Astronauts on the shuttle Discovery have finished their first spacewalk.
The British-born astronaut Piers Sellers and colleague Mike Fossum have been carrying out repairs to the International Space Station's exterior.
They gave a tentative thumbs-up to a wobbly boom-arm which Nasa hopes future missions could use to to carry out inspections and repairs.
Sellers said it was like being "a bug on the end of a fishing rod", but that he could do most of the tasks required.
All the tasks carried out on the boom-arm were simulated, designed to test the platform in case astronauts one day have to make repairs on a shuttle's belly.
The spacewalk, the first of three planned for the mission, lasted about six and a half hours.
It was Fossum's first spacewalk. Sellers did one on a previous shuttle mission, in 2002.
"Enjoy the view, gentlemen!" Nasa communicator Megan McArthur said from Houston, as the two men stepped through the airlock.
DISCOVERY SHUTTLE FLIGHT
Mission known as STS-121
Discovery's 32nd flight
18th orbiter flight to ISS
Lift-off: 1438 EDT, 4 July
Location: Kennedy Space Center, Launch Pad 39B
Objective: To test new safety equipment and procedures
Payload: Cargo bay has 12.75t of equipment and supplies
Crew: Lindsey, Kelly, Fossum, Nowak, Wilson, Sellers, Reiter
During the walk both men carried out cabling work on a mobile transporter system on the exterior of the station.
But the boom-arm tests - where the 15m (50ft) arm was coupled to a new 15m inspection rod - were of particular interest.
The tests went well for Sellers, but Fossum's turn at standing at the end of the arm was delayed by a problem with the tether connecting him to it.
The arm swayed as the astronauts pretended to take photos and made swimming movements with their arms.
But both described the sensation as smooth and gentle.
Sellers said it was a "very slow gentle sway in and out of the bay".
They may get the chance to use the arm for genuine repair work on their third space walk, on Wednesday.
Both men had practised the walk back on Earth, in a virtual reality simulation and in the US space agency's (Nasa) Neutral Buoyancy Laboratory.
The latter is a giant swimming pool that goes some way to replicating the "weightless" conditions of space.
The ISS repairs Discovery docked with the ISS on Thursday and on Friday attached an Italian-built cargo module.