Robotic Arms in Space

Canadarm2 and the station's heavy lifting

The Canadian Space Agency describes Canadarm2 as a 17-metre arm that was extensively involved in assembling the International Space Station. It has an identical hand, called a Latching End Effector, at each end, so it can walk end over end between fixtures on the station's exterior rather than staying fixed in one place. The CSA says it can handle loads of up to 116,000 kilograms and shows it capturing visiting cargo ships as they arrive. Astronauts can drive it from inside the station, and ground teams at CSA headquarters or NASA can operate it too, which frees crew time for other work.

Europe's arm on the Russian segment

The European Robotic Arm, or ERA, serves the Russian side of the station. ESA reports that it was launched in July 2021 alongside the Multipurpose Laboratory Module, Nauka, and stretches to 11.3 metres, working to an accuracy of five millimetres. ESA says it works autonomously and can also be operated by crew inside the station, with its operations monitored from a control centre in the Netherlands. For its first two years, ESA lists jobs such as installing a radiator, moving an airlock and testing how it could carry spacewalkers, along with helping to inspect a coolant leak on the Soyuz MS-22 spacecraft in December 2022.

Arms that work on a planet's surface

Landers use smaller arms to reach the ground around them. NASA's InSight lander on Mars carried an Instrument Deployment Arm 1.8 metres long, with four joints driven by four motors, a grapple of five mechanical fingers and a camera between elbow and wrist. NASA says the arm placed the SEIS seismometer and the HP3 heat probe on the Martian surface, with the arm camera imaging the workspace around the lander. Surface arms face different problems from station arms: real gravity, dust and soil whose behaviour nobody can fully predict from orbit. Lunar landers and rovers carrying scoops, drills and sampling tools will meet the same problems.

Remote control, delay and autonomy

Who drives an arm depends on where it works and how long signals take to arrive. On the station, routine moves can be handed to ground teams, which keeps busy crews free for tasks only they can do. ERA's ability to work autonomously points towards arms that carry out whole tasks while people supervise. Arms on planetary landers work further from help, so their motions are scripted, checked against camera images and paused when something looks wrong. For future lunar missions, the practical goal is similar: let the arm handle routine motion on its own and bring people in for judgement, especially when it is handling hardware that cannot be replaced.

Sources and further reading

• About Canadarm2 — Canadian Space Agency.
  CSA's guide to the station's 17-metre arm: how it moves, what it can lift and who operates it.
• Europe's robotic arm excels in first two years on Space Station — European Space Agency (ESA).
  ESA's account of the European Robotic Arm's launch with Nauka, its precision and the jobs it has done.
• InSight Spacecraft — NASA Science.
  NASA's description of the InSight lander, including the robotic arm that set its seismometer and heat probe down.

Common questions

How is a space station arm different from a factory robot arm?

A factory arm is bolted to the floor and repeats fast, precise motions. A station arm moves very large masses slowly in weightlessness, can relocate between anchor points and is often driven from the ground, so its design favours careful control over speed.

What went wrong with InSight's heat probe?

NASA's InSight spacecraft page says the arm placed the HP3 heat probe on the surface, but the probe, known as the mole, could not reach the intended depth and take its measurements because the soil behaved unexpectedly. Arms and tools often meet ground nobody has touched before.