Two astronauts have carried out the first spacewalk of Space Shuttle Discovery's 12-day mission to the International Space Station (ISS).
The first spacewalk was to install the P5 truss to the ISS
The pair installed a truss that forms the backbone of the station during their walk of more than six hours.
Earlier, the crew used a camera on the ISS's robotic arm to examine an area on the shuttle's left wing where sensors detected a "very low" impact.
Nasa officials said they did not expect the incident to affect the mission.
The shuttle docked with the ISS at 1706 EST (2206 GMT) on Monday, ahead of a week-long stay to carry out a range of tasks in what Nasa has described as one of the most complex missions to date.
Engineers are analysing images of the shuttle's left wing
Engineers will examine data gathered during the inspection of the shuttle's wing before deciding whether any further inspections are necessary. Officials said that, so far, there was no cause for concern.
While in orbit with the space station, Discovery astronauts are scheduled to perform three spacewalks, and wire new solar arrays into the ISS power grid. This will need to be done without interrupting the station's life-support and other critical systems.
Christer Fuglesang, the first Swede in space, and American Robert Curbeam took part in Tuesday's spacewalk.
Their task was to install the two-tonne P5 truss, which will be used to connect power and cooling lines and act as a "spacer" between the ISS's solar arrays.
A British-born astronaut, Nicholas Patrick, is among Discovery's crew. For five of the seven astronauts, this is their first shuttle flight.
Discovery's launch left a fiery trail in the Florida sky
One of crew, US astronaut Sunita Williams, will stay on at the ISS when Discovery heads home, taking German Thomas Reiter back to Earth.
At least 14 more missions are needed to finish the $100bn (£50bn) station.
Discovery blasted off from Florida at the weekend in the first night launch of a space shuttle for four years, after being delayed for two days because of bad weather.
The US orbiter's flight is scheduled to last 12 days, with a landing date set for 21 December back at the Kennedy Space Center.
Discovery's crew consists of Commander Mark Polansky, pilot William Oefelein and mission specialists Robert Curbeam, Joan Higginbotham, Nicholas Patrick, Sunita Williams and the European Space Agency astronaut Christer Fuglesang.