NASA Administrator Jim Bridenstine participates in a press preview event of the upcoming Paris Air Show at the National Press Club in Washington, U.S. June 6, 2019. REUTERS/Leah Millis

ORLANDO, Florida: As NASA scrambles to meet U.S. President Donald Trump's mandate to return humans to the moon by 2024, two longtime heads of NASA's human exploration wing were demoted Wednesday (Jul 10) in a slew of administrative shakeups, officials said in an internal memo.