The Lyappa (or Ljappa) arm was a robotic arm used during the assembly of the Soviet/Russian space stationMir. Each of the Kvant-2, Kristall, Spektr and Priroda modules was equipped with one of these arms, which, after the module had docked to the core module's forward port, grappled one of two fixtures positioned on the core module's hub module. The module's main docking probe was then retracted, and the arm raised the module so that it could be pivoted 90 degrees for docking to one of the four radial docking ports.
It was a mechanically driven arm used to move modules from the forward (or axial) docking ports which had rendevouz equipment fitted to the permanent radial docking ports. The arm mated with a socket located on Mir’s multiple docking assembly node adjacent to the -XB end of the Base Block. Once connected, the module's main docking probe retracted and the arm raised the module so that it pivoted 90 degrees for docking to a radial port.