Astronaut Jeff Williams gives a "thumbs-up” while exercising on a treadmill aboard the International Space Station.

STARDATE: One of the science goals for this mission is learning more about how the body adapts to the space environment in preparation for missions to Mars. What are some examples of the types of things you hope to learn? For example, I know you’re working on the central nervous sytem’s reaction to cosmic rays.

JEFF WILLIAMS: The primary thing is, we know that muscles and bones atrophy in a weightless environment. And we have to be able to travel to, for example, to a planet like Mars and be able to function on the planet’s surface in a heavy suit, even though the force of gravity is lower there. So we’re verifying and continuing to develop the countermeasures that we have on board to prevent that atrophy in muscle and bone density.

Another example would be the susceptibility of kidney stones, because the body reduces its fluid loading in weightlessness, so you become more susceptible to kidney stones. So there’s another study that we have going on to validate and test a potential countermeasure that we have for that. So those are just a couple of examples.