Without Unity, Astronauts Couldn't Get Anywhere on the Space Station

The Unity Module is the core of the International Space Station, the hub connecting all the specialized modules into a functional structure. It was carried into orbit as the primary cargo of STS-88 on the space shuttle Endeavour. The module was mated with the previously-launched Zarya module on December 6, 1998, marking the first step in assembling the International Space Station.