The "Quest" Joint Airlock Module is designed to be the primary airlock for the International Space Station, designed to be able to host spacewalks with both the American and Russian spacesuits. Before Quest was attached, Russian spacewalks were required to be done from the service module and American spacewalks were only possible when the Space Shuttle was docked.

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 side of the Unity Module 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.

The Quest Airlock 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 airlocks, 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 suit.

Quest is designed to provide 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 pure-oxygen atmosphere of the spacesuit.

The airlock and tank systems were built out of Aluminum and tested at NASA's Marshall Space Flight Center in Huntsville, Ala. by the Boeing Company

The airlock is 5.5 meters long, has a diameter of 4 meters, weighs 6,064 kg, and encompasses 34 cubic meters of volume. The total cost was $164 million.

Airlock specifications

• Material: aluminum
• Length: 5.5 m (18 ft)
• Diameter: 4 m (13 ft)
• Weight: 6,064 kg (13,368 lb)
• Volume: 34 m³ (1,200 ft³)
• Cost: $164 million, including tanks