Nuclear test place
History,  Rocket science

Operation Plumbbob: How a manhole cover became the fastest object launched by Humans

⁠The Story you are about to read is unbelievable but true. It involves Spacetravel, 1,200 Pigs, 18,000 US soldiers, Mythbusters and  lots and lots of Nuclear Detonations.

The Background

The time is 1957 and after World War II Atomic Bomb testing is the thing everyone is talking about. Unimaginable now but at the time there where Blast Watch Partys in Las Vegas and even crazier some people only came to Vegas to watch these Tests from afar. They even had a Miss Atomic Bomb beauty competition there. Between 1945 and 1992 the US detonated 1054 Nuclear bombs. And this is the story about how one of these Tests might have unintentionally resulted in not only the fastest man-made object so far but also the first Human Object in space two months before Spudnik.

Nuclear Explosion
Fig 1: First Atomic Test shown on live Television in February 1951. Courtesy of US NNSA

Operation Plumbbob

Operation Plumbbob was a series of nuclear tests conducted between May 28 and October 7, 1957. These tests were conducted at the Nevada Test Site and it was the biggest, longest, and most controversial test series in the United States. One could describe the scientists responsible for these experiments as Atomic Mythbusters because that is what they did. At one time they placed 1,200 Pigs at various points in the Blast radius to find out what an Atomic blast would do to living beings.

Men watching nuclear explosion

Fig 2: During a test in 1951 that didn’t belong to the Plumbbob series, US troops watch a nuclear bomb detonate above-ground from about 9.5 km away. Resulting in them being exposed to dangerous amounts of radiation. Credit: The Nuclear Weapon Archive

Just like the men in the picture about 18,000 members of the U.S. Air Force, Army, Navy, and Marines participated in exercises during Operation Plumbbob. It is not know how many of these men died due to the exposure but research shows that the life expectancy of soldiers who participated in such a test is much much lower than normal. With the Limited Test Ban Treaty in 1963 and the Threshold Test Ban Treaty in 1974, tests had to move underground. Even though the first underground test “Uncle” was in 1951 tests continued above ground till 1962.

Operation Plumbbob alone was responsible for about 32% of all radiation exposure to the public due to continental nuclear tests. But there were a lot of concerns about detonating Nuclear Bombs far underground. Some of the fears were that a crack in the Earth’s crust could be created or that a Vulcano would be produced. But never the less radioactive contamination had to be reduced so the underground testing began.

Underground atomic testing

Fig 3: One of the early underground tests, nicknamed “Luna”, exploding from an unstemmed hole underground during Operation Hardtack in 1958. Credit: NNSA

Pascal A

One of the MythBuster scientists working on Operation Plumbbob was astrophysicist Robert R. Brownlee. He was responsible to design a test that would contain all the radiation releasing it  into the ground with minimal above ground exposure. The test he designed was called Pascal A.

They dug a 147 meter deep and 0.9-meter wide hole in the ground. They placed a nuclear bomb at the bottom and a metal plate on top. There was a 1.5 m thick concrete plug in the hole with a hole in the middle for some kind of detector. The expected yield was about 0.9 Kg.

But like many Mythbuster experiments, this Test didn’t go as planned. In a big way. Meaning the actual yield was 51,000 times larger at 55 Tones. Eyewitnesses say the explosion looked like the biggest Roman candle ever to be seen. The steel plate and the concrete plug where nowhere to be found. Like the good scientist Brownlee was, he decided to detonate another bomb just to film another metal plate with a high-speed camera.


Pascal B

This test was called Pascal B and it was performed on August 27, 1957. The hole was a bit deeper at 152 meters and the plate was now a 900 kg heavy manhole cover. In addition to that, they placed a 2-ton concrete plug right above the nuclear bomb. After the test, they searched the area within a 150 km radius but the manhole cover was nowhere to be found.

When they looked at the film they saw that even though the camera they used was able to film at one frame every millisecond the manhole cover was only seen in one frame. That meant they couldn’t calculate the velocity of the thing directly but they calculated how fast the manhole cover would have to go to be only seen on one frame. They ended up at 66 km/s which is 6 times greater than the escape velocity of earth at around 11.2 km/s.

After some thinking, they realized that the two-ton concrete cylinder was placed too close to the center of the detonation. The heat and pressure at that point probably vaporized the whole thing in seconds creating superheated gas that traveled along the shaft like lit gunpowder. This gas would have reached the manhole cover at a speed of 201.000 km/h which is still 5 times the escape velocity of earth.

If these numbers are real then the manhole cover of Pascal B would be not only the fasted man-made object ever created but also the first man-made object to reach space. Remember this test was performed two months before the launch of the Russian satellite Sputnik Oktober 4. 1957. The (second) fasted man-made object is the New Horizon probe with a speed of 58.500 km/h. But soon even the speed record of Pascal B will be broken by the Parker Solar Probe that will reach a speed of 690.000 km/h.

But People have doubts!!

Burning up in the atmosphere

Fig 4: Here you can see European Space Agency´s ATV Spacecraft burning up during re-entry. This took place on Sept. 29. 2008.

But as you might have guessed many people have doubts that this manhole cover actually reached space. One of the most obvious cases against reaching space is the immense friction created by moving through the atmosphere at such speeds. To stay in orbit above earth objects have to maintain a speed of about 28.000 km/h. That means during re-entry they hit the atmosphere at 1/8 the speed of the manhole cover and they break up and then burn up. So how can an object traveling 8 times that speed does not burn up before escaping earth?

When asked about this Brownlee said that the manhole cover just traveled to fast to have time to completely burn up. Another argument in favor of reaching space is the theory that the metal manhole cover was formed into an aerodynamic shape by the immense pressure during flight resulting in a heat deflecting form. Meaning that just like a spacecraft the shape guides the heat along with the vehicle.

There is actually something just like that used in the military. It is called an Explosively formed penetrator (EFP) and it works like this. A round plate is placed over some tube filled with explosives and when they explode they propel the plate forward. This causes the plate to form a penetrator shape.

Explosively formed Penetrator

Fig 5: This is what an Explosively formed penetrator (EFP) looks like. You can see that due to pressure, the plate-formes into something that resembles a penetrator shell. Credit: Air Force Research

Also, rocket propulsion by nuclear bombs is not unheard of. Sometime after the Pascal B test, the US government had a Project called Project Orion. They looked at and tested Nuclear powered propulsion. Meaning they used A-Bombs to propel a spaceship to space.

Project Orion

Fig 6: A design of what the Orion Spaceship could have looked like. Credit: NASA


So what do you think? Is there a huge metal plate somewhere out there or did it burn up? I have my doubts but I hope it’s true. This story is just too amazing not to be true don’t you think!

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