Two astronauts from the US space shuttle Endeavour have attached a new beam to the International Space Station (ISS) on the mission's first spacewalk.
Meanwhile, Nasa experts on Earth are analysing pictures of the shuttle's heat shield to assess damage detected as the vessel docked with the ISS.
A robot arm will be used on Sunday to further inspect the 3in (7.6cm) gouge.
Nasa said ice falling from the shuttle's fuel tank may have struck the heat shield on the ship's underside.
If the damage is deemed to be dangerous, astronauts may have to repair it during a spacewalk.
The astronauts will use the shuttle's robotic arm and extension boom, tipped with a laser and a camera, to determine the exact size and depth of the gouge, said mission manager John Shannon.
If the damage cannot be fixed, the crew may have to wait at the space station for several months until a rescue shuttle can be launched, Mr Shannon said.
The gouge was first spotted as the shuttle approached the ISS prior to docking on Friday.
The crew guided it into a backflip manoeuvre once it was about 200m (650ft) away from the station, so it could be photographed and checked in a routine inspection for possible damage from foam insulation.
Nine pieces of foam are thought to have broken away during launch.
Three of them appear to have struck the shuttle but none are believed to have been big enough to cause serious damage.
Foam damage has been a major concern for Nasa since the Columbia disaster in 2003 when a briefcase-sized chunk of foam insulation broke off during launch and pierced the shuttle's heat-protection tiles.
This caused the shuttle to disintegrate on re-entry into the atmosphere, killing all seven crew.
Damage to the shuttle was seen as it docked with the space station
The mission is scheduled to last for 11 days but can be extended to 14 thanks to a new piece of equipment that can tap into the power grid of the ISS.
On Saturday, American Rick Mastracchio and Canadian Dave Williams attached the 1.58-metric ton beam, or truss, to extend the space station's length to 108m (354ft).
At least two other spacewalks will be held to replace a defective gyroscope, one of four keeping the ISS on an even keel, and install a 3.3-ton stowage platform.
Each of the spacewalks is scheduled to last six-and-a-half hours.
If the mission is extended, a fourth walk may take place to repair the shuttle's heat shield if necessary or to finish other work needed to prepare the ISS for further additions.
The mission is the second of four that Nasa plans this year to finish the $100bn (£49.1bn) space station before the shuttle fleet retires in 2010.