NASA postpones first mission since Columbia because of ice problem

CAPE CANAVERAL, Fla. -- NASA on Friday pushed back the first post-Columbia space shuttle flight by at least two months, after last-minute analyses suggested that ice falling off the fuel tank could prove as catastrophic as the foam that doomed the last mission two years ago.

Discovery is now set to fly in mid-July, assuming engineers can perform the necessary repairs to eliminate the danger. The flight had been scheduled for late May.

The plan calls for installing a heater along a 70-foot liquid-oxygen pipe that runs along the tank.

The decision followed a flurry of launch-debris reviews in recent weeks that found to NASA's surprise that ice forming on certain unprotected spots on the tank could prove a potentially deadly source of shrapnel during liftoff.

Because it was a 1 1/2-pound chunk of fuel-tank foam insulation that damaged Columbia's wing and led to the spacecraft's destruction during re-entry in February 2003, NASA had focused on keeping large pieces of foam from coming off during launch. Ice -- the normal result of the tank being filled with super-cold fuel -- was considered less threatening and therefore less important for analysis.

Once ice began looming as a bigger threat, NASA hurriedly conducted tests and data analyses that concluded, just in the past few days, that even small, slushy patches of ice could fly off the oxygen feedline and strike the shuttle with deadly force. Engineers did not believe before that ice shards would actually hit the shuttle.

The shuttle team is dealing with a few other unrelated problems with Discovery, involving balky engine-cutoff sensors in the fuel tank. The extra two months will give NASA time to solve those problems.

Discovery and its crew of seven have from July 13 through July 31 to lift off. Otherwise, the 12-day supply and repair mission to the international space station will have to be put off until September.

The two-week launch window is dictated by both the position of the space station and NASA's insistence on launching Discovery in daylight, to provide good photographs of the shuttle that can be examined for any liftoff damage.

Griffin said he wants to launch as soon as possible. "Schedule matters," he said, referring to the need to finish building the space station. But he added: "It shouldn't matter to the point of causing people to do dumb things or to take ill-advised actions."

Station program manager Bill Gerstenmaier said the orbiting complex should be able to keep flying safely until Discovery gets there, even though the main oxygen generator is broken and the steering system is operating with the bare minimum number of working gyroscopes.

The shuttle fuel tank has already gone through extensive modifications since the Columbia catastrophe. NASA changed the way it applies some of the foam to the tank, and removed large sections of foam from certain trouble spots. Then heaters were installed to prevent ice from forming at those areas.

But the newly recognized ice problem involves expansion joints that have always been left bare, because insulation would only fall off the moving hardware.

Before the postponement, NASA devised a foam skirt, or "drip lip," to wick moisture away from those joints. Engineers believe it would reduce ice formation by 50 percent. But Parsons and others decided a more comprehensive repair was needed.

Parsons said more testing is needed on the heater that will be installed, and warned there is no certainty it will be a sure fix. Less-desirable options include putting infrared lamps near the launch pad to melt any ice, or putting gel in the joints and then covering that with shrink wrap.

The shuttle team is dealing with a few other unrelated problems with Discovery, involving balky engine-cutoff sensors in the fuel tank. The extra two months will give NASA time to solve those problems.

---

On the Net:

NASA: www.nasa.gov