Remember those kids in your neighborhood who played with M-80's? Now you know what they did when they grew up.

Back in the 90’s, they were seeing how fast they could light a BBQ using LOX. At the time, There wasn’t much in the way of digital video — and MIME (data object encapsulation in email, something we take for granted today) was relatively new. That said, someone was kind enough to put a film capture up on youtube.

BTW/FWIW, my first thought was Voyager 1 or 2, which are currently going ~3.5AU/year (10,604mph) but this clearly has that beat.

Aaaand relating that to your ‘manhole cover’: back in ’47, “Nuclear Pulse Propulsion” was proposed by Stanislav Ulam, who was involved in nuclear testing. This eventually became Project Orion (good intro here) but, as you point out, atmospheric use was ruled out — but there’s no reason it can’t be considered for interplanetary propulsion.