Published: May 20, 2011 7:21 PM EDT
Updated: May 20, 2011 7:22 PM EDT

HOUSTON (AP) - Two astronauts cut short Friday's otherwise routine spacewalk because of a broken spacesuit sensor, but most of their work was already finished outside the International Space Station.

Nearly five hours into the 6½-hour spacewalk, mission controllers noticed that Gregory Chamitoff's carbon dioxide sensor wasn't working. NASA needs to know if levels of carbon dioxide - expelled when you breathe - get too high.

It's likely that moisture caused the infrared sensor to fail, said lead spacewalk officer Allison Bolinger. She said engineers hope it will dry out by Chamitoff's next spacewalk in one week because there's only one extra large spacesuit on board that fits him.

The levels were probably not too high, but controllers told Chamitoff and spacewalking partner Drew Feustel not to finish installing an antenna on the space station because it would take too much time.

Instead the duo did cleanup and other tasks. The spacewalk lasted six hours and 19 minutes, just 11 minutes shy of the scheduled time. Astronauts said the spacewalk was still a success.

"Really happy how it worked out today," Chamitoff said.

Feustel and Chamitoff had already installed a light fixture, swapped out some experiments parked outside the space station and were installing the antenna when the work was halted.

NASA officials said this spacewalk was supposed to be as routine as they get for what is always a risky task of strolling outside in space. Unlike other spacewalks, when the tasks were so tough their labored breathing could be heard on the radio, Chamitoff and Feustel didn't sound like they were out of breath.

This was the first spacewalk for Chamitoff. He called it "a dream come true for me."

Endeavour's astronauts will make four spacewalks while docked at the space station. Their 16-day mission, which ends June 1.

This is Endeavour's last flight and the second last of the space shuttle program. NASA is shutting down the program this summer after 30 years, to focus on interplanetary travel. One more mission remains, by shuttle Atlantis, to carry up a load of supplies and equipment.

On Friday, NASA set July 8 as the target date for that launch.

Mission controllers are still analyzing two damaged thermal tiles on Endeavour's underbelly. Unless ground engineers can prove that the two gouges - one of them the size of a deck of cards - are not a safety problem, Endeavour will make an unusual added inspection of the underbelly Saturday. That examination would involve a camera and laser at the end of a boom at the end of the shuttle's robot arm.

Damage on tile was blamed for the disintegration of space shuttle Columbia in 2003. But similar damage to Endeavour in 2007 did not cause problems.

NASA managers on Friday approved a first-of-its-kind maneuver on Monday for a photo op when a Russian Soyuz capsule undocks from the space station with three astronauts aboard. The capsule will back away to about 600 feet and stop. Then the station will slowly rotate so the Soyuz can get rare photos of the shuttle docked to the station from different angles and from another spaceship.

Endeavour arrived at the space station Wednesday, and the next day installed a $2 billion physics experiment that looks for antimatter and dark matter. Saturday, the two crews will get an unprecedented VIP call - Pope Benedict XVI will make the first papal call to space.

Endeavour's day started Friday with a wake-up song written by two Kennedy Space Center employees, Dan Keenan and Kenny McLaughlin. The song is called "We All Do What We Can Do" and honors workers who prepare the shuttles for launch.

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