They are testing the waters again.<br /> <br />Two NASA astronauts floating outside the International Space Station embark on a series of spacewalks - as part of a marathon project to repair the outpost's cooling system.<br /> <br />It's the first spacewalk since July, when Italian astronaut Luca Parmitano's helmet started filling with droplets of water. It could have caused him to drown.<br /> <br />Flight engineers Rick Mastracchio and Mike Hopkins are conducting the spacewalk.<br /> <br />Hopkins is a first-time spacewalker. He's wearing the same spacesuit the Italian astronaut was wearing when his helmet began filling with water.<br /> <br />Both NASA astronauts have rigged their helmets with homemade snorkels, in case of another water leak. NASA's confident that won't happen.<br /> <br />This spacewalk was prompted by a shutdown of one of the station's two ammonia cooling systems on Dec. 11.<br /> <br />That forced the crew to turn off non-essential equipment stopping dozens of science experiments.<br /> <br />Although the six
