Mallory and Naird discuss training tradesman to be astronauts as opposed to training astronauts to be tradesmen. This is exactly what NASA did with Apollo astronaut Harrison Schmidt who was actually a geologist who was trained to be a member of the Apollo 17 mission.
The discussion about training tradesmen to be astronauts as opposed to training astronauts to be tradesmen is also one of the bases of the movie Armaggedon (1998). In Armageddon a crew of oil drillers is trained to become astronauts instead of training astronauts how to drill for oil.