Giant Steps: Are we heading for more footsteps on the moon?

Man hasn't set foot on it for decades but Nasa is now confident that a moonbase could be operational by 2020, leading to the manned exploration of Mars. Steve Connor reports

Rocket scientists at Nasa have identified the lunar south pole as the best probable landing site for the next manned mission to the Moon. They believe it is a prime location to build a permanent lunar base because some of its deep craters may harbour frozen reserves of valuable water.

Nasa, the US National Aeronautics and Space Administration, is developing a plan to send people back to the Moon half a century after it was first visited by Apollo astronauts.

Only this time Nasa intends to stay on the Moon by building a lunar base permanently manned by astronauts who will help prepare the groundwork for an even more ambitious manned mission to Mars.

Nasa is keen to act on the directions of President George Bush who said in January 2004 it was time for the US to return to the Moon, set up a permanent outpost and even use it as a launch pad to send man to Mars.

But the key to a permanent base is water, not just because it can sustain life but also because it can be split into its constituent parts - hydrogen and oxygen - for use as rocket fuel.

Nasa announced this month it will explore the lunar south pole with an extra module or satellite it has decided to add to its 2008 exploratory mission to the Moon, the first to involve a new rocket system. The extra payload or satellite is designed to analyse the plume of material caused by a high-speed impact into a south-pole crater. Some craters are so deep they are in permanent shadow which means if any ice from a passing comet fell into them, it would not have melted or vaporised.

Nasa said the extra craft will be designed to direct the used upper stage of a lunar rocket so that it crashes into a crater. The satellite will then observe the plume and even fly through it several times with instruments designed to detect and analyse trace amounts of water.

Then the satellite will itself become an impactor, creating a second plume visible to a lunar-orbiting spacecraft and observatories on Earth which could analyse the ejected material for water, explained Scott Horowitz, a Nasa scientist.

"This type of payload is not new to Nasa. We are taking advantage of the payload capability of the launch vehicle to conduct additional high-risk, high-pay-off science," he said.

The 2008 mission to the Moon will be the first of many robot missions that will culminate in a manned lunar landing between 2018 and 2020, the first since Apollo 17 in 1972.

"Apollo was restricted to landing sites along the Moon's equator. Our new systems let us land anywhere on the Moon's surface," a Nasa spokesman said.

"Scientists consider the lunar south pole a good landing site because researchers believe that the area has elevated quantities of hydrogen and possibly water ice that can be used in a habitat environment."

Nasa is developing a new generation of space vehicles from the best features of the heavy-lift engines used in the Apollo programme - notably the giant Saturn V rockets - and the reusable elements of the Shuttle, which is due to be retired by 2010.

At the heart of the new concept is a manned capsule much like the one that took the Apollo crew to the Moon, only this time it will be three times as spacious and be capable of carrying a crew of six rather than three.

The capsule is designed to orbit the Moon automatically without a crew while its lander vehicle carries the astronauts to the lunar surface.

Initially, missions on the surface will last four to seven days but once a lunar outpost is established, the astronauts could stay on the Moon for six months.

The crew capsule is designed to be reused 10 times and Nasa is incorporating an escape rocket on its nose so that astronauts will be ejected to safety if a problem develops on the launch pad.

Nasa is also planning to have a manned version of the rocket - called the Crew Launch Vehicle - ready in five years to ferry people and supplies to the International Space Station. A separate, heavy-lift version of the system - the Cargo Launch Vehicle - will take up to 125 tons of supplies and material to the Moon to build a permanent base.

"With a minimum of two lunar missions a year, momentum will build quickly toward a permanent outpost," Nasa said. "Crews will stay longer and learn to exploit the Moon's resources, while landers make one-way trips to deliver cargo. "A sustained presence will show we can survive on another world by living off the land and will build confidence that we can venture still farther and stay for longer periods."

Mission to the moon

1 A heavy-lift Cargo Launch Vehicle blasts off from Kennedy Space Centre in Florida carrying a lunar lander and a "departure stage", needed to propel the crew beyond the Earth's orbit.

2 Once the Cargo Launch Vehicle is safely in orbit, the crew will be launched separately in the smaller Crew Launch Vehicle which has extra safety features.

3 The two vehicles dock and, once the "departure stage" is connected, the crew and their capsule are propelled out of the Earth's orbit and on to the Moon.

4 Three days later, the crew go into lunar orbit, having safely ejected the "departure stage" rockets. The crew climb into the lunar landing vehicle which is jettisoned down to the surface of the Moon.

5 Once their lunar mission is complete, the crew blast off from the landing vehicle, carried by an ascent capsule that takes them back to the orbiting lunar module. Once safely aboard, the capsule takes them back to Earth.

6 The capsule lands over water or lands on Earth with the help of parachutes. Its heat shield can be replaced and the capsule reused up to 10 times.