Science Article

SPACE exploration may have a new direction. In the 1960s, humans did the exploring but since the last moon landing in 1972, NASA's only explorers beyond low Earth orbit have been semi-autonomous robots. Now the agency is pondering a third approach, sending astronauts who would remain in orbit around alien worlds and explore via robotic rovers.

Mars Rover

On Earth, human-controlled robots are used for tasks ranging from delicate surgery to exploration of the deep sea. But in space, robotic "telepresence" could be even more promising.

Telerobotics would be orders of magnitude more productive for exploration than semi-autonomous robots like the Mars rovers Spirit and Opportunity, says NASA's George Schmidt, an organiser of the Exploration Telerobotics Symposium earlier this month at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Nothing beats having human cognition and dexterity in the field," he says.

But there is a hitch in trying to control from Earth a robot that's exploring another planet: the huge time lag as the signals travel back and forth. Real-time reactions are needed for it to work. For example, surgeons can perform operations well as long as the robot responds to their actions within about half a second. Greater latencies cause problems.

Latency on Earth is no more than a few hundred milliseconds, but latency between the Earth and moon is about 3 seconds, and that delay is enough to slow telerobotics dramatically, says Daniel Lester of the University of Texas at Austin, another organiser of the symposium. "You could use telepresence to tie a knot in 30 seconds on Earth, but it would take 10 minutes to tie it with 3-second latency."

Latency for signals to Mars is much longer - from 8 to 40 minutes depending on the planets' positions - so real-time control from Earth is impossible. The most plausible way to have robotic telepresence on Mars would be to station astronauts in orbit around the planet.

The first step towards this might be testing out robotic telepresence on Earth with simulated latencies. Rovers on the moon controlled from lunar orbit might come next. Rovers could also be controlled in real-time to explore the far side of the moon, not visited by the Apollo missions. To do this, NASA would have to station astronauts at lunar Lagrangian point L2 - a gravitationally neutral area of space which lies about 60,000 kilometres beyond the moon, in line with Earth.

Mars is a bigger challenge, of course, as is Venus, which is usually considered beyond the scope of human exploration because of its boiling, corrosive atmosphere. A Venus mission could be shorter as it is closer to us than Mars. However, any robots would require extensive modification to survive in Venus's hostile environment and, even then, they would not last the years that a Mars rover might. Nevertheless, having human telepresence would make exploration much more productive than if autonomous robots had to await commands from Earth.

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