(AP) -- Flight controllers struggled Wednesday to open a stuck valve in a cooling loop at the International Space Station, as the 13 orbiting astronauts enjoyed a little time off after an intense week of hauling supplies and swapping tanks.
The ground controllers tried twice, without success, to command the nitrogen valve by remote control to open. They were debating their next step.
The nitrogen valve failed to open Tuesday after spacewalking astronauts hooked up a new ammonia tank. Nitrogen is needed to pressurize the ammonia coolant.
For now, the space station is being cooled properly. But the valve needs to be opened in the coming days - or the entire nitrogen unit replaced in a spacewalk. Otherwise, half of the station's electronics may have to be turned off.
Any spacewalk repairs would wait until space shuttle Discovery is gone. Discovery and its seven astronauts are due to leave Saturday.
The two crews spent Wednesday morning packing up a cargo carrier that Discovery delivered last week. The job needs to be completed by Thursday; that's when the storage compartment will be removed from the station and placed back aboard the shuttle for the trip home. It will return filled with trash and old equipment.
Mission Control gave the astronauts a few hours off, a day after they finished installing the ammonia tank on the third and final spacewalk of the mission.
The two astronauts who struggled with stiff bolts on each of the spacewalks - Rick Mastracchio and Clayton Anderson - said they weren't too tired.
"It may have seemed like we were working hard," Mastracchio told reporters. "But actually as we were struggling with those bolts, we were just doing a lot more thinking than we were actually working."
"Today, Clay and I feel fine ... and we're looking forward to more work and returning home shortly."
During the news conference, the four female astronauts floated, head-down, on top of their eight colleagues.
Until this mission, there has never been so many women in space at the same time.
"It really is a testament to the hard work and accomplishments of women," said astronaut Stephanie Wilson, "and we hope to inspire young women to follow in our footsteps and pursue their dreams."
Shuttle commander Alan Poindexter said the astronauts have kept on top of all the news happening back home - space news included.
President Barack Obama will visit Kennedy Space Center on Thursday and deliver a speech outlining NASA's future in exploration. He is reviving development of a post-shuttle capsule that would ferry crews to the space station and, as a result, lessen NASA's dependence on Russian launch vehicles.
Poindexter said he knew of no plans to provide a real-time link of Obama's speech to the astronauts in orbit.
Explore further: NASA issues 'remastered' view of Jupiter's moon Europa