Fluorescent gas was pumped into the damaged Spektr laboratory module, but none of the nine astronauts could see any sign of it escaping into the vacuum of space.

Discovery took off despite fears of delays

The experiment will be repeated on Monday when the Americans undock their shuttle craft Discovery and fly alongside Mir, giving improved visibility.

The collision with a Russian cargo vessel on June 25 last year almost forced an evacuation of the three-man crew on board Mir at the time.

Final mission to Mir

Discovery is taking part in Nasa's ninth and final shuttle hookup with the ailing Russian space station.

Watch the last 15 metres of Discovery's journey to Mir

The two craft docked 245 miles (400 kilometres) above the Earth, with Mir being guided by an automatic steering system that was repaired just days ago.

The shuttle is due to bring home Andrew Thomas, the last of seven American astronauts to live on the ageing space station. It is due to return to Earth on June 12.