Grapple fixture

Grapple fixtures are used on spacecraft or other objects to provide a secure connection for a robotic arm.

The fixtures allowed the Space Shuttle's Canadarm (also known as the Shuttle Remote Manipulator System, or SRMS) to safely grapple large objects. It currently does the same for the International Space Station's Space Station Remote Manipulator System (SSRMS) (also known as Canadarm2) and the Japanese Experiment Module Remote Manipulator System (JEMRMS). The grapple fixtures are flat in appearance, with a central grapple pin topped with a sphere which the snares in the end of the arms latch on to. They use three "ramps" that help guide the robotic arm correctly onto the grapple fixture.

The North American grapple fixture was developed at Spar Aerospace in the 1970s. Its invention is credited to Frank Mee, who also invented the Canadarm end effector for the Space Shuttle. The Grapple Fixture design was further refined by Barrie Teb.

The Flight-Releasable Grapple Fixture (FRGF) is the simplest variation of the North American grapple fixture, it allows only for grappling and does not have any electrical connectors. Its use began early in the Space Shuttle program and was developed from the Flight Standard Grapple Fixture (FSGF) by allowing the Grapple Shaft to be installed during extravehicular activity (EVA).

Unpiloted ships like the SpaceX Dragon, Orbital ATK Cygnus and Japanese H-II Transfer Vehicle include a standard FRGF which is used by the Canadarm2 to grapple the capsule on approach to the International Space Station for berthing. The fixture can have a maximum payload rating of 65,000 pounds or 30,000 kg. An orbital replacement unit may also have a grapple fixture.

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