Shuttle tank delays push back Hubble mission

HOUSTON (Reuters) - Delays in producing space shuttle fuel tanks, which were substantially redesigned after the 2003 Columbia disaster, will postpone NASA's final servicing mission to the Hubble Space Telescope by a month or longer, officials at the U.S. space agency said on Thursday.

Originally due to launch on August 28, the space shuttle flight to the telescope will be postponed four to five weeks, shuttle program manager John Shannon said.

"We cannot make the August 28 date," he said during media briefings at the Johnson Space Center in Houston.

To fly to Hubble, NASA decided it needed a second shuttle ready to launch in case the ship carrying the crew became too damaged to return home.

Other missions don't require a backup shuttle because stranded astronauts can take shelter in the International Space Station. The orbital outpost will be too far away for the Hubble crew to reach, however.

Needing two tanks ready for launch strained the manufacturing process, Shannon said, adding that it took time for the agency's contractors to learn new assembly procedures following the 2003 Columbia accident.

NASA suspended tank production and grounded its remaining shuttles to investigate why a piece of insulation foam that fell off Columbia's fuel tank during launch triggered the fatal accident.

Investigators determined the debris had hit a heat panel on Columbia's wing, damaging it and allowing superheated gases to flow inside the structure during atmospheric re-entry.

NASA redesigned the tank to minimize foam shedding, added inflight inspections, developed repair kits and set up the space station as a safe haven for shuttle crewmembers.

Shannon said a lot of care had gone into the preparation of fuel tanks since, and it was not a job NASA wanted its contractors to rush.

"I think it's a small price to pay for all the improvement that we're getting on this tank," he added. "It's a much, much better tank than we were flying pre-Columbia. It just took a little extra time."

NASA plans to fly 11 shuttle missions before the fleet is permanently retired in 2010.

All but the Hubble repair mission are devoted to completing the $100 billion space station. The agency's next flight, scheduled for May 31, will deliver the main part of Japan's huge Kibo space laboratory to the station.

The tank delays will also force NASA to bump a sixth mission the agency had hoped to fly this year to early 2009.

(Editing by Michael Christie and Eric Walsh)