Two major impediments for space exploration area Fuel and Speed. They seem mutually exclusive.
This article may have pointed the solution in the right direction

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My gradparents would often play tricks on me when I was a child. I suspect Stonehenge is much the same sort of thing, only over many more generations... "I've got a brilliant idea that's gonna keep our great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great, great grandkids wondering for a while!"