Fourth Spacewalk Testis Shuttle's Heat Shield

March 21, 2008

Mission Specialists Robert L. Behnken and Mike Foreman continue their work outside the International Space Station as the docked station and space shuttle Endeavour orbit high above the Earth. The two shuttle crew members began the fourth spacewalk of the STS-123 mission at 6:04 p.m. EDT.

STS-123 Mission Specialist Robert L. Behnken prepares for the mission's fourth spacewalk inside the station's Quest airlock.

Behnken and Foreman successfully replaced a failed Remote Power Control Module – essentially a circuit breaker – on the International Space Station’s truss. However, there were difficulties removing a power connecter from the Z1 truss. If time permits, the astronauts may go back at the end of the spacewalk and make another try.

They are now working to test a repair method for damaged heat resistant tiles on the space shuttle. This technique uses a caulk-gun-like tool named the Tile Repair Ablator Dispenser to dispense a material called Shuttle Tile Ablator-54 into purposely damaged heat shield tiles. Once the test is complete, the sample tiles will be returned to Earth to undergo extensive testing on the ground.

Behnken and Foreman will begin the mission’s fifth and final spacewalk Saturday at 5:23 p.m. Among other tasks, they will stow the Orbiter Boom Sensor System on the station’s main truss to be retrieved by the crew of Discovery on STS-124, the next space shuttle mission.