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MS. STILSON: Martine from Midlothian. We understand that each EVA is scheduled for six and a half hours. Is an EVA extremely fatiguing for the two astronauts and do they have backup EVA suits? Can you compare EVA's to scuba diving? MS. HIRE: For the EVA, our crew members train for years for this, and it is very physically demanding. And the reason is, the EVA, or extravehicular activity, or spacewalk, is actually performed in a special suit that is pressurized. And outside of the suit is the vacuum of space. This suit is its own spaceship in itself. It has its own power system, its own communication system and its own cooling system, all these different systems that operate on its own that the astronaut is only attached to the Space Shuttle or the Space Station by a tether, not by a tube that's feeding power or water or cooling or anything like that. So it's a very complicated suit. But the suit is pressurized. If you'll think about, if you've ever had your blood pressure taken and when they inflate the blood pressure cuff on your arm, that type of pressure. If you think about the little blood pressure cuffs around each and every finger and around the majority of your body, that's what it feels like. So just to move your fingers back and forth like this, you're pushing against that pressure. So it actually uses every little muscle and it is quite fatiguing. We practice this and almost choreograph these EVA's or space walks ahead of time just for that reason. As far as backup suits, we don't typically fly a backup suit. We will have some spare parts if we need them. And on this mission, we are carrying four space suits, but that's because two of them are going to be left behind on the International Space Station. So in this mission, it's a little unique and we might have some extra spare parts if we needed them. But for a full-up spare suit, we typically do not fly them.