Canada contributed the Canadarm and Canadarm2 for the Shuttle and ISS, respectively. With the Lunar Gateway Canada will contribute the Canadarm3. How did Canada come to make the Canadarm in the first place? Do they continue to just because it's "tradition" now or is there something particular about the Canadian Space Agency that makes them especially suited for robotic arm design/construction?
Business concerns require a small, tightly integrated supply chain. Paying attention to this is one of the many reasons for the successes of the Space Exploration Technologies Corporation (SpaceX). The problem with tight supply chains is there are only a few big winners. Political demands oftentimes result in large, loosely integrated supply chains. If NASA operated like a business it would be dead because there would be a dozen or so happy senators pitted against seven dozen rather unhappy senators. From the very beginning, NASA has touted how many states (almost all of them) participate in / contribute to NASA's missions.
Where it makes sense, it has helped NASA to have other countries participating in NASA's missions. Cancelling a NASA program that involves international partnerships would be tantamount to breaking a treaty. The Canadarm and its successors represent one of those areas where it makes sense to have international involvement.
I think there is a better answer than just saying "Politics". That is just too glib and shallow. There is obviously more substantial reasons behind the development and use of Canadarm than partisanship and perhaps these reasons should be explored.
At the time the shuttle was being planned in the post-Apollo era, although there may have been many kinds of robotic handlers being developed, not all of them had the technology that suited the harsher environment of space and also were sufficiently developed to provide a reliable arm. Many vendors might have been willing to research and develop such an arm but few had one that could be demonstrated.
By a quirk of serendipity Dilworth, Secord, Meagher and Associates (DSMA Atcon) of Toronto had already researched and created a long reach robotic handler for hazardous environments in the 1970s as part of the CANDU nuclear reactor programme.
It was the closest to what NASA required and they won the contract for CANADARM as a result. Later the technology was used by MacDonald, Dettwiler and Associates (MDA) for CANADARM2, who later became Maxar Technologies.
Source: The Canadian Encyclopaedia
Good day all. I the hope that you find the following information valuable, from my memory: having worked on both programs as an engineer at the prime Canadian contractor SPAR (late on SRMS and at the start of SSRMS), I was told by the veterans at the time that Canada had a particular expertise in very high precision gears, and that was one of the reasons that Canada proposed the Canadarm as its contribution for the Shuttle Program. I am not getting into politics here :-). As a complement of information, the SRMS on the Shuttle Program was an analog system with fixed-parameter analog control loops in each of the 6 rotation axes, coordinated by a unit inside the Shuttle, with the arm permanently mounted on its base. Interesting fact: I was told that it could be jettisoned if it couldn't be folded back in the payload bay. Its successor, the SSRMS on the ISS program, incorporates many differences, including 7 degrees of freedom with digital control loops that have the capability to be adapted in real-time, coordinated by redundant units on the arm, with an end effector that was also much stronger, capable of handling a fully-loaded Shuttle as a payload (this has not been used). The big improvement with the SRMS that challenged us designers, was that the SSRMS needed to be completely symmetrical about the elbows, and that both ends could be detached (not at the same time...) so that the SSRMS could do a slinky-style walk across the ISS (this is used regularly); in other words, we needed to design a robotic system where the wrist of the arm could also be the shoulder... tricky but it worked in the end.