SUBMITTED BY ARTHUR N1ORC - AMSAT A/C #31468

Mission Specialists Dave Williams and Rick Mastracchio will go spacewalking for the second time today. Their primary task is to replace a faulty attitude control gyro on the International Space Station. The spacewalk is slated to begin at 11:31 a.m. EDT ( 1531 UTC ) and last 6.5 hours.

The faulty gyro is one of four devices, called control moment gyros (CMGs), located in the Z1 truss that are used to control the station’s orientation. The new CMG rode to the station on External Stowage Platform-3 in Space Shuttle Endeavour’s payload bay.

Mission Specialist Tracy Caldwell will resume her role as the mission’s spacewalk coordinator and Pilot Charles Hobaugh will operate the station’s robot arm. Two more spacewalks are scheduled for STS-118’s stay at the station.

Meanwhile on Earth, experts continue to analyze imagery collected Sunday during the STS-118 crew’s focused inspection of five areas of concern on the Endeavour’s heat shield.

*Managers Add Three Days to Shuttle Mission*

Mission managers decided Sunday to extend the STS-118 mission by three days. The decision came after the successful operation of the new Station-to-Shuttle Power Transfer System (SSPTS).

Endeavour is now scheduled to undock from the International Space Station on Aug. 20 and land Aug. 22. In addition to the extra time at the orbital outpost, managers added a fourth spacewalk that is scheduled to take place Aug. 17.

The SSPTS reroutes power from the space station to the shuttle during docked operations, allowing the orbiter to conserve materials needed to generate power and spend more time in space.