On October 4, 1957, an R7 rocket lifted off from Baikonur Cosmodrome, Kazakhstan, carrying Sputnik I, the world’s first artificial satellite. This historic feat stunned the West and pushed the Cold War into a terrifying new phase, for if the R7 could launch a satellite into orbit, it could also place a nuclear warhead anywhere on the globe. But while Sputnik was the first manmade object to orbit the earth, it was not the first to leave the atmosphere. That honour belongs to a German V2 rocket, which crossed the 100 kilometre Karman Line on October 3, 1942. Between this date and the launch of Sputnik, dozens of objects made suborbital flights into the wild blue yonder. But one such object stands out among the others, for it was not a sophisticated rocket but rather a 1-ton cast-iron disk, propelled – in true Cold War fashion – by an atomic bomb. This is the bizarre story of the nuclear-powered manhole cover, the fastest manmade object ever launched.

Between 1945 and 2017, the world’s eight nuclear-armed powers – the United States, Russia, the United Kingdom, France, China, India, Pakistan, and North Korea – conducted a total of 2,476 nuclear weapons tests. In the early days, nuclear tests were largely conducted in the atmosphere, but as public concern grew over radioactive fallout drifting over populated areas, testing increasingly moved underground. This culminated in a three-year testing moratorium from 1958 to 1961, and finally the signing of the Partial Test Ban Treaty of 1963, which banned the United States and Soviet Union from conducting nuclear tests in the atmosphere.

The techniques for conducting underground nuclear tests were largely developed through trial and error. The first U.S. underground nuclear test was Test Buster-Jangle Uncle, conducted on November 29, 1951 at the Nevada Test Site. Designed to simulate the effects of an earth-penetrating “bunker buster” bomb, the 23 kiloton weapon was detonated at a depth of only 5 metres, sending a soil-laden mushroom cloud 3,500 metres into the sky and spreading radioactive contamination far and wide – and for more on similar tests conducted for ostensibly peaceful purposes, please check out our previous video That Time the Soviets Tried to Extinguish a Fire With a Nuke for…Reasons. The first U.S. underground test designed to completely contain the fallout produced by the explosion would not be conducted until 1957 as part of Operation Plumbbob. The device, codenamed Pascal A, was lowered down a 148 metre shaft capped with a 900 kilogram, 10-centimetre-thick iron plate resembling a manhole cover. The experiment was designed as a safety test, wherein the conventional explosives in the device would detonate but the nuclear core would not undergo nuclear fission. This would not only validate the inherent safety of the warhead in an emergency – for example, if a nuclear-armed bomber crashed and burned on takeoff – but generate important data for the design of future underground nuclear tests.

…unfortunately, things didn’t quite go as planned, and when Pascal A was detonated at 8AM on July 26, 1957, the device underwent a low-level nuclear detonation or fizzle with a yield of approximately 55 tons of TNT, blowing the cap off the top of the shaft and sending a jet of flame soaring into the night sky like a giant Roman candle. Strangely, despite extensive searching, the 900-kilogram metal cap was never found. This result intrigued scientist Robert Brownlee, who designed both Pascal A and its subsequent follow-up, Pascal B. As Brownlee recounts in his 2002 essay Learning to Contain Underground Nuclear Explosions, while calculating the physics of the blast wave travelling up the burial shaft, he had the following conversation with Bill Ogle, the deputy division leader:

“Ogle: What time does the shock arrive at the top of the pipe?
Brownlee: Thirty one milliseconds.
Ogle: And what happens?
Brownlee: The shock reflects back down the hole, but the pressures and temperatures are such that the welded cap is bound to come off the hole.
Ogle: How fast does it go?
Brownlee: My calculations are irrelevant on this point. They are only valid in speaking of the shock reflection.
Ogle: How fast did it go?
Brownlee: Those numbers are meaningless. I have only a vacuum above the cap. No air, no gravity, no real material strengths in the iron cap. Effectively the cap is just loose, traveling through meaningless space.
Ogle: And how fast is it going!?

Brownlee: Six times the escape velocity from the earth.

