Friday, July 24, 2009

Live in orbit: Fourth spacewalk set to begin

Blogger update, 9:53 a.m.: The Quest airlock hatch is open.

Endeavour spacewalkers Chris Cassidy and Tom Marshburn are preparing to head outside the International Space Station to swap out a set of old batteries.

The two rookie mission speciliasts, both making their second spacewalk, are depressurizing the Quest airlock from sea level to a vaccuum. They paused at 5 pounds per square inch to perform spacesuit leak checks.

The fourth of five planned spacewalks during Endeavour's 16-day mission was scheduled to start just before 10 a.m.

It is expected to last about seven hours and 30 minutes.

Cassidy and Marshburn hope to replace four more solar array batteries at the far left side of the station's football field-length central truss.

Two were replaced Wednesday during the mission's third spacewalk, which was ended early because Cassidy's spacesuit showed above-normal carbon dioxide levels.

Endeavour mission specialists Julie Payette, of the Canadian Space Agency, and Koichi Wakata, of the Japanese Aerospace Exploration Agency, will operate station robotic arms to help move the batteries into position at the end of the truss.

Endeavour commander Mark Polansky and pilot Doug Hurley will operate the shuttle's robotic arm.

The spacewalkers will remove the four remaining old nickel-hydrogen batteries and fasten them to a carrier for return to Earth, and install new ones.

Station flight engineer Tim Kopra will choreograph the spacewalkers' moves from inside Endeavour's flight deck.

Check out this NASA TV schedule for a look at highlights of the day and mission ahead.

This Flight Day 10 Execute Package includes more detailed timelines and messages sent to the crew by Mission Control.

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