NASA (search) on Friday delayed by another two months the first space shuttle flight since the Columbia (search) disaster, saying it needs more time to ensure that the fuel tank does not shed dangerous pieces of ice at liftoff.

Discovery (search) is now scheduled for launch no earlier than July 13. The flight had been targeted for late May.

A large chunk of foam insulation from the external fuel tank punched a hole in Columbia's wing that led to the shuttle and crew's demise during re-entry in February 2003. Now, the lingering concern involves the possible buildup of ice on the tank once it's filled with super-cold fuel, and the hazard such shards would pose if they came off during the launch and hit the shuttle.

NASA's new administrator, Michael Griffin (search), announced the delay at a midmorning televised news conference, saying it was the result of recent launch-debris reviews.

"This is consistent with our overall approach to return to flight, which is that we're going to return to flight. We are not going to rush to flight, and we want it to be right, so we're doing what we need to do to ensure that," Griffin said.

Extra repairs to Discovery's fuel tank will be needed, namely the addition of a heater, said NASA's top spaceflight official, Bill Readdy (search).

The work means that NASA will have to remove Discovery from the launch pad and return it to the massive Vehicle Assembly Building.

The prime area of concern is a 17-inch-diameter liquid oxygen line that runs 70 feet down the lower half of the 154-foot tank. Its expansion joints have produced ice in the past. After the Columbia accident, NASA devised a foam skirt, or so-called drip lip, to wick moisture away from the joints. Engineers believe it would reduce ice formation by 50 percent.

Shuttle managers decided a more comprehensive repair was needed.

Technicians will install a heater at the uppermost joint, something already planned for flights beyond Discovery's. To add the heater on Discovery, the shuttle will have to be hauled back to its hangar, which will add days if not weeks to launch preparations.

NASA is also concerned about possible ice formation on the brackets that hold the oxygen line to the tank.

The shuttle team is dealing with a few other unrelated problems with Discovery, involving balky engine-cutoff sensors in the fuel tank and thermal blankets contaminated recently with hydraulic fluid. Readdy said the extra two months will provide time to resolve all of these issues, and they will be tackled first while the shuttle is still at the launch pad.

Another fueling test of Discovery's tank may be necessary, Readdy said. The test a month ago ago uncovered the intermittent sensor trouble and a few other problems.

Griffin said he accepted shuttle managers' recommendation to postpone the flight, to perform the extra work.

"I want to launch as soon as we can," said Griffin, who took over the top NASA job just two weeks ago. But he added that he wants the launch to be safe.

"Schedule matters," he said. "It shouldn't matter to the point of causing people to do dumb things or to take ill-advised actions ... We want to launch Discovery when we can because the completion of the international space station depends upon an expeditious launch schedule. We don't want to launch it sooner than we can."

Columbia was brought down on Feb. 1, 2003, by a gash in the left wing that was caused by a suitcase-size piece of foam that broke off the tank during liftoff. All seven astronauts were killed 16 days later during re-entry.

NASA wants the first two post-Columbia launches held in daylight to ensure good photography of the shuttle and its fuel tank, which has been modified to prevent big pieces of foam insulation from coming off. Daylight also is needed over the North Atlantic in order to capture good photos of the fuel tank as it drops off eight minutes after liftoff.

The July window extends from July 13 until July 31. If Discovery does not fly in July, the next opportunity would come in September. The 12-day mission will supply much-needed supplies and replacement parts to the space station.