The docking module was added to Mir during the second Shuttle/Mir docking mission, STS-74, in late 1995. The first shuttle docking, STS-71 in June 1995, required the a spacewalk by Russian cosmonauts to move the Kristall module to a docking port regularly used by Progress-M and Soyuz-TM spacecraft, so the shuttle could dock to Kristall without bumping into any of the solar arrays in the vicinity of the module. Kristall was moved back to its regular location after the docking mission.
The docking module is attached to the end of the Kristall module and allows the shuttle to dock with Mir without brushing against any of the solar panels. Experiments to measure the cosmic radiation environment outside the shuttle have been attached to it, and were removed during a joint American-Russian spacewalk during the STS-86 docking mission in October 1997.