The Docking Module was delivered and installed by STS-74, making it possible for the space shuttle to dock with Mir. On STS-71 in June 1995, the shuttle docked with the Kristall module on Mir. However, to make that docking possible, the Kristall configuration had to be changed to give the shuttle enough clearance to dock. Russian cosmonauts performed an extravehicular activity (a spacewalk) to move the Kristall module from a radial axis to a longitudinal axis, relative to Mir. After the shuttle departed, Kristall was moved back to its original location.
It would be impractical to leave Kristall in the longitudinal axis position because the longitudinal dock is used by the Russian vehicles Progress-M and Soyuz-TM. Moving Kristall back and forth between the two ports is not feasible. Therefore, the only workable solution was to add an extension to Kristall as it remains in its radial axis. This makes it possible for the shuttle to dock with Mir without interfering with the solar arrays, which are deployed near Kristall.