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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When I visited Stonehenge in 1972 one was permitted to walk within the henge. There was graffitti carved into the stone with dates from the 1800s. Currently tourists must remain on the outskirts. Times have changed. Again.

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!"