Astronauts Aim To Tackle 1st Spacewalk

Two American astronauts are camping out in the International Space Station's U.S. Quest airlock, preparing to venture outside to stow a failed coolant pump and lay new track for the outpost's Canadian railway.

Discovery mission specialists Stephen Bowen and Al Drew aim to exit the airlock late this morning, capping an overnight effort to get ready for the first of two spacewalks planned during the shuttle's weeklong stay at the station -- a joint endeavor of 15 nations that include the U.S., Russian, Europe, Canada and Japan.

Bowen and Drew donned special head masks and breathed pure oxygen for about an hour last night to help purge nitrogen from their circulatory systems. The move is meant to prevent the type of decompression sickness -- know as 'the bends' -- that SCUBA divers encounter.

The two mission specialists then sealed themselves in the Quest airlock, where pressure was reduced to 10.2 psi from 14.7 psi, the latter of which is normal pressure at sea level. The reduced pressure decreases the amount of time the astronauts must spend preparing to enter a vacuum environment.

Here's a look at the day ahead:

11:18 a.m.: Spacewalk begins.

11:48 a.m.: Spacewalkers rig up electrical extension cable.

1:13 p.m.: Failed pump module moved to stowage platform.

3:18 p.m.: Spacewalkers install video camera stanchion extension on starboard station truss segment.

4:18 p.m.: Spacewalkers lay new section of rail track on starboard truss.

5:03 p.m.: Spacewalkers retrieve Japanese education payload.

5:48 p.m. Spacewalk ends.

You can watch mission operations unfold right here in The Flame Trench. Click one of the NASA TV links on the right to launch our NASA TV viewer and live coverage. And be sure to refresh this page for periodic updates.