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S123-E-007907 (21 March 2008) --- Astronaut Robert L. Behnken, STS-123 mission specialist, participates in the mission's fourth scheduled session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 6-hour, 24-minute spacewalk, Behnken and astronaut Mike Foreman (out of frame), mission specialist, replaced a failed Remote Power Control Module -- essentially a circuit breaker -- on the station's truss. The spacewalkers also tested a repair method for damaged heat resistant tiles on the space shuttle. This technique used a caulk…