Robby the Robot could create anything -- from diamonds to dresses -- for humans living on another world. But he lived on Altair IV in the fictional film Forbidden Planet; not here on Earth where we send some robots to Mars while others serve as toys or vacuum cleaners in human households.

Although today's real-life robots may lack Robby's sophistication, they are quite adept as human proxies for space exploration. In fact, robots and space go together so well that some critics have doubted whether manned space exploration is needed at all since we can always send a cheaper, mechanical replacement.

"Robots are good explorers because you don't have to deal with life support systems that humans would need," said Ronald Arkin, director of the Mobile Robot Laboratory at Georgia Institute of Technology. "They're easier to take care of and much more adaptable for hostile environments than people."

The latest target for space robots is Mars, where two orbiters, a pair of twin rovers and one lander are expected to arrive at the end of this year.

The European Space Agency's (ESA) Mars Express probe should arrive at the red planet on Dec. 26 carrying with it the British lander Beagle 2. On the heels of Mars Express are NASA's twin robot rovers Spirit and Opportunity, which are scheduled to land by January 2004. Japan's Nozomi should arrive sometime in December as well.

"We send these robots into space where astronauts can't yet go," said Eddie Tunstel, senior robotics engineer for NASA's Jet Propulsion Laboratory in Pasadena, California. "But they are still quite limited in how they function and need our guidance."

Ground controllers for Spirit and Opportunity, the Mars Exploration Rovers (MERs), he explained, still have to check in with the robots daily to issue directions of where to explore since the systems are not completely autonomous.

NASA's last robot to the red planet was Mars Pathfinder's compact, solar-powered Sojourner rover, which landed on July 4, 1997. The space agency's first red planet robots were the two Viking landers launched in the mid-1970s, which contained a suite of scientific instruments including a mechanical arm to collect Martian soil samples. Both of the Viking missions also included orbiters to circle Mars from above.

The space robot revolution owes much of its success to advances in computer technology, allowing the development of more powerful and autonomous machines in smaller packages.

"Sojourner flew with what the public would equate to the first PC computer," Paul Schenker, director of JPL's robotics laboratory, adding that the onboard computer processor was hardened to handle hazards like space radiation.

Onboard computers and cameras allow the MER rovers to detect and avoid obstacles without waiting for orders from Earth, Schenker told SPACE.com. Performing these computations themselves allows a probe to cut down the amount of time spent communicating with Earth and waiting for scientists to prepare and return avoidance directions.

"It gives them more time to actually do more in terms of science and exploration," Tunstel said.

In the future, Robby-like robots may accompany planet-hopping astronauts to Mars or places elsewhere, serving as assistants for base construction and other tasks.

"You could even send robots as a precursor to set up habitation and science bases before humans even get there," Schenker said. "Once astronauts get there, the robots can be used as assistants."

Schenker estimates that these robotic taskmasters won't be available until 2025 or so, although NASA has already made some headway with its Robonaut automaton for the International Space Station (ISS). Last month, astronaut Nancy Currie successfully assembled a metal truss with the help of two Robonauts, dexterous robots that could participate in future space station construction.

"Robonauts are highly specialized in terms of their intelligence capability," Tunstel said. "They are meant to solve specific problems in tool manipulation."

Meanwhile, back on Earth humans rely heavily on unintelligent robots to build cars, computer chips and other industry products that don't require too much independent thinking. But the mechanical automatons are making their way into the home too.

The Roomba vacuum cleaner by iRobot will clean your floors for you if you have $200 to spare and Sony offers the robot dog Aibo in case allergies keep you sneezing around the flesh and bone variety. Honda's Asimo robot has perfect the complicated art of walking and could one day be put to work as a helper robot for the disabled. Right now, however, it's just for show.

The expectation of robot servants around the house, though, is farther off, since there are still hurdles to overcome in the fields of autonomy and artificial intelligence. Some robot experts also think the creation of a robot servant class may be a bit misguided in the first place.

"The one thing that worries me s the creation of another slave race for humans," said Arkin, adding that there are ethical use issues should be addressed before pressing intelligent robots into servitude. "So I would rather see robots be partners and peers to humans as opposed to servants and slaves."

Tunstel said those ethical issues are just beginning to come under NASA study, where researchers are trying to decide how much intelligence and independence their space robots should have. The difficulty lies in learning how to quantify exactly what robotic systems are capable of and establishing standards that would allow comparison across different platforms, such as comparing the intelligence of NASA machine against one from Georgia Tech or Europe.

"But it will be advancements in artificial intelligence that is truly going to make us jump to the next generation of robots," Tunstel added.