A Professional Paranoid's Blog

The fastest man-made object ever: A nuclear-powered manhole cover (true!)

The Holy Grail of space-minded dreamers and researchers has always been nuclear-powered propulsion. Nuclear-powered propulsion would be far cleaner, far cheaper, far more efficient, and far less noisy than current roar-and-a-fireball rocket propulsion. (Not sure the last is an advantage. I’m a big fan of roar-and-a-fireball in almost anything, including rocket launches, howitzers, and NASCAR races.)

And in fact we’ve had nuclear propulsion for some time. The small maneuvering engines of deep-space probes are typically nuclear-powered, but not in the way usually envisioned: They are tiny, nearly soundless (even on Earth) little fast-particle emitters that generate fractions of an ounce of thrust. That’s enough to rotate a spacecraft, given time, and their nuclear sources last virtually forever, but they’re hardly the earth-shaking monsters we envisioned blasting from Earth into space. Too bad we’ve not been able to accomplish that.

Or have we? In a round-about way I recently came across the Nuclear Weapons Archive, a wonder world of historical documents, photos, and personal accounts of the Nuclear Age as seen through the history of nuclear bombs and bomb tests. For the historian, the scientist, or the intellectually curious the whole archive is a trove of riches, every link and page another revelation. Jump in anywhere and start reading — you’ll be hooked. And it’s not just about the U.S. nuclear program — it has material covering every declared and non-declared nuclear power.

For illustration I’ll pass along just one event documented in the archives that by itself merits a whole book and a movie:

While all the early nuclear tests had been above ground (what could possibly be wrong with that, right?), by 1956 Los Alamos was working on how to contain radiation and fallout by detonating the bombs underground. Initially the concept was very simple: drill a deep hole, say, 500 feet deep by four feet wide, lower the bomb to the bottom, light the fuse and run. (Well, OK, not quite that simple. But the hole was.) Originally the idea was to leave the holes uncapped, the thinking being that even with the top of the shaft open relatively little would escape. (Which was largely true, though not exactly up to modern expectations.)

By mid-1957 Los Alamos scientist (and famed astrophysicist) Robert Brownlee was ready to try testing with a capped shaft (known as a “stemmed” shaft in nuke-speak). In a test known as Pascal-A, a cap of four-inch-thick solid steelĀ  — what one might call the biggest, baddest manhole cover in history — was securely welded to the top of the shaft. With nothing else in the way, that far from the bomb the plate would likely have popped off, but wouldn’t have gone very far.

But something else was in the way. Way down the shaft, hundreds of feet below the cap, was a collimator, a five-foot-thick, multi-ton plug of concrete with a small hole in the middle. The hole served as a small window through which a special detector attached to the inside of the steel cap could make measurements during the first few milliseconds of the explosion. After that first fraction of a second the detector itself would be annihilated, but its brief set of readings would have been captured by above-ground recorders.

It’s significant that what was being tested in Pascal-A was an experimental bomb that was designed to be “one point safe.” That meant that if it was accidentally detonated (a significant concern back then), it would only fire only one of its many trigger points around the explosive core, resulting in a tiny fraction of the yield, not the whole megillah. The explosion in the test was therefore expected to be (relatively) very small.

That’s not quite what happened.

At 10:35pm on August 27, 1957 in Area U3d of the New Mexico Nuclear Test Site, the bomb was detonated. But instead of the expected small yield the bomb detonated with a yield approximately five orders of magnitude greater than expected (that’s about 100 000 times greater). The blast instantly vaporized the entire multi-ton concrete collimator and shot it up the tube as a multi-ton wave of vaporized matter at extremely high temperature, pressure, and velocity. The shaft had, in effect, become a enormous 500-foot long, four-foot wide gun barrel with the energy of billions of pounds of TNT released at one end and, at the other end, the now insignificantly small metal cap, about the equivalent of a bottle cap on the end of a naval gun.

As it happens, a very high speed film camera was recording the event and was expected to capture in slow motion the path and speed of any ejecta from the hole. Unfortunately, the camera, which had quite a wide view of top of the hole and and the area around and above, recorded the “manhole cover” on only one frame. There was no malfunction of the camera, it’s just that the “manhole cover” blasted out of sight so fast that the camera only saw it for one frame. Later calculations showed that the heretofore mundane four-foot metal disk had been launched at six times Earth’s escape velocity. That’s one hundred fifty thousand miles per hour. Forty-five miles per second. Nine times faster than the Space Shuttle, six times faster than the fastest moon rockets. Faster than the Voyager spacecraft, which, having reached over 35000 miles per hour, are now leaving the solar system and have for years been claimed to be the fastest man-made objects ever. To which I now say: Pshaw and poppycock — the Pascal-A “manhole cover” in a fraction of a second achieved more than four times the speed it took Voyager 1 decades to attain.

The “manhole cover” was, of course, never found. And, to my deep disappointment, cold-sober calculations indicate it’s not on its way to the Hercules Cluster which, late on a summer night shot from a vertical hole in New Mexico, may well be about where it was aimed. Instead it almost certainly suffered a meteor’s fate in reverse: At such an extreme speed it would have created an enormous fireball (a fireball going up) and been slowed so much that what didn’t burn off would eventually have come back down.

Being such a tough and massive object, most of it would have survived its “reverse re-entry” (or just plain “entry”?), so it would have come down as a burned, edge-melted, and perhaps quite misshapen chunk of solid steel, a very formidable projectile that would have done very serious damage even to large buildings. Given that no one that night reported any macerated cars or demolished buildings and that the huge object had been launched nearly vertically, it likely came down in the desert somewhere in the wide vicinity of the test site in New Mexico. It would have had some serious hang-time, though.

So somewhere in the New Mexico desert, unknown and unmourned, lies an American relic, a piece of history like no other: the fastest man-made object ever. And I harbor the hope that, whether it’s found or not, our nation and the world of science will someday realize our error all these years and recognize that the Pascal-A Manhole Cover, not Voyager 1, is the fastest man-made object ever.

Here’s hoping.


  1. [...] [...]

    Pingback by what's a cannon? - Page 3 — 30 September 2012 @ 2:39 pm

  2. These stories remind us of how much power there really is in a nuke. We tend to get used to “big badass bomb” but every time you study the badass-ness, you do tremble a bit. Nuclear power is the only hope for man’s future and more so in space, IMO (but I could be badly misinformed)

    Comment by Dave — 5 September 2012 @ 1:38 pm

  3. Highly energetic post, I loved that a lot. Will there be a part

    Comment by tube hi — 13 July 2012 @ 11:18 pm

  4. [...] Read the story, including links to ample official documentation. [...]

    Pingback by Fastest object ever? « A Professional Paranoid's Blog — 1 June 2010 @ 9:34 pm

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