Astronauts traveling to and from Mars would face a minimum radiation exposure of 0.66 sieverts.

The journey alone presents deep physical dangers. Space is filled with high-energy cosmic rays. Without Earth's protective magnetic field, astronauts on a round-trip mission would absorb at least 0.66 sieverts of radiation. This is a massive dose. It significantly increases long-term health risks, making radiation shielding one of our greatest engineering hurdles.