The optimization treadmill
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But no one is ready to say when hundreds of new missile silos, dug from the windswept Great Plains, will be finished, how much they cost, or, for that matter, how many nuclear warheads each Sentinel missile could actually carry.
Helium is used to pressurize tanks and help push fuel into the engines. Without proper helium flow, the rocket cannot safely fly. Because the upper stage is hard to reach at the launchpad, NASA rolled the stacked rocket back into the Vehicle Assembly Building, the sky-scraping hangar where it was originally put together.