When astronauts first step foot on Mars, they won't be alone.

NASA scientists plan on pre-positioning robots and robotic rovers on the red planet before the first astronauts arrive. That way, the robots will be ready to help their human counterparts on what probably will be NASA's most taxing mission yet.

And while that's years away, NASA is testing its robotic muscle now. With three robotic arms aboard the International Space Station and the space shuttle Discovery returning from the most robotically intense mission yet, NASA is using this robotic work as a test bed for future missions.

"We're using robots a lot more," said Allard Beutel, a spokesman for NASA. "We keep increasing the complexity of the robotics work we do. This really complex robotics work is becoming commonplace. This mission was entirely dependent on robotics. We couldn't have done this work without them."

When astronauts get to Mars, they'll be using robots as part of their everyday existence, added Beutel. They'll also need robotics to help them build any workstation or habitat structure on Mars, or on the moon.

"The Space Station is a really good proving ground for the robotics," he said. "This is just the beginning."

Early in 2004, President George W. Bush set the goal of living and working on the moon for increasingly extended periods of time, and of sending human missions to Mars.

This week, the space shuttle Discovery detached from the International Space Station and is slated to land Saturday morning (US time).

The crew on the 123rd shuttle mission helped deliver a 33-foot-long, 1,716-pound Japanese-built robotic arm, called HTV, to the space station. The arm has six joints and is designed for use outside the Japanese Experiment Module, moving materials outside the airlock so scientists can see, for example, how they react when exposed to space.

This is the first of two Japanese-built robotic arms that will be used on the space station. Beutel said the second arm, which will be about 6 feet long with a grapple on one end, is scheduled to be delivered to the space station next year. The first arm isn't slated to be used until the second arm arrives.

The new Japanese arm joins two other robotic arms on board the space station.

Dextre is a 12-foot-tall robot with a 30-foot wingspan built by the Canadian Space Agency in Saint-Hubert, Quebec. Delivered by the space shuttle Endeavour in March, the US$200 million robot is designed to take on most of the maintenance jobs required outside of the space station, thus cutting back on the number of dangerous space walks the astronauts must make.