By Irene Mona Klotz at Cape Canaveral, Florida

Nasa's boss, Mike Griffin, has mapped out the way ahead Watch Nasa briefing

By failing to incorporate the long-term goals of establishing a permanent base on the Moon and missions to Mars in its new manned space programme, the US space agency is missing a prime opportunity, say critics.

"To be blunt, we have big problems with this plan," Henry Vanderbilt, head of the Space Access Society advocacy group, wrote in an e-mail newsletter.

"It's the same basic approach as Apollo: disposable (mostly) spacecraft, on big Nasa-proprietary boosters, flown a few times a year, by a standing army of Nasa and contractor employees. This is Apollo 2.0."

The plan, outlined by Nasa administrator Michael Griffin on Monday, is based on a new capsule that initially would be used to ferry crews and cargo to the space station.

Like Apollo, Nasa's new plan has built into it the seeds of its shutdown Henry Vanderbilt, Space Access Society

By 2018, however, the spacecraft, with four astronauts aboard, would be routed to the Moon atop a newly developed rocket for the first in a series of lunar expeditions.

The plan leaves open the possibility for developing a permanently occupied base on the Moon, but does not require Nasa to do so.

"Like Apollo, Nasa's new plan has built into it the seeds of its shutdown by some future Congress once the warm glow of the first few daring missions has once again faded," Vanderbilt said.

'Right cast'

Nasa flew a series of missions to the Moon more than 30 years ago as part of its Apollo programme. The project was cancelled in 1972 after just six lunar landings.

Heeding the advice of experts investigating the 2003 Columbia accident, President Bush in January 2004 called for the retirement of the shuttle fleet by 2010, after which time the panel believed the ships would need major re-certifications to continue flying.

Bush proposed redirecting the US human spaceflight programme back to exploration, with the Moon as the first destination.

Some see the vision as merely "Apollo 2.0"

Mars settlement activist and author Robert Zubrin applauded Griffin for coming up with the "the first rational plan in any sense that I've seen from Nasa in decades."

However, he argued, by continuing to spend money on the shuttle over the next five years - even though key missions had not been identified - the agency was wasting billions of dollars that could be used to develop a heavy-lift booster.

The new vehicles were not only key to building lunar settlements and staging manned missions to Mars, Zubrin said, they also could be used to finish building the space station more efficiently and for less money.

The notion that you would be able to launch this programme with a different cast seems incredible Robert Zubrin, Mars settlement activist

"What they're really developing is equipment to do a rational space station and a Moon programme later," said Zubrin in an interview with the BBC News website.

"But if someone comes in (as US president) in 2009 and has no interest, he can just say, 'Thank you for rationalising the space station,' and leave it at that.

"I really don't see that there is a better time to get a Moon programme going than now when there is a president interested in space and an engineer in charge of Nasa. The notion that you would be able to launch this programme with a different cast seems incredible," he added.

'Back on track'

Zubrin argues that the rationale for going to the Moon - to learn how to live off Earth - rings hollow, especially when new technologies and equipment can be tested for a fraction of the cost at a simulated base in the Arctic.

For those who grew up during the Apollo programme, the resumption of Moon flights seems a far cry from where human space exploration could be.

"I can't believe that we're not already living and working on Mars," Elliot Pulham, president of the Space Foundation industry trade organisation, said.

HAVE YOUR SAY It will be wonderful to be able to look up and know that we have dared to explore the unknown once more Mark, Basingstoke, Hampshire Send us your comments

"It's a shame we wasted the past 20 or 30 years, but we do need to get back on track and get on with this sooner or later. I wish we could go faster, but that is not the political and economic reality today."

Unlike Apollo, Pulham argued, the point of the new Moon programme was not to plant a flag and leave. "We're going to the Moon to learn how to do things," he said.

Despite any shortcomings with his exploration blueprint, Griffin expects clear sailing as the plan moves from the White House into Congress for review and funding.

The fatal 2003 Columbia accident and the difficulties returning the shuttle fleet to flight left few if any people calling for the shuttle to remain operational for a decade or longer, as once envisioned.

That leaves the newly proposed Crew Exploration Vehicle as the only option.

"Unless the US wants to get out of the manned spaceflight business completely, this is the vehicle that we need to be building," Griffin said.

(1) A heavy-lift rocket blasts off from Earth carrying a lunar lander and a "departure stage" (2) Several days later, astronauts launch on a separate rocket system with their Crew Exploration Vehicle (CEV) (3) The CEV docks with the lander and departure stage in Earth orbit and then heads to the Moon (4) Having done its job of boosting the CEV and lunar lander on their way, the departure stage is jettisoned (5) At the Moon, the astronauts leave their CEV and enter the lander for the trip to the lunar surface (6) After exploring the lunar landscape for seven days, the crew blasts off in a portion of the lander (7) In Moon orbit, they re-join the waiting robot-minded CEV and begin the journey back to Earth (8) On the way, the service component of the CEV is jettisoned. This leaves just the crew capsule to enter the atmosphere (9) A heatshield protects the capsule; parachutes bring it down on dry land, probably in California