NASA managers today set May 15 as the target launch date for the first post-Columbia shuttle mission, saying they are confident remaining technical issues, an independent review and a mountain of paperwork can be closed out in time for flight.

Launch director Michael Leinbach said the processing schedule includes about 12 days of contingency time to handle unexpected problems between now and then and "we feel good about that date."

The current schedule calls for engineers to attach Discovery's redesigned external fuel tank to a pair of already assembled solid-fuel boosters around Feb. 25 and for Discovery to be bolted to the side of the tank March 18.

The assembled spacecraft then will be hauled to launch pad 39B on March 25 and the tank will be loaded with supercold liquid oxygen and liquid hydrogen rocket fuel April 7 in a test that will serve as a dress rehearsal for launch.

Commander Eileen Collins and her six crewmates plan to strap in aboard Discovery on April 29 for a practice countdown and if all goes well, the actual countdown will begin May 12 for a launch around 3:50 p.m. on May 15.

Columbia's launch window extends to June 3, based on the orbit of the shuttle's destination - the international space station - and because of a self-imposed requirement to not only launch the first two post-Columbia flights in daylight but also to ensure external tank separation in sunlight for photo documentation.

If NASA can't get Discovery off the ground by June 3 or thereabouts, the flight will slip to mid July. But Leinbach is optimistic it won't come to that.

"After the tanking test is done, the remainder of the pad flow is very standard to us," he said. "And so I'll just tell you, this date feels real good to me."

Fifteen of the 29 recommendations made by the Columbia Accident Investigation Board must be completed before Discovery's return to flight. As of today, only seven of those 15 have been fully addressed to the satisfaction of an independent panel charged with monitoring NASA's implementation of those recommendations.

But on Thursday, panel co-chairman Richard Covey, a Boeing executive and former shuttle commander, said he saw no major roadblocks to closing out the remaining items before the board ends its work March 31. William Readdy, NASA's associate administrator for space operations agreed and told reporters today "we have every expectation we are going to close all of them."

"We have a continuing dialogue with the three panels that they have," he said. "At this point, we really don't see any show stoppers, that's been their commentary all along, so we expect to close all of them."

Major technical questions remain, however, including work to determine how much damage the shuttle's wing leading edges and heat-shield tiles can withstand before repairs are needed.

The Spaceflight Leadership Council, co-chaired by Readdy, met today at the Kennedy Space Center and approved plans to test three rudimentary tile and leading edge repair techniques during Discovery's mission. But those techniques will not be certified before launch and as such would only be used in a true emergency.

Readdy said any repair techniques would have to be tested in space before certification and in any case, the kind of external tank foam debris blamed in the Columbia disaster has been eliminated. Other potential weak spots have been addressed as well.

"Given the depth of inspection that we've gone into in each and every last subsystem and element of the program, I'd be very, very surprised if we had any kind of damage as a result of debris shedding," he said. "We just heard ... a very thorough debrief on the analysis they have conducted. That analysis continues, but I think it should give everyone tremendous confidence that we have done what we needed to to eliminate critical debris from the external tank and other sources on the solid rocket motors."

Combined with efforts to fully characterize the strength of the thermal protection system and improvements in other systems, "we'll be flying much more safely than we ever have before."

Walter Cantrell, deputy chief engineer for NASA's new Independent Technical Authority and co-chairman of the agency's Spaceflight Leadership Council, said the Return to Flight Task Group chaired by Covey and Thomas Stafford has participated in the engineering discussions and understands the processing schedule.

Regarding the open items in the RTF recommendations, Cantrell said "we have received from the Stafford-Covey group their expectations that, if satisfied by us, they could be comfortable in saying that their assessment would be that we have complied with the intent of the CAIB recommendations. Some of them are obviously harder than others because of timing, given that the Stafford-Covey group wants to be able to give its recommendations to the administrator at least one month before return to flight.

"We're in careful contact with them and know what we think we need to do and we know what they think we need to do," Cantrell said. "A significant number of their members participated today, not only listened but actually provided comments during the Spaceflight Leadership Council (meeting), so we're all tracking the same things.

"Our sense of it, and the last sense that we have from them, is there are no show stoppers, we're in very tight agreement on the schedule for closure. Anything can happen, but we do not anticipate that being a problem."

He said NASA had set higher standards "in almost every case" than the CAIB recommendations required and "we're holding ourselves to that raised bar."

"Obviously, we're going to comply with what Stafford-Covey is looking for and what the CAIB is looking for," he said. "But we are the ones who accept the risk and we've set that standard where we think it should be."