Kaleri and Foale arrived at the station in October

Crewmen Michael Foale and Alexander Kaleri reported hearing a metallic crushing sound, apparently from the rear of the Zvezda living module.

Russian controllers said there appeared to be no damage to the outside of the craft or change in air pressure inside, and that the two men were safe.

They have now confirmed the noise came from an onboard instrument.

Impact event

Foale, the station's commander, and Kaleri said they heard the sound as they were completing their breakfast and cleanup period.

Foale is one of the most experienced astronauts in Nasa history More details

But the US space agency said that after conferring, the crew concluded the sound was more like a piece of sheet metal being flexed than a tin can being crushed - as Foale first reported.

The belief now is the sound had to have come from equipment inside the space station.

The US Department of Defense monitors the platform's orbit for space debris using radar. If it forecasts that a close approach is about to occur, the station can be moved out of the way.

Michael Foale, who was born near Louth in the UK, is no stranger to space station impacts.

He was on board the Mir space station in 1997 when a Progress supply ship crashed into it - one of the most dangerous incidents to have ever taken place in space.