Space shuttle Atlantis nears its launch pad at Kennedy Space Center in Cape Canaveral, Fla., Thursday, Sept. 4, 2008 in preparation for the upcoming mission to the Hubble Space Telescope. Atlantis is scheduled to launch Oct. 8. (John Raoux/Associated Press)

A long journey to the Hubble Space Telescope will expose the space shuttle Atlantis to a greater risk of being hit by a piece of space junk when it launches in October, NASA said Monday.

Space agency shuttle program director John Shannon said the odds of the shuttle having a catastrophic strike with debris orbiting the Earth was 1-in-185, compared to 1-in-300 odds for a mission to the International Space Station.

Most of that increased risk is because of distance; Hubble orbits at an altitude of 569 kilometres, while the space station travels around the Earth at an altitude of about 350 km. There is also more debris farther out, NASA said.

The odds are relative, however, with NASA setting 1-in-200 as the baseline chance for a catastrophic collision with space debris. Shannon said Monday that because the risk to the Hubble mission was greater than that baseline, NASA's top-level executives will need to sign off on the mission.

Atlantis and its crew of seven astronauts are scheduled to launch from Earth on Oct. 8 and travel to the 18-year-old telescope for one final repair before it is retired.

The Atlantis crew will repair and upgrade Hubble to keep it operational until 2013, when NASA hopes Hubble's successor, the James Webb telescope, will be sent into orbit.

Under the Hubble mission plan, NASA needs a second shuttle waiting to launch at Kennedy Space Center in case of an emergency. It's a situation unique to the Hubble mission, as the shuttle and telescope will be too far from the International Space Station for it to provide shelter if the shuttle was damaged.

With files from the Associated Press