Discovery Astronauts Go for a Spacewalk

Two astronauts are spacewalking outside the International Space Station.

Rick Mastracchio and Clayton Anderson, members of Discovery's visiting crew, ventured out early Friday on the first spacewalk of their mission. They will remove a new ammonia tank from the shuttle and disconnect the station's old tank that supplied the cooling system. It will take three spacewalks to complete the job.

Mastracchio and Anderson were supposed to do some battery work on the far left end of the space station, along the sprawling power truss. But NASA canceled the task this week because of concern the two might get shocked. The work instead will be carried out on the next shuttle flight, once astronauts' suits are better protected.

"Gentlemen, the weather's beautiful outside, it's a great day for an EVA," pilot James Dutton radioed from outside the airlock prior to the two astronaut's leap into space. EVA is an acronym for Extravehicular Activity. "Have a great time, guys."

CBS News space consultant William Harwood reports that Friday's is the 141st EVA devoted to the assembly and maintenance of the ISS since construction on the massive international project began in 1998.

Click here to follow Harwood's up-to-the-minute updates on the shuttle mission at CBS News' Space Place.

It is the fourth spacewalk overall for both Mastracchio and Anderson, and the fifth so far this year. Two more EVAs are planned for the Discovery astronauts during this visit to the ISS.