CAPE CANAVERAL, Fla. – Astronauts up on the international space station faced the longest and hardest spacewalk of their mission Saturday, a seven-hour-plus excursion to wrap up repair work on a gummed-up joint.
As the crews of the orbiting shuttle-station complex focused on the greasy outdoor extravaganza, engineers back on Earth struggled to understand a potentially serious problem with a newly delivered recycling system that is supposed to turn astronauts' urine into drinking water.
The $154 million system shut down again Friday and had managers wondering whether space shuttle Endeavour would bring back any samples of processed urine. The equipment has to work properly and the water has to pass safety tests in order for the space agency to double the size of the station crew next year.
At a news conference Friday, astronaut Heidemarie Stefanyshyn-Piper said her upcoming spacewalk — the third of the mission — would be busier than usual. She and Steven Bowen have to finish cleaning and lubricating a jammed solar wing-rotating joint, and put in new bearings.
"It looks like it's going to be challenging," she said. "We have a lot of work to do."
Late Friday, Stefanyshyn-Piper and Bowen got permission to take out an extra tool. Mission managers decided a caulking gun set aside for potential repair work on Endeavour's heat shield could double as a grease gun in a pinch.
The astronauts ended up with a grease gun shortage after a $100,000 tool kit floated away during Tuesday's spacewalk. Stefanyshyn-Piper was trying to clean up grease that had leaked all over when the bag and the tools inside got away.
The joint is supposed to keep the solar wings on the right side of the space station pointed toward the sun. It stopped working normally more than a year ago, after grinding parts left it full of metal grit.
Unlike the two previous spacewalks, only joint repair work is on Saturday's outdoor agenda. A fourth and final spacewalk, on Monday, will have astronauts adding grease to a twin joint on the opposite side of the space station that is working fine.
As for the trouble with the water recycling system, no one was surprised.
Space station commander Mike Fincke said it's common for things to go wrong in a flight test and stressed that he wasn't worried — so far. Nor was he concerned about eventually drinking the final product.
"It's just the water that's taken out," Fincke said Friday. "It's really clean and purified water. In fact, it's probably more pure than most people's tap water. So I'm not afraid to drink it."
Of all the home-improvement gear delivered to the space station by Endeavour, the water recycling system has drawn the most attention. NASA sees it as the future in deep-space exploration — and also to future life on the home planet.
"This technology of how to reuse our things and be careful with them is really applicable to life on planet Earth," Fincke said.
The system's urine processor was started up as Thursday's spacewalk was ending, but promptly shut down. Flight controllers reactivated the device Friday. It ran for two hours before sensors detected motor problems and shut it down again.
If it's a bad sensor, it might be possible to bypass or repair it, Fincke said. But if the motor itself is at fault, NASA would have to send up a spare part on a future flight.