Expedition Four Flight Engineers Carl Walz left and Daniel Bursch right, positioned in the equipment lock of the Quest Airlock, perform prebreathe operations in preparation for Extravehicular Activity EVA 3. Both astronauts are fully suited in their Extravehicular Mobility Units EMUs. Walz and Bursch will base the EVA from the U.S. built Quest Airlock, the first EVA to be performed from the airlock without a shuttle docked to the International Space Station ISS.
