The story of the fastest man-made object begins in 1957 during Operation Plumbbob, a series of nuclear weapons tests conducted at the Nevada Test Site. This event involved the accidental launch of a massive steel plate at speeds that held the unofficial record for decades. The launch was achieved using the raw power of an atomic explosion. The resulting velocity cemented the plate’s place in scientific lore as a unique experiment in extreme physics.
The Setup: Operation Plumbbob Pascal-B
The Pascal-B test was part of a larger effort by scientists at Los Alamos National Laboratory to understand and contain the effects of underground nuclear detonations. Dr. Robert Brownlee and his team were tasked with preventing radioactive fallout from venting into the atmosphere. The experiment involved digging a deep, vertical shaft, approximately 500 feet into the earth, with a nuclear device placed at the bottom.
To cap the bore hole and contain the anticipated blast, a heavy, round steel plate was used. This object, often popularly but incorrectly called a “manhole cover,” was actually a solid piece of armor plate, about four feet in diameter and four inches thick. The steel cap was estimated to weigh around 900 kilograms (2,000 pounds) and was welded over the top of the shaft opening at ground level.
The Estimated Velocity
Based on calculations performed by Dr. Brownlee, the steel plate was estimated to have been launched at a velocity of approximately 66 kilometers per second, or roughly 147,600 miles per hour. This speed was not measured directly, but rather calculated based on the known energy yield of the nuclear device and the mass of the plate.
This theoretical velocity is nearly five to six times greater than Earth’s escape velocity. Escape velocity is the speed an object needs to permanently break free of the planet’s gravity. The extreme difference confirms the plate would have been launched into interplanetary space had it survived its trip through the atmosphere.
The Mechanism of Acceleration
The extraordinary speed was achieved through a unique mechanism known as the plasma piston effect. When the nuclear device was detonated deep underground, it instantly vaporized the surrounding rock, concrete, and the air within the narrow shaft. This created an extremely hot, high-pressure plasma gas that was channeled rapidly upward.
The narrow, 500-foot-long shaft acted like the barrel of an immense, single-shot gas gun. The expanding column of superheated gas functioned as a powerful piston, transferring its kinetic energy directly to the steel plate resting at the top. This immense pressure accelerated the 2,000-pound plate from a standstill to its peak velocity in a matter of milliseconds.
The acceleration experienced by the plate was calculated to be in the millions of Gs, an instantaneous force far exceeding the yield strength of the steel itself. The sheer force and heat from the nuclear plasma likely caused significant deformation or even initial vaporization of the material as it began its flight.
Tracking the Fastest Man-Made Object
Scientists attempted to capture the event using high-speed Rapatronic cameras designed for nuclear testing. These cameras were set up to photograph the launch at an incredibly rapid rate, capturing one frame every millisecond.
However, the steel plate was only visible in a single frame of the resulting film before it vanished. This limited visual data only provided a lower bound for its speed, prompting Dr. Brownlee to famously joke that the object was “going like a bat.” The lack of a second frame confirmed the object had moved out of the camera’s field of view in less than one millisecond.
The steel plate was never recovered, and the consensus among scientists is that it was destroyed shortly after launch. Traveling at over 147,600 miles per hour through the dense lower atmosphere created immense atmospheric friction and compression heating. This extreme heating would have likely caused the massive steel plate to vaporize completely, essentially burning up like a meteor in reverse before it could ever reach space.