The moon is about to get walloped by 3 tons of space junk, a punch that will carve out a crater that could fit several semi-tractor-trailers. The leftover rocket will smash into the far side of the moon at 5,800mph (9,300km/h) on Friday, away from telescopes’ prying eyes. It may take weeks, even months, to confirm the impact through satellite images. It’s been tumbling haphazardly through space, experts believe, since China launched it nearly a decade ago. But Chinese officials are dubious it’s theirs. No matter whose it is, scientists…