[9876543210]

I think reactive armor might be an interesting strategy. But, then again, it was traveling at 40,000 MPH, which, I think, places it at about twice the velocity of high explosive plastique... So, would blasting it, before it blasts you, actually work?

I think there would need to be a complex early detection and warning system, capable of intercepting high speed objects, well beyond what we consider normal terrestrial speeds. Being lazy, I'm tempted to just say "why not some lasers, maybe?" and shrug, but maybe there are some cooler options possible?

Seems like a pretty unexplored deficiency of moon habitation.