The Quest Airlock consists of two segments, the "Equipment lock" that stores spacesuits and equipment, and the "Crew Lock" from which astronauts can exit into space. It was derived from the Space Shuttle airlock, although it was significantly modified to waste less atmospheric gas when used. It was attached to the starboard CBM of the Unity during STS-104. It has mountings for four high-pressure gas tanks, two containing oxygen and two containing nitrogen, which provides for atmospheric replenishment to the American side of the space station, most specifically for the gas lost after a hatch opening during a space walk. Quest was necessary because American suits will not fit through a Russian airlock hatch and have different components, fittings, and connections. The airlock is designed to contain equipment that can work with both types of spacesuits, however, it is currently only able to host American spacewalks because the equipment necessary to work with Russian space suits has not been launched yet, which required the Expedition 9 crew to take a circuitous route to a worksite because of problems with the American space suits.
Camp-out procedure
Quest provides an environment where astronauts can "camp out" before a spacewalk in a reduced-nitrogen atmosphere to purge nitrogen from their bloodstream and avoid decompression sickness in the low-pressure pure-oxygen atmosphere of the spacesuit. In April 2006, Expedition 12 Commander Bill McArthur and Expedition 13flight engineerJeffrey Williams tested this new method of preparing for spacewalks by spending the night in the Quest Airlock. In the chamber, the pressure was reduced from the normal. Four hours into the Expedition 13 crew's sleep period, an error tone prompted mission controllers to cut short the activity, but the test was still deemed a success. American spacewalk activities thereafter have employed the "camp-out" pre-breathing technique. The previous method of preparing for spacewalks involved breathing pure oxygen for several hours prior to an EVA to purge the body of nitrogen.
High-pressure gas tanks
Two oxygen and two nitrogen high-pressure gas tanks are attached externally to the airlock. These tanks provide a replenishable source of gas to the atmosphere control and supply system and oxygen for recharging the space suits. Recharging the high-pressure tanks was accomplished by the Space Shuttle fleet until its retirement. When an orbiter was docked to the station's Pressurized Mating Adapters, oxygen was routed through pressure lines from the PMAs to the Quest Airlock. The pumping of the oxygen from the docked spacecraft tanks into Quests high-pressure tank was accomplished by the Oxygen Recharge Compressor Assembly. After the retirement of the Space Shuttle fleet, the Nitrogen Oxygen Recharge System and spacecraft from the Commercial Crew Development program will take over this task.
