Grapple Fixture

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Grapple Fixtures are used on capsules, satellites and other objects to provide a secure connection for robotic arms. The fixtures allow arms aboard the former Space Shuttle or Canadarm2 and the Japanese Remote Manipulator System aboard the International Space Station to safely grapple large objects.[1] 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 lock the robotic arm correctly onto grapple fixture.[2]

Development[edit]

The 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.[3] The Grapple Fixture design was further refined by Barrie Teb.[3]

Variants[edit]

Power Data Grapple Fixture[edit]

Power and Data Grapple Fixture

A Power Data Grapple Fixture (PDGF) is a quick connect fixture used on the International Space Station (ISS). PDGFs can be "grappled" by the Canadarm2 robotic arm, in order to allow the arm to manipulate and power a grappled object, or be commanded by operators based inside the ISS. PDGFs located around much of the station provide connections for the arm. They have four rectangular connectors to transfer data, video and electrical power. During STS-134 a PDGF was installed on the Zarya module to support Canadarm2 operations based from the Russian segment.[4]

Flight-Releasable Grapple Fixture[edit]

Flight-Releasable Grapple Fixture

A Flight-Releasable Grapple Fixture (FRGF) is a passive fixture which is identical to the Power Data Grapple Fixture (PDGF) but lacks its power and data ports. Unpiloted ships like the SpaceX Dragon, Cygnus (spacecraft) and Japanese (HTF) or 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.[5] The fixture can have a maximum payload rating of 65,000 pounds or 143,000 kg [sic].[6] An Orbital replacement unit may also have a grapple fixture.

European Robotic Arm Grapple Fixture[edit]

Although the European Robotic Arm planned for delivery in 2017 uses grapples to relocate in a similar fashion to Candarm2, the grapple fixtures are not compatible with each other. This means the European arm can only work on the Russian segments of the station.[7]

Canadarm2[edit]

The 1,641 kg, 17 metre long, three jointed, robotic arm is self-relocating and can move end-over-end on the PDGFs to reach many parts of the Space Station in an inchworm-like movement.[8] In this movement, it is limited only by the number of Power Data Grapple Fixtures (PDGFs) on the station. Power and data are supplied to Canadarm2 from the ISS, and to a grappled payload from Canadarm2.[9] Canadarm2 can grapple a PDGF on one end of Dextre (two arms with power tools). The other end of Dextre has the same latching end effector as Canadarm2, so the two of them connected together can still perform the end-over-end inchworm movement to move around the ISS.

Mobile Base System[edit]

Delivered by Space Shuttle Atlantis the Mobile Base System travels 108 meters along the length of the main truss and has four PDGF's that the Canadarm2 and/or the two armed Dextre can grapple.[10] The Mobile Base System also has one latching end effector for carrying payloads with a grapple fixture.

Remote Manipulator System[edit]

The Remote Manipulator System (JEMRMS) is a 10m long robotic arm, secured to the port cone of the Japanese Experiment Module-Kibo, it is intended to service the "Exposed Facility" and to move equipment to and from the "Experiment Logistics Module". The arm can use two types of ISS-common grapple fixtures: the Flight Releasable Grapple Fixture (FRGF) and the Power and Video Grapple Fixture (PVGF). The "Small Fine Arm", is 2m long and has a grapple fixture to attach to the end effector of the main arm.

References[edit]

External links[edit]