S121-E-06199 (10 July 2006) --- Astronauts Michael E. Fossum and Piers J. Sellers (partially out of frame), STS-121 mission specialists, participate in the mission's second session of extravehicular activity (EVA). During today's six-hour 47-minute spacewalk, Sellers and Fossum 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.