Washington - Even today, 20 years later, debris occasionally washes up on Florida's coasts from a U.S. space disaster that counts as one of the 20th century's most tragic events.
On January 28, 1986, little more than a minute after launch, the space shuttle Challenger turned into a ball of fire that consumed it and killed all seven astronauts on board, sending tendrils of smoke shooting out of control and bits of debris raining down against the bright blue sky over Cape Canaveral.
Millions of television viewers in the United States and around the world watched in horror when the disaster occurred 73 seconds after lifting off from Kennedy Space Center.
After five years of successful, almost routine, shuttle flights starting in 1981, the true dangers of space travel finally hit home. It would take years for the shock waves to subside and the public to begin enjoying shuttle launches without holding its collective breath.
Seventeen years later, the public was again brought up sober to those dangers when the Columbia shuttle disintegrated on re-entry into Earth's atmosphere, handing another setback to the National Aeronautics and Space Administration (NASA) and its human space flight programme.
The launch of the Challenger on January 28, 1986, was no ordinary launch - precisely because of the ordinariness of one of its passengers, teacher Christa McAuliffe, the first participant in a new NASA 'teacher in space' programme.
The 38-year-old elementary school teacher from New Hampshire had been selected from more than 11,000 applicants. The intent was to find a gifted teacher who could communicate with schoolchildren while in orbit. She had planned to hold class from outer space.
Her presence onboard also was meant to make space flight more tangible for the public, to rekindle a pioneering spirit in the exploration of space and to create a sense of unity in astronomical research.
But instead, people were united only in their grief over the loss of the young hero. Today there are numerous schools and at least one planetarium in the United States named after her, along with an asteroid and a crater on the moon. There's also a memorial to the Challenger astronauts at Arlington National Cemetery.
'Challenger, go with throttle up,' said James D. Wetherbee of mission control in Houston about 11:39 A.M.
'Roger,' replied astronaut Francis 'Dick' Scobee, 'Go with throttle up.'
Those were the last words heard on the ground from the shuttle.
Then suddenly a small flame appeared on the underside of the outer fuel tank with 2 million litres of liquid hydrogen and oxygen. It grew into a blaze to the right side of the tank, burning even stronger. Audiotapes in the shuttle's on board computer recorded the bang of an explosion.
A spokesman in mission control who apparently couldn't see a television screen continued giving flight data: '2,900 feet per second, altitude 9 nautical miles, downrange distance 7 nautical miles.'
The first indication that something was wrong came from that spokesman, who reported, 'a major malfunction.'
At 11:40 a.m. the spokesman's words signaled the gravity of the situation: 'We have no downlink,' he said, referring to communications from the Challenger. 'We have a report from the flight dynamics officer that the vehicle has exploded.'
The mission had been intended to last six days and 34 minutes. It was over in 73.621 seconds.
President Ronald Reagan postponed the state of the union address that evening before Congress. Instead he spoke to the nation via television from the White House, calling the astronauts and McAuliffe heroes. The nation mourned as millions participated in nightly vigils.
Americans had not been so moved by an event since the assassination of President John F. Kennedy.
A commission that investigated the accident found that the so- called O-ring seals in a joint of the solid rocket booster failed after becoming porous in cold overnight temperatures. Fuel that leaked through the seal caught fire, leading to what NASA described as a 'full structural failure'. <!--page-->
Technically, the shuttle did not really explode - the all- consuming fire caused it to rapidly disintegrate, the commission found.
Shuttle flights were suspended for more than two years while numerous safety measures were implemented.
NASA was at a low point, but it recovered, and the shuttle programme restarted and ran successfully until 2003, helping to bridge the end of the Cold War in space as the U.S. and Russian space programmes joined to construct the international space station.
After the second major tragedy in 2003, when the Columbia and its seven astronauts were destroyed over Texas, NASA has only flown one shuttle to the space station - and put the programme on hold again because of tears in the heat shield similar to those blamed for the Columbia crash.
Meanwhile, the space station programme relies on the aging Russian Soyuz and Progress vehicles to transport humans and materials back and forth.
© 2006 dpa - Deutsche Presse-Agentur 
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