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xkcd #2929: Good and Bad Ideas
(imgs.xkcd.com)
Alt text:
While it seemed like a fun prank at the time, I realize my prank fire extinguishers full of leaded gasoline were a mistake.
Project Orion is a bad idea??
Just don't start the nuclear propulsion until you're outside of earths gravity well...
A tricky bit of math to achieve, certainly.