Buzz Aldrin on the moon, Mars and space tourism
16 September 2015 Last updated at 06:25 BST
Buzz Aldrin secured his place in history when he joined Neil Armstrong on the surface of the moon on July 21 1969.
Now he hopes to inspire children to travel even further when they grow up.
He has written a book about a mission to Mars - where he believes, in 25 years' time, humans can establish a permanent presence.
He told the BBC's Tim Muffett why it was an important step, during a visit to the London Science Museum's new exhibition about Russian space exploration.