NASA’s Human Exploration and Development of Space enterprise tackles one of the toughest and most redeeming problems of all: sending humans into space. When Apollo astronauts were traveling to the Moon, they occasionally saw flashes of light inside their eyes. It was a sign that high-energy cosmic rays were coursing through their bodies. Fortunately, the dose of such radiation during a round trip to the Moon was not enough to cause health problems. No one was harmed. But the first astronauts couldn’t have known that’s how it would turn out. Blasting off for the Moon was a risky venture.