Warfare is constantly progressing, constantly changing. During World War II we pitted troops against each other on great fields of war in ways in which we haven’t seen since. Modern battles are fought with drones, smaller skirmishes and strike teams, surgical and careful. The concept of a Relativistic Kill Vehicle (or RKV), in some ways, it’s just the natural progression of warfare. Leaving the stone age, we developed weapons that took advantage of our newfound ability to manipulate metals. Later, we had a revolution as our understanding of chemistry grew and we realised we could use chemical reactions to propel projectiles. It’s foolish to think that the space age won’t do the same, despite our best efforts to keep space weapons free: The Outer Space Treaty bars placing weapons of mass destruction in orbit of Earth, installing them on the moon, or on or around any other celestial body, or stationing them in outer space in any capacity.
However, the RKV doesn’t appear to be a weapon of mass destruction on the surface of things; it doesn’t need materials like uranium or plutonium in order to function, instead relying upon mass and acceleration.
So how does an RKV work? It's actually very simple; it’s all in the kinetic energy. When we think about how fast we can propel an object we tend to think in a very down to Earth manner; a human can handle an acceleration of a few G-forces, whereas a missile can handle dozens, its non-biological components able to withstand far more than biological components ever could. The RKV, however, can simply be a solid slug launched from a cannon such as a mass driver. What’s a mass driver? It’s also known as an electromagnetic catapult and is a hypothetical non-rocket launching system that would use a linear motor to accelerate the solid slug of the RKV to high speeds and catapult it. The R in RKV comes into play when the mass driver is built to the scale that allows for the slug to reach relativistic speeds. Because the slug is a solid object with no biological or moving parts it is able to handle G-force much more like a bullet would, taking on G’s in the hundreds, if not thousands.
By travelling near the speed of light, an RKV could substantially limit the usefulness of an early warning detection system. Furthermore, since the destructive effects of the RKV are carried by its kinetic energy, destroying it when it nears its target would do little to reduce the damage caused by it; the cloud of particles that would be left over from intercepting it would still be travelling at nearly the same speed, and would have little time to disperse. The result would be the raining down of thousands of destructive fragments rather than one large one.
The RKV would likely have no internal guidance systems due the fact that the electronics needed for such a thing would have a very poor chance of surviving the acceleration. Taking this into account, it would likely be most effective when being launched at large targets that have a predictable path, such as a planet or moon. If the intended target as a ship or fleet, the RKV would need to be able to fragment itself on approach, littering space with projectiles. Doing this, however, would mean the integration of electronics and explosives, as well as a timer that was capable of compensating for the relativistic problems of moving at the proposed velocities.
The damage an RKV could bring to its target would be devastating. As the RKV impacts, all of its kinetic energy would transfer to its target, unleashing a force far greater than that of nuclear weapons—providing the RKV slug has the mass. If an RKV were to target Earth it would be much like the impact of an asteroid, superheating the air as it passes through the atmosphere in the blink of an eye, before ploughing deep into the crust of the planet. Its shockwave would level everything around it. Asteroids, however, do not move at relativistic speeds the way an RKV would. The impact from such an object would be unlike anything we have seen before… but suffice to say whatever it is targeting would not survive...
As well as being efficient at destruction, though, the basic slugs will also be cheap to produce once the launch system is built, meaning that this weapon could be effective and near unstoppable once launched.
The first people to have access to an RKV system will be able to wield huge influence. Today individuals are capable of building basic railguns in their garage without spending much money, and in some ways the RKV is just the next step. One day the RKV may be an individual’s garage project (figuratively speaking) that could give them the power to sway the entire solar systems politics and at no point would they have needed to acquire any dangerous or radioactive materials. Of course, the garage would have to be pretty massive to contain an RKV launch system, but it would be theoretically possible for a small group of people to develop something on this scale for a low cost.
On the bright side though, if you were to find yourself on the receiving end of an RKV you wouldn’t have much time to worry about it!