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Lyappa arm

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The Lyappa (or Ljappa) arm, officially Automatic system of re-docking (Russian: Автоматическая система перестыковки (АСПр), romanized: Avtomaticheskaya sistema perestykovki (ASPr)), was a robotic arm used during the assembly of the Soviet/Russian space station Mir. 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 Mir Core Module's forward (or axial) 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.[1][2][3]

Lyappa arm on Mir mock-up at the Gagarin Cosmonaut Training Center.
Indexing Robot Arm on Wentian

Likewise the Prichal module will host the grapple fixtures for the redocking of future modules docked to it from one port to another using the Lyappa Arm attached to those modules, if needed.

Both the Wentian and Mengtian modules of the Tiangong space station carry arms to enable them to manoeuvre around the docking hub of the Tianhe core module. A mechanical arm dubbed the Indexing robotic arm, which looks similar to the Lyappa arm, allowed them to dock to a radial port of the CCM.[4] It is different from Lyappa as it works on a different mechanism. Lyappa arm is needed to control the pitch of the spacecraft and redocking in a different plane. Where as the Indexing robot arm is needed for docking in the same plane. In addition to this arm used for docking relocation, the Chinarm on Tianhe module could also be used as a backup.[5][6]