Miraculous things happen in space, roughly 350km above the Earth, where the International Space Station (ISS) speeds across the sky at about 8km per second.
Here, where the ISS’s constant free fall over the planet’s horizon simulates the conditions of microgravity, you can twirl weightlessly, launch a 230-kilogram object with a small flick of a finger, and fly across the room, arm outstretched, like Superman in full save mode. In fact, visit Mission Control at NASA’s Johnson Space Center in Houston, USA, with its theatre-size video screen showing live what’s happening in space, and you’ll sometimes see firsthand an astronaut doing exactly that.
But terrible things also happen to your body there — some catastrophic, some even irreversible. Spending just weeks floating out of the reach of gravity is equivalent to being in a lengthy hospital bed rest: Your blood volume drops, which means the heart has less blood to pump and begins to atrophy. With that goes your stamina (from VO2 loss), your aerobic and anaerobic fitness, and your strength. Some of the bodily fluids in your lower extremities shift to your head, swelling your face and causing bruising headaches. One of those liquids, spinal fluid, flattens the back of your eyeballs and inflames your optic nerve, which may cause blurry vision and could even cause far-sightedness, new research shows — in fact, almost two-thirds of astronauts who’ve spent months at the ISS have reported problems with their eyes. You also run a heightened risk of kidney stones.
As if that’s not devastating enough, in a reduced-gravity environment, your bones lose minerals and begin decreasing in density at a rate of more than 1% per month. (By comparison, elderly men and women on Earth lose density at
