As a follow-up to yesterday's railgun post, one of my co-workers shared this little historical tidbit with me. (Search for "Pascal-B" in the linked page)

Apparently, during one of the first underground nuclear tests, they discovered that if you have a 2-ton concrete plug directly above the bomb, it turns into two tons of superheated concrete gas which are shooting upwards at a rather alarming pace. When said gas runs in to the metal plate at the top of the well, the metal plate moves a bit.

Upwards, in fact.

At about six times escape velocity from the Earth.

It should be noted that this manhole cover almost certainly didn't survive its trip through the lower atmosphere, but if it had done so, it would have actually become the first man-made satellite, beating Sputnik into space by a few months.

Dr. Bob Brownlee, who was responsible for this test, tells more of the story here:
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