CAPE CANAVERAL, Florida — Fifty years after humanity’s first lunar footsteps, the moon is back in NASA’s court. The White House wants U.S. astronauts on the moon pronto — by 2024, a scant five years from now. The moon will serve as a critical proving ground, the thinking goes, for the real prize of sending astronauts to Mars in the 2030s. The billionaires’ space club is on board.