Spacewalkers Peggy Whitson and Dan Tani mounted coolant supply and return lines on the hull of the Destiny laboratory module today, hooked up quick-disconnect fittings on each end and opened valves to route ammonia coolant to and from the new Harmony connecting module on the front of the lab complex.

Whitson and Tani installed the coolant loop A tray during a spacewalk Tuesday and hooked up data and power lines to the new module. With today's installation of the loop B coolant loop tray on the left side of Destiny, the critical power and cooling connections between Harmony and the station's main power truss were complete.

"I know my Mom's watching on the internet in Chicago, so hi Mom," Tani called as the station sailed down the western coast of South America. "See, I do work for a living!"

Today's spacewalk began an hour and 10 minutes ahead of schedule. Floating in the Quest airlock module, Whitson and Tani switched their spacesuits to battery power at 4:50 a.m. today to officially kick off a planned six-and-a-half-hour spacewalk.

Before the loop B tray could be unstowed from its mounting point on the central S0 solar array truss segment, Whitson and Tani removed a so-called "shunt jumper" from the quick-disconnect fittings on the S0 loop B supply and return lines. They also removed caps from the Harmony loop B coolant inlet and return ports.

Using power tools, the astronauts, positioned on each end of the loop B tray, released bolts to free the bulky coolant line carrier and began manually maneuvering the 18.5-foot-long, 300-pound tray down to the Destiny laboratory module.

Tani now plans to move back to the right-side solar alpha rotary joint, or SARJ, on the main power truss that normally is used to turn outboard solar arrays to keep them face on to the sun. The starboard SARJ currently is locked in place because of metallic contamination discovered during an inspection by Tani late last month.

Tani plans to remove thermal cover No. 7 today, along with two debris shields, to provide access to a different part of the 10-foot-wide rotary joint. He and Whitson then will inspect the interior of the joint and take additional pictures in a bid to help engineers determine the source of metallic filings seen on the main gear bearing race during the first inspection. He also may use adhesive tape to collect additional samples of the debris, if present under panel No. 7, for analysis on Earth.

While the station can operate normally in the near term with the starboard SARJ locked in place, the joint must be able to rotate normally before Japan's Kibo research module can be launched in April.

After looking over Tani's shoulder during the SARJ inspection to familiarize herself with the joint, Whitson plans to make her way back to the front of the lab complex to complete electrical connections that will permit docked shuttles to tap into the station's solar power grid.