NASA (search) estimated Monday it will cost $104 billion to return astronauts to the moon by 2018 in a new rocket that combines the space shuttle with the capsule of an earlier NASA era.

NASA Administrator Michael Griffin (search), in unveiling the new lunar exploration plan announced by President Bush (search) last year, said he is not seeking extra money and stressed that the space agency will live within its future budgets to achieve this goal.

He dismissed suggestions that reconstruction of the Gulf Coast (search) in the wake of Hurricane Katrina might derail the surface. The rockets -- there would be two, a small version for people and a bigger one for cargo -- would come close in height to the 363-foot Saturn 5 moon rocket. They would be built from shuttle booster rockets, fuel tanks and main engines, as well as moon rocket engines. The so-called crew exploration vehicle perched on top would look very much like an Apollo (search) capsule, albeit larger.

"Think of it as Apollo on steroids," Griffin said.

The crew exploration vehicle would replace the space shuttle, due to be retired in 2010, but not before 2012 and possibly as late as 2014 depending on the money available, Griffin said. It could carry as many as six astronauts to the international space station.

If all goes well, the first crew would set off for the moon by 2018 -- or 2020 at the latest, the president's target year.

Unlike Apollo, the new lunar lander would carry double the number of people to the surface of the moon -- four -- and allow them to stay up to a week, or twice as long. It also would haul considerably more cargo, much of which would be left on the moon for future crews.

The Earth-returning capsule would be able to parachute down on either land or water, although land is preferable, most likely at Edwards Air Force Base in California.

Griffin said NASA did not set out to mimic Apollo with the new spacecraft and that many options were considered over the summer.

"It's a significant advancement over Apollo. Much of it looks the same, but that's because the physics of atmospheric entry haven't changed recently," he said. "...We really proved once again how much of it all the Apollo guys got right."

The space agency's ultimate goal is to continue on to Mars with the same type of craft, but Griffin said there is no current timetable for Mars expeditions.

NASA believes the crew exploration vehicle would be far safer than the space shuttle, largely because of an old-style escape tower that could jettison the capsule away from the rocket in the event of an explosion or fire.

Two shuttles and 14 astronauts have been lost over 114 flights, Challenger (search) in 1986 and Columbia (search) in 2003. Nonetheless, NASA puts the existing failure rate for the shuttles at 1-in-220. The failure rate for the crew exploration vehicle is put at 1-in-2,000.