Defensive Missiles are the main defensive weapon against incoming Offensive kinetic kill missile in ship to ship combat and can also be used against enemy fighters. Defensive missiles are smaller missiles (about 1/3 of a kilogram), which move slower than offensive missiles (60 to 70 PSL), but with twice the acceleration. They have a range of only 6 to 8 Light Seconds.
Kinetic warheads do not carry an explosive payload, but rather rely on the fact that kinetic energy equals one-half mass times velocity-squared (i.e., .33 kilogram x 70% of 300,000 kilometers per second). Thus when defensive missiles impact with a ship, they cause incredible damage, with many megatons of energy.
At 1/3 kilogram, traveling at 70 PSL, a defensive missile would have a kinetic impact of 1.75 megatons.
70 PSL = 0.7 x 299,792,458 (speed of light in meters / second) = 209,854,720.6 m/s.
Kinetic Energy (Joules) = 1/2 x kilograms x speed (in meters / second) squared, or 0.5 x 0.333 x (209,854,720.6)^2.
This is ~7.332 x 10^15 Joules, equivalent to 1,753 kilotons of TNT, or 1.753 megatons.