A space station air purifier was working again Sunday after it shut down at the worst possible time, when company was still visiting and had swollen the on-board crowd to a record 13.
The repair by flight controllers, albeit temporary, came as a great relief to NASA.
Even if the carbon dioxide-removal system had remained broken, shuttle Endeavour would not have had to undock early from the international space station, said flight director Brian Smith. But the system needs to work to support six station residents over the long term, he said.
The machine for cleansing the station atmosphere, on the U.S. side of the sprawling outpost, failed Saturday when it got too hot and tripped a circuit breaker.
Flight controllers managed to get the unit up and running again 8 1/2 hours later in manual mode. That means extra people are needed in Mission Control — six each day — to handle the approximately 50 computer commands that need to be sent up every few hours.
Normally, the system runs automatically. Smith said engineers hope to come up with a software solution soon to have the system back in automatic.
An air-cleansing system on the Russian side of the station is working fine. In addition, the station has about three weeks' worth of canisters for removing the carbon dioxide exhaled by six crew members. The astronauts would have relied on those canisters to prevent an early undocking of Endeavour, if the U.S. carbon-dioxide removal machine not been coaxed back into operation.
The shuttle and its crew of seven will depart Tuesday, as originally planned.
Before leaving, the shuttle astronauts have their fifth and final spacewalk to perform.
During Monday's spacewalk, Christopher Cassidy and Thomas Marshburn will rearrange some power cable hookups, fold down a piece of popped-up insulation on a small, dexterous robot arm, and install TV cameras on the brand new porch of Japan's space station lab.
"We're all keenly aware that (spacewalks) carry some risk to them, and so we're going to be very, very deliberate and careful," said shuttle commander Mark Polansky. "In my book, the last one you do is always the one that you have to watch out for the most."
After experiencing elevated carbon dioxide levels on the past two spacewalks, astronaut Christopher Cassidy promises to take it nice and slow Monday. His first spacewalk last week had to be cut short because of the problem.
Mission Control has urged Cassidy to rein himself in, not so easy for a former Navy SEAL.
"Yes, I am taking quite a bit of teasing about this," Cassidy said at a news conference as his crewmates erupted in laughter. "I have a whole lot of confidence in the suit and the system there. ... It's not like you leave them out on the loading dock overnight or anything."
A spare carbon-dioxide removal system for the space station, meanwhile, will be launched at the end of August on the next shuttle flight, a plan put in place long before this weekend's trouble.
NASA has wrapped up extensive testing of the foam insulation on the fuel tank for that mission, and so far everything looks to be in good shape. Engineers wanted to make sure that the insulation was attached properly after considerable foam was lost during Endeavour's July 15 launch. The tests delayed Discovery's mission by a week.
Liftoff is now targeted for Aug. 25 at the earliest.