Maintenance on the S1 Truss.
Expedition 24 astronauts are floating above the Earth on a planned 7-hour spacewalk this morning. The EVA started at around 4 a.m. MDT. Spacewalkers are Flight Engineers Doug Wheelock and Tracy Caldwell. They are attempting to replace the ammonia pump located on the S1 Truss, part of the central "backbone" of the ISS. A second spacewalk is planned for Wednesday. The repair is part of the procedure for fixing the current cooling and power problem on the station.