Of the 24 Nasa astronauts who travelled to the Moon in the Apollo missions of the 1960s and 1970s, just five remain.
There was giddy euphoria at the Kennedy Space Center after the launch, writes the BBC's Pallab Ghosh.
The 98m tall Space Launch System (SLS) and Orion spacecraft made a four mile journey from their assembly building to Pad 39B at the Kennedy Space Center in Florida.
Nasa is preparing a mission to send astronauts around the Moon for the first time in more than 50 years.
The University of Kent says the pits may be able to support human survival on future space missions.
The reactor would provide power for humans on the Moon but there are questions about feasibility.
Volcanic rock, dating back billions of years, has been detected in the first samples collected from the mysterious "dark side".
The mission hopes to bring rocks back to Earth from the far side of the Moon for the first time.
A rocket carrying the Chang'e-6 probe will collect lunar soil and rock samples during its 53-day mission.
