 is to figure out how to do these long-duration space flights, going places like Mars, where you're out there for months, zero gravity. Zero gravity, the human body don't get on well. Your vision starts to fail, especially in men, for some reason. There are cardiovascular issues suspected. Bone density, we know, goes away. Muscles atrophy. And there's even some concern about mental acuity. And the last thing you want is a bunch of astronauts landing on Mars not being able to walk or make decisions.