From an European perspective labour in the US is cheaper
138 karma · joined April 20, 2017
https://spectrum.ieee.org/energywise/energy/renewables/diggi...
It is basically using ramjet technology (such as in the Lockheed D-21), but it's kind of the inlet shape which moves through air enriched with combustible at hyper-sonic speed, on impact the projectile just vaporizes.
edit: the gif animation at the top of the article is very misleading