity. Payload specialist Gregory Jarvis was an engineer from Hughes Aircraft.

And then there was Christa McAuliffe, a 37-year-old social studies teacher from New Hampshire. She had been selected from over 11,000 applicants for NASA's 'Teacher in Space' program. Her mission was to teach two lessons from orbit and inspire a generation. Schools across America prepared to watch her launch.

The morning of January 28 was unusually cold for Florida - temperatures dipped below freezing overnight. Engineers from Morton Thiokol, manufacturer of the solid rocket boosters, were concerned. The O-rings that sealed joints in the boosters had never been tested at such low temperatures.

The engineers recommended delaying the launch until the weather warmed. NASA managers pushed back. The launch had already been delayed several times. The agency was under pressure to maintain its flight schedule. The managers overruled the engineers' concerns. The launch proceeded.

Challenger lifted off at 11:39 AM. Within a second, a puff of gray smoke appeared at a joint in the right solid rocket booster - evidence that the O-ring was failing. The cold had caused the rubber seal to harden and fail to seat properly.

For 72 seconds, the flame was contained by solidified propellant. Then the propellant burned through. A flame shot out and struck the external fuel tank. At 73 seconds, the tank ruptured. The shuttle was torn apart by aerodynamic forces. The solid rocket boosters spiraled away, trailing smoke across the Florida sky.

The crew cabin survived the initial breakup and likely remained intact as it arced through the sky. Evidence suggests some crew members activated emergency air supplies - meaning they were alive and conscious for at least some of the nearly three-minute fall to the ocean. They may have been alive until impact, falling from 48,000 feet.

The nation watched in shock. Classrooms full of children saw their teacher die on live television. President Reagan postponed his State of the Union address. 'The crew of the space shuttle Challenger honored us by the manner in which they lived their lives,' Reagan said that night. 'We will never forget them.'

The Rogers Commission investigation revealed a catastrophic failure of engineering culture. NASA managers had known about O-ring problems for years. Engineers' warnings had been dismissed. Production pressure had overridden safety concerns. The system had failed.

NASA was grounded for over two years while reforms were implemented. The O-ring design was changed. Decision-making processes were overhauled. But the fundamental lesson - that complex systems require constant vigilance, that organizational culture can kill - would have to be relearned. Seventeen years later, Columbia broke apart during reentry, killing seven more. Some lessons take more than one teaching.