NASA (search) said Thursday it is pushing the next shuttle flight into 2006 to give engineers time to understand dangerous fuel-tank foam loss and to avoid the string of unrealistic launch dates that preceded Discovery's just-completed mission.

In stinging comments Wednesday, seven members of a return-to-flight oversight group said the best solutions for improving Discovery's (search) safety were not always pursued because of "this false schedule pressure."

They also blasted NASA for still exhibiting many of the same behavioral problems that contributed to the Columbia tragedy, poorly assessing shuttle risks and making the shuttle's return to space more complicated and costly than it needed to be.

NASA Administrator Michael Griffin (search) said he urged the dissenters to "speak their minds" and wanted their views included in the task force's final report, which was issued Wednesday.

"When I was asked the question, 'Do you want to hear this stuff,' the only answer I could ever give would be 'Yeah, I want to hear it,' " Griffin said at a news conference. "We do not shrink in NASA from criticism of our engineering processes, our decisions or anything else. We will listen to it, we'll evaluate and we'll make a decision and we'll move on."

NASA's three remaining space shuttles are grounded as the agency investigates why a large, potentially catastrophic chunk of foam insulation broke off Discovery's fuel tank during liftoff last month — the same problem that doomed Columbia (search) in 2003. Discovery's tank lost sizable pieces of foam from five areas, in fact.

The space agency wants to understand and stop this kind of foam loss before the shuttle flies again.

Bill Gerstenmaier (search), NASA's new space operations chief, said the next mission will not take place before March and will be carried out by Discovery. Atlantis was supposed to fly next, in September, but managers decided to switch spaceships so Atlantis can be ready for a heavy-lift space station assembly mission once Discovery returns.

All three external fuel tanks at Kennedy Space Center (search), meanwhile, will likely be returned to the manufacturing plant in New Orleans for repairs.

Both Griffin and Gerstenmaier said they will avoid setting multiple launch dates for the next mission.

By the time Discovery blasted off July 26 on the first shuttle flight since the Columbia disaster, it had gone through 15 launch dates. Some safety improvements that could have been made were not because of the push to meet a launch date that was always just a few months away, the seven task force members noted in their critique.

"That's why we're going out as far as March and giving ourselves what we hope is plenty of time to evaluate where we are," Griffin told reporters.