# Kinetic Energy Weapon

Ever since I read “Count Zero”, I’ve had a weakness for the idea of kinetic energy weapons. So, when I read about the latest (more-or-less) successful test of the X-51A hypersonic demonstrator, I immediately started to wonder how much damage it could do if you smacked it into something.

### Kinetic Energy

Kinetic energy is measured in Joules, and equal to 1/2 mass times velocity squared, where mass is measured in kilograms, and velocity in meters per second. The X-51A has an empty weight of 1814kg, and it can reportedly hit Mach 6. The conversion of Mach numbers to SI velocities is not straight-forward, but let’s take 340 m/s as an estimate for Mach 1. This gives us:

``KE = 0.5 * 1814 * (6*340) * (6*340) = 3774571200J``

3.8 billion Joules sounds like kind of a lot. It’s not really all that much, though: It’s about 90% of a one-ton TNT equivalent explosion, or a few seconds of the power output of a large power plant. On the other hand, it’s about 75% greater than the yield of a Mk84 “2000lb” bomb (by my admittedly back-of-the-envelope calculations), so it could still ruin your day.

### Mach 25

Reportedly, the ultimate goal of this technology is a Mach 25 vehicle. If we re-run our calculations for that speed, the weapon looks considerably more destructive:

``KE = 0.5 * 1814 * (25*340) * (25*340) = 65530750000J``

65.5 billion Joules is about 15.7 tons TNT equivalent. That’s bigger than MOAB, but still a long way from any but perversely small atomic devices.

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