The shuttle's troubles have been numerous: a worn cable, a contaminated motor, a damaged hydrogen tank, and now concerns about the quality of welding on the spacecraft.

The technical problems have delayed its mission to repair the Hubble telescope, which was initially planned for mid-October.

"It is disappointing," said Ron Dittemore, director of the shuttle program. "This is the first time this has ever occurred."

But, officials are being careful to avoid another disaster like the 1986 Challenger explosion that killed six.

"By delaying 24 hours for us to do the homework, to check the quality and the paperwork, really does prove the point, Dittemore said. "I do believe the vehicle is safe to fly."

Late Wednesday, NASA learned of a welding flaw in one of the external tanks of one of its space shuttles.

An inadequate material was used to solder the seams on an enormous tank that contains liquid oxygen and hydrogen under pressure and keeps them chilled at 82 degrees Celsius (180 degrees Fahrenheit). Their combination provides the necessary fuel for the shuttle's engine to power the lift-off.

At the time, NASA called it an "isolated case" that did not affect the Discovery mission.

But on Thursday the agency decided not to take any chances, and delayed the launch for 24 hours. NASA plans to further examine the welding flaw to see if it could threaten Discovery.

Inspectors are scrutinizing the system that carries the oxygen-hydrogen mixtures to the motors as well as the reinforcing rods. Those parts were made in the late 1970s and early 1980s, when the shuttles were built.

The shuttles -- Atlantis, Columbia, Discovery and Endeavour -- were designed to fly about 100 times and have completed about a quarter of that. The first spacecrafts designed to be reused, they are aging, and return from each mission reveals their flaws.

In July, NASA just missed a catastrophe when a two computers short-circuited aboard a shuttle seconds after lift-off. If the backup systems had not taken over, the craft would have been forced to make an emergency landing.

A stripped cable was the culprit. Repairs were ordered when an inspection of the fleet revealed similar problems with other shuttles.

"It was a wake-up call," Dittemore said. "We spent the last four months to inspect, to repair and protect the wiring."

On the Discovery, some 160 kilometers (99 miles) of cables were inspected.

NASA has had a tough year. In addition to the Discovery's problems, an experimental probe and two Martian probes lost, the Hubble telescope out of service and another telescope blinded shortly after being launched.

But the nadir was a conversion error that led to the loss of the 327-million-dollar Mars Climate Orbiter.

NASA's Shuttle Web Center

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Satellite Launch To Boost DTH In India
Calcutta, India (SPX) Dec 28, 2005
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