launch at very high velocity speed like mach 15 in order to have any massive impact. I doubt anyone can launch anything at mach 3 at that time let alone mach 15. Rockery tech are non existence at that time. 

The beauty of this thing is won't burn up in the atmosphere and very heat tolerant, wont melt. Usually meteorites burn up completely when they travel at high speed entering the atmosphere, but this thing won't burn up and it carry all the kinetic energy. Little of this in high velocity can have devasting impact like craters in the moon according to some researcher. I think China now has the rocketry tech to launch these becasuse China is able to send spaceships to the Earth orbit.  Usually it take mach 20 for a spaceship with rockets to escape the gravity traveling to the orbit.