The next generation of explorers to walk on the moon or Mars could be called robonauts. They may perform similar scientific tasks to astronauts, but wouldn't require any of the life support equipment or shelter. The first robonaut could travel to the space station to work side by side with astronauts in the next three years, if plans at NASA come to fruition.

NASA and General Motors are developing the first of these humanoid robots, called Robonaut2. Unlike NASA's Mars rovers, Robonaut2 is designed to closely mimic the shape, movement, and behavior of a human. This could make it ideally suited to working alongside humans, or for testing human spacecraft and living quarters, but it also presents some unique engineering challenges. GM hopes to use the robots in its manufacturing plants and to incorporate the resulting technology into some of its products, including vehicle safety systems.

The engineers behind Robonaut2 began working on the robot in 2007; its design originated from a version that NASA created more than 10 years ago.

Robonaut2 currently consists of just an upper torso. It weighs about 45 kilograms and is equipped with over 350 sensors. These include tactile sensors on the contact points of the robot's fingers and its palms, and proximity sensors in its arms. Engineers have also built springs and elastic materials in the joints to give the robot better control and flexibility, and to allow it to move at faster, more humanlike speeds. The robot can carry payloads of about nine kilograms--four times more than other humanoid robots.

Rob Ambrose, chief of the Software, Robotics and Simulation Division at NASA's Johnson Space Center in Houston, says the new robot is a significant improvement over its predecessor. "It's designed to operate at a speed and scale similar to humans, and when it encounters people it complies and safely works with them," he says.

The technology needed to perceive humans and respond to human action is particularly important, and this is something that researchers all over the world are working on, says Matthew Mason, a professor of robotics and computer science at Carnegie Mellon University in Pittsburgh. Robonaut2 is an important platform for developing and testing such techniques, he adds.

Another key challenge is enabling Robonaut2 to communicate effectively with astronauts. "This is really a new area," adds Bilge Mutlu, an assistant professor in computer science at the University of Wisconsin-Madison, and a member of the human computer interaction lab at CMU. "How does a robot interpret social cues? How does it communicate back? We want robots to be team members, and the new work is a step in that direction." For the moment, Robonaut2 is limited to communicating with humans in simple ways. For example, when it points its head toward something, it is a cue that the human working alongside the robot should look in that direction.