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Friday, March 21, 2008 - 3:00 a.m. CDT
Mission Control Center, Houston, Texas
STS-123 MCC Status Report #21
Astronauts Bob Behnken and Mike Foreman completed the fourth spacewalk of Endeavour’s STS-123 mission early today. The duration of the spacewalk was 6 hours 24 minutes, and it was the 108th spacewalk in support of the construction of the International Space Station.

Behnken and Foreman replaced an electrical circuit box called a Remote Power Controller Module (RPCM) on the station's truss. One of the goals of the task was to restore redundant power to control moment gyroscope (CMG) 2, but the astronauts were unable to remove one of the connectors from the Z1 truss. CMG-2 will continue to operate on its primary RPCM until that connector is removed.

The major focus of today’s spacewalk was a demonstration of the Tile Repair Ablator Dispenser – a caulk-gun-like device – and the application of a substance called Shuttle Tile Ablator-54 (STA-54) into intentionally damaged heat shield tiles. The astronauts applied the STA-54 into various molds, including a few that were created to resemble damage seen on previous shuttle missions and damaged tiles from prior flights. The test samples will be returned to Earth to undergo extensive testing on how STA-54 performs in both a microgravity and vacuum environment.

Behnken and Foreman also removed a cover from Dextre, the station’s new robotic attachment, and some of the launch locks that were still attached to the Harmony module. Those locks were removed in preparation for the arrival of the pressurized Japanese Kibo laboratory aboard Discovery in May.

Mission managers on the ground are continuing to assess what is believed to be a software error involving the shoulder roll joint of Dextre. The shoulder joint had been working properly yesterday, but commands detected errors as the teams worked through power-up procedures. Both of Dextre’s arms are currently stowed in their proper position.

The next STS-123 status report will be issued after crew wake-up at 12:28 p.m., or earlier if events warrant.

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