Relativistic kill vehicle

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 traveling at a significant fraction of light speed to strike the target. Therefore the weapon is an extreme example of the real-life concept of a kinetic bombardment.

RKVs have been proposed as a method of interstellar warfare, especially in settings where faster than light travel or sensors are impossible. By traveling 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 traveling 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.

As providing terminal guidance for such a high-speed object would likely be difficult, RKVs are usually proposed as a strategic weapon targeted against large and relatively immobile targets such as planets. However, they can still be used against smaller targets like spaceships, by aiming the weapons in the area they are in, and detonating a fuse in advance to shatter the mass into swarms of smaller particles, all traveling at nearly the same speed. This would cover a much larger area, and destroy smaller targets in space. 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).Fact|date=January 2008 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.Fact|date=January 2008 Space-based RKVs have the advantage of being able to accelerate over a vastly longer distance and period of time.

Calculating energy content

Newton's formula for kinetic energy, given as , 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.

:$E\_k\; =\; gamma\; m\; c^2\; -\; m\; c^2$

Where:
"m" is the object's mass in kg,
"c" is the speed of light in m s^-1,
$gamma$ 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:

:$E\_k\; =\; m\; c^2\; left(\; frac\{1\}\{sqrt\{1-frac\{v^2\}\{c^2\}\; -1\; ight)$

Example

A 1kg mass traveling at 99% of the speed of light would have a kinetic energy of 5.47×10¹⁷ joules. In explosive terms, it would be equal to 132 megatons of TNT. That's about 32 megatons more than the theoretical max yield of the tsar bomba, the most powerful nuclear weapon ever detonated. 1kg of mass-energy is 8.99×10¹⁶ joules or about 21.5 megatons of TNT.

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 an 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.(see Eridani Edict)

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' setting (specifically the 'Man-Kzin Wars' shared-world series), RKVs were used as part of the counterattack against the Kzinti occupation of the Alpha Centauri system, impacting against the planet Wunderland with a combined energy release equaling 12 gigatons of TNT.

In issue 18 of Marvel Comics' Supreme Power series, the main character Hyperion uses his indestructible body as an RKV, slamming himself into the far Northern Hemisphere with enough force to generate a one teraton explosion.

In the webcomic Schlock Mercenary, RKVs of various sorts are used, such as the cee-sabots deployed by the Partnership Collective fleet [cite web| url=http://www.schlockmercenary.com/d/20001105.html| title=Schlock Mercenary for Sunday, November 5, 2000| year=2000| first=Howard| last=Taylor| accessdate=2006-03-20] and the Tohdfraug assault on the planet Qlaviql. [Cite web| url=http://www.schlockmercenary.com/d/20050828.html| title=Schlock Mercenary for Sunday, August 28, 2005| year=2005| first=Howard| last=Taylor| accessdate=2006-03-20]

In the video game series "Halo", over three hundred orbital defense platforms have been positioned by the United Nations Space Command in defense of Earth. These Super-MAC stations fire magnetically accelerated projectiles which weigh hundreds of tons and travel at approximately 40% of the speed of light.

References