Discovery shuttle astronauts Saturday helped to fix and fine-tune the oxygen filter and carbon dioxide scrubber at the International Space Station, using two extra days added to the end of their mission, dpa reported.
Discovery astronaut Michael Barratt and station flight engineer Paolo Nespoli fixed a failed heating circuit used to bake out the carbon dioxide from the air system on the station. The system had failed during the shuttle mission's first spacewalk. The repair involved a bypass to the faulty circuit.
The system was now "up and running," NASA said in an update on its website.
Station commander Scott Kelly was nearly finished with installing a new filter in the oxygen generating system.
"All in all, it was a great day in orbit," said Royce Renfrew, lead station flight director.
Earlier Saturday, Russian space officials said the Russian oxygen generator Elektron had been disabled but presented no threat to the crew, the agency Ria Novosti reported.
Russian officials said the system was under repair.
Discovery, on its last flight into outer space, is to return to Earth on Wednesday after its 13-day mission.
The US shuttle programme has at the most two more missions with Atlantis and Endeavor before the ageing shuttle programme is shut down. After that, Russia's Soyuz craft will be the only transport for astronauts to and from the space station.