The U.S. space agency NASA has postponed returning shuttles to flight for two months to give it more time to address safety issues that caused the Columbia disaster in 2003. The first shuttle mission in 2.5 years to the International Space Station is now scheduled for the second half of July instead of May.

NASA is still not satisfied that it has done all it can to prevent a repeat of the Columbia tragedy, when a piece of hard foam insulation peeled off the huge external fuel tank during launch and punched a hole in the wing. This hole allowed extremely hot atmospheric gases to penetrate and destroy the orbiter and kill its seven astronauts minutes before landing.

The new head of NASA, Michael Griffin, says shuttle engineers need more time to make the fight of the orbiter Discovery safe.

William Readdy, NASA's associate administrator for space operations (r)accompanied by NASA's Administrator Michael Griffin, meets reporters in Washington
"This is consistent with our overall approach to return to flight, which is we're going to return to flight, we're not going to rush to flight," he stressed. "We want it to be right."

The main problem delaying the flight was found during a test to fill Discovery's external fuel tank. Technicians saw ice along the liquid oxygen fuel pipe running the tank's length. Liquid oxygen must be kept frigid to prevent it from vaporizing, but in the humid Florida air, this low temperature can cause ice to form. NASA fears it could break off and endanger a shuttle during launch just as the insulating foam did to Columbia.

Deputy shuttle manager Wayne Hale says the potential problem was not discovered until recently because the priority had been to solve the foam shedding problem first.

"We knew that we had three or four more items to work on and we also knew that there was this ice that forms in certain places on the external tank, which we thought was probably not a major concern, but we needed to ensure that," he explained.

NASA engineers will install a heater high on the oxygen fuel line to prevent ice formation, similar to one at another location where foam insulation was removed for safety reasons. In addition, Mr. Hale says engineers are examining some other technical issues, including a few remaining potential foam hazards near the tip of the external tank.

The shuttle Discovery's mission is to supply the international space station, whose assembly has been stopped during the long launch hiatus. Station manager Bill Gerstenmeier says NASA's foreign partners in the venture, Russia, Europe, Japan, and Canada, are disappointed by the two-month delay, but understanding.

"They are willing to do anything that is required and any way they can help out to help return the shuttle safely to flight, they're willing to do their part and do what it takes," he said.

An important piece of hardware the station is awaiting from Discovery is a backup spinning gyroscope for the system that stabilizes the outpost's position in orbit. Only two of four are working, the minimum necessary. But Mr. Gerstenmeier says steering jet maneuvers can do the job if another gyroscope fails. He also says Russian rockets can continue to supply the station with basic goods until the shuttle returns.