[Spktyr]

Well, whether or not a lunar rock is a relativistic projectile depends on how powerful your railgun is and how massive the rock is.

At the very least, you’re looking at something coming down at orbital velocity.

[GonzoGOP]

At the very least, you’re looking at something coming down at orbital velocity.

Thats the point, you don't need a relativistic projectile. I know there is no such thing as overkill, just a continuum between open fire and the need to reload. But at some point the additional cost to build the thing just isn't justified. You don't need the worlds largest dragline to dig a hole for a fence post.

Besides the higher the velocity the longer the rail-gun has to be. And the longer it is the harder it is to hide it. You would to a lot better with four or five hidden rail-guns than one giant relativistic weapon that can get taken out in a preemptive strike before it becomes operational.