Nasa officials have said they now believe at least one shard of protective foam may have hit a wing of the Discovery space shuttle.
But they said they were confident the craft would make a safe return.
Nasa deputy programme manager Wayne Hale said new photographic evidence appeared to suggest an impact with one of the wings.
But he stressed there was a "divergence of opinion" at Nasa on whether the foam had actually made contact.
"There are 11 indications of potential impacts," said Steve Poulos, manager of the orbiter project office.
"We might have four areas of the wing leading edge where there might have been an impact."
Mr Hale said he did not believe the impact had caused any damage to the shuttle.
But in January 2003, the Columbia shuttle broke up as it re-entered the Earth's atmosphere after a piece of insulating foam struck its wing.
Although officials said the shuttle Atlantis could be launched as part of a rescue operation and was being held "on readiness", they stressed they were "nowhere near doing that".
The agency has suspended all future orbiter flights until it can find an effective way to stop foam sliding off the vehicle's external tank on launch.
But the work to inspect Discovery's external surfaces is expected to go on for another few days yet.
All together: Docking occurred over the South Pacific
The concern about Discovery's structural integrity stems from video footage of Tuesday's spectacular launch that showed foam falling about the vehicle a few minutes into its ride to orbit.
Before arriving at the space station, Discovery performed an unprecedented 360-degree flip. It allowed the crew on the ISS the chance to train long lenses on the vehicle's underside.
The digital images were sent down to Nasa's Johnson Space Center in Houston, Texas, for engineers to work over.
Discovery's docking with the ISS was completed at 0718 EDT (1218 BST; 1118 GMT) above the South Pacific just west of Chile.
SHUTTLE RETURN TO FLIGHT
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: 1039 EDT, 26 July
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
The ISS crew, American John Phillips and Russian Sergei Krikalev, warmly greeted Discovery's seven-member team, led by Commander Eileen Collins.
Work was immediately started to allow the 15 tonnes of supplies ferried up by the shuttle to be moved across to the station.
During Tuesday's launch, at least three pieces of foam came off the Discovery, including one about 80cm (31 inches) by 35cm (14 inches), slightly smaller than the piece which caused Columbia's destruction.
"We will simply never be able to get the amount of debris shed by the tank down to zero," Dr Griffin told NBC television. "We are trying to get it down to a level that cannot damage the orbiter."
Of more immediate concern will be apparent signs of small damage to tiling near Discovery's nose landing-gear doors and to a square "chine" tile further toward the aft (back) end of the ship.
Nasa will want to establish if these areas have been compromised in a way that might prohibit a safe return to Earth for Discovery. That landing is currently scheduled for 7 August.
Three spacewalks are planned for the mission.
The first on Saturday will test repair kits designed to deal with small damage areas on the shuttle's heatshield tiles.
The two other spacewalks will repair and install critical hardware outside the space station.