well, the actual concept of making a hypervelocity projectile is pretty sound, the delivery system, however is still up to conjecture...
hypervelocity works kinda like this, imagine if you will a bullet, say around .50 cal, now, accellerate that sucker up to a fair few meters a second(delivery is a moot point could be rail,gauss, or just the orbit of a planet over time) now imagine that hits something, say for the sake of a general reference... the ISS, at that speed, it would do a helluva lot of damage to the fragile surface of the station as well as everything else beneath..
i've seen a doco showing a hypervelocity projectile the size of a pinhead blasting apart a small satellite..
sf or not, the basic concept is pretty sound, now to figure out an effective delivery system..