Christmas will be another work day for the crew of the International Space Station (ISS) this year. While many Earthlings are sitting down to turkey and plum pudding, NASA astronauts Rick Mastracchio and Mike Hopkins will be carrying out the third and final of three spacewalks announced by NASA managers on Tuesday.

The spacewalks are being conducted to deal with an ammonia leak in one of the station's cooling systems. The spacewalks, scheduled for December 21, 23 and 25, are aimed at replacing a faulty pump module that stopped working on December 11.

The pump’s Flow Control Valve (FCV) regulates the temperature of the ammonia coolant by mixing warm ammonia with cool ammonia from the station’s radiators. During the spacewalks, the astronauts will replace the pump with a spare stowed on an external stowage platform. All three spacewalks are expected to last six and a half hours and will be televised live with a 7:10 am US EST start.

According to NASA, the urgency of the repairs has delayed the flight of Orbital Sciences’ unmanned Cygnus cargo ship to the ISS until at least mid January.

Source: NASA