For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot, now stuck on a pedestal, is going mobile at the International Space Station.
"Legs are going to really kind of open up the robot's horizons," said Robert Ambrose, from the US space agency Nasa's Johnson Space Centre in Houston.
It's the next big step in Nasa's quest to develop robotic helpers for astronauts. With legs, the 2.4-metre Robonaut will be able to climb throughout the outpost 420 kilometres above earth, performing mundane cleaning chores and fetching things for the human crew.
The robot's gangly, contortionist-bending legs arrived yesterday, more than a month late, aboard a SpaceX supply ship.
Each leg, 1.42 metres long, has seven joints. Instead of feet, there are grippers, each with a light, camera and sensor for building 3-D maps.
This robot will stay indoors as it learns how to climb. The next-generation modelwill venture outside on spacewalks.