The space station's new robot, Dextre, is fitted out and ready for duty.
In the third spacewalk of the latest shuttle mission, Endeavour astronauts Rick Linnehan and Robert Behnken fixed tools and cameras to the machine.
The robot, which is properly called the Special Purpose Dextrous Manipulator, will in future do much of the external work on the space station.
Dextre will now undergo a series of tests and trials before it is asked to do major tasks.
Ultimately, it will be commanded to install and remove small payloads such as electronics boxes, computers and batteries.
Linnehan and Behnken worked for six hours and 53 minutes in what was the third Extra Vehicular Activity (EVA) of the Endeavour visit.
The astronauts had difficulty fixing a science payload to Columbus
They were unable to attach a materials science experiment to the Columbus module, but may have another opportunity later in the mission.
A fourth spacewalk will take place on Thursday. This will see astronauts test a shuttle tile repair kit and change a circuit breaker on the station.
Endeavour has already fitted the new Japanese Logistics Module brought up on this flight.
This is a storage facility for the Japan Aerospace Exploration Agency's (Jaxa) Kibo laboratory, the main section of which will travel to the station on the next shuttle mission.
The US space agency has 10 more flights planned after Endeavour to complete the space station and deliver supplies before the orbiters are retired in 2010.
Endeavour is due back on the ground on 26 March.
SPECIAL PURPOSE DEXTEROUS MANIPULATOR (DEXTRE)
Dextre is remotely operated from inside the ISS or from the ground
The robot has seven joints in its arms for maximum movement
During operations, one arm holds onto the ISS while the other works
This maintains stability and ensures the arms do not hit each other
Dextre will install and remove small payloads such as batteries