Astronauts don't have it easy when they come home, and it's not just because of the change in gravity: their red blood cell production drops while they're in space, leaving them weakened on Earth. But why? That's what a Canadian experiment aboard the International Space Station hopes to find out. The research is testing red and white blood cell functions, as well as bone marrow fat levels, to see how they change before, during and after spaceflight. It should not only show how microgravity (and the resulting lack of activity) affects blood cells, but how reversible the effects are. How soon could you go back to normal?