The U.S. Joint Airlock is a spacewalker's gateway to the infinite void and back.
It is also the solution to a problem that may sound alien to Earthlings: American spacesuits can't use Russian airlocks for leaving or entering the International Space Station.
Russia's airlocks have the support systems required for Russian spacesuits, but weren't designed for those of other countries. U.S. astronauts used the Space Shuttle as an airlock until the Joint Airlock was delivered in 2000. It accommodates both American and Russian spacesuits.
The Airlock is connected to the right side of Node 1 Unity with Canada's 55-ft. robot arm. It has two components: a Crew Lock from which astronauts and cosmonauts exit the ISS and step into space, and an Equipment Lock used for storing gear and for overnight "campouts."
The Crew Lock's design was derived from the Space Shuttle external airlock. It has element lighting, handrails and an "Umbilical Interface Assembly."
The Assembly is located on one wall and provides water, wastewater return, oxygen, communication gear and spacesuit power. It simultaneously supports two spacesuits—two American, two Russian, or one of each.
Before spacewalkers open its hatch to the vacuum of space, the Crew Lock is depressurized to 3 pounds per square inch (psi) of atmospheric pressure, then to zero psi. The atmosphere inside their spacesuits will be pure oxygen pressurized at 4.3 psi.
Space-walking astronauts and cosmonauts will have been prepared for these unusual regimes during the previous night's "campout" in the Equipment Lock.
The Equipment Lock campout is similar to any other campout in name only. The name stems from the requirement that the one or two astronauts who will be emerging from the ISS sleep in the Equipment Lock the night before. While they sleep, atmospheric pressure is reduced from 14.7 psi (the normal, sea-level pressure that is maintained in the ISS) to 10.2 psi. This purges nitrogen from their bodies and thus prevents decompression sickness (the "bends" that SCUBA divers sometimes experience) when they adjust to the 4.3 psi pressure inside their spacesuits.
The Equipment Lock houses stations that make it easier for astronauts and cosmonauts to don and off their spacesuits -- not an easy task -- and to service them. It also houses two racks, one for avionics, the other for cabin air. Batteries, power tools and other supplies will be stored in specially-designed storage areas.
High pressure tanks that will supply the atmospheric gases oxygen and nitrogen will be mounted externally on the Joint Airlock. Until the Airlock was attached to the ISS, Russia';s Service Module supplied those gases.
The 6.5-ton, 20-ft. long, 13-ft. diameter module is built by Boeing at Marshall Space Flight Center in Huntsville, Alabama.