August 27, 1957 – Underground Nuclear Test Launches Giant “Manhole Cover”

On August 27, 1957, a four-inch-thick steel plate weighing several hundred pounds shot into the stratosphere over the Nevada Test Site, never to be seen again.  Operation Plumbbob’s Pascal-B was an underground test of a nuclear safety device designed to limit the amount of destructive energy released by a bomb in the event of an accidental detonation.  Buried at the bottom of a 500-foot shaft and sealed with an over-2-ton plug of cement, Pascal-B generated sufficient energy – the equivalent of a few hundred tons of dynamite – to vaporize the concrete plug.  The concrete vapor expanded and raced up the shaft, propelling a massive steel plate sealing the shaft opening into the sky.

According to the February 1992 issue of the Smithsonian’s Air and Space Magazine, astrophysicist Bob Brownlee was in charge of designing the Pascal-B test.  “He knew the lid [steel plate] would be blown off; he didn’t know exactly how fast.  High-speed cameras caught the giant manhole cover as it began its unscheduled flight into history.  Based on his calculations and the evidence from the cameras, Brownlee estimated that the steel plate was traveling at a velocity six times that needed to escape Earth’s gravity when it soared into the flawless blue Nevada sky.  ‘We never found it.  It was gone,’ Brownlee says, a touch of awe in his voice almost 35 years later”.

Even though the eventual whereabouts of the steel plate forever remained a mystery, it’s unlikely, according to the laws of physics and the character of the Earth’s atmosphere, that the plate headed into outer space.  Unable to maintain escape velocity on its own (not being equipped with mini-rocket engines), it would not retain sufficient speed to pass completely through the layers of nitrogen, oxygen, and other gases surrounding our planet.  Most likely it either vaporized in the explosion, disintegrated in the atmosphere, or landed somewhere far from the Nevada Test Site.  It’s also possible it became some innocent person’s “close encounter”, or enormous fish story.

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