Canadarm2 can move around the outside of the International Space Station in a way that looks almost biological: release one end, swing the arm to another fixture, latch on, then release the other end.
That “inchworm” movement is possible because the Canadian-built robotic arm has similar latching end effectors at both ends. NASA's Mobile Servicing System documentation describes Canadarm2 as a 57.7-foot arm that can attach to compatible grapple fixtures around the station and reposition itself for different jobs.
The system becomes more useful when it is combined with two other pieces of station infrastructure: the Mobile Base System and the Mobile Transporter.
The arm and the transporter are different machines
The Mobile Base System is a work platform for Canadarm2 and the smaller Dextre robot. It sits on the Mobile Transporter, a rail car that travels along rails running across the station's main truss.
That distinction became especially relevant on September 28, when NASA confirmed it was investigating communication errors involving non-robotic components associated with the Mobile Transporter.
Initial reports made the problem sound like the large robotic arm itself had stopped working. NASA's later statement, reported by Ars Technica, was more precise: Canadarm2 was operating as expected and was being used to inspect the Crew-12 Dragon spacecraft. Engineers were troubleshooting communication errors before moving the transporter from Worksite 6.
In other words, the arm, its mobile base and the rail transporter work together, but a problem with one part should not automatically be described as a failure of the others.
Why put a robot arm on a rail car?
Canadarm2 can “walk” between suitable fixtures, but the station is huge. The Mobile Transporter lets the base platform move along the truss so the robotics system can reach work sites spread across the structure without requiring the arm to bridge every distance by itself.
NASA says the Mobile Base System provides the movable work platform while the transporter carries it along the rails. Once positioned, Canadarm2 can handle large payloads, support station assembly and maintenance, help with visiting vehicles and work with Dextre on more precise servicing tasks.
The architecture is a good example of modular engineering. The arm provides reach and manipulation. The base provides a mounting platform. The transporter provides long-distance movement along the station.
That is why the September 28 troubleshooting note matters beyond a temporary fault report. It exposes the layers hidden behind the familiar image of a single robotic arm.
NASA said teams were also checking whether the transporter's current position could affect GPS reception for a Dragon docking approach and expected the issue to be resolved before Crew-13's launch. That was an operational target, not proof of a hardware failure or a completed fix.
For readers watching station robotics, the useful mental model is three connected systems, not one giant robot. Canadarm2 can walk. The Mobile Base System gives it a moving platform. The Mobile Transporter carries that platform along the truss.
That distinction is also a reminder to be careful with breaking technical reports. A dramatic first description can collapse several linked systems into one failure. NASA's clarification narrowed the problem and preserved an important fact: the arm was still being used operationally while engineers investigated the transporter's associated communications.
The station's robotics stack is complex enough that naming the right component is part of understanding the story.
Reporting notes