NASA is hoping to launch the space shuttle Atlantis on the last service call to the Hubble Space Telescope a day earlier than planned to avoid schedule conflicts near its Florida launch site, agency officials said Thursday.

The long-delayed Hubble repair flight, which mission managers have now found to be less risky than initially thought, would lift off on May 11 at 2:01 p.m. EDT if the earlier target is approved next week.

"I feel fairly confident that we can make a May 11 launch date," said LeRoy Cain, NASA's deputy shuttle program manager, during a series of mission briefings. Cain added that after further study, the risk of damage to Atlantis from space debris has fallen within tolerable limits.

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Top NASA officials will decide whether Atlantis and its crew of seven astronauts will be ready to launch early. The mission was previously slated to launch on May 12 from NASA's Kennedy Space Center in Cape Canaveral, Fla.

Launch Date Shuffle

Veteran shuttle commander Scott Altman and his Atlantis crew initially planned to launch toward Hubble in October 2008, but NASA postponed the flight after a serious glitch popped up aboard the space telescope. The astronauts plan to perform five back-to-back spacewalks to install new instruments and make vital repairs to Hubble, which celebrates its 19th birthday tomorrow. The upgrades are expected to extend the space telescope's operational life through at least 2014.

Cain told reporters that by targeting an earlier liftoff, Atlantis would have at least two more chances to launch on May 12 and May 13 before standing down due to a planned military operation at the nearby Cape Canaveral Air Force Station.

If Atlantis cannot launch by May 13, NASA would have wait until May 22 to try again, Cain said.

Preston Burch, NASA's Hubble project manager, said engineers are working around the clock to pack Atlantis with the new instruments, tools and other gear to support the five spacewalks on tap to upgrade Hubble. But only time will tell if they can finish in time for May 11, he added.

"Everything really needs to go our way in terms of completing our installations and hookups," Burch said. "Really, our primarily goal is to get it right, to make sure we don't mess anything up."

Space Debris Risk Revealed

NASA officials initially said that Atlantis and its crew would face a higher than normal risk of damage from space debris, about a 1-in-185 chance, because the shuttle must fly in a higher orbit than the International Space Station to reach the Hubble Space Telescope. Hubble orbits the Earth at about 300 miles, while the space station flies about 220 miles above the planet.

NASA guidelines call for no more than a 1-in-200 chance of damage from debris. After more study, Cain said Thursday that NASA believes the risk to Atlantis is lower, about a 1-in-221 chance, and within acceptable limits. Atlantis will also be moved to a lower orbit soon after its crew releases Hubble back into space in a move to further reduce the risk, he added.

Atlantis also has another backup, the space shuttle Endeavour, which is currently perched atop a second launch pad and standing by to serve as a rescue ship if needed.

Because Hubble flies in a higher orbit and different orbital inclination than the International Space Station, Atlantis astronauts will not be able to seek refuge aboard the orbital laboratory like recent station-bound shuttle crews. Instead, NASA has primed Endeavour and a skeleton astronaut crew to launch a rescue flight and retrieve Atlantis' crew within 25 days of an emergency.

Shuttle flight director Tony Ceccacci told reporters that NASA is confident it will not need any such rescue mission, but will keep Endeavour and its four-man crew on standby "just in case."

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