It’s been 47 years since Americans walked on the moon in Apollo. Why haven’t we gone back?

In 1989, former President George H.W. Bush had a vision: “The Apollo astronauts left more than flags and footprints on the moon — they also left some unfinished business,” he said on the moon landing’s 20th anniversary. “…The time has come to look beyond brief encounters. We must commit ourselves anew to a sustained program of manned exploration of the solar system.”

Fifteen years later, his son, former President George W. Bush, took another stab at it: “It is time for America to take the next steps,” he said during a speech at NASA headquarters in 2004. “Today I announce a new plan to explore space and extend a human presence across our solar system.” Read more here.