Future lunar explorers may set out from their base at one of the moon's poles for long-distance surface sorties in pressurized rovers hardened against the galactic cosmic radiation that makes extravehicular activity (EVA) dangerous to their health in the long run.

NASA Administrator Michael Griffin has given his OK to refinements in his agency's lunar-surface architecture -- the set of broad concepts that will drive development of the hardware human explorers will use in the decade after 2020, according to Doug Cooke, deputy associate administrator for exploration systems.

"We've drilled down on the concepts to get a more detailed understanding of performance and capabilities," Cooke told the Space Transportation Association Sept. 11.

The needs of scientists drove some of the work, since scientific interest in the moon will extend beyond the fixed base NASA plans to build at one of the lunar poles. To get there, four-member lunar-surface teams would take two pressurized rovers dubbed "Freds," for Flexible Roving Exploration Devices, which Cooke said was a sort of tribute to the Fred Flintstone cartoon character.

"With two rovers we could actually send them out farther than walk-back distance, which has always been kind of a requirement when you had a rover," Cooke said. "And that limits your range significantly. So we came up with an approach that we think we could live with, where you have two of these and they go long distances."

While "they're fairly small," and normally would carry only two astronauts, in a pinch they could carry all four members of a surface team for self-rescue. The rovers also would be radiation-hardened, and designed to limit crew exposure to galactic cosmic rays. The current concept calls for step-in spacesuits docked to the outside of the rovers, so crews could step directly into them from the pressurized interior and move out on the surface.

Also under study are plug-in appliances for the rovers, such as backhoes or robotic arms, and perhaps having the rovers dock directly to the pressurized habitats of the lunar base. Those habitats would be larger than originally planned, landed early in the base-assembly sequence to minimize assembly time later. Inflatable structures remain a possibility for habitats, Cooke said, although no final decisions have been made.

For longer sorties than would be possible with the pressurized rovers, NASA is considering a robotic chassis that could carry unmanned landers or the larger habitats long distances to scientifically interesting sites for extended crew stays. Crews would arrive at the portable outpost by rover or perhaps even in a direct launch from Earth.

Cooke said the hardware that would be needed for the architecture refinements could be built by NASA's international partners or commercial companies. To that end, the agency will brief its concepts in detail at upcoming conferences in the U.S. and abroad, starting with the AIAA Space 2007 conference in Long Beach, Calif., Sept. 18-20.

All of the new concepts, chosen from among six options NASA studied, "seemed to us a very good way of maximizing the crew's abilities once we get them there," Cooke said. "We spend a lot of money to get them there. We want to make them as effective as we can."