Some observations on the Canadarm2, the Canadian robotic arm on the International Space Station.
A recent blog by David Ashton “Keeping an eye on the International Space Station” posed the question: “There are plenty of embedded systems up there keeping it going – have any readers been concerned with those?” Actually I have been involved. I worked on the Canadarm2, the robotic arm that was Canada’s contribution to the International Space Station. Instead of attempting a lengthy comment to David, I made a short comment and happily turned the rest into this blog. Let me hasten to add that when I worked as a rocket scientist, I in fact was writing specifications – the robotic arm was being defined on paper. I left (unwillingly) before anything real existed and the details that I present may well have evolved and changed since I left.
NASA (do I need to decrypt that?) is a world of acronyms; there are even nested acronyms. It was a major headache for me just to get up to speed as to what they were talking about. I promise to try and define every acronym, although I must warn you that sometimes the real name is just as meaningless as the acronym. For example an “EE” is an “end effector”. Are you any the wiser?
The Canadarm2 (technically the SSRMS – Space Station Remote Manipulator System) was a logical contribution to the proposed space station after Canada had made the Canadarm (SRMS – Shuttle Remote Manipulator System) for the shuttle program. Aside from dimensional details the only real difference was the number of joints – the so-called degrees of freedom. The SSRMS has seven, the SRMS has six. Today Japan and the Europeans also have robotic arms on the ISS (International Space Station), but the SSRMS was the first and was used in the later stages of the original construction. Canada also has produced Dexter (technically SPDM –Special Purpose Dextrous Manipulator), a hand, if you will, to go on the end of the arm.
An artist’s concept of the SSRMS in operation. This signed picture was my parting memento when I left.
It is more important for devices in space to be reliable and safe than to be on the technological cutting edge. Up there you are a long way from home in a very hostile environment. In addition development and space qualification of parts takes so long that the latest technology today is rather dated when it gets up there. Anything that is designed must work in temperature extremes with sudden swings between the extremes, intense vibration, high acceleration and deceleration (deceleration only on the SRMS), and zero air pressure, but there are additional restrictions placed by NASA. For instance the materials used cannot off-gas and there cannot be any metal particles since they become micro-meteorites. This has impacts down to the bolts and nuts – if the fit during assembly up there isn’t perfect you could get shavings coming off.
Continue reading on EE Times' sister site, Embedded.com.