Grapple fixtures are used on spacecraft or other objects to provide a secure connection for a robotic arm.
- 1 North American grapple fixture
- 2 European grapple fixture
- 3 References
- 4 External links
North American grapple fixture
The fixtures allowed the Space Shuttle's Shuttle Remote Manipulator System (also known as Canadarm1) to safely grapple large objects. It currently does the same for the International Space Station's Space Station Remote Manipulator System (also known as Canadarm2) and the Japanese Experiment Module Remote Manipulator System. 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 lock 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.
Flight-Releasable Grapple Fixture
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. Earlier in the Shuttle Program it was referred to as the Flight Standard Grapple Fixture (FSGF).
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. The fixture can have a maximum payload rating of 65,000 pounds or 143,000 kg [sic]. An orbital replacement unit may also have a grapple fixture.
Latchable Grapple Fixture
The Latchable Grapple Fixture (LGF) allows for grappling and latching, intended to be used for longer‐term stowage on the Payload Orbital replacement unit Accommodation (POA) (greater than 3 weeks). It does not have any electrical connectors.
Electrical Flight Grapple Fixture
The Electrical Flight Grapple Fixture (EFGF) allows for grappling. It has a single electrical connection for data, video and power. The electrical connection is compatible with the Shuttle Remote Manipulator System (also known as Canadarm1) and the Japanese Experiment Module Remote Manipulator System.
Power and Video Grapple Fixture
The Power and Video Grapple Fixture (PVGF) allows for grappling and latching. It has electrical connectors for data, video, and power. The electrical connections are compatible with the Space Station Remote Manipulator System (also known as Canadarm2).
Power and Data Grapple Fixture
The Power Data Grapple Fixture (PDGF) allows for grappling and latching. It has electrical connectors for data, video, and power; it is also the only North American grapple fixture that is replaceable on-orbit. The electrical connections are compatible with the Space Station Remote Manipulator System (also known as Canadarm2).
It is 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.
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. 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.
Remote Manipulator System
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.
Grapple fixture on the Hubble Space Telescope(red arrow pointing at dark circle). This allowed Hubble to be moved with the Space Shuttle Canadarm.
End effector on Canadarm2 uses three cables to snare a grapple fixture and is surrounded by four latch mechanisms.
European grapple fixture
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.
- http://iss.jaxa.jp/en/htv/mission/htv-1/presskit/htv-1_presskit.pdf pg19
- 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.
- Callen, Phillip (June 2014). "Robotic Transfer and Interfaces for External ISS Payloads" (PDF). NASA. Retrieved 23 November 2015.
- Savi S. Sachdev, Brain R. Fuller (1983). "The Shuttle Remote Manipulator System and Its Use In Oribital Operations". Spar Aerospace. Retrieved 23 November 2015.
- Space station catches Dragon by the tail
- Progress in Astronautics and Aeronautics V.161: Teleoperation and Robotics in Space. American Institute of Aeronautics and Astronautics. 1994. p. 460. Retrieved 30 January 2015.
- Mobile Servicing System
- http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140008875.pdf pg324