How Underground Nuke Tests Inspired Radical New Spaceship Designs
Underground atomic tests didn’t launch a manhole cover into space, but they did spark a dream
America’s first underground nuclear tests put on quite a show.
The experiments—dating to the 1950s—not only revealed new information about the feasibility of storing nukes underground, but they spawned some radical new designs for space travel, including a nuclear bomb-powered spaceship theoretically capable of traveling to Mars.
The story begins just around 10 p.m. on July 26, 1957 when the bomb, known as Pascal-A, exploded.
Part of the Operation Plumbbob series of nuclear tests, Pascal-A was intended to allow scientists to explore new designs, components and techniques for nuclear combat.
At the time, atomic weaponeers were worried that stockpiled nuclear bombs could explode without a full nuclear detonation occurring. If shock or the accidental triggering of a weapon’s chemical explosives accidentally shoved a bomb core together, a subcritical incident can occur—a nuclear chain reaction that peters out before the mushroom cloud.
Even without a full explosion, such tests would still release lots of destructive energy. The nuclear labs already looked to underground shafts to address public concerns about nuclear fallout caused by atmospheric tests.
The shafts could now explore two problems at once.
Seconds before Pascal-A exploded, the 65-pound device—just under a foot in diameter and 15 inches long—hung suspended at the bottom of a 500-foot shaft drilled into the surface of the Nevada desert.
Just above the bomb, a thick concrete plug with a hole drilled through it acted as a collimator, which adjusts scrambled beams of light so they instead travel in parallel lines. A detector sat atop the shaft, ready to absorb the parallel light for study.
The bomb exploded with 50,000 times the force expected—equivalent to some 55 tons of TNT. “[I]t was the world’s finest Roman candle … blue fire shot hundreds of feet in the air,” weapon designer Bob Brownlee said.
“Everybody was down in the area, and they all jumped in their cars and drove like crazy,” he added.
Nuclear pulse power
The next underground test, Pascal-B, was similar to Pascal-A with two notable exceptions.
This time, instead of a pierced collimator, scientists stuck a solid concrete plug just above the bomb. They also welded a four-inch-thick steel cap atop the shaft’s four-foot-diameter casing pipe.
Brownlee’s pre-shot calculations predicted the cap could be flung very far—and fast—by the blast. To learn how far and fast it would go, the crew aimed a high-speed camera at the cap.
But this didn’t happen quite as Brownlee predicted. Later analysis suggests that when the bomb exploded, it vaporized the concrete plug, turning the cased shaft into the equivalent of a gigantic gun. It was this blast of incandescent concrete vapor, not the blast itself, that launched the steel cap on its odyssey.
Only a single frame of film captured the cap’s flight, but the image and the numbers from Pascal-B seem to confirm that the steel cap far exceeded the planet’s escape velocity.
The atomic test theoretically blew its lid into outer space.But this is only theoretical.
Brownlee didn’t believe his manhole cover beat the Soviet satellite Sputnik into orbit. Even had the object survived the initial thrust, the acceleration would have quickly turned the cover into a reverse-meteorite, torn into gas by its rush through the atmosphere.
The Pascal shots ushered in underground testing just as above-ground nukes produced some of the worst fallout of any American test series. It would become harder and eventually impossible to conduct above-ground tests.
But the rocket-like effects of contained nuclear blasts caught the eye of some weaponeers looking for less martial uses for their machines. The Pascal tests amply demonstrated that atomic explosions could generate tremendous thrust.
Between 1958 and 1964, the scientist dreamers of Project Orion proposed a giant spacecraft to travel the solar system.
Pushed to huge speeds by machine-gun atomic explosions, these frigate-sized spaceships would ride the blast waves of exploding nuclear bombs to Mars and beyond. The proposal called for mounting a giant copper-coated plate on the back of the spaceship to absorb the blasts.
But it was not to be. The Partial Test Ban Treaty of 1963 and the Outer Space Treaty of 1967 closed off atmospheric testing of Orion bomb drives, and banned nuclear explosions in space.
Some technical details of the fully-conceived nuclear-pulse rocket remain classified to this day.
Meanwhile, out in the Nevada desert, scientists tested nuclear rockets and nuke-tested spacecraft until the active test programs ended with the Cold War. Now renamed the National Nuclear Security Site, the Nevada Test Site still supports a variety of missions.
One of them provides “program direction for the receipt, staging, assessment, disassembly, and/or destruction of nuclear or radiological devices during emergency scenarios,” stated the National Nuclear Security Administration.
Let’s hope that particular scenario doesn’t happen.