Live in orbit: Battery replacement on schedule

Blogger update, 1:25 p.m.: The day's second new battery is installed, accomplishing the minimum goal missin controllers set for the spacewalk. Ground controllers got good reading from the first. Two more new batteries remain to be installed during the spacewalk's second half.

Two Endeavour astronauts are a third of the way through today's planned seven-hour, 30-minute spacewalk, and working on schedule.

Mission specialists Chris Cassidy and Tom Marshburn have installed one new solar array batteriy on the left end of the International Space Station's central truss, or backbone. It is the third new battery installed during the mission, and three more are left.

The spacewalkers have also removed one old battery from the truss and fastened it to a cargo palette, which will return all six old batteries to Earth in shuttle Endeavour's payload bay.

The nickel-hydrogen batteries store power supporting the U.S. Destiny module when the station's orbit swings around Earth and away from direct sunlight.

In total, four old batteries have been removed from the solar array assembly on the Port 6 truss, Nos. 1 through 4. Battery No. 4, No. 3 and No. 2 are fastened to the cargo palette, while No. 1 is in a temporary storage spot.

The spacewalkers are getting set to remove a fourth new battery from the palette. The new batteries are identified by letters, and this one is D.

NASA mission controllers say Cassidy and Marshburn's spacesuits are performing well. If they run low on oxygen, it can be replenished with a stop back at the Quest airlock.