An Evolution in Design for Canada's Robotic Arms

When Canadarm2 (also known by its technical name, the Space Station Remote Manipulator System), took the first step off its pallet and onto the International Space Station (ISS), it was a dramatic moment that signified an evolution in space robotics.

Unlike the Shuttle's Canadarm, Canadarm2 is not permanently anchored at one end. Instead, each end can be used as an anchor point while the other performs various tasks.

End-to-end mobility

This design gives Canadarm2 the unique ability to walk around the Station on its own, moving end-over-end to the power data grapple fixtures placed around the Station exterior. Each fixture provides the arm with power and a computer/video link to astronaut controllers inside.

The end-over-end concept was born early in the development of Canadarm2. Engineers realized that the arm would need extra mobility to reach all parts of the Space Station—far more reach than the Canadarm, which was attached at one end to the Shuttle.

Canadarm2 as seen through a porthole of the ISS. (Credit: NASA)

Canadarm2 is larger and heavier than the original Canadarm. On Earth, it weighs about 1,640 kilograms compared with 410 kilograms for the Canadarm. It can handle payloads of up to 116,000 kilograms-that is, the weight of the Shuttle, for the arm was designed to pull the Shuttle in to berth with the Station.

With seven joints, or degrees of freedom, rather than Canadarm's six, Canadarm2 is the more flexible of the two. It can bend, rotate and manoeuvre itself into tight spots—crucial qualities for the larger and more complex operational tasks it must perform.

Component design

Most of the equipment on the outside of the station will be made up of orbit replaceable units, components that can be swapped for new units when they wear out or fail and are designed to be easily handled by robots or astronauts. Canadarm2 is an important tool in maintenance operations.

In fact, Canadarm2 is itself made of components that can be replaced on orbit. In June 2002, the wrist roll joint component was replaced by spacewalking astronauts. Unlike the Shuttle's Canadarm, Canadarm2 is designed to be refurbished in space and will probably never return to Earth.