Continuing the U.S. space shuttle program past its planned retirement in 2010 would cost $3 billion US a year, says NASA's chief.

Administrator Michael Griffin told an industry group Thursday the space agency has looked into what it would cost to keep the aging shuttle fleet past 2010, but said such a plan would also pose potential dangers, as shuttle flights are inherently risky.

"We would have a one-in-eight chance of losing the crew in one of the 10 flights," Griffin said, basing his estimate on the current risk, about 1 in 80, of a shuttle accident with each flight.

NASA is retiring the shuttle fleet to concentrate on developing a new spaceship capable of heading to the moon, part of an ambitious space plan set out by President George W. Bush.

The new spaceship, a capsule called Orion that will launch from a rocket called Ares 1, is not expected to be ready until 2015 at the earliest.

The concern for NASA is how to send its astronauts to the International Space Station in the five years after the shuttle fleet retirement.

Plan to piggyback on Russian rockets

NASA is mulling a plan to piggyback its astronauts aboard Russian Soyuz rockets, and has handed out contracts to two private space firms to deliver cargo to the space station — normally carried aboard shuttles — after 2010.

President-elect Barack Obama has proposed delaying the shuttle's retirement as an alternative plan.

Griffin said there are geopolitical reasons for extending the shuttle fleet. But he also said spending an additional $3 billion could move the date of the Orion spaceship launch a year earlier.

NASA has not broken down the cost of its astronauts hitching a ride aboard the Russian ships, but the space agency's last budget calls for cargo costs to rise from $100 million in 2008 to $422 million in 2011 and $751 million in 2012.

The space agency plans to release an official study on what extending the shuttle program would entail later this month.

There are nine flights scheduled through May 31, 2010, for the remaining three shuttles — Endeavour, Atlantis and Discovery.

Tight schedule

All but one of those missions is to the space station; the other is to the Hubble Space Telescope.

The tight schedule is further complicated by the planned timing of the Hubble mission.

NASA's current schedule calls for Atlantis to launch from the Kennedy Space Center in Florida on May 12.

But the space agency schedule calls for Endeavour — bound for the space station — to launch three days later from the same launch pad, a virtually impossible task given the preparation required before a vehicle can launch.

NASA has yet to reschedule either mission.

Canadian astronaut Julie Payette is scheduled to fly on the May 15 Endeavour mission to the space station.

With files from the Associated Press