While originally envisioned as glorified crane, the robotic arms on first the space shuttles and later the International Space Station have repeatedly proved to be invaluable for delicately manipulating anything that comes within reach.
Canada's space program is understated — it has only a handful of astronauts, lots of suitcase satellites, and no photogenic rockets. But it excels in remote robotic arms, creating the iconic Canadarms. More than cranes, these arms delicately grasp and manipulate all the things an astronaut needs.
A sliver of light highlighting the Canadarm and Space Shuttle Atlantis in May 2009. Image credit: NASA
The International Space Station has Canadarm, a robotic arm grapple to pull, pluck, and place objects around the space surrounding the station. Yesterday, the arm pulled the unbolted Dragon capsule off the Harmony module and carried it away from the station for release, but how does it work?
A Manipulator for the Space Shuttles
The first generation of Canadarms were mounted to the space shuttles directly, each shuttle equipped with a manipulator system arm to make it feasible to load and unload the cargo holds. The arm exhibited a certain bias towards unloading, moving at 60 centimeters per second compared to the more sedate loading speed of 6 centimeters per second.
Atlantis using its arm to release the Hubble after the STS-125 servicing mission.
These original arms were undeniably useful, but also limited. The total reach was the length of the arm (15 meters), and the range of motion was similar to that of a human arm with a double-joined shoulder, a single-jointed elbow, and a triple-jointed wrist. The elbow could rotate up to 160 degrees, but an astronaut bent on proving the superiority of human over machine could have thwarted the arm by leaving necessary tools 180 degrees to taunt it. The arm was designed as an exercise in brawn, a glorified crane to do the heavy lifting. Yet the demands of space required a more delicate dance, carefully manipulating loads, and the arm managed to meet the challenge.
Astronaut Jerry L. Ross balanced on the arm of space shuttle Atlantis. Image credit: NASA
The arms were used for moving gear in and out of the cargo holds and helping astronauts build the space station, but also served more creative functions. Back in 1984, on the space shuttle's 12th flight, ice built up on the base of the shuttle. This could pose a hazard as pieces broke off, but a quick tap from the arm knocked the ice loose and sent the shuttle safely on its way.
Tools from the crew compartment were improvised to build a fly-swatter to flip a switch on a misbehaving satellite in 1985. Image credit: NASA
The next year, a satellite misfired after being released from the cargo hold, so the arm was called upon to swat it, flipping a switch. When that didn't work, the arm was later used to retrieve the satellite and bring it home for repairs. And after the Columbia accident, the arm was called into service as a camera boom, giving the shuttles a once-over inspection to check for damage before heading home.
Astronauts Richard J. Hieb, Thomas D. Akers and Pierre J. Thuot cluster around the Intelsat VI satellite in 1992, with Thuot balanced on the Canadarm. Image credit: NASA
The Canadian Space Agency produced a video commemorating thirty years of the Canadarm in 2011, a montage of catches and captures set to a deliciously outdated soundtrack.
With the retirement of the space shuttles, the original design for the Canadarm was also retired. But, with plenty of time to plan ahead and the knowledge that the space station would certainly still need to interact with large objects, engineers were able to design and install the next generation arm.
The International Space Station's Indispensable Limb
The birth of the second generation Canadarm 2 is an orgy of firsts for the Canadian space program. It was launched in the space shuttle Endeavour on April 19, 2001, and unloaded using that shuttle's Canadarm.
Chris Hadfield and the Canadarm 2 in 2001. Image credit: NASA
Days later, it was installed during the first ever Canadian spacewalk, by the now-beloved Chris Hadfield. Finally, as proof of function, the new Canadarm shook hands with the old Canadarm, performing the first-ever robotic handshake in orbit. Ever since then, the arm has been working hard at supporting station operations.
While the first-generation arm was just that — an arm — the second generation arm is more like The Thing out of Addam's Family. The limb is capable of climbing all over the exterior of the International Space Station, latching on at Power Data Grapple Fixtures (PDGF) using its Latching End Effectors (LEE) to suck power, data, and video. If it needs to go somewhere outside the reach of a PDGF, it even has a Mobile Base System to get it to the farthest reaches of the station. Both ends of the arm have LEEs, so it can literally flip end-for-end and still hold on.
Canadarm 2 has the HTV-3 Exposed Pallet firmly in its grasp to install it on the Japan Aerospace Exploration Agency H-II Transfer Vehicle in 2012. Image credit: NASA
The arm itself is also far more flexible, sticking to the same shoulder-elbow-wrist analogy but exceeding human capacity with 7 joints capable of rotating 540 degrees. As a highly precise tool capable of delicate operations, of course the arm can adjust its configuration while keeping its hands rock-steady. To prolong its lifespan, the arm has replaceable components allowing for in-orbit servicing. A wrist roll-joint was serviced during a spacewalk in June 2002.
Canadarm 2, the ISS cupola, and shuttle Endeavour in 2010. Image credit: NASA
The next-generation Canadarm also includes a suite of sensors for better automated performance. Force movement sensors are analogous to touch, while automatic vision features tied to the four colour cameras (located at each LEE and on either side of the elbow) allow for the capture of free-flying payloads. Cautious of the disaster that are high-speed collisions in space, the arm has automated collision avoidance just in case someone isn't paying attention.
Canadarm catching the Dragon capsule during its 2012 demonstration flight. Image credit: NASA
The Canadarm 2 is essential for playing cosmic catch, intercepting uncrewed resupply cargo freighters and bringing them in close to the station to be bolted into place for unloading and reloading. The arm is a bit more sedate in its pacing than the original Canadarm, performing unloading operations at 37 centimeters per second and loading at 2 centimeters per second. However, it also performs a greater variety of functions, helping assemble the space station at that same 2 centimeter per second pace, slowing down even further to 1.2 centimeters per second when supporting orbiter operations, and getting downright frisky with astronauts by speeding up to 15 centimeters per second when performing EVA support.
Astronaut Stephen Robinson dangling from the Canadarm 2 during an EVA in 2005. Image credit: NASA
For a slightly different perspective on the same concept, NASA astronaut Mike Hopkins from Expedition 38 produced a more technical video of how to grapple and snare objects around the station using the Canadarm.
If you're feeling inspired, you can try it yourself by playing this Canadarm simulator game.
Aside from all its entirely utilitarian functions, the Canadarm also serves a symbolic function. By providing the Canadarm on the space shuttles and the space station, the Canadian Space Agency earned its astronauts the privilege of participating in international space missions. Quite literally, without the Canadarm, we never would have had the joy that is Commander Hadfield singing Space Oddity from orbit.
The Canadarm and Chris Hadfield were both commemorated on a 2006 Canadian coin, celebrating the country's space program. The arm later showed up on a stamp from Canada Post in 2011 featuring the first Canadian handshake in space between a Canadarm on a space shuttle, and the Canadarm 2 on the Space Station.
Canadarm and Canadarm 2, the first robotic handshake in space. Image credit: NASA
Since original publication, the Canadarm and Dextre teamed up to become the first self-repairing robotic system in space.
If you liked learning about the Canadarms, you might also be interested in the machines behind the Deep Space Communication Network, or all about the planet-hunting Kepler Space Telescope. For more monster-machines, Otto and Lore are the crawlers that haul around telescopes.