What is the Fastest Man-Made Object? The Manhole Cover Mystery

When discussing the fastest man-made objects, the mind often turns to spacecraft like NASA's Parker Solar Probe, which currently holds the official record for the fastest speed achieved by a human-made object, traveling at an astonishing 430,000 mph. But there is an intriguing, less-known story about a manhole cover that may have briefly broken all speed records—if it even survived its journey. The story comes from the 1957 Operation Plumbbob nuclear tests, which launched this simple steel cap into legend.

The Operation Plumbbob Test

In 1957, the U.S. military conducted a series of nuclear tests known as Operation Plumbbob at the Nevada Test Site. These tests were meant to study the effects of nuclear explosions on a variety of materials, as well as understand the behavior of nuclear yields. The particular test in question, Pascal-B, involved detonating a nuclear device at the bottom of a long, narrow shaft dug into the desert floor. The aim was to study the containment of nuclear explosions underground.

Before the detonation, the shaft was sealed with a 4-inch thick, 900-kilogram steel manhole cover. The expectation was that the cap would be blown off, but no one predicted just how fast it would travel.

The Incredible Speed of the Manhole Cover

When the nuclear device was detonated, the energy released was so enormous that the steel cover was blasted off the top of the shaft at a calculated speed of 150,000 mph (241,400 km/h)—about six times the Earth's escape velocity. This incredible speed, if accurate, would have made the manhole cover the fastest man-made object ever launched from Earth, far surpassing even modern spacecraft.

The cover was visible for only a single frame on the high-speed cameras capturing the event, and after that, it was never seen again. Because of the camera limitations at the time, the exact speed could only be estimated. Some calculations suggest it was fast enough to escape Earth's gravity entirely, launching it into space.

Did the Manhole Cover Really Leave Earth?

While it’s tempting to believe that the manhole cover became Earth's first unintentional interstellar object, there are many reasons to doubt this. The speed of the object might have allowed it to reach space, but most scientists argue that the cover likely vaporized due to atmospheric compression as it traveled through the Earth's atmosphere at such extreme velocity.

The lack of recovery and further evidence of the object has left the story in the realm of speculation. Whether the manhole cover escaped Earth or was destroyed before exiting the atmosphere remains a mystery.

Modern Fastest Objects: NASA's Parker Solar Probe

Fast forward to today, and the fastest officially recognized man-made object is NASA’s Parker Solar Probe, launched in 2018. The probe's mission is to study the Sun by getting closer to it than any previous spacecraft. During its journey, the Parker Solar Probe reached a speed of 430,000 mph (700,000 km/h) when slingshot around the Sun at its closest approach. This is the fastest speed ever officially recorded for a human-made object.

Comparing the Manhole Cover and Modern Technology

Although the manhole cover likely holds the unofficial title for the fastest man-made object, there are key differences in how it achieved its speed compared to modern spacecraft like the Parker Solar Probe.

Duration of Travel: The Parker Solar Probe is designed to travel at high speeds for extended periods, while the manhole cover’s high-speed travel was likely short-lived, either burning up or slowing down quickly.

Purpose and Design: The Parker Solar Probe was engineered specifically for space travel, with heat shields and propulsion systems to sustain its mission. In contrast, the manhole cover was an unintended object propelled by a nuclear explosion and was not designed for long-term space travel.

Evidence: The Parker Solar Probe's speed is verifiable, with precise measurements and data. The manhole cover’s speed is speculative, based on rough calculations from the test conditions.

Legacy of the Fastest Object Debate

Despite the lack of hard evidence, the story of the manhole cover remains a fascinating tale in the history of science. It shows the unpredictable consequences of extreme forces and has inspired engineers and scientists to think about the limits of speed and velocity for man-made objects. Even though modern spacecraft have surpassed it in terms of speed, the manhole cover retains its place in popular culture as a quirky but compelling piece of engineering lore.