This won't be the longest spaceflight of all time. Scott Kelly set the US record by staying in space for 340 consecutive days between 2015 and 2016, while Russia's Valeri Polyakov spent just over 437 days aboard Mir. It's still a very long stretch, however, and it comes on the back of Koch joining fellow astronaut Jessica Meir in NASA's first all-female spacewalk this October.

The extended trip isn't just about bragging rights. Koch's longer-than-planned mission should tell NASA more about the effects of long-term spaceflight on the human body. That, in turn, could be vital for the return to the Moon as well as eventual plans to touch down on Mars. What sacrifices Koch has made could pay off if they ensure that explorers come back healthy.