Anchored to the Space Shuttle Discovery's Remote Manipulator System/Orbiter Boom Sensor System (RMS/OBSS) foot restraint, astronaut Piers J. Sellers, STS-121 mission specialist, participates in the mission's first session of extravehicular activity (EVA) while the shuttle was docked with the International Space Station. Discovery's vertical stabilizer is at right. A blue and white Earth provides the backdrop for the scene.