NASA managers won't decide until April when to reschedule a space shuttle mission that was postponed after hail damaged the craft, officials said.

Golfball-sized hail left thousands of dings on the foam insulation on the space shuttle Atlantis' fuel tank as it sat on the launch pad last month. Postponing a decision on when to reschedule the launch, which was originally planned for last week, will give technicians more time to assess damage, NASA officials said Wednesday.

"We can get some more analysis done; then we will have enough data to make a good decision," said Bill Gerstenmaier, NASA's associate administrator for space operations.

Managers will likely wait until April 10 before deciding whether to use the current tank — which would make a May flight possible — or swap it with another tank, pushing back the launch date until June, Gerstenmaier said.

Technicians at the fuel tank's manufacturer in Louisiana want time to practice applying foam on a mock-up of its nose cone before they apply it in Florida to the real tank, which is still attached to Atlantis and two solid rocket boosters. They also want to test it to make sure the new foam can withstand heat from the launch.

The foam is used to prevent dangerous ice from building up on the tank during fueling on the launch pad.

The space shuttle was rolled off the launch pad and sent back for repairs to the Vehicle Assembly Building. Technicians have spent two weeks erecting scaffolding around the external tank and sanding down some parts of the foam insulation.

The fuel tank has about 2,500 dings, of which 1,600 may need to be filled with new foam. Technicians can sand down some of the other dings — an easier repair.

"If it becomes uncertain that we can make this tank a good tank, then we will swap to a new one," said Wayne Hale, space shuttle program manager. "The whole goal is to have a good tank."

Atlantis' launch has to come after a Russian Soyuz vehicle completes a mission to the international space station in the first part of April.

Despite the delay, Hale said he is confident the space agency can pull off four space shuttle flights this year to continue construction on the international space station. NASA originally had hoped to fly five shuttle missions this year, but the extra flight will be bumped into next year's schedule, he said.

"The overall manifest will have a ripple effect of several months, but we will catch up about the middle to the end of next year," Hale said.

The insulating foam is of special concern to NASA since a chunk of it flew off during space shuttle Columbia's launch in 2003 and struck the orbiter. The damage allowed fiery gases to penetrate Columbia during re-entry, breaking up the craft and killing its seven astronauts.

NASA redesigned the external tank, removing large amounts of foam, before last year's three successful shuttle missions. The space agency plans another design change to the tank before the shuttle program ends in 2010.