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.
Kelly and Kopra worked together to release the brake handles on either side of the mobile transporter rail car so it could be latched in place ahead of Wednesday's docking of the cargo resupply spacecraft.
If the transporter was not locked in place, vibrations from the docking could damage the space station's structure.
The resupply mission is an important one. Progress is loaded up with 5,753 pounds of propellant, supplies and equipment. The spacecraft is expected to dock at 5:31 a.m. E.T. on Wednesday.
After taking care of the issue with the MT, the astronauts spent the rest of the spacewalk routing an Ethernet cable that will one day connect to the Russian laboratory module, as well as retrieving tools that had been stored outside of the station and routing a second pair of cables that will ultimately support U.S. commercial crew vehicles when they are up and running.