EVA on the station truss. NASA TV.
Early Monday morning, astronauts Scott Kelly and Tim Kopra of NASA made an unplanned spacewalk out onto the station truss to fix a jammed piece of equipment. On December 17, ground controllers in the ISS mission control were remote-moving the Mobile Transporter (MT), which is a sort of cart that carries equipment along the Truss grid. The manipulator arm can attach to it as well as several other tools. Engineers suspected a brake had somehow activated and was preventing the MT from moving any further. At this location, the MT was unsecured. It was thought that when the next Progress spacecraft arrived for docking, the station would be unable to change attitude in preparation for docking maneuvers, and the MT could become unstable and move dangerously. With ground control clearance, the astronauts went outside for a three and a half hour spacewalk to free the mechanism. They successful disengaged the brake, and ground controllers were then able to move the MT to a safe location. The astronauts were safely back inside after 3 hours and 16 minutes.