A Grapple Fixture is a connection fixture used on capsules, satellites and other objects handled by the Space Shuttle and International Space Station (ISS). The fixture allows Canadarm robotic arms aboard the Space Shuttle orbiters and Canadarm2 aboard the ISS to safely grapple large objects. Grapple fixtures are flat in appearance, with a central grapple pin topped with sphere which the snares of Canadarm2 latch on to. They also feature three curved "ramps" that help to lock the end effector on the robotic arm to the fixture.
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. The Grapple Fixture design was further refined by Barrie Teb.
Power 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 all have four rectangular connectors to transfer data, video and electrical power. Delivered by Space Shuttle Atlantis there are four PDGFs on the American made Mobile Transporter (MT) that travels 108 metres along truss mounted rails. During STS-134 a PDGF was installed on the Zarya module to support Canadarm2 operations based from the Russian segmet.
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 ISS to grapple the capsule on approach to the station for berthing.
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. 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. There is one PDGF on Dextre, which has smaller arms and tools for Canadarm2.
FRGF visible (dark circles at the bottom) on the Hubble Space Telescope prior to its launch
- CanadaArm2 End Effector
- Dotto, Lydia (1992). A Heritage of Excellence: 25 years at Spar Aerospace Limited. David Steel. Canada: Spar Aerospace Limited. pp. 42–43. ISBN 0-9696618-0-0.
- Space station catches Dragon by the tail
- Mobile Servicing System
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