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. 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. The arrival of Pirs docking compartment on September 16, 2001 provided another airlock from which Orlan spacewalks can be conducted.
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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.[1] 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.
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, 5 psi (34 kPa), pure-oxygen atmosphere of the spacesuit.[2] The previous method of preparing for spacewalks involved breathing pure oxygen for several hours prior to an EVA to purge the body of nitrogen. In April 2006, Expedition 12 Commander Bill McArthur and Expedition 13 flight engineer Jeffrey Williams tested a new method of preparing for spacewalks by "camping out" or spending the night in the Quest airlock.[3] In the chamber, the pressure was reduced from the normal 14.7 to 10.2 psi (101 to 70 kPa).[2] 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.[2][3][4]
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 900 psi (6.2 MPa) oxygen for recharging the space suits (EMUs). Recharging the high pressure tanks is accomplished by the orbiter when it is docked to the station's Pressurized Mating Adapter 2 or Pressurized Mating Adapter 3, using lines that are routed through the pressurized elements. The Oxygen Recharge Compressor Assembly (ORCA) is used to pump oxygen from the shuttle tanks into the high-pressure oxygen tanks on the space station.[5]
The airlock and tank systems were built out of aluminium and tested at NASA's Marshall Space Flight Center in Huntsville, Alabama by the Boeing Company.
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