Jan 29, 2006, 9:56 GMT
Washington - A small service was held Saturday at the Kennedy Space Centre at Cape Canaveral, Florida, as the U.S. space agency NASA commemorated the seven astronauts killed in the Shuttle Challenger disaster on January 28, 1986.
The 20th anniversary also saw individual citizens visiting the space centre and laying flowers in honour of the Challenger astronauts. A fuel leak caused the spacecraft to explode 73 seconds after lifting off from the Florida launch pad.
Relatives of the dead astronauts participated in the NASA service. There were short memorial speeches and military honours.
Millions of television viewers in the United States and around the world watched in horror as tendrils of smoke from the shattered spacecraft spun into the blue sky and bits of debris rained on the launch area.
Challenger's doomed mission was meant to be a special celebration of human space conquest and boosted interest in the shuttle flight. On board was Christa McAuliffe, the first 'teacher in space.'
The elementary school teacher had planned to hold class from space, and millions of U.S. schoolchildren watched the ill-fated, late-morning takeoff live. The disaster became a shared national trauma for a generation.
A commission that investigated the 1986 accident found that so- called O-ring seals in a joint of the shuttle's solid rocket booster failed after becoming porous in frigid overnight temperatures.
Fuel leaking through the seal caught fire, causing a catastrophic fire that led to the shuttle's fiery breakup, the commission found.
Shuttle flights were suspended for more than two years while NASA boosted safety measures. The programme restarted and ran successfully until 2003, helping to bridge the end of the Cold War in space as Russia and the US joined to build the International Space Station.
The United States plans to end the 25-year-old shuttle programme by 2010 due to safety problems exposed in the 2003 Columbia disaster, a reentry breakup that killed all seven astronauts aboard.
The three remaining space shuttles - Discovery, Atlantis and Endeavour - are grounded because NASA is still fixing the liftoff insulation problems that damaged Columbia and led to the breakup on re-entering the Earth's atmosphere. The next shuttle launch is set for May at the earliest.
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