From: veritasium
A kinetic energy weapon is a hypothetical space weapon concept that relies solely on the kinetic energy of a dropped object to destroy targets, rather than explosives [02:56:00]. The principle is that a heavy object traveling at extreme speeds carries an immense amount of energy [03:00:00].
Project Thor: Rods from God
The concept of kinetic weapons, colloquially known as “Rods from God,” emerged in the late 1950s in response to the Soviet Union’s advancements in missile technology [00:42:00].
Historical Context
In 1957, the Soviet Union launched Sputnik, the first artificial satellite, and successfully tested the first intercontinental ballistic missile (ICBM) [00:45:00]. This ICBM could deliver a nuclear warhead to the US East Coast in about 30 minutes [01:03:00].
Facing this threat, Jerry Pournelle, a researcher at Boeing, conceived a space weapon that could strike any location on Earth in 15 minutes [01:13:00]. This weapon could destroy targets buried 30 meters underground, such as Soviet nuclear silos, and theoretically intercept ICBMs mid-flight [01:24:00].
Weapon Design and Capabilities
Pournelle’s concept, named Project Thor after the Norse God of lightning, involved placing telephone-pole-sized pieces of tungsten in orbit [01:37:00]. These tungsten rods could be released to re-enter the atmosphere and strike a target in minutes [01:56:00].
The rods would enter the atmosphere at orbital speeds of about eight kilometers per second [02:06:00]. Despite slowing down due to atmospheric drag, they would still impact at approximately Mach 10 (three kilometers per second) [02:10:00].
A single tungsten rod would carry the same energy as the MOAB (Massive Ordinance Air Blast), also known as the Mother of All Bombs [02:46:00]. The MOAB is one of the most powerful non-nuclear explosives, releasing the equivalent of 11 tons of TNT [02:37:00]. These rods are not bombs; they contain no explosives, but their kinetic energy alone matches that of the largest conventional bombs ever detonated [02:56:00].
Evolution of the Concept
The kinetic missile interceptor idea was seriously considered by the Reagan administration in the 1980s, codenamed “Brilliant Pebbles,” but the project was eventually abandoned [03:21:00]. In 2003, it was resurrected by the Air Force Transformation Plan as “hypervelocity rod bundles” [03:33:00].
The Physics of Kinetic Energy
Kinetic energy is directly proportional to an object’s mass and the square of its velocity [03:48:00]. This means that increasing an object’s mass by 10 times increases its kinetic energy by 10 times, but increasing its velocity by 10 times increases its kinetic energy by 100 times [03:54:00].
This explains why even very light objects can carry significant kinetic energy at high speeds [04:06:00]. For example:
- A 15-gram piece of plastic traveling at six kilometers per second can severely damage a block of aluminum [04:11:00].
- Micro meteorites, small bolts, or even flecks of paint pose serious risks to satellites and astronauts on the International Space Station (ISS) due to their massive orbital speeds [04:19:00]. A tiny speck of dust caused a chip in an ISS window, and a small piece of space junk punctured a hole in its robotic arm [04:34:00].
Impact Effects: Explosive Kinetic Energy
When objects collide at incredibly high speeds, their kinetic energy behaves explosively [10:02:00].
- Lunar craters, despite being formed by asteroids impacting from various angles, are almost all circular [10:02:00]. This is because the asteroids impact with such speed that their kinetic energy instantly heats the ground, turning it into liquid and gas that spray outwards in a symmetrical explosion [10:32:00].
- Similarly, “Rods from God” impacting at Mach 10 would create an explosion equivalent to the largest conventional weapons [11:03:00].
The immense speed allows these rods to penetrate approximately 30 meters of soil, sufficient to destroy bunkers or silos [11:15:00]. The explosion is localized, allowing for precise, surgical strikes [11:22:00]. Unlike nuclear weapons, there is no radioactive fallout to consider, nor do they contravene international laws on weapons in space, which currently only prohibit nuclear weapons [11:29:00].
Experimental Drop Test
To understand the potential damage of a “Rod from God,” an experiment was conducted involving dropping large metal weights onto a sandcastle city [05:01:00]. Professional sandcastle builders constructed a detailed city for the experiment [05:10:00].
