SAN FRANCISCO (AFP) -- Astronauts could be trained to cross-country ski across the surface of the moon as preparations for the next generation of lunar missions take shape, a conference heard.

The National Aeronautics and Space Administration (NASA) announced plans last year to build a base on the moon by 2020, hoping to use the lunar outpost as a launchpad for exploring the solar system in future generations.

Apollo 17 astronaut Harry Schmitt said that future inhabitants of the moonbase should be taught Nordic skiing to travel around the moon, where lower gravity means large distances can be covered with minimum effort.

"If I was running the astronaut office I certainly would recommend cross-country skiing, yes," Schmitt told reporters during a presentation at the American Association for the Advancement of Science annual meeting.

"If you've ever done cross-country skiing you know that on a level surface once you get a rhythm it is very easy to move quickly over large surfaces," said Schmitt, one of the last two men to set foot on the moon in 1972.

"Of course on the moon you don't slide, you glide above the surface, but again you use the same kind of rhythm. "There's nothing to restrict how far you eventually go or how fast you go, other than your own strength."

Schmitt said cross-country skiing should be seriously considered because it would increase the "walk-back" distance, allowing astronauts to wander farther away from their starting point. "On Apollo 17 we had a walkback distance of seven kilometers (four miles) ," Schmitt said. "I think that could have been increased by a factor of two."

"Cross-country skiing is the best way to move rapidly and easily across the surface of the moon without expending much energy. It's like skating across a giant trampoline," he said.

Schmitt was sent to the moon as a geologist to gather and analyze rock samples from the surface. "I took beer and crackers with me just in case we discovered that the moon was made of cheese after all," he quipped.

The plan unveiled by NASA in December envisages a manned base possibly on the moon's south pole by around 2020, powered by sunlight and perhaps hydrogen and oxygen.

The colony would enable scientific research that could lead to eventual industrial ventures, processing rocket fuel and other products from oxygen or other materials that might be found beneath the moon's surface.