The late 1950s saw the United States face a problem when the Soviet Union launched the first artificial satellite, Sputnik, into orbit and successfully tested the first intercontinental ballistic missile (ICBM). In response, a researcher at Boeing named Jerry Pournelle came up with an idea for a space weapon which could hit any location on Earth in half that time, just 15 minutes. This weapon, codenamed Brilliant Pebbles and more commonly known as Rods from God, would use telephone pole sized pieces of tungsten to drop on a target at any time. This would be done by strapping giant metal weights to the belly of a helicopter, flying it up several kilometers in the sky and then dropping the weights. This inspired the concept of MOAB (Massive Ordnance Air Blast), known as the “Mother of All Bombs”, which was one of the most powerful non-nuclear explosives on the planet. The kinetic energy of an object is directly proportional to its mass and its velocity squared, meaning that even very light objects can carry lots of kinetic energy. This is seen in the chip in the window of the ISS caused by a tiny speck of dust and even a small piece of space junk puncturing a hole in the robotic arm. Although this weapon appears in fiction, could it ever become a reality? To answer this question, we are currently in the middle of the desert, strapping giant metal weights to the belly of a helicopter, flying it up several kilometers in the sky and then dropping the weights, on a sandcastle city. But when they hit the surface, the energy is released in a radial pattern and so it creates a circular crater.So, when we drop our rod, it’s gonna be the same thing.It’s gonna release energy in a radial pattern.And if we do it right, we should be able to hit the swimming pool with a 100 kilogram or a 220 pound mass, from 500 meters, with very little damage. So it can penetrate deep into the ground.And the second is that tungsten is really strong.So it can withstand the incredible speeds that it’s traveling at without breaking apart.Plus, it’s relatively inexpensive.So that makes it a great choice for these kinds of weapons.
We shouldn’t expect oblong shapes when asteroids come in - the kinetic energy from their speed creates an explosive collision which heats up the ground, turns things into liquid and gas, and sprays outwards in a symmetric explosion. This kinetic energy is explosive and can penetrate up to 30 meters of soil, which can be used for precise surgical strikes. There is an international agreement about nuclear weapons in space, but no laws prohibiting the use of Rods from God, which are made of tungsten due to its density and strength, plus it’s relatively inexpensive. A cubic meter of tungsten weighs 19 tons, more than twice the density of steel. This means tungsten rods can take up less than half the volume of steel, and thus experience less resistance in the atmosphere. Additionally, tungsten has an incredibly high melting point of almost 3,500 degrees Celsius, meaning it requires much less shielding from heat during re-entry. Aerodynamics is also important for minimizing drag, which is why arrows, bullets, and ballistic missiles have a sleek, aerodynamic shape. Despite the challenges, the goal was to hit the target with as much speed as possible, and although the team was close, they were not able to make a successful test of Rods from God. Aiming an object travelling at hypersonic speeds is incredibly difficult, and communicating with the rod from the ground or from space is nearly impossible due to the superheated plasma surrounding it. Additionally, sending a rod from geostationary orbit would take several hours to fall to the earth. If you placed a rod in low Earth orbit around 350 kilometers above the ground, it would take up to an hour and a half for it to reach its target. You might think that you could reduce this time by placing 10 satellites in the same orbit, but due to the Earth’s rotation, the orbits would drift and you would need hundreds of satellites to ensure that a rod is always close by the target. Launching and maintaining a hundred rods into space would cost billions of dollars.
Using a smaller rod for missile defense would be much cheaper, but even then it’s a tricky process. To intercept an ICBM, you need to hit it during the boost phase, when it splits into multiple payloads. To stop North Korean ICBM launches, the US would need around 400 rods spread among eight orbits. A global defense system would require a few times that amount, and it would cost around 300 billion dollars - nearly half of the US military annual budget. This system would still be vulnerable to enemies launching multiple missiles at the same time.
Rods from God turns out to be unfeasible to execute in reality. Jerry Pournelle, who came up with the idea, went on to become a science fiction writer. In his 1985 New York Times bestselling book, Footfall, an alien race uses kinetic weapons to invade the Earth.
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