The space shuttle Columbia broke apart as it re-entered the Earth's atmosphere high over Texas, killing all seven astronauts and plunging the nation into a sense of grief not felt since the September 11 2001 tragedy.
The disaster, almost 17 years to the day that seven astronauts were killed in the Challenger explosion, placed the space shuttle programme on hold as investigators began searching a debris field stretching hundreds of kilometres across heavily wooded areas of Texas and adjoining states.
Those killed were the commander of the 16-day mission, Rick Husband, and a team of dedicated professionals that included an Indian-born US woman scientist and the first Israeli in space, Ilan Ramon, the son of Holocaust survivors who had been the lead pilot in the 1981 bombing raid that destroyed a nuclear reactor being built in Iraq.
With the United States jumpy about the countdown to possible war with Iraq and the Israeli astronaut included in the shuttle crew, officials were quick to rule out terrorism. "At this time we have no indication that the mishap was caused by anything or anyone on the ground," NASA administrator Sean O'Keefe said.
Dramatic television images of the shuttle's descent showed several white trails, seemingly tinged with fire, streaking through crystal clear blue skies after the shuttle suddenly fell apart just 16 minutes from home.
The disaster 65 kilometres above the Earth sent thunderous shock waves rolling across eastern Texas.
A grim-faced President George W Bush led the nation in mourning. "The Columbia is lost. There are no survivors," he said in a message broadcast on television. "The crew of the shuttle Columbia did not return safely to Earth but we can pray that they are safely home," the president said.
VIPs who were lined up to greet the returning astronauts at Kennedy Space Center in Florida were led away from a grandstand near the shuttle's landing strip by NASA officials after reports of the break-up. They included Israeli astronaut Ramon's wife and children.
Israelis and Americans watched their televisions in shock as details of the space craft's fate unfolded.
Speculation on the cause of the accident immediately centred on the loss of temperature sensors in the spacecraft's left-wing on re-entry - an area that had been hit by a piece of foam rubber insulation just after the mission's launch.
Officials said they would look closely at the impact of the foam insulation that had struck the orbiter's left wing.
"We lost data and that's when we clearly began to know that we had a bad day," Ron Dittemore, NASA's space shuttle programme manager, said as he fought back tears. "We're devastated."
Dittemore said the insulation came off the fuel tanks at liftoff on January 16 and banged into the spacecraft's left wing, but was judged by ground controllers not to have damaged the orbiter's critical heat shield.
But on Saturday (local time), after the Columbia had re-entered the earth's atmosphere to head home, sensors in the left wing began to fail in a possible indication that excessive heat was seeping into the shuttle structure, he said.
The shuttle's disintegration spread possibly toxic debris over a wide swath of Texas and neighbouring states. The corridor of debris could be toxic because of poisonous rocket propellant.
The disaster came on the heels of the 17th anniversary of the Challenger disaster on January 28, 1986 and in a poignant moment, astronauts on board Columbia had observed a minute's silence in their memory last Tuesday.
The most dangerous moments
Take-off and re-entry into the atmosphere are the most dangerous parts of a space mission. But in 42 years of US human space flight, there had never been an accident during the descent to Earth or landing. Challenger exploded just after take-off.
Administration officials said the shuttle had been way beyond surface-to-air missile range, and no threat had been received targeting the spacecraft.
NASA, which was assembling debris from the shuttle for its inquiry, put future shuttle flights on hold until it had worked out the cause of the Columbia loss.
At the Vatican, Pope John Paul prayed for the dead astronauts during a mass at St Peter's Basilica. Condolences poured in from the leaders of a raft of countries including Britain, France and Germany.
NASA lost contact with the shuttle, which was completing a 16-day mission, at around 1400 GMT (2am Sunday) while it was 63,000 metres above Earth.
"The first indications of a potential problem.... were of the loss of sensors, temperature sensors in the hydraulic systems on the left," Dittemore said at Johnson Space Center.
"They were followed seconds and minutes later by several other problems, including loss of tire pressure indications on the left main gear," he said.
On Friday, NASA flight entry director, Leroy Cain, was asked about possible damage to the left wing of the orbiter which might have occurred on lift-off. He said analyses by NASA engineers had shown any damage to be minor, adding: "We're not working any concerns on the orbiter."
Disaster raises questions about space travel
The accident is likely to raise questions over the longevity of the shuttle fleet as Columbia was NASA's oldest shuttle and first flew in 1981. It was 32 months after the Challenger disaster before NASA flew a space shuttle again.
It also raised questions about the resupply of the International Space Station. The shuttle is the main resupply vehicle for the outpost in space.
Astronauts stranded by events
Three astronauts still on board the ISS are not in any immediate danger, although NASA shuttles have been the main means of transport to and from the station.
"They are not stranded, and if necessary they can be repatriated on board the Russian Soyuz rocket," said Lionel Suchet, an ISS senior official based at the French space agency CNES in the French capital.
The complex always has a three-seater Russian Soyuz vehicle docked to it in case of emergencies.
Russian Nikolai Budarin and Americans Ken Bowersox and Don Petit were due to return to Earth on board the US Space Shuttle Atlantis on March 1, but NASA's halting of shuttle flights until investigators determine what caused the Columbia tragedy puts their return in limbo.
The astronauts have enough supplies to last until the latter part of June without a shuttle visit, said NASA Shuttle Program Director Ron Dittemore in Houston when announcing the halt to shuttle flights.
Bush was grieving for the astronauts but adamant. "The cause in which they died will continue," he said, adding: "Our journey into space will go on."
Besides Husband and Ramon, the Columbia crew consisted of Pilot William McCool, Payload Commander Michael Anderson, Mission Specialist David Brown, Mission Specialists Laurel Clark and Kalpana Chawla, the first Indian-born woman in space.
Nacogdoches, Texas, received one report of the finding of what appeared to be a door from the orbiter.
"We do have a debris field. It is scattered all throughout Nacogdoches," said Victoria Lafollett, city manager of Nacogdoches about 230km northeast of Houston.
A spokesman for Nacogdoches County said jurisdiction over any human remains that are found had been handed to the FBI.
© Reuters
