NASA's senior spaceflight officials decided Thursday evening to push back the next launch to March 2005 because of lingering work and engineering concerns, and picked Discovery to be first up.
The space agency had been aiming for a fall 2004 launch.
"We said, 'Stop. Let's go ahead and extend the schedule and let's figure out what the right way is to go about'" meeting the recommendations of the Columbia accident investigators, said NASA Administrator Sean O'Keefe. "We're not going to be driven by the calendar. This is going to be a milestone-driven event."
The delay will give engineers more time to develop in-flight repair procedures and to take advantage of more favorable launch windows, reports CBS News Space Consultant Bill Harwood. The slip also will give NASA and its contractors time to resolve problems with actuators in the shuttle's rudder and speedbrake assembly in the ship's vertical tail fin.
At the same time, engineers continue to refine plans to have a second shuttle ready for launch on an emergency rescue mission in case something goes wrong during Discovery's flight. In that case, commander Eileen Collins and her crew could be forced to seek "safe haven" aboard the international space station until a rescue flight could be attempted.
NASA plans to process a second shuttle that could be rolled to the pad and launched within 70 days of notification, assuming a three-shift around-the-clock work flow and no waived requirements, sources said. The flow possibly could be shortened to 35 days in a crisis.
The rescue flight, known as STS-300, would be crewed by four of the six astronauts already assigned to mission STS-115, the third flight in NASA's post-Columbia launch sequence. The STS-115 crew is made up of commander Brent Jett, pilot Chris Ferguson, Joe Tanner, Dan Burbank, Steve MacLean and Heidemarie Stefanyshyn-Piper.
The mission would feature a normal rendezvous and docking with the space station.
Michael Kostelnik, deputy associate administrator for the shuttle and station programs, told reporters the space station could support a stranded shuttle crew for up to 90 days and possibly longer if required.
With Discovery now slated for the first post-Columbia mission, the shuttle Atlantis will serve as the STS-300 "launch-on-need" vehicle.
"I don't believe there's an awful lot of extra training or extra things we have to do for a rescue mission," said Bill Parsons, shuttle program manager. "Overall, it would be very similar to an STS-121 mission. It would be going to the international space station, docking, picking up crew, making sure we had the appropriate hardware and things we needed to bring that crew on board and then returning safely."
NASA managers are still talking about how to pull off a rescue if a damaged shuttle can't reach the space station, or if it's damaged after it leaves there, reports CBS News Correspondent Peter King.
In the case of Columbia, such a rescue would have been impossible. The shuttle did not visit the space station; it was in a different orbit than the station and lacked the fuel to get there.
Any shuttle sent to Columbia's aid would have had to fly in formation, and spacewalks would have been needed to transfer Columbia's seven astronauts to the rescue ship.
The shuttle fleet has been grounded and space station construction on hold since Columbia shattered over Texas on Feb. 1, 2003.
NASA managers originally said they hoped to launch the first post-Columbia flight this March or April. But last October, the target was pushed back to a launch window that opened around Sept. 12 and closed Oct. 10.
A variety of factors conspired to push the flight into 2005, including work to minimize foam shedding from the shuttle's external fuel tank and development of tile and wing leading edge repair materials and techniques. Other "long poles" include development of a camera and laser sensor package needed for in-flight inspection of the ship's thermal protection system.
Tile repair development is "going as well or better than expected," Parsons said Thursday. Wing leading edge repair is "not as mature as the tile repair, but it is coming along."
Another complicating factor is a photo documentation requirement to have daylight lighting for both launch and external fuel tank separation to determine whether any large pieces of foam separated from the tank and, if any did, whether the shuttle suffered any damage. The lighting requirement, combined with thermal constraints at the space station, translated into very limited launch windows through early 2005. After the September window, NASA had just three available days in November, none in December and three in January.
NASA now plans to target a launch window that would open around March 6, 2005, and extend into early April. But a Russian Soyuz crew transfer flight is scheduled for launch around April 10 and flight rules forbid launching a shuttle within 13 days of that date. As a result, NASA will have until roughly the end of March to get Discovery off the ground during that window.
The STS-121 mission is tentatively targeted for launch in May 2005.
CBS News Space Consultant William Harwood has covered America's space program full time for nearly 20 years, focusing on space shuttle operations, planetary exploration and astronomy. Based at the Kennedy Space Center in Florida, Harwood provides up-to-the-minute space reports for CBS News and regularly contributes to Spaceflight Now and The Washington Post.