NASA Television will broadcast the third spacewalk of the Expedition Four increment aboard the International Space Station (ISS) with commentary and available downlink television beginning at 6:30 a.m. EST on Wednesday, Feb. 20.

On the 40th anniversary of the first U.S. orbital spaceflight by John Glenn, Flight Engineers Carl Walz and Dan Bursch will conduct the planned six-and-a-half-hour Extravehicular Activity (EVA), or spacewalk, to revalidate all systems of the Quest Airlock. Hatch opening on the Quest is expected shortly after 7 a.m. EST.

This will be the first use of the station's airlock since July 2001 and sets the stage for four spacewalks out of Quest to attach the first of several large truss segments to the complex during the STS-110 shuttle mission scheduled for early April.

Commander Yury Onufrienko, who will serve as the spacewalk choreographer from inside the Destiny Laboratory, will assist Walz and Bursch, who will be wearing U.S. spacesuits called Extravehicular Mobility Units. Walz will be visible by the red stripes on his suit, while Bursch's suit will have no markings. Each already has conducted a spacewalk since boarding the ISS in December.

This will be the second spacewalk mounted from Quest, which was delivered to the ISS and inaugurated by STS-104 spacewalkers Mike Gernhardt and Jim Reilly last July.

The Expedition Four crew is in the third month of a planned five-month stay on the complex.

NASA TV can be found on GE-2, Transponder 9C, vertical polarization at 85 degrees West longitude, 3880 MHz, with audio at 6.8 MHz.

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