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Canadarm and its U of A Connections
by Dr. Garry Lindberg (Engineering Physics '60) November 12, 1981, was a very exciting day for engineering in Canada, the day when riveting images of Canadarm were first transmitted to earth and Canadians were able to witness our latest endeavour in space. Canadarm’s success captured the attention of all Canadians and fueled their imaginations. Canadarm remains one of the most recognized Canadian engineering achievements and enabled us to become a major player in human space flight. Canada was first invited to participate in the space shuttle program (the Space Transportation System) in 1969 when NASA invited the European Space Agency (ESA), Canada, and others to become partners in the program. But it wasn’t until 1974 that Canada decided to participate, determined what to contribute, and obtained the necessary Government policy approvals and funding to commence the project. Canada’s role was to design and build the shuttle-attached remote manipulator system (as Canadarm was originally called)—a space crane, some 15 metres long that was to be located at the edge of the cargo bay of the orbiter vehicle. The cargo bay had a volume of nearly five metres in diameter and 20 metres long and was large enough to carry payloads with a mass of up to approximately 30,000 kg (the size and mass of a fully loaded semi-trailer). Canadarm had to be able to precisely lift payloads out of the cargo bay and deploy them into space, retrieve payloads from space, and place them into the bay.
The arm had to be designed to fit into a very small cylinder of space between the envelope of the largest possible payload and the doors of the payload bay, and the displays and controls panel had to fit into a small area of very crowded cockpit. The arm had to be very stiff to limit dynamic movement but still had to weigh very little since the mass allotment was very small. To further complicate matters, it was impossible to do three-dimensional testing of the arm here on earth since it could not support itself. The arm is similar to a human arm with a shoulder joint, an elbow joint, a wrist joint, and an end effector or hand. (See diagrams on page 14.) It is commanded and controlled from the orbiter cockpit through two hand controllers: translational and rotational. Astronauts make extensive use of closed circuit television cameras positioned on the wrist and the elbow of the arm.
Canadarm has very complicated control systems with complex control algorithms. The primary automatic mode permits the astronauts to command the arm as though they were riding on the end effector, but several other modes are available together with a completely separate joint-by-joint control system in case of a major fault in the primary system. The final safety feature is a jettison capability to ensure that the payload bay doors can always be closed. The program was funded by the Government of Canada (at a total cost of just over $115 million) and led by a project office within the National Research Council (NRC) of Canada. NRC contracted with a group of Canadian companies led by SPAR Aerospace of Toronto to carry out the design and building phases of the hardware and software. The Canadarm project represented a real team effort. At its peak, more that 800 Canadian engineers, scientists, technologists, and skilled craftspersons worked on the program. The team included both government and private sector personnel, working in a new relationship (pioneering the government’s contracting out policy, the first time that a Canadian company acted as the prime contractor and design authority for a major Canadian space project). This large team included many engineers educated across Canada and abroad. It is interesting to focus on three U of A engineering graduates who played key roles and to explore the common linkage between them and Dr. George Ford (Civil ’42, MSc Civil ’46, DSc [Hon] ’88).
Dr. Garry Lindberg was assigned as the Canadarm project manager. While enrolled in engineering physics (aeronautical option), he had taken many courses in common with the newly created mechanical engineering option and was inspired to pursue engineering mechanics by Dr. George Ford. After winning an Athlone fellowship, Lindberg went to the University of Cambridge for a PhD in engineering mechanics, then returned to Canada in 1964 to work in the structures and materials lab of the National Aeronautical Establishment (NAE), a Division of the National Research Council (NRC)—in large part because Ford suggested it. Lindberg found himself working for the laboratory head, A. Henry (Harry) Hall (Engineering Physics ’42), a fellow graduate of Ford’s. Indeed, Ford seemed to act as a talent scout for the NAE because another of the co-workers was Dr. Lloyd Pinkney (Engineering Physics ’52). Pinkney, too, had been influenced to obtain a PhD in engineering mechanics from Stanford (just like Ford) and had been “pushed” towards the NRC.
Assigned to Canadarm in 1974, Lindberg had a clearly defined role while Pinkney’s was more “backroom.” The baseline control system of the arm was not closed loop. Instead it relied upon close control of each joint—and the end point errors would be the sum of the backlash errors of the joints, magnified by arm lengths plus arm flexibilities. The prime contractor, SPAR, was convinced that its design could meet the very tight tip movement specification, plus or minus one inch, but NRC felt it was prudent to have a back up plan. Under the direction of Hall, Pinkney started an investigation into alternate forms of end point control. Pinkney determined that real time photogrammetry could provide the capability to measure the relative distances and velocities between the end point of the arm (the “hand”) and the payload to be captured. Such a system could provide additional essential control information to the astronaut and enable tasks to be completed, even if the basic Canadarm did not meet spec. Pinkney and his colleague Charles Perratt developed and patented such a system and demonstrated that it would work in the lab. Fortunately, it was not needed for the basic Canadarm. But, it has been further developed and tested in space and now the Canadian Space Vision System forms an essential element of payload docking and control on board the Space Station. Many at NASA and within the U.S. aerospace industry were concerned that Canada might not be able to deliver this space shuttle mission critical system. But the Canadian team was always quietly confident and the results show that the Canadarm is one of the most successful and reliable systems of the space shuttle. Canadarm passed its initial flight testing with flying colours and has gone from success to success. While not originally rated to transport astronauts, it performed so flawlessly that it is routinely used to move and support astronauts and for many other unforseen uses. All astronauts praise the arm, be they Canadian, American, European, Japanese or Russian. It led to the Canadian Astronaut program, a highly visible and highly successful program. Eight Canadians have flown in space, andeventually a Canadian will participate as a crewmember of the International Space Station, living in space for three for six months. Now the Canadarm has a lower profile, often taking a back seat to Canadarm 2, the second generation arm that Canada has contributed to the International Space Station. But it remains an essential part of space station assembly, removing modules from the cargo bay and handing them to Canadarm 2 for assembly on the space station. Following the Columbia disaster, Canadarm will play an even more vital role in space shuttle flights—in supporting on-orbit inspection of the orbiter and in supporting in flight repairs if another problem occurs with the exterior of the orbiter. The Canadarm has been named one of the top 25 engineering wonders of Canada and has become a “touchstone,” a symbol of Canadian scientific and engineering excellence. Lindberg is proud to have been part of Canadarm and one of the U of A engineers on the Canadian team.
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Summer 2004
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