Bill was quite delighted with the answer, for he had never before heard a velocity given in terms of the escape velocity from the earth!”

Though purely theoretical, Brownlee’s calculations suggested an astonishing possibility. So, for Pascal B, he arranged to have a high-speed camera aimed at the top of the shaft, recording at 1,000 frames per second. At 10:35 P.M. on August 27, 1957, Pascal B was detonated at a depth of 152 metres. In addition to the steel cap, the test shaft was also fitted with a 2-ton concrete plug just above the bomb in an attempt to further contain the explosion. As with its predecessor, however, the safety test failed, the device detonating with a yield of 300 tons of TNT. As Brownlee explained in a 2016 interview:

“The pressure at the top of that pipe was enormous.The first thing that you get is a flash of light coming from the device at the bottom of the empty pipe, and that flash is tremendously hot. That flash that comes is more than 1 million times brighter than the sun. So for it to blow off was, if I may say so, inevitable.”

When Brownlee checked the footage from the high-speed camera, he found that the cap appeared only partially in a single frame, causing him to exclaim rather unscientifically that it was “going like a bat!” Later, however, he used this limited information to estimate the cap’s velocity at a whopping 200,000 kilometres per hour – nearly five times the velocity required to break free of earth’s gravity. This would theoretically make a humble manhole cover the fastest manmade object ever launched into space. By comparison, NASA’s New Horizons probe – officially the fastest manmade object on record – has only reached a relatively pedestrian 58,196 kilometres per hour. And given that the cap was travelling straight upwards from the earth’s surface, it would not have entered orbit rather but continued out into interplanetary – and eventually interstellar – space, becoming the first manmade object to do so.

But did a manhole cover actually beat Sputnik into space by more than a month? Unfortunately, the answer is probably no, with most physicists agreeing that atmospheric friction likely caused the iron cap to burn up like a giant reverse meteor. Indeed, Brownlee himself was initially dismissive of the notion, considering it to be little more than an amusing thought experiment. He soon came to resent the legend that had grown up around his back-of-the-envelope calculation, writing in 2002 that:

“As usual, the facts never can catch up with the legend, so I am occasionally credited with launching a “man-hole cover” into space, and I am also vilified for being so stupid as not to understand masses and aerodynamics, etc, etc, and border on being a criminal for making such a claim.”

Later, however, Brownlee revisited his calculations, and realized that thanks to its large mass and enormous velocity, the cap would not have had time to completely burn up before it left the atmosphere. Nonetheless, other physicists have since argued that even if the cap did reach space, its decidedly un-aerodynamic shape would have slowed it down below escape velocity, causing it to fall back down to earth. But as the cap has never been recovered, the jury remains very much out on this peculiar incident.

But while it may not have inadvertently launched humanity’s first interstellar probe, the Pascal-B test did inspire Project Orion, a completely bonkers effort to create a giant interplanetary spacecraft propelled by small nuclear explosions and a subject worthy of a whole other video. It also contributed greatly to the development of later, safer underground nuclear tests, as Brownlee explained in 2016:

“I’ll add that we learned a lot with our series of low-yield tests. Plugs helped, but the closer to the nuclear device, the better. “Tamping” the device is better yet, and there are some ways to do that which are more clever than others. Mostly we learned that even an empty hole could cause a reduction to the atmosphere of as much as 90 percent, depending on specific design parameters. Later we were to see that if the hole is deep enough and the yield is high enough, an empty hole will close completely, allowing nothing whatsoever out except the initial light, which is not radioactive of course. In time, the tests became very sophisticated-and expensive, but we were able to achieve complete containment for almost every test, and for all but a handful of those that had containment “failures”, nothing was detected off-site. So I would judge our containment efforts to be quite successful.”

Still, it is amusing to imagine that instead of sophisticated probes like Pioneer, Voyager, and New Horizons, the first manmade object to be found by extraterrestrials might be a humble manhole cover. If so, then perhaps the first message we receive from another world won’t be a peaceful greeting, but a ticket for interstellar littering.

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