Nuclear Testing - The Thunderwell Story

The February/March 1992 issue of Air & Space magazine, published by the Smithsonian, contained an article about nuclear rocket propulsion:


Overachiever
"Every kid who has put a firecracker under a tin can understands the principle of using high explosives to loft an object into space. What was novel to scientists at Los Alamos [the atomic laboratory in New Mexico] was the idea of using an atomic bomb as propellant. That strategy was the serendipitous result of an experiment that had gone somewhat awry.
"Project Thunderwell was the inspiration of astrophysicist Bob Brownlee, who in the summer of 1957 was faced with the problem of containing underground an explosion, expected to be equivalent to a few hundred tons of dynamite. Brownlee put the bomb at the bottom of a 500-foot vertical tunnel in the Nevada desert, sealing the opening with a four-inch thick steel plate weighing several hundred pounds. He knew the lid 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 upon 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.
"The following October the Soviet Union launched Sputnik, billed as the first man-made object in Earth orbit. Brownlee has never publicly challenged the Soviet's claim. But he has his doubts."

This article appears to be largely responsible for the presence of the "Sputnik manhole cover" legend on the Internet, where it has been often discussed. It does not identify the test, but from the information in the article it can be deduced that it had to be Pascal-B, which has since be confirmed to me by Dr. Brownlee

The article is more-or-less accurate, but gives a false impression of what was actually known about the plate's journey (and is wrong in its use of the term Project Thunderwell). For an authentic account of this incident by Dr. Robert Brownlee himself, this web site is pleased to host:Learning to Contain Underground Nuclear Explosions.

As Dr. Brownlee explains, the figure of "a velocity six times that needed to escape Earth's gravity" refers to the results of a simulation, that may not of been a good model of the actual test conditions (the actual yield for example, was unknown even if all other parameters were correct). No measurement of the actual plate velocity was made.

If the description of the plate is accurate - 4 feet wide, 4 inches thick and made of steel - then it would weigh about 900 kg (a lower weight is possible if the dimensions are inaccurate or if it was not of uniform thickness). A velocity of 6 times Earth's escape velocity (67 km/sec, since escape velocity is 11.2 km/sec) would give the plate a kinetic energy 60% larger than the total energy released by the explosion. This is clearly impossible.

Brownlee explained to this author, by email, that the concrete plug placed in close proximity to the bomb was vaporized by the explosion. Thus the propulsion of the plate could be considered to be due to the energy imparted by this expanding vaporized material, rather like the propellant of a gun. From the descriptions available of the plug a mass of at least 3000 kg can be estimated, and if half the bomb's energy were deposited in it then it would have an energy density of 50 times that of normal gun propellant. From the physics of high velocity guns, it can be estimated that velocities produced by the gas expanding up the long shaft could propel and object to velocities exceeding Earth's escape velocity, perhaps as much as twice escape velocity.

For the rest look at the Pascal-B subcritical test on this list :

OPERATION PLUMBOB

How sad No one liked this post. it is one of the oldest i could find on the site!

Originally posted by badgerman24
How sad

No one liked this post. it is one of the oldest i could find on the site!

I think when I posted this there were about 300 members belonging to ATS. It's an interesting story.

What they didn't know in 1957 is that it would take a larger bomb in a deeper well with water filling the whole to the top. The heat would vaporize the water almost instantly and the pressure increase would throw the cap into the atmosphere with ease. Some scientist talk about it on "Curiosity: Could We Survive an Alien Attack".