Satellites - Grapple Fixture

The Canadarm can be used for launching or retrieving satellites (satellites can also be launched using rockets)
So that the Canadarm can grip these satellites, they are built with a part called a grapple fixture, which is attached to the bus of the satellite
The original grapple fixture consisted of a foot-long metal pin, a baseplate, and a target
The end of the Canadarm (called its End Effector) has three snare wires which wrap around the grapple fixture using small motors
The wires are then retracted, and the satellite is pulled snugly against the end of the Canadarm
Today, grapple fixtures have removable grapple pins so that if the Canadarm fails, an astronaut can manually remove the pin to release the satellite
Grapple fixtures now have an electrical connector on the end of the pin
This can join with an electrical adaptor (called a Special Purpose End Effector or SPEE) at the end of the Canadarm
This allows electrical power and data communications to move from the shuttle to the satellite when it is grappled
This is used to preserve a satellite's batteries during deploy and retrieval activities
The Canadarm is unable to grasp older satellites, or satellites not expected to be repaired in orbit, because they were not fitted with grapple fixtures when they were originally launched
The Canadarm can also only capture satellites which are in the same orbital path as the shuttle (for example, the shuttle never flies in a polar orbit)

Produced by Galactics.
Comments: galactics@spacesim.org.
Last updated on: 8 August 1997.