(09/19/2000) --- Workers inside the vacuum chamber in the Operations and Checkout Building watch as an overhead crane lowers the Joint Airlock Module inside. The airlock is being tested for leaks. The module is the gateway from which crew members aboard the International Space Station (ISS) will enter and exit the 470-ton orbiting research facility. The airlock is a critical element of the ISS because of design differences between American and Russian spacesuits. The Joint Airlock Module provides a chamber where astronauts from every nation can suit up for space walks to conduct maintenance and construction work or to do science experiments outside the Station. The Space Shuttle Atlantis will carry the airlock to orbit on mission STS-104, the 10th International Space Station flight, currently targeted for liftoff in May 2001. The Shuttle crew will secure the airlock to the right side of Unity, the American-built connecting node that currently comprises one-third of the current Space Station, along with the Russian modules Zarya and Zvezda