Jim Bridenstine -- the head of NASA -- says Steph Curry just HAS to be joking about his moon landing theory ... telling TMZ Sports, "I can't imagine he really believes that!!"
The Warriors superstar sent space nerds into a frenzy Monday when he declared on The Ringer's "Winging It" podcast that the moon landing in 1969 never happened.
Enter Bridenstine ... who says Curry's claim is so outrageous -- the point guard just cannot be serious.
"I think it's funny," Jim tells us ... "I can't imagine he really believes that.