Astronauts Gear Up For Historic Spacewalk

The U.S. Quest airlock is being partially depressurized at this hour as the joined crews of Atlantis and the International Space Station prepare for the last shuttle-era spacewalk.

Space Station flight engineers Mike Fossum and Ron Garan just finished breathing pure oxygen to rid their vascular systems of nitrogen bubbles that could cause severe bouts of decompression sickness during a spacewalk in a low-pressure spacesuit. SCUBA divers call this phenomenon "the bends," and it can be quite painful -- even deadly.

The two astronauts soon will finish suiting up inside the airlock with an assist from Atlantis commander Chris Ferguson. And then they'll use a new procedure to complete the nitrogen purge. Once fully suited, Fossom and Garan will move their arms and legs in what is called an In-Suit Light Exercise (ISLE) protocol.

Used for the first time on Endeavour's final flight in May, the new procedure obviates the need to camp out in the Quest airlock all night prior to a spacewalk.

Today's planned 6.5-hour spacewalk remains scheduled for a start at 8:44 a.m.