HOUSTON (AP) — Astronauts hope they have a solution for getting a pivotal piece of equipment working so it can convert urine and sweat into drinkable water and allow the international space station to grow to six crew members.

Flight controllers asked station commander Michael Fincke on Sunday to change how a centrifuge is mounted in the $154 million water recycling system. The centrifuge is on mounts and Mission Control asked Fincke to remove them.

“Fantastic! That is something we can do,” Fincke told Mission Control.

The astronauts have been working for the past three days to get the system running so that it can generate samples for testing back on Earth, but the urine processor only operates for two hours at a time before shutting down.

The water recycling system, delivered a week ago by the space shuttle Endeavour, is essential for allowing more astronauts to live on the space station next year.

Lead flight director Ginger Kerrick said engineers hope the problem is fixed, but they were studying whether six crew members would still be able live at the space station with the urine processor only working for two hours at a time. The space station crew is scheduled to grow from three to six residents next year.

“If this is as good as it’s going to get, we do need to be able to answer that question,” Kerrick said.

Flight controllers had hoped that the water samples brought back for testing had a mixture in which 70 percent came from condensation and 30 percent came from urine. Given the problems with the urine processor, that ratio stands at 90 percent condensation and 10 percent urine. Crew members won’t be able to use the contraption until several rounds of tests show that it is safe.

Mission managers have decided not to extend the mission by an extra day since the astronauts have obtained enough water samples, Kerrick said. Endeavour is scheduled to undock from the space station on Thanksgiving Day.

While Fincke tinkered on the urine processor, Endeavour’s seven astronauts were being given part of the day off Sunday. The time off followed an intense day of work that included the third of four spacewalks planned during Endeavour’s two-week visit to the space station.

Astronauts Heide Stefanyshyn-Piper and Stephen Bowen spent nearly seven hours outside the space station cleaning and lubing a jammed joint which allows the station’s solar wings to follow the direction of the sun for generating power.

Stefanyshyn-Piper — who lost a $100,000 tool kit during Tuesday’s spacewalk — had to share grease guns again with Bowen. To make up for the grease gun shortage, they took out a caulking gun normally reserved for repairs to the shuttle’s heat shield, but they didn’t need it.

The spacewalkers ran out of time before they could finish all the desired tasks, but NASA officials said they could be finished during the fourth and final spacewalk of the mission set for Monday.

“We really appreciate how hard you’re all working,” Mission Control radioed for them to come inside. “I know it’s painful to call it quits like that, but we think it’s the right thing to do.”