The attention for the first of three scheduled spacewalks is the installation of the starboard truss segments (S3/S4), the second starboard truss segment, which will be attached to the first starboard truss segment, S1.

The truss segment (part of the backbone of the Space Station) is scheduled to be removed from the Shuttle Atlantis before the start of the first spacewalk. The $367.3 million truss segment will be lifted out of the Atlantis’ payload bay with the Shuttle’s robotic arm.

The 17.5-ton Starboard 3/Starboard 4 (S3/S4) truss segment contains a set of solar arrays, along with other energy systems. It will then be transferred to the Space Station’s robotic arm. The S3/S4 unit will then be installed on Monday during the first spacewalk.

These solar arrays are identical to those arrays installed on the port side (P3/P4 truss segment) of the Space Station in September 2006 on the STS-115 mission, also involving the Space Shuttle Atlantis.

U.S. astronauts and STS-117 mission specialists John “Danny” Olivas and Jim Reilly spent the night in a reduced atmospheric environment breathing pure oxygen (to remove nitrogen) within the U.S. Quest Airlock. After exiting the airlock, the two astronauts will perform their spacewalk in order to connect the new 35,000-pound S3/S4 segment to the Space Station. They will also remove the bolts and restrains that hold in place a solar array. It will be unfolded during a later spacewalk.

Reilly has performed in three previous spacewalks, while this one is the first spacewalk for Olivas.

The new solar array on the S3/S4 truss segment will provide an additional 14 kilowatts of power to the Station, which will eventually help to run new modules and laboratories attached to the truss segments.

The first spacewalk on Monday, June 11, 2007, can be watched live on NASA TV. It will last approximately 6.5 hours.

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