Officially, Apollo 17 was the last manned mission to the moon. But a year later in 1973, three American astronauts were sent on a secret mission to the moon funded by the US Department of Defense. What you are about to see is the actual footage which the astronauts captured on that mission. While NASA denies its authenticity, others say it's the real reason we've never gone back to the moon. Decades-old found footage from NASA's abandoned Apollo 18 mission, where three American astronauts were sent on a secret expedition, reveals the reason the U.S. has never returned to the moon. + More