Nasa has announced they are stopping all space shuttle flights as they look into what happened when bits fell off Discovery during its launch on Tuesday.
A spokesman for the space agency said big chunks of foam came off the fuel tank, but they don't think the debris caused any serious damage.
The Columbia shuttle was destroyed in 2003 after a similar incident.
If the shuttle is damaged, its crew could wait in the International Space Station until a rescue craft arrives.
The astronauts themselves used a robot arm to take a look at the outside of the shuttle in space on Wednesday.
SHUTTLE RETURN TO FLIGHT
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
It's thought two heat shield tiles were damaged on the bottom of the shuttle.
Nasa say it's too early to say what this could mean for plans to send another shuttle, the Atlantis, into space to rescue Discovery's crew.
Discovery launched on Tuesday as it began a 12-day space mission to take supplies to the ISS.
The launch itself was delayed for 13 days because of a problem with an indicator showing how much fuel was on board, but after safety checks the problem didn't come back.
Discovery is due to return to Earth on the morning of 7 August.