mastracchio as he prepares to fix a faulty pump on the international space station. so, what is this is christmas eve mission in space like? >> we wanted to know from someone who knows firsthand. we are joining by colonel ron guerin, a former astronaut with four space walks under his belt. it's so good to have you here. you actually handled that pump module that the torontos woastr worked on today. what are they doing here? >> they're switching out this pump which is responsible for a lot of the cooling thattings on the international space station. a lot of equipment both inside and outside the station require cooling. the way we do that on the space station is through ammonia. that ammonia is on the outside of the space station. so we have two redundant systems. the system that failed is on the starboard side of the space station and you know, we have a flow control valve in there that failed. so we have to replace the whole pump module, about 800 pounds.