WASHINGTON — One of NASA’s biggest challenges in designing a mission to Mars is how to protect astronauts on the long journey through space.

NASA’s Human Research Program is researching how space radiation affects the human body.

“One of our biggest challenges on a mission to Mars is protecting astronauts from radiation,” said NASA Space Radiation Element Scientist Lisa Simonsen, reported Science Daily. “You can’t see it; you can’t feel it. You don’t know you’re getting bombarded by radiation.”

Space radiation has enough energy to violently collide with nuclei that make up spacecraft shielding and human tissue, according to Science Daily.

The collisions cause both the shielding nuclei and space radiation to break-up into several different types of new particles known as secondary radiation.

NASA is currently investigating the effects of galactic cosmic rays (GCRs) on the human body.

One of the main difficulties is that it’s hard to simulate space radiation on Earth. Lab doses of radiation could be stronger and given for a shorter time than actual conditions in space.