Cosmonauts Sergei Zalyotin and Alexander Kalery continued their search for a small leak on the Mir station – and may have found its source today.

The leak originally was detected in 1999 by the previous crew on Mir, but those cosmonauts were not able to investigate it before leaving the station last August.

Locating and fixing the leak are among the initial tasks for Zalyotin and Kalery as they prepare Mir for its extended life as a commercial and scientific facility in space.

To prepare for today’s leak check, the cosmonauts disconnected certain cables running through Mir in order to shut hatches – allowing sections of the station to be isolated.

As they proceeded through their long and detailed work plan, the cosmonauts heard what might be the sound of escaping air at the pressure gauge on the Spectr module’s hatch.

They installed a sealing plug on the hatch, and then retired for a well-deserved night’s sleep at 11h20 GMT on Wednesday after working for more than 17 hours.