The Quest Joint Airlock, previously known as the Joint Airlock Module, is the primary airlock for the International Space Station. Quest was designed to host spacewalks with both Extravehicular Mobility Unit (EMU) spacesuits and Orlan space suits. The airlock was launched on STS-104 on July 14, 2001. It was attached to the starboard CBM of the Unity during STS-104. The four external HP tanks were installed in pairs on two occasions. Before Quest was attached, Russian spacewalks using Orlan suits could only be done from the Zvezda service module, and American spacewalks using EMUs were only possible when a Space Shuttle was docked, allowing the astronauts to use the Shuttle's airlock, located in its payload bay. The arrival of Pirs docking compartment on September 16, 2001 provided another airlock from which Orlan spacewalks can be conducted. Requirements Quest was necessary because American suits (EMUs) 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. It is sized to allow EVAs with two crew. Early use EMU EVAs were conducted from the ISS Joint Airlock in July 2001, February 2002, April 2002, and June 2002. Design 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 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. Equipment lock segment The larger equipment lock has storage space for EMU suits and equipment to check and maintain the EMUs. There is a Battery Charging Assembly, a Battery Stowage Assembly, a Fluid Pumping Unit (FPU) (to refill the EMU water tanks after each EVA), and much else. Crew lock segment The hatch to space (EV hatch) has an inward