Tomorrow a risky emergency space walk by two americans to repair the international space station. Six astronauts on board. You'll remember the last time an astronaut stepped outside he nearly drowned... See More
Tomorrow a risky emergency space walk by two americans to repair the international space station. Six astronauts on board. You'll remember the last time an astronaut stepped outside he nearly drowned when water leaked into his space helmet. Abc's neil karlinsky on how they tackled a problem to fix another. Reporter: These are the final critical preparations for two american astronauts. Final con figuration of all the tools they will use. Reporter: Mike hopkins on his first walk and rick mastracchio will try to fix the cooling systems which keep the nine room space station, long enough inside to take up more than half a football field, from overheating. Mike hopkins will be the free float crew member. Reporter: Space walks were supposed to be suspended after astronaut luca parmitano nearly drowned earlier this year, when a full gallon of water from the suit's cooling system leaked into his helmet. My head is wet. Reporter: Nearly robbing him of oxygen. A terrifying malfunction you can see happening again, when the suit was retested. I experienced what it's like to be a goldfish in a fish bowl, from the point of view of the goldfish. Reporter: Now the last minute MacGYVER LIKE FIX, 20 INCH Snorkles fitted inside. So the astronauts can breathe through the tube, if water leaks in again. Equally low tech, absorbent PADS, VELCRO'd INSIDE THE BACK Of the helmets as a warning system. If a pad feels squishy, astronauts are told to alert mission control. We train hours, days, weeks, months, years for this very thing. Reporter: The nail biting mission is only part one, a second walk will happen monday, and if they don't finish, a grueling third space walk will set out on christmas day. Neil karlinsky, abc news, seattle.
This transcript has been automatically generated and may not be 100% accurate.