CAPE CANAVERAL, Florida — The astronauts in orbit, all 13 of them, enjoyed their first day off in more than a week Saturday after a series of grueling spacewalks.

"Today we hope you can enjoy some well-earned time off," Mission Control said in a morning message. "At orbital rates, you can't stop to smell the roses, but you can savour the view from the best seats in the house."

The astronauts wrapped up their fourth spacewalk Friday, completing critical battery changes at the international space station. One more spacewalk is planned for Monday to perform additional station work.

In a series of TV interviews, two-time spacewalker Christopher Cassidy said he's learned to go slowly, especially right after he goes out the hatch. Cassidy's carbon dioxide levels were high during both spacewalks, but not enough to make him sick. He said he felt fine the whole time.

His first spacewalk was cut short because of the problem.

NASA officials attributed the former Navy SEAL's gung-ho approach to his military training.

"Slow and steady wins the race," Cassidy said, describing the lesson he's learned. He promised to "go nice and slow" during Monday's spacewalk.

In response to a question, shuttle pilot Douglas Hurley acknowledged there's been "a little bit of a traffic jam" at the bathrooms every morning because of the record number of people up there. Nonetheless, last weekend's breakdown of one of the three toilets wasn't a big deal, he said. It was out of order just one day.

Endeavour's commander, meanwhile, said the mission has been so jam-packed with activity that he's had trouble finding time to "tweet." Mark Polansky is only the second astronaut to file Twitter updates from space.

"Certainly up here, the complication of a shuttle mission is that it is hard to find the time, believe it or not, to write a 140-character tweet," Polansky said. "At the end of the day, you barely have enough time, sometimes, to catch dinner and get yourself to bed."

However, he said he's enjoyed the Twitter experience and the opportunity to reach a segment of the public that might not otherwise pay attention to space travel.

Later Saturday, a circuit breaker popped and knocked out the U.S. carbon dioxide removal system for the space station. A similar system on the Russian side, however, was working fine and the astronauts had backup options as well for cleansing the air. Mission Control said there was no immediate effect on shuttle or station operations.

It was not immediately known whether the large number of people contributed to the problem.

Polansky and his six shuttle crewmates will depart the space station Tuesday, after delivering and installing a porch and outdoor experiments for Japan's huge science lab, and return to Earth at the end of the week. They rocketed into orbit July 15.