Challenger exploded 85 seconds after lift-off from Cape Kennedy, on the icy morning of January 28, 1986. Enormous rubber seals, or O-rings, in the booster rockets, had frozen and failed. Flames escaped through the joint, causing liquid hydrogen and liquid oxygen to burst out of their giant tanks and ignite.
NASA had felt under pressure to launch. The shuttles were not flying enough missions. Challenger's departure had already been delayed for months and chances of a last glimpse of Haley's Comet were fading.
But the weather was against it. The ships that recovered the shuttle's reusable rockets were confined to harbour by strong winds. NASA decided to sacrifice the rockets, but the problem of temperature was not so easy - a shuttle had never launched in such cold weather.
The space agency contacted the O-ring manufacturers, Morton Thiokol, whose engineers urged a postponement. A year earlier the same employees had warned of the possible consequences of O-ring failure. They had been encouraged to keep their fears to themselves. NASA management took the warning seriously and put pressure on its supplier to change its advice, and Morton Thiokol did so.
At a meeting on launch day NASA engineers called for a delay, but a manager told the vice-president of engineering to put on his management hat. Challenger was to launch.
Much changed at NASA after the disaster. Many more people are now consulted over launches and safety is the determining factor. Ultimately, however, one person says yea or nay - a person whose life depends on making the right decision. An astronaut.