S121-E-06217 (10 July 2006) --- Astronaut Piers J. Sellers, STS-121 mission specialist, works in the Space Shuttle Discovery's cargo bay during the mission's second session of extravehicular activity (EVA). During today's six-hour 47-minute spacewalk, Sellers and astronaut Michael E. Fossum (out of frame), mission specialist, restored the International Space Station's Mobile Transporter rail car to full operation and delivered a spare pump module for the station's cooling system.