Space medicine is an emerging field that blends emergency care, physiology, psychology and toxicology to help astronauts manage the health challenges of space flight. Its key focus is understanding how the body responds in the absence of gravity. In space, astronauts live in microgravity, a state of near weightlessness caused by continuous free fall while orbiting the planet.

     Although gravity is still present, its effects are greatly diminished. Fluids move upward, muscles weaken and bones lose mass. These changes can disrupt normal body function in ways that are still being studied.

     “Microgravity is not an environment we evolved for,” says Dr. Lisa McNamee, who works with space medicine. “It acts like a stress test on the body, and that tells us things about human physiology that we’d never discover in a lab,” she adds.

     Other risks include radiation, pressure changes, disrupted sleep cycles, lunar dust and g-forces. These forces, caused by changes in acceleration, can place added strain on the body.