Canadian Inventions – Canadarm Robotic System

The Canadarm is a remotely operated robotic arm which was first installed in NASA's orbiter shuttles during the 1980s and remained in service for nearly 30 years. The arm allowed astronauts to deploy hardware from the shuttle’s payload bay, capture unrestrained objects in space and inspect the orbiter’s exterior insulation for damage, all from within the shuttle vehicle. It was capable of manoeuvring up to 293 tons in space and had a reach of over 15 metres when fully extended. The arm was officially retired at the conclusion of NASA’s space shuttle program in July 2011, after contributing to 90 space missions. By the time the Apollo 11 mission successfully touched down on the moon in 1969, NASA had conceived the next step in its burgeoning space exploration program: the orbiter space shuttle. The orbiter shuttle was a reusable winged 'space plane' that would be deployed into lower earth orbits and glide back to earth after each mission. One of its primary goals was to carry hardware to and from space, but it introduced many new design challenges. One of the more complicated assignments facing NASA was devising a way for the orbiter’s crew to manipulate the shuttle’s cargo and other objects in space. The orbiter shuttles were given several precision tasks, including the deployment, assembly and servicing of various satellites and telescopes. Ideally, orbiter crews would be able to accurately deploy whatever hardware the shuttle was carrying, retrieve objects from space and manipulate other hardware in Earth’s orbit. It was apparent that the orbiter shuttles needed a remotely operated manipulator to achieve NASA objectives. However, what little robotics research existed at the time was highly experimental and NASA was reluctant to involve itself directly in such a risky development project. To reduce their exposure to the project, NASA approached several robotics companies with their specification for the manipulator system. They were particularly interested in the response they received from DSMA Atcon, a small Canadian robotics company. DSMA Atcon had recently developed a nuclear reactor refuelling robot that replaced spent fuel rods in the reactor core with new fuel, an operation that required similar precision to NASA envisioned manipulator system. However, the company was small and lacked the resources necessary for such a large project. After some negotiations, the Canadian Government resolved to support development of the manipulator system for NASA. In return, NASA agreed to purchase four of the units, so long as the system met their stringent design specification. It was an ambitious project. Development of the manipulator system was entrusted to a consortium of Canadian companies, including DSMA Atcon and SPAR Aerospace (an Edmonton based descendant of Avro Canada). The National Research Council (NRC) of Canada was to oversee the project. NASA specified strict performance criteria for the manipulator. The system had to be capable of performing a diverse range of tasks at various load ratings with great precision. Additionally, as the system would be housed in the shuttle’s payload bay and exposed to the harsh conditions of space, it had to conform to stringent physical constraints, including limits on the weight, stiffness, heat tolerance and toughness of all components. NASA’s design criteria meant that every component of the system had to be designed from scratch. Even seemingly simple components (such as the gears that drove the arm) had to be produced in specially devised fabricating processes to achieve acceptable tolerances (often specified in micrometres). The project began in 1974. To achieve the desired dexterity, the manipulator incorporated three joints (equivalent to a shoulder, elbow and wrist) and a hand (the end effector), effectively mimicking a human arm. The design gave the arm a total of six degrees of freedom, enabling it to manoeuvre about the shuttle to capture stationary or free-floating objects in space. The versatility of the system, however, also complicated its control. To simplify manipulation of the arm, the DSMA Atcon devised a control algorithm that allowed the astronaut to concentrate solely on positioning the manipulators hand (end effector). The control system received the astronaut’s positioning input from a joystick and determined how the various joints of the arm should react to position the hand, making the system intuitive to control. The end result was a 15-metre-long arm that could place a peg in a hole with little more than 1.5 mm clearance. Following six years of development and extensive testing, the arm was first used on the Space Shuttle Columbia in 1981 (the second space flight in the space shuttle program),. By 1985 the arm was installed on all of NASA’s orbiter shuttles. Over almost 30 years of use, the arm exceeded every expectation and was put to uses that were never anticipated during its design. Summary by: Richard Murphy