Relativistic Kinetic Kill System (RKKS)
Relativistic kinetic kill system
Image from Steve Bowers
The world of Fiori is attacked by relativistic kinetic missiles in the Oracle War conflict
RKKS (pronounced rocks) are a relativistic weapons system consisting of an unmanned launch vehicle and dense projectiles. Used in interstellar warfare for extreme planetary bombardment. Used a number of times during the Second Consolidation War, by the Geminga Orthodoxy, and during the Oracle War. The use of RKKS systems is outlawed in the Sephirotic Empires and many other metaempires, but still sees occasional illegal use in conflicts on occasion.

The launch vehicle has a powerful drive system and can accelerate to near light speed fairly quickly. Upon arrival in the target star system the launch vehicle orients itself to its target(s) and releases its payload of projectiles. Each projectile is little more than a dense block of mass with a minimal amat maneuvering system for terminal course corrections. The launch vehicle may either continue through the target star system, decelerate and be reused or be used as an additional weapon in its own right.


Upon impact each projectile releases its accumulated relativistic mass in a huge explosion. At 99.9% of light speed, an RKKS projectile has a gamma of 22.4, and each proton has an energy of about 21 GeV, each electron 11 MeV. After penetrating a sectional density of about 0.7 ton/m^2, each proton or neutron in the spacecraft will have collided with a nucleus of a molecule in the air. This will disintegrate any atomic nucleus involved and give a spray of hadrons and mesons. Since the atmosphere of an Earth-like world holds about 10 tons per square meter of surface area, no part of the projectile can be expected to reach the ground un-disintegrated.

The protons, neutrons, and mesons produced will interact with air nuclei before they hit the ground, and the particles they produce will interact, and so on, until 10 tons/m^2 is reached. This about 14 interaction lengths, with each interaction dividing the energy of that hadron or meson amongst all the particles coming out of that collision. Since electronic losses alone will stop a 1 GeV proton within about 3 tons/m^2 (and the 1 GeV proton will participate in several nuclear interactions before this, thus dumping its energy even sooner), none of the hadrons or mesons produced in this collision will hit the ground.

Muons from charged pi-meson decays will hit the ground, this requires the pi-mesons to decay before they hit an air nucleus in order to produce muons. Neutral pi-mesons will decay almost immediately into high energy gamma rays, which will produce electromagnetic showers (a gamma ray is absorbed in producing a high energy electron and positron pair, which then produce more gamma rays as they slam into atoms, which produce more electrons and positrons). Some of the gammas from these showers
may also make it to the ground. In fact the proportion of primary radiation that will reach the ground from the 20 GeV initial proton and neutron energies will be very small, but a small proportion of a large number (the original kinetic energy of the spacecraft) is still significant.

The radiation that makes it through the air to the ground will be scattered over a footprint with a radius of several hundred meters. Anything within that footprint will suffer the effects of the radiation. Anything outside that footprint is likely safe from the primary radiation. This means that a RKKS projectile will dump most of its energy in the upper to middle stratosphere. This amounts to about 2E18 J per kg of spacecraft, or about 400,000 MT per kg. It takes about 1 MJ/m^2 of radiant flux to flash fabric to flame and cause third degree burns to exposed skin.

Assuming a 100,000 ton RKKS weapon the energy of impact would be 2E26 J. If half of this energy goes into the heat pulse, this produces a radiant flux of 1 MJ/m^2 at a distance of 3 million km. Anything within line of sight of the air-burst is burnt to a crisp. The impact energy of 2E26 J is almost sufficient to blow off an Earth-like planet's atmosphere, which woould require around 3E26 J to remove completely. In addition the oceans and lakes of the rivers within sight of the impact explosion would start to boil, replacing the breathable atmosphere with high-pressure steam and effectively sterilising the planet.

In practice the RKKS is almost always split into numerous smaller projectiles (sabots) which spread the same amount of impact energy over a larger area. A saturation type attack of hundreds or thousands of microprojectiles can shred a space habitat cluster, or a single megascale structure such as a Bishop Ring or McKendree Cylinder.

Detection and countermeasures

Because a sizable drive is used to accelerate a RKKS, this makes them somewhat detectable during their early acceleration phase if they are launched fairly close to the target. Another detectable signature is the friction between the RKKS projectile and the interstellar medium, and in the final stages of approach, with the much denser interplanetary medium; this friction creates detectable gamma rays. But use of streamlining and a narrow cross-sectional area reduces this signature to a minimum.

A RKKS moving at .999c will arrive a fraction of a second behind its own light or gravitational radiation or any warning message sent about it. This makes it difficult for even the most powerful hyperturing to detect the incoming projectile, identify it, send instructions to its defensive systems, and have those systems lock on and destroy the projectile so completely that not enough debris will get through to cause massive damage.

Wormhole based detector systems, in which distant warning stations watch for incoming RKKS and communicate their data via communication wormholes can greatly alleviate this problem. The metric disturbance in the fabric of space-time caused by the movement of a large relativistic mass is sufficiently great to be detected by advanced sensors at a considerable distance. However, outside of the Inner Sphere or other archai protected systems, not many worlds have the resources to set up such a complex, expensive detector system on the off-chance that someone will attempt this type of attack.

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Development Notes
Text by Todd Drashner, with additional material by Luke Campbell

Initially published on 12 December 2001.