Kinetic energy weapon

A kinetic energy weapon (also known as kinetic weapon, kinetic energy warhead, kinetic warhead, kinetic projectile, kinetic kill vehicle) is a projectile weapon based solely on a projectile's kinetic energy to inflict damage to a target, instead of using any explosive, incendiary, chemical or radiological payload. All kinetic weapons work by attaining a high flight speed – generally supersonic or even up to hypervelocity – and collide with their targets, converting their kinetic energy and relative impulse into destructive shock waves, heat and cavitation. In kinetic weapons with unpowered flight, the muzzle velocity or launch velocity often determines the effective range and potential damage of the kinetic projectile.

Kinetic weapons are the oldest and most common ranged weapons used in human history, with the projectiles varying from blunt projectiles such as rocks and round shots, pointed missiles such as arrows, bolts, darts, and javelins, to modern tapered high-velocity impactors such as bullets, flechettes, and penetrators. Typical kinetic weapons accelerate their projectiles mechanically (by muscle power, mechanical advantage devices, elastic energy or pneumatics) or chemically (by propellant combustion, as with firearms), but newer technologies are enabling the development of potential weapons using electromagnetically launched projectiles, such as railguns, coilguns and mass drivers. There are also concept weapons that are accelerated by gravity, as in the case of kinetic bombardment weapons designed for space warfare.

The term hit-to-kill, or kinetic kill, is also used in the military aerospace field to describe kinetic energy weapons accelerated by a rocket engine. It has been used primarily in the anti-ballistic missile (ABM) and anti-satellite weapon (ASAT) fields, but some modern anti-aircraft missiles are also kinetic kill vehicles. Hit-to-kill systems are part of the wider class of kinetic projectiles, a class that has widespread use in the anti-tank field.

Kinetic energy is a function of mass and the velocity of an object. For a kinetic energy weapon in the aerospace field, both objects are moving and it is the relative velocity that is important. In the case of the interception of a reentry vehicle (RV) from an intercontinental ballistic missile (ICBM) during the terminal phase of the approach, the RV will be traveling at approximately 15,000 miles per hour (24,000 km/h) while the interceptor will be on the order of 7,000 miles per hour (11,000 km/h). Because the interceptor may not be approaching head-on, a lower bound on the relative velocity on the order of 16,000 miles per hour (26,000 km/h) can be assumed, or converting to SI units, approximately 7,150 m/s.

At that speed, every kilogram of the interceptor will have an energy of:

${\displaystyle KE={\frac {1}{2}}m{v^{2}}={\frac {1}{2}}\times 1\,\mathrm {kg} \times \left(7,150\,\mathrm {\frac {m}{s}} \right)^{2}=25,561,250\ \mathrm {J} \approx 26\ \mathrm {MJ} }$

TNT has an explosive energy of about 4,853 joules per gram, or about 5 MJ per kilogram. That means the impact energy of the mass of the interceptor is over five times that of a detonating warhead of the same mass.

It may seem like this makes a warhead superfluous, but a hit-to-kill system has to actually hit the target, which may be on the order of half a meter wide, while a conventional warhead releases numerous small fragments that increase the possibility of impact over a much larger area, albeit with a much smaller impact mass. This has led to alternative concepts that attempt to spread out the potential impact zone without explosives. The SPAD concept of the 1960s used a metal net with small steel balls that would be released from the interceptor missile, while the Homing Overlay Experiment of the 1980s used a fan-like metal disk.