NASA, the American space agency, has unveiled plans for one of the largest rockets ever built to take a manned mission to the far side of the moon.

It will ferry a mother ship and lunar lander into Earth orbit to link up with a smaller rocket carrying the crew. Once united they will head for the moon where the larger ship will remain in orbit after launching the lunar lander and crew.

The design emerged during a space science conference in Houston, Texas, last week. The plan is part of Nasa’s “Return to the Moon” programme set in motion by President George W Bush two years ago.

Under the project, up to four astronauts at a time will land on the far side of the moon to collect rock samples and carry out research, including looking for water that might one day support a lunar base.

The scale of the missions is much larger than the earlier Apollo programme, which is why Nasa will need two separate rockets to take the mother ship and crew into space.

Some missions will also see manned spacecraft landing in unexplored areas such as the lunar mountains and on the moon’s south and north poles.

John Connolly, manager of Nasa’s lunar lander project, said the system was designed to carry crews to almost every part of the moon’s surface.

“The samples they collect and the research they carry out will help solve many mysteries about the origins and composition of the moon and its suitability as a base,” he said.

The Apollo programme carried out six lunar landings between 1969 and 1972. The feat was a triumph, but the technical limitations of the Apollo craft, plus ignorance of lunar terrain, meant all six missions had to be sent to the moon’s plains.

These regions, all on the near side of the moon, were the only areas known to be flat enough for a safe landing. This has frustrated scientists because the samples collected by the six missions are all similar. They are also thought to be younger than lunar mountain rocks.

The far side — so called because it always faces away from the Earth — was first photographed in 1959 by a Russian probe. In 1968 the astronauts of Apollo 8 became the first to view it directly.

The evidence gathered by such missions was enough to deter any attempt to land because most of the far side appeared to be covered in large craters. Additionally, any craft landing there would be cut off from radio contact with Earth.

Connolly believes, however, that Nasa will be able to overcome such problems by sending a series of robotic probes ahead of the manned missions.

The first of these, the Lunar Reconnaissance Orbiter, to be launched in 2008, will map the moon’s surface in detail.

Cameras will photograph the surface, backed by a laser altimeter to create a three-dimensional relief map from which Nasa can identify landing sites.

Then, from 2010, a series of “companion lander” missions will carry out test landings on selected sites to see if they are worth a visit by humans.

The final element will be a system of communications satellites, dubbed the “lunar internet”, so astronauts will be able to relay signals to Earth from any part of the moon.

Connolly said the first humans could arrive as early as 2015, although 2018 was more likely. The agency would then aim to send two crews to the moon each year for up to five years. The programme will cost around £56 billion and may also be used to test technology for any future mission to Mars.

Some have questioned whether the programme will produce enough good science to justify the costs.

Manuel Grande, head of the planetary science group at the Rutherford Appleton Laboratory in Oxfordshire, dismissed such fears. “Finding out more about the moon will help us understand where the Earth and moon came from,” he said. “There do not have to be good scientific reasons . . . It’s like going up Everest; we want to go to places like the moon and Mars just because they are there.”

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