WASHINGTON (Reuters) - NASA unveiled its $104 billion plan on Monday to return Americans to the moon by 2018 aboard a capsule-like vehicle the space agency's chief described as "Apollo on steroids."
Like the Apollo program that carried the first humans to the moon in 1969, the new system would put crew members into a capsule sitting atop a rocket, and would have a separate heavy-lift vehicle to take only cargo into orbit.
"It is very Apollo-like ... but bigger," NASA chief Michael Griffin said at a briefing. "Think Apollo on steroids."
The capsule's base would be considerably larger than Apollo's -- 18 feet (5.5 metres) compared with 12.8 feet (3.9 metres) -- and it would weigh about 50 percent more, Griffin said. It would carry six people, instead of Apollo's three, and be able to stay in lunar orbit for six months.
The first human mission to the moon since 1972 would likely take place in 2018, Griffin said, carrying four people for a four- to seven-day stay.
He defended the program's cost, which is expected to spark criticism in light of U.S. commitments in Iraq and areas devastated by Hurricane Katrina. He said the program will cost 55 percent of what Apollo cost, in constant dollars spread over 13 years.
"There will be a lot more hurricanes and a lot more other natural disasters to befall the United States and the world" before the launch in 2018, Griffin said. "... We must deal with our short-term problems while not sacrificing our long-term investments in our future. When we have a hurricane, we don't cancel the Air Force ... and we're not going to cancel NASA."
Sen. Kay Bailey Hutchison, a Texas Republican who chairs a Senate panel on science and space, quickly voiced her support in a statement: "I will do everything possible to keep the shuttle and crew exploration vehicle programs on course."
NASA's Johnson Space Center in Texas controls the U.S. manned spaceflight program and employs thousands.
Another Republican, House Science Committee Chairman Sherwood Boehlert of New York, wondered about the plan's timing in light of the space shuttle program's limited funding.
"There is simply no credible way to accelerate the development of a crew exploration vehicle unless the NASA budget increases more than has been anticipated," he said in a statement.
Charles Lurio, an independent space consultant who strongly favors commercial space exploration, was sharply critical.
"It's painful to watch them propose something that will give you the least human space exploration for the most dollars spent," he said by telephone. "(Griffin) shuffles around the old NASA and old contractor establishment. What is needed is fundamental change to go to the new people on the block."
The new launch system is part of President George W. Bush's 2004 Vision for Space Exploration, which called for a human mission to the moon by 2020 and an eventual trip to Mars and other planets in our solar system.
The new space system is meant to replace the aging and now-grounded shuttle fleet, but would use some shuttle components, including its solid rocket boosters, main engine and massive external tank, Griffin said.
In the meantime, the United States is committed to completing the International Space Station, using the hobbled shuttle fleet.
The shuttles are slated to retire in 2010, but Griffin said the new Crew Exploration Vehicle, as it is known, will not be up and running until 2012, leaving the United States with no way to get people into space on its own.
Asked about the gap, "We're willing to live with it because it is what we believe we can afford, based on the budget which is in play."
Griffin had no answer when asked when the first human mission to Mars would be.
The three shuttles are grounded while experts work to solve problems with falling debris that doomed the shuttle Columbia in 2003. Russian vehicles now ferry people and cargo to the orbiting station.
The next moon mission would get there in several stages, with a cargo vehicle launching to Earth orbit, where it would dock with a later launch of the crew capsule. It would then be propelled to lunar orbit, with a landing craft, whose bottom half is meant to stay on the moon as a long-term base.
Moon voyagers would return to the capsule in the top half of the lander and travel back to Earth, floating down safely with the help of parachutes and airbags to the projected landing site at Edwards Air Force Base in California.