Relativistic kill vehicle

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"RKV" redirects here. It is also the IATA airport code for Reykjavík Airport.

A relativistic kill vehicle (RKV) or relativistic bomb is a hypothetical weapon system sometimes found in science fiction. The details of such systems vary widely, but the key common feature is the use of a massive impactor travelling at a significant fraction of light speed to strike the target. At these relativistic velocities the mass could carry immense amounts of kinetic energy, potentially several times that of its rest mass energy equivalent (i.e. the amount of energy that would be released if its rest mass were totally converted into free energy).

RKVs have been proposed as a method of interstellar warfare, especially in settings where faster than light travel or sensors are impossible. By travelling near the speed of light an RKV could substantially limit the amount of early warning detection time. Furthermore, since the destructive effects of the RKV are carried by its kinetic energy, destroying the vehicle near its target would do little to reduce the damage; the cloud of particles or vapor would still be travelling at nearly the same speed and would have little time to disperse. Indeed, some versions of the RKV concept call for the RKV to explode shortly before impact to shower a wide region of space.

Since they would likely be difficult to provide much terminal guidance to, RKVs are usually proposed as a strategic weapon targeted against large and relatively immobile targets such as planets. Accelerating a mass to such velocities in the first place will likely require vast amounts of energy and large, unwieldy accelerators.

An RKV could theoretically be launched using any of the spacecraft propulsion techniques that are capable of accelerating starships to relativistic velocities, such as antimatter rockets, Bussard ramjet systems, or nuclear pulse propulsion (see also relativistic rockets). Since an RKV would be unmanned, higher accelerations could be used (though with most propulsion methods high acceleration may not be the most efficient approach).

In some science fiction smaller relativistic projectiles can sometimes be found depending on the technologies imagined in any particular scenario. In the movie Eraser, for example, characters used man-portable "gauss rifles" that were able to fire bullets at relativistic velocities. Man-portable weapons of this type would have extreme issues with recoil, however; accelerating a 1 gram projectile up to a mere 1% of light speed would produce enough force to send a 100kg (220 pound) man flying backward at 3000 meters per second (9800 feet per second or 6000 miles per hour). A further difficulty is reaching such high speeds over such a short distance; to reach 1% of light speed over the length of a one-meter accelerator would require $4.5 \cdot 10^{12} \mbox{m}/\mbox{s}^2$ (or over 450 billion g); of acceleration. Space-based RKVs have the advantage of being able to accelerate over a vastly longer distance and period of time.

[edit] Calculating energy content

Newton's formula for kinetic energy, given as $\begin{matrix}\frac{1}{2}\end{matrix} m v^2$ , is only an approximation for the kinetic energy of an object, reasonably accurate for speeds well below c, approximately 3 × 10⁸ m s^-1. For higher speeds, Einstein's formula for kinetic energy, E_k, must be used.

E k = γ m c 2 - m c 2

Where:
m is the object's mass in kg,
c is the speed of light in m s^-1,
$γ$ is the Lorentz factor, given by:

$\gamma = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$

Where v is the velocity of the object in question.

Therefore, expanded our equation is:

$E_k = m c^2 \left( \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} -1 \right)$

[edit] Examples of RKVs in fiction

A good example of RKV use in science fiction novels is in Charles R. Pellegrino and George Zebrowski's The Killing Star and Flying to Valhalla, wherein aliens exterminate all human life on Earth by kinetic weapons traveling at relativistic velocities called "R-bombs".

W. Michael Gear's "Forbidden Borders" trilogy, Requiem for the Conqueror, Relic of Empire and Countermeasures also include RKVs. In A Fire Upon the Deep by Vernor Vinge, the destruction of a human civilization is preceded by a RKV assault. In Iron Sunrise by Charles Stross, attempts are made to obtain the deactivation codes which will stop a destroyed planet's automated RKV retaliation from destroying another world. In David Weber's Honor Harrington series, RKVs are mentioned as a historical weapon, later banned as uncivilized. In Joe Haldeman's The Forever War, a drone traveling at relativistic speeds changes the outcome of a battle by destroying a much larger enemy battlecruiser as well as, accidentally, part of a moon. In Larry Niven's 'Known Space' series (specifically the 'Man-Kzin Wars' shared-world era), RKVs were used as part of the counterattack against the Kzinti occupation of the Centauri system, impacting against the planet Wunderland with a combined energy release equalling 12 gigatons of TNT.

In the webcomic Schlock Mercenary, RKVs of various sorts are used, such as the cee-sabots deployed the Partnership Collective fleet^[1] and the Tohdfraug assault on the planet Qlaviql.^[2]

One of the earliest, if not the earliest examples come from E. E. "Doc" Smith's Lensman series.