The space shuttle Discovery's commander has said her crew is "surprised" and "disappointed" the foam debris problem still exists.
Eileen Collins is Discovery's commander
A similar scenario of falling foam during lift-off caused the Columbia shuttle disaster in 2003.
However Commander Eileen Collins told journalists she believed Nasa would "fix" the problem and that Discovery would return safely.
Officials expect to be able to give the shuttle the all clear by Sunday.
On Friday, Discovery's crew conducted a close survey of the shuttle's thermal heat shield to see if it had suffered damage during Tuesday's lift-off.
Foam debris came away during the launch, prompting the US space agency to suspend flights after Discovery's return on 7 August.
'Must be fixed'
"We were actually quite surprised to hear we had some large pieces of debris fall off the external tank, it wasn't what we had expected," Commander Collins told media in an interview from the shuttle. "Frankly we were disappointed to hear that had happened.
"We thought we had this problem fixed."
Commander Collins said she believed Nasa had been right to suspend flights, even though the announcement was made while Discovery was still in space.
"What I'd like to say is this is something that has to be fixed," she continued. "I don't think we should fly again unless we do something to prevent this from happening again."
A chunk of insulating foam fell off Columbia's external fuel tank and struck its outer skin, allowing superheated gases to get inside, causing the shuttle to break up as it re-entered the Earth's atmosphere on 1 February 2003.
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
All the astronauts were killed and the shuttle programme was suspended until Discovery's blastoff on Tuesday.
Nasa officials acknowledged that shards of foam may have hit Discovery's wing, but they said they were confident the shuttle was not at risk.
However, despite a flight suspension, the shuttle Atlantis is on standby to stage a rescue mission, if needed.
At a press conference on Friday, officials said there were six areas where impact could have occurred on Discovery and they would continue to analyse sensor and image data over the weekend.
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.