Nasa, the US space agency, has given the first details of its plans to set up a permanent human settlement on the moon by 2024, as the first part of a scheme for manned exploration of Mars and beyond in the solar system.
The project, first outlined by President George Bush almost three years ago in a speech outlining America's space ambitions, would return a man to the moon for the first time since the Apollo 17 mission of December 1972. That stay lasted just three days.
Under the new programme, beginning in 2020, astronauts would make stays of a week. These would be gradually lengthened, so that within four years the base would be permanently manned, with astronauts living on the base for six-month stretches.
The chosen site will be at or near one of the moon's poles, probably the south pole, because of the long periods of sunlight those regions enjoy.
That would permit solar power generation, and the production of electricity, in keeping with Nasa's aim of "living off the land". The south pole has a special attraction: the suspected nearby presence of key elements, most notably helium-3, a lighter form of the gas that can be used for nuclear power. There have also been some signs that deep craters could contain ice, which would provide water and fuel.
The moon base, said Scott Horowitz, NASA's director of lunar exploration, "will be a central theme in our plan for going back to the moon, in preparation to go to Mars and beyond". He added that agency scientists knew less about the lunar poles than they did about Mars, although the moon was only 250,000 miles from Earth.
The rockets and landing capsules - the Ares I and Orion programmes - which will ferry astronauts back and forth will be exclusively American, Nasa said. But the agency wants to bring in other countries, including Britain, India, Russia and China, as well as the European Space Agency. The key question, unanswered by Nasa officials this week, is how much the base might cost. Unofficial estimates put the price tag at around $100bn (£50.8bn), compared with Nasa's present annual budget of $18bn.
But costs will be spread over two decades, and the agency hopes to offset part of the bill by attracting private sector investment. The total cost of sending a man to Mars will be far higher however, at least $600bn (£304bn).
The US also appears determined to avoid the problems that have plagued the still uncompleted international space station, by bringing other countries into the process at an early stage. Contacts with key partners have already been made, and a conference is scheduled for early 2007.
Nasa claims the end of the Shuttle programme in 2010, and the winding-down of the space station, mean that the lunar base can be funded within existing budget ceilings. But critics dispute that, arguing that less high-profile but highly valuable scientific programmes will have to be scaled back, if the agency is to avoid going cap in hand to Congress for extra money.
The programme appears to have broad support on Capitol Hill, even with Democrats in charge from next month. The hope is that the public interest in space will be rekindled by the prospect of men actually living on the moon.