Until a couple of years ago the Soyuz capsules had usually docked at the aft end of the Zvezda module, which had been the "tail" of the ISS. More recently a new module called the Hub had been attached to the Zvezda, extending the main axis of the space station "rearward," and providing the axle around which the torus revolved. In order to maintain compatibility with the ubiquitous and time-tested Soyuz, the Hub had been equipped with a suitable port and hatch.