After getting a little free time Thursday, the last space shuttle crew was woken up to deal with a second computer failure on Atlantis.
The astronauts switched to another of the five main computers on board, and NASA said the shuttle was in "stable condition with no concerns for the crew's safety." A computer had also failed on Sunday.
The crew had gone to bed late Thursday afternoon, but Mission Control woke them up about 1½ hours later because of the failed computer. NASA said they would troubleshoot the problem on Friday.
Sunday's computer glitch occurred just before the shuttle linked up with the International Space Station. Engineers said the problem was likely caused by a bad switch throw. That computer was working again Monday after new software was installed.
The check-and-balance network of computers provides redundancy during the most critical phases of the mission, and will be needed when Atlantis lands next week to close out the 30-year shuttle era.
Earlier Thursday, the crew got some time off after a hectic week to savor their historic experience.
"This is one of the first days we've been able to take a deep breath and appreciate what we're doing up here," said shuttle commander, Christopher Ferguson.
Until Thursday, the workload in orbit was so intense that the four astronauts had only fleeting moments of realizing "wow, this is really it," astronaut Rex Walheim said in a series of TV interviews.
"But boy, it's going to hit when we land and wheels stop," he added.
On Friday afternoon, the 10 astronauts aboard the linked Atlantis and space station will get another break from their chores to take a phone call from President Barack Obama.
Before kicking back and relaxing, Ferguson said the space station delivery mission was going well and that the back-and-forth cargo hauling was three-quarters completed.
"Atlantis is purring like a kitten," he said. "I think she's about 25 years or so old, but she performs just like a newborn."
Atlantis first rocketed into orbit in 1985. This is its 33rd flight and the 135th shuttle mission overall. Atlantis will join Discovery and Endeavour in retirement, following its landing next week.
The space shuttle delivered nearly 5 tons of food, clothes and other household goods in a giant canister to the space station — an entire year's worth of supplies. NASA wants the orbiting lab well stocked in case private companies fall behind in their effort to take over shuttle supply runs. The first such commercial flight is expected by year's end.
While the unmanned cargo ships are smaller than NASA's shuttles, Ferguson pointed out there are many more of them, launching from all over the world. But the craft burn up in the atmosphere after they undock.
"From a return standpoint, bringing things back from the space station and getting them to Earth, we're going to miss the space shuttle," he said.
Atlantis, for instance, will return more than 7,000 pounds of discarded equipment and trash from the space station, freeing up much needed room. Engineers will take apart some of the broken machinery to see what went wrong and, hopefully, learn from the mistakes.
Astronaut Sandra Magnus — who spent more than four months on the space station a few years back — said she's amazed at how much bigger it is now that it's finished. She said she sometimes thinks: "Wow, look what we did. We built this huge, huge, monster laboratory orbiting the Earth, with cooperation from countries all over the world."
Mission Control allotted plenty of time Thursday for the two crews to linger over an "all-American meal" of grilled chicken and barbecued beef brisket that was packed for them, complete with baked beans and Hostess apple pie.
And while space station resident Ronald Garan Jr. tweeted that he "had a great dinner tonight," it wasn't clear to controllers whether the astronauts had eaten the special meal or whether they were saving it for another day. NASA had urged the public to share in the virtual dinner, publishing the recipes online.
Three of the space station crew marked their 100th day in space Thursday: Garan and Russians Andrey Borisenko and Alexander Samokutyaev. They will remain on board until September.
Atlantis' trip, by comparison, is a scant 13 days. It will undock Tuesday and aim for a Florida homecoming Thursday.
A TV broadcaster asked Ferguson if he'll make "a Neil Armstrong type statement" at touchdown. Atlantis will miss landing on the 42nd anniversary of Armstrong's "one small step for man" speech by one day; by adding a day to the mission earlier this week, NASA bumped Atlantis' homecoming to July 21.
"I put some thought into how we're going to reflect on the moment," Ferguson said, "and perhaps we'll just save that until the wheels-stop call and we'll let you know then."