In this photo provided by NASA, Astronauts Mike Barratt (top-C), Expedition 20 flight engineer, and Dave Wolf (bottom C), STS-127 mission specialist, assist astronaut Tom Marshburn (L) and Christopher Cassidy following the completion of the fourth spacewalk for the joint shuttle-station crews currently aboard the International Space Station while it is docked to the Space Shuttle Endeavour July 24, 2009 in Space.