NASA is sending two astronauts outside the International Space Station to fix the Canada Arm 2, the orbiting laboratory's large robotic arm, after it ran into trouble during normal use. The agency set out the plan at a briefing, where station operations integration manager Bill Spetsch walked through how a piece of hardware that has worked for years came to need a hands-on repair in orbit.
The first sign of a problem came on May 27. As the arm carried out a routine job, it began drawing an elevated motor current and stopped moving the way it was supposed to. That combination tends to flag a fault inside the mechanism itself rather than a glitch in the wider station, and it was enough for controllers to stop and take a closer look before doing any further damage.
Instead of forcing the balky arm to keep working, flight controllers shut it down and put it into a safe configuration. That left the limb parked and out of service while engineers on the ground worked through the data, a deliberately cautious step meant to preserve the hardware until they understood exactly what had failed.
Because the arm is Canadian-built, NASA carried out that investigation hand in hand with the Canadian Space Agency. Together the teams pinned the fault on one of the arm's joints and concluded it could not be nursed back to health remotely; the joint would have to come off and be replaced. A spare is already sitting aboard the station, which means the swap can happen in orbit rather than waiting for a new part to launch on a future cargo run.
Officials were keen to present the repair as planned-for maintenance rather than a crisis. The Canada Arm 2 was built from the start with parts that can be taken off and changed out, on the expectation that components would eventually wear and need replacing across a service life measured in decades. The failed joint, by that reasoning, is precisely the kind of piece engineers always assumed a crew would one day go out and replace by hand.
The job falls to astronauts Chris Williams and Jessica Meir, who will head out through the station's Quest airlock to reach the arm and install the new joint. It will be the second time Williams has worked in open space and the fifth for Meir, and against the long arc of the program it will count as the 280th spacewalk devoted to building, maintaining and upgrading the station.
The repair amounts to a careful piece of orbital surgery the agency expects to fill most of a working day. The crew is targeting the arm's joint five, but to reach it they must first detach the latching end effector and two neighbouring joints, park that cluster in the slot where the spare is currently stowed, then pull the failed joint and bolt the replacement in its place before reattaching the cluster so the arm is whole again. Officials put the full sequence at about six and a half hours. Rather than throw the broken joint away, the astronauts will carry it back inside the station so it can eventually be returned to Earth, examined to establish what failed and refurbished for future use.