A robotic arm that works on the outside of the International Space Station got a hand today from two astronauts.

Space station commander Scott Kelly and newly arrived flight engineer Tim Kopra spent a little over three hours on a spacewalk Monday morning to fix a stalled transporter that carries the robotic arm, used to grab onto docking space crafts and unload their cargo.

Without today’s fix, the Russian supply ship, named Progress, would not be able to dock with the space station as scheduled on Wednesday.

The arm’s mobile transporter, known as the MT, stalled after NASA ground controllers uplinked commands to move the MT from work site 4 to work site 2 on the station’s power truss, or backbone. The problem hit after the transporter moved only four inches along the truss and then jammed.

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