An Evolution in Design for Canada's Robotic Arms

The Shuttle's Canadarm was used to launch the Hubble Space Telescope (Photo: NASA) Click to enlarge

When Canadarm2, the Space Station Remote Manipulator System (SSRMS), took the first step off its pallet and onto the International Space Station, 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-known as a Latching End Effector, or LEE-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-more than Canadarm which is attached at one end to the Shuttle.

Canadarm2 as seen through a porthole of the International Space Station by an Expedition 11 crewmember prior to the launch of STS-114 in July 2005.(Photo: NASA) Click to enlarge

Canadarm2 is larger and heavier than the original Canadarm. On Earth, it weighs about 1,640 kilograms compared with 410 kg for the Canadarm. It can handle payloads of up to 116,000 kilograms-that is, the weight of the Shuttle, for the the arm was designed to pull the Shuttle in to berth with the Station. However, today, the Shuttle is flown in to dock without the use of Canadarm2.

Canadarm2 and the original Canadarm work together, handing payloads to one another. With seven joints, or degrees of freedom, rather than Canadarm's six, the SSRMS is the more flexible of the two. It can bend, rotate and manoeuvre itself into difficult spots-crucial qualities for the larger and more complex operational tasks it must perform.

Animation showing the extraordinary capacity of Canadarm2 and its seven joints, easily manipulating payloads, large or small. (Animation courtesy of NASA) Animation (2.4MB) Windows Media Player

Component design

Most of the equipment on the outside of the station will be made up of orbit replaceable units. These ORUs are components that can be swapped for new units when they wear out or fail and are designed to be easily handled by robot arms 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 Canadarm, the SSRMS is designed to be refurbished in space and will probably never return to Earth.