Discovery is scheduled to blast off as early as May 15. That date is in question because of a critical engineering review and stack of paperwork that still need to be completed. The review is scheduled for Tuesday at Kennedy Space Center, and Griffin will be there with other NASA managers.

"I have no illusions about the fact that I am the person in the chain of command least knowledgeable about the full details of shuttle operation and its readiness for return to flight," said Griffin, who took over NASA on Thursday.

"I will make certain that everyone has given me the most convincing technical arguments on why it's OK to launch - if it is OK to launch - before we commit to going ahead," he told reporters.

The task force overseeing NASA's return-to-flight cannot offer any guidance without the results of Tuesday's design certification review. It had hoped to issue a final opinion on NASA's readiness to launch a full month in advance, no longer possible if NASA holds to a May 15 launch date.

Griffin said he will seriously consider the task force's determination as to whether the space agency has complied with all 15 return-to-flight recommendations put forth by the Columbia Accident Investigation Board. But the launch decision is ultimately NASA's, regardless of what the task force concludes, he said.

Griffin, a rocket scientist with seven degrees, said he will rely on shuttle managers and engineers who have been working since the Columbia tragedy to resolve technical problems.

A chunk of foam insulation from the external fuel tank broke off during Columbia's liftoff and slammed into the left wing, creating a hole that led to the shuttle's breakup during re-entry in February 2003. All seven astronauts on board died. The fuel tank has since been modified to prevent any large pieces of foam from coming off.

Griffin said there is still considerable uncertainty about how effective any repair would be to a damaged shuttle in orbit. "But the clearance for return to flight cannot be simply a 'go' or 'no-go' decision based on, can you repair a tile in orbit," he said.

As for the aging Hubble Space Telescope, Griffin said as soon as Discovery returns from the international space station, he will institute an internal review on sending a shuttle for one final service call to the observatory.

His predecessor, Sean O'Keefe, decided more than a year ago to call off the last mission to Hubble. He refused to reconsider, saying the mission to extend the telescope's life was too dangerous in the wake of the Columbia catastrophe.

         Fixing NASA: Continuing Coverage of Space Shuttle Return to Flight