Arizona's famous Meteor Crater is a long way from the Moon. But for a menagerie of intelligent robots hoping to earn supporting roles in NASA's lunar exploration plans, the massive impact crater east of Flagstaff is center stage.

In September, several such robots and an autonomous Moon buggy called Scout were put through their paces in the rough desert terrain. During a two-week campaign conducted by NASA's Desert Research and Technology Studies team -- a collection of government, university and industry scientists and engineers known as the Desert Rats -- the robots demonstrated their ability to work side-by-side with space-suited researchers, helping with the kinds of tasks that actual astronauts will have to perform as they begin exploring the Moon and establishing outposts.

NASA's current expenditure on so-called robotic field assistants is fairly modest. Of the $3 billion NASA's Exploration Systems Mission Directorate spent this year developing a new space transportation system and preparing for an eventual return to the Moon, only $13 million went to Human Robotics Systems, a recently established program meant to focus the agency's investment in robotic helpmates.

Chris Culbert, the NASA Johnson Space Center engineer in charge of the Human Robotic Systems program, said his current stable of prototype field assistants consists almost entirely of robots inherited from various programs around the agency, some of which pre-dated President George W. Bush's 2004 call for the United States to return to the Moon.

"There's not enough money in this program and it hasn't been around long enough to build up new robots," Culbert said.

In addition to Scout, NASA's current line up of field assistants includes a nimble six-legged rover called Athlete, a dexterous humanoid torso on wheels called Centaur, and K-10, a boxy little rover specially equipped for site survey work.

Culbert said all four robots help NASA in one way or another to address the three big themes of the Human Robotics Systems program: surface mobility, surface handling, and human-systems interaction.

"The interaction between robots and humans is very important to me," Culbert said. "Industrial robots are typically behind barriers and big alarms ring if humans come within 10 feet. Our robots live with the humans."

Athlete and Centaur, two of the robots that were used at Meteor Crater this fall, will be on display and demonstrated at NASA's 2nd Exploration Conference being held Dec. 4-6 in Houston.

When Centaur rolls into the exhibit hall at the George C. Brown Convention Center, it will be a sort of homecoming for the wheeled robot's humanoid half, a skilled construction worker formerly known as Robonaut. NASA originally developed Robonaut with an eye toward helping astronauts with tedious tasks like those they were encountering assembling the international space station. At the 2002 World Space Congress in Houston, a stationary Robonaut was on exhibit showing off its dexterity with hand tools. NASA officials present there talked about how Robonaut could one day help assemble very large aperture space telescopes in orbit.

Since mounting Robonaut on a wheeled platform and renaming him Centaur after the half man/half-horse of Greek mythology, NASA has devoted more attention to thinking about how the dexterous robot might help build and maintain outposts on the Moon. Culbert said a robot like Centaur might make an excellent lunar plumber, for example, tackling various pipefitting chores and freeing astronauts to concentrate on more important activities. But Centaur can also do grunt work. In the desert in September, Culbert said, the robot helped the stand-in astronauts unload the Scout rover.

Athlete got its start in late 2004 when NASA was spending relatively freely on human and robotic technology projects that supported a wide mix near and longer-term exploration goals.

NASA initially planned to spend $25 million on Athlete over four years. But after NASA Administrator Mike Griffin took over in early 2005 and decided the agency could not afford the $1 billion-a-year technology portfolio his predecessor had set in motion, all but 38 of the original 118 competitively-selected projects were canceled. Athlete made the cut, but had its funding reduced substantially. After receiving $3 million in its first year, Athlete's funding was paired back to $1.5 million.

Brian Wilcox, the Jet Propulsion Laboratory-based principle investigator for Athlete, said the funding reduction ruled out building a high-fidelity prototype out of mission-grade components as the team originally proposed. But the team has managed to build three somewhat lower fidelity Athlete prototypes, including two fully-functional vehicles, from commercially-available components. The semi-autonomous rovers run software brought over from the Mars Exploration Rover program.

Wilcox said Athlete is first and foremost a versatile cargo vehicle that has demonstrated its ability to tackle a wide range of tasks and terrain challenges, including climbing hills and rappelling into ravines.

Athlete also would make a great set of landing legs for NASA's next human lunar lander, Wilcox said. "We have been promoting the concept that Athlete would make superb landing legs for the [Lunar Surface Access Module]," he said. "It would give the first lander superb mobility as well as a general purpose manipulator, so it would have the ability to do self maintenance."

What the future holds for Athlete and the rest of its robotic brethren depends in part on how NASA's lunar exploration plans take shape in the years ahead. NASA is due to release its first stab at a lunar surface architecture during the Exploration Conference in Houston.

Culbert said NASA has more work to do before it can say whether six-legged rovers like Athlete are the answer to its lunar surface mobility needs, or if a "simple flatbed truck" approach might be a better way to go. "We may find out outpost on the Moon doesn't require a lot of climbing up and down hills," he said.

To help answer these questions, Culbert and his team plan to keep building robots and putting them through their paces. But he admits that these important early efforts are for the time being rather resource constrained.

"With the amount of money I've got available I won't be able to do everything that needs to be done," he said.

NASA hopes to spend more money on Human Robotic Systems in the years ahead. NASA's 2007 budget request, still awaiting approval from Congress, includes $18 million for Culbert and the team of 40 or so civil servants and contractor personnel spread across the agency. NASA's most recent five-year-plan forecast ramping the program up to $25 billion a year by 2011, but Culbert admitted that might be a tough sell given some of the other pressures on the Exploration Systems Mission Directorate's budget.

If additional money is forthcoming, Culbert said the program would like to build a new moon buggy next year equipped with an active suspension system tuned to handle tougher terrain. Human Robotic Systems group may also build a crane in 2007 and possibly add it to one of the Athlete rovers.