CAPE CANAVERAL, Fla. -- A three-day countdown to the planned launch this week of shuttle Discovery is scheduled to pick up Monday at Kennedy Space Center, but a potentially serious booster rocket problem still could delay its flight to the International Space Station.
Discovery and a quartet of astronauts remain scheduled to blast off at 5:38 p.m. EDT (2138 GMT) Thursday on a mission to taxi a new crew to the station and then return to Earth with current outpost tenants Yuri Usachev, Susan Helms and Jim Voss.
The four shuttle astronauts and their passengers flew to KSC Sunday despite an ongoing investigation into a suspect fuel injector within a hydraulic power unit on one of two solid rocket boosters that will help propel Discovery into orbit.
"We've very happy to be this close to launch, and very happy to be here in Florida and getting started with it," said incoming station commander Frank Culbertson, a U.S. astronaut destined to spend four months on the outpost with Russian cosmonauts Vladimir Dezhurov and Mikhail Turin.
"It's been a long time coming."
Senior NASA managers, however, still might delay the Discovery launch until Aug. 15 or later.
Engineers earlier this week discovered cracks within the fuel injector of a hydraulic power unit that that last flew on a 1997 shuttle mission to Russia's Mir space station.The hydraulic power unit on Discovery's left-hand solid rocket booster, meanwhile, is outfitted with a fuel injector that was built during the same manufacturing run, raising concerns about whether it is fit for flight.
The device regulates the flow of fuel needed to drive a turbine within the unit, which provides the hydraulic power that enables a booster nozzle to be steered in flight.
NASA engineers, consequently, are concerned that a cracked injector stem could interrupt fuel flow, triggering booster steering problems during the critical initial minutes of Discovery's flight.
The shuttle's reusable boosters are jettisoned two minutes into flight and then fall into the Atlantic Ocean where they are recovered and refurbished for future flights.
Engineers now think the damaged injector was bent during routine ground processing, creating five cracks within the tube-like line, which is the size of the ink cartridge in a ballpoint pen. Injectors not subjected to that type of damage should be safe to fly, engineers believe.
"That's the prevailing theory," said Rob Navias, a spokesman for NASA's Johnson Space Center in Houston, Texas.
Manufacturing, launch processing and inspection records show that the fuel injector within the suspect hydraulic power unit on the Discovery's left-hand booster is not bent.
NASA on Sunday inspected 37 other fuel injectors -- half of which were from the same manufacturing lot of the damaged part -- and found one that had unusual internal markings.
A second inspection of that fuel injector will be carried out Monday before NASA makes a decision on whether to replace the hydraulic power unit on Discovery's left-hand booster.
Any replacement work likely would take 8 to 10 days, pushing Discovery's planned launch back by almost a week.
In that case, the postponed launch of a Delta 2 rocket and NASA's Genesis solar science satellite -- now slated for Aug. 12 -- might be moved up to Wednesday or Thursday.
Senior managers will regroup at 2 p.m. EDT (1800 GMT) Monday to discuss the status of the fuel injector investigation. The launch countdown, meanwhile, remains scheduled to pick up at 5 p.m. EDT (1700 GMT) that day.
A launch Thursday would result in a docking two days later at the international station. With the station's current crew in tow, the shuttle astronauts would return to Earth on Aug. 21.
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