Space Radiation: An Important Concern for Human Spaceflight

Astronauts are considered radiation workers; in other words, they’re employees who work in the proximity of a radiation environment. Per OSHAOccupational Safety and Health Administration standards, they require radiation training and protection to be able to complete their jobs. However, astronauts are considered special radiation workers due to the difference between the space and terrestrial radiation environments, and they have a separate set of standards than Earth-based radiation workers.

There are two basic types of radiation: non-ionizing radiation and ionizing radiation. Non-ionizing radiation has enough energy to move atoms around, while ionizing radiation liberates electrons from atoms, which causes the atoms to ionize. Typically, “space radiation” refers only to the ionizing radiation found in space, but non-ionizing radiation in the space environment does impact astronaut health. UVUltra Violet light from the sun can cause skin cancer and eye damage, and lasers and radio-frequency equipment onboard spacecraft have the potential for health impacts. Astronauts are protected from non-ionizing radiation with R2D2 day and night glasses, EVAExtra-Vehicular Activity helmet visor filters, and “keep out zones” for radio-frequency radiation hazards onboard and around the spacecraft.

ISS Expedition 51 crew with glasses
ISSInternational Space Station Expedition 51 crew members inside the Cupola wearing day and night glasses to help protect their eyes from non-ionizing radiation while looking outside the Cupola windows.

When ionizing radiation enters the body, electrons are stripped from their atoms thus damaging DNA. When DNA damage occurs, one or both strands of its structure break apart. When one strand breaks, the other strand can be used as a template for repair. However, when both strands break, mistakes in repair are more likely, and the incorrect DNA sequence can lead to potentially harmful mutations.

Ionizing radiation on Earth is different from ionizing radiation in space. On Earth, there typically needs to be a radiation source nearby for it to be harmful, and it is usually limited to low-energy types of radiation. In space, different types of radiation are everywhere at a wider range of energies. On Earth, we are protected from space radiation because of the atmosphere and magnetic field surrounding the planet. Once in interplanetary space, astronauts lose the protective shielding of Earth's magnetosphere and are exposed to the full effects of SEPsSolar Energetic Particle and GCRsGalactic Cosmic Ray (see What is Space Radiation for more details). While we can protect astronauts to some extent with shielding provided by the spacecraft structure, this shielding isn’t as effective as the Earth’s magnetic field. Our most powerful tool to protect astronauts from radiation is to limit their time spent in space.

There are two types of effects that can happen after exposure to ionizing radiation: deterministic and stochastic effects. Deterministic effects will only occur after exposure to a high dose of radiation, and include ARSAcute Radiation Syndrom and cataract development. If a high dose is received within a few hours or days, ARSAcute Radiation Syndrom will develop, which can lead to nausea, vomiting, skin rash, and other outcomes. As dose increases, symptoms worsen and can ultimately lead to death. It is very unlikely astronauts will experience severe symptoms from ARSAcute Radiation Syndrom , as space radiation doses are usually received in small amounts chronically over time. While a solar particle event could lead to higher doses in a smaller time-frame, spacecrafts protect well against this type of radiation, and the amount of radiation astronauts are exposed to is mitigated. Astronauts are further protected by a warning system from onboard dosimeters and SRAGSpace Radiation Analysis Group console operators that can provide advanced warning time to crew in order for crew to get to higher shielded areas of the spacecraft (see How Do We Protect Astronauts for more details). These measures will limit exposure, though they cannot prevent it. To protect against all deterministic effects, NASANational Aeronautics and Space Administration enforces short- and long-term dose limits for astronauts.

Stochastic effects are long-term effects that are possible following ionizing radiation exposure. The risk of these effects increases as dose increases. Cancer is the stochastic effect of most concern. A detailed model is used to estimate individual astronauts’ risk of cancer following radiation doses they receive in space. Cancer deaths are minimized for astronauts through implementing career limits and screenings to ensure these limits aren't reached.

Two other potential risks from ionizing radiation exposure include long-term cardiovascular and short- and long-term CNSCentral Nervous System impacts. Increased cardiovascular disease risk has been seen for people exposed to ionizing radiation on Earth, though this risk is not well understood as it is for cancer. CNSCentral Nervous System effects have not been seen following exposure to ionizing radiation on Earth to date, but animal models suggest space radiation may have a different impact. Active research is being conducted to determine the risk of these effects in astronauts, and to uncover whether these effects are deterministic or stochastic.

For more information about NASA'sNational Aeronautics and Space Administration astronaut radiation protection, please visit the NASA Space Cancer Risk Model: 2020 Operational Implementation:

For more information about ongoing research, please visit the Space Radiation Element Page: