TODAY | December 19, 2013
>> urgent mission to replace the international space station have taken an unexpected turn. the astronauts will now be wearing snorkels after the last astronaut nearly drowned when his helmet filled with water. let's get to nbc's tom costella in washington with more on this. good morning.
>> reporter: hi, savannah the snorkels they will be wearing are unlike we use in pools and the oaks. they think they've solved the problem of the water leak. the snorkels are just in case. it's the kind of macgyver moment which nasa is famous.
>> houston, we have a problem.
>> reporter: apollo 13 was about using what was available.
>> we have to find a way to make this fit into the hole for this.
>> reporter: now, another urgent repair mission, some 230 miles above the earth. astronauts will conduct three space walks to remove and replace one of two 780-pound ammonia pumps to kooem keep the space station cool. the last space walk ended with the astronaut nearly drowning in his helmet after it started filling with water.
>> water is in his eyes now. it seems to be increasing.
>> reporter: fellow astronauts quickly pulled him back into the station. when they did, water poured from the helmet. nasa ordered no space walks until they solved the problem. five month later they think they know what happened swapping out many of the components. now these astronauts are checking their suits for saturday's job, but nasa engineers have a few on the fly fixes in case the water returns.
>> this is our first line of defence.
>> reporter: an absorbent pad worn behind the head and a snorkel cut from rubber tubing.
>> this snorkel is pence the crew in the front of his suit. this is your last resort, if water is encroaching your face, that the crew member can lean down and use this to breathe.
>> reporter: former astronaut steve robinson performed three space walks .
>> it's one of the most demanding, challenging, physically difficult and fun things you could ever imagine doing.
>> reporter: each of these space walks is scheduled for six-and-a-half hours. it's not a dangerous walk. every time you have everyone on a space walk , everyone at nasa is on high alert.