“But with the knowledge we presently have, we know we cannot make a comparison between high exposure versus chronic exposure,” Hricak says. Furthermore, Hricak says, having a single, universal radiation limit for all space travelers is operationally advantageous because of its simplicity. But unlike someone in the vicinity of a nuclear explosion, the risk to an astronaut exposed to space radiation is long-term rather than immediate. In a person’s cells, space radiation can sever both strands of a DNA molecule’s double helix. In addition to medical technologies, propulsion systems and shielding to protect against space radiation will likely advance as well.