Spaceships hull armor…solid?

[Anthony]

Originally Posted by Agemegos

You are failing to take the momentum of the impactor into account

The momentum really doesn't matter -- at these velocities you're just looking at colliding fluids and penetration barely changes across a range of something like 10 to 10,000 km/s, it's just about length and density of the penetrator relative to the thickness and density of the armor.

What happens is that, by the time the penetrator has encountered total mass equal to its own, it will have turned into a spray expanding at around 60 degrees and the resulting plasma is moving at half speed. As it continues, it mixes with more and more armor mass, and spreads faster and faster, so it's going to slow down to subsonic velocities in only a couple projectile lengths.

The way you improve penetration (which is what HEAT and long rod penetrators do) is by having a thin jet, which therefore takes longer to encounter its own mass in armor.