Quote:
Originally Posted by Piotrsko
Last I heard they have massive pumps (turbines) feeding the thrust motors. The helium should be used to prevent cavitation and tank collapse because there's no appreciable atmosphere to vent the tank. Only reason to use helium that I can think of is that it's readily available as either a compressed gas or liquid all over the launch site. Not so sure about inert.
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Yeah, my description wasn't right. The spent fuel has to be backfilled with something. I still think the inertness is a consideration because you don't want to change the fuel/oxidizer ratio by using a flammable gas, and just generally you want as little flammable stuff as possible in places that shouldn't be on fire.