How does radiation affect the human body in space?

What is radiation?

Radiation is the spread of energy through space or matter in the form of waves or particles.

What kind of radiation are humans exposed to on Earth?

There are two types of radiation:

  1. Natural background radiation from cosmic sources (e.g., galactic cosmic rays, solar radiation) and from terrestrial sources (e.g., radiation emitted by rocks, radon)
  2. Manmade radiation (e.g., diagnostic X-ray imaging, nuclear reactors)

What kind of radiation are humans exposed to in space?

Soft x-ray image of a solar flare on the Sun. Solar flares give off harmful solar particles that make up one type of space radiation. (Credit: Yohkoh Soft X-Ray Telescope, courtesy of NASA)

There are three kinds of space radiation:

  • Galactic cosmic rays (GCR) originating outside the solar system;
  • Solar particles emitted by the sun during solar flares (solar particle events);
  • Radiation trapped by the Earth's magnetic field.

On the surface of the Earth, these types