Initial Attempts and Challenges
The first test involved dropping a 100-kilogram (220-pound) mass from 500 meters (1500 feet) towards a swimming pool, using GPS for targeting [06:11:00]. However, aiming proved extremely difficult, and the weight missed the pool significantly, landing far past the sandcastle city [08:48:00]. At 500 meters, the rod accelerated for 10 seconds, and even with air resistance, it hit the ground at about 350 kilometers per hour, carrying nearly half a million joules of kinetic energy [09:27:00].
A subsequent attempt from 100 meters (300 feet) using visual targeting also missed the pool, landing 60 feet off target [13:10:00]. It was noted that cylindrical “Rods from God” might tend to fall on their sides rather than straight down [12:16:00]. Strong wind and swinging of the weight while suspended by the helicopter further complicated aiming [12:43:00].
Successful Impact and Unexpected Results
A 200-kilogram (440-pound) mass was eventually dropped from 50 meters (150 feet) and successfully hit the edge of the pool [13:55:00].
Finally, a drop onto the sandcastle city from 100 meters (300 feet) aimed for the capital building [16:45:00]. Despite the challenges, the weight landed extremely close to the building, though it did not cause the expected widespread devastation, only creating cracks and taking down one side [18:21:00]. This demonstrated that while effective for pinpoint strikes, it might not cause mass devastation [18:37:00].
Factors Affecting Kinetic Projectile Performance
Material and Shape
The proposed “Rods from God” would be made of tungsten for two main reasons [15:31:00]:
- Density: Tungsten is exceptionally dense; a cubic meter weighs 19 tons, more than twice the density of steel [15:36:00]. This allows for less volume for a given mass, reducing air resistance during atmospheric passage [15:48:00].
- Melting Point: Tungsten has the highest melting point of any metal, nearly 3,500 degrees Celsius [16:00:00]. This is crucial because significant heat builds up around the rod as it decelerates through the atmosphere, and tungsten’s high melting point minimizes the need for extensive shielding [16:08:00].
The shape of the projectile is also critical [16:21:00]. A sleek, aerodynamic rod shape is ideal for minimizing drag and maintaining speed, similar to arrows, bullets, and ballistic missiles [16:26:00]. The experimental drop test highlighted the mistake of not adding fins to the rods, which would help with stability [16:40:00].
Feasibility and Challenges of Rods from God
Despite their theoretical power, “Rods from God” are currently unfeasible to execute in reality [22:28:00].
Aiming and Communication
Steering a Rod from God is theoretically possible using thrusters, adjustable fins, or by changing the rod’s center of mass [19:52:00]. However, in practice, aiming an object at hypersonic speeds is incredibly difficult [20:00:00]. Furthermore, communicating with the rod from Earth or space would be nearly impossible due to the superheated plasma that would surround it during atmospheric re-entry [20:06:00].
Orbital Mechanics and Coverage
To hit a target within 15 minutes, the rod cannot be in geostationary orbit (over 35,000 kilometers away), as it would take several hours to fall to Earth [20:16:00]. Placing it in low Earth orbit (around 350 kilometers above Earth) means the rod would orbit the Earth every 90 minutes, moving relative to the ground [20:37:00].
This orbital drift means that the time between ordering a strike and impact could be up to an hour and a half [20:46:00]. To reduce this to about 30 minutes, hundreds of satellites would be needed to ensure a rod is always close to a target, especially considering the Earth’s rotation [20:52:00].
Cost and Defense Evasion
Launching a hundred rods into space would cost billions of dollars, with ongoing maintenance costs for thrusters that would break down and malfunction over time [21:09:00].
For missile defense, a smaller rod could be used to intercept ICBMs during their boost phase, before they split into multiple payloads and decoys [21:27:00]. However, even a limited system to stop North Korean ICBM launches would require around 400 rods spread across eight orbits [21:49:00]. A global defense system would need several times that amount [21:59:00].
A very limited system has been estimated to cost around $300 billion, nearly half of the US military’s annual budget [22:04:00]. Even then, enemies could evade the defense by launching multiple missiles simultaneously, as a single rod in the right location could only intercept one missile [22:15:00].
Ultimately, the concept of “Rods from God” remains feasible only in science fiction [22:46:00].
Engineering often involves trial and error, and learning about physics, math, and engineering can be facilitated by interactive platforms like Brilliant [23:01:00]. Brilliant offers courses on calculating the motion of falling objects and provides interactive lessons that build an intuitive understanding of complex problems [23:21:00].