Shutterstock Cosmic rays are a powerful type of radiation that pose a risk to astronauts. Beyond Earth's protective magnetic shield, they increase the risk of cancer and other health effects. The first Mars explorers may face a two-fold higher risk than previously thought, according to a recent study in mice. However, researchers may soon develop better radiation shielding. NASA is dead-set on sending astronauts to Mars within the next 15 to 20 years.