NASA plans to redesign the space shuttle's external tank again, this time removing a section of protective foam that broke off during the launch of Discovery last July, an official with the space agency said Thursday.

The removal of more foam from the external tank, and further testing to determine the root cause of cracks on it could lead to a longer delay until the next shuttle flight, tentatively set for May. But NASA official Bill Gerstenmaier said that's not necessarily the case.

Gerstenmaier is leading the investigation into the foam loss.

The troublesome foam section protects a cable tray that runs along the tank. "We think that's the best thing to do, just take it off," Gerstenmaier said.

NASA had redesigned the fuel tank after a large piece of insulating foam hit the wing of the shuttle Columbia in 2003, causing the disaster that killed seven astronauts. The shuttle fleet was grounded after that and again last July after a smaller piece of foam broke off Discovery's tank.

Discovery also lost other pieces of foam in four other areas, including the same spot where a large chunk came loose during Columbia's liftoff.