The shuttle Atlantis was preparing for a manoeuvre to avert "a piece of debris" en route to the International Space Station after its liftoff, NASA said.
A NASA official said the debris, one of an estimated 13,000 pieces of space junk orbiting Earth, was possibly in the path of the shuttle, which blasted off with six astronauts earlier in the day.
"We are tracking a piece of debris," said associate NASA administrator Bill Gerstenmaier. "We alerted the team to go do a manoeuvre."
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Gerstenmaier said the situation was "unique" because Atlantis was en route to a rendezvous with the ISS.
"So we need to be very careful of what kind of manoeuvres we do," he said. "I think the manoeuvre will be on Sunday if we determine we need to do it."
The shuttle blasted off from Cape Canaveral, Florida into a clear blue sky on time at 4.20am AEST on Saturday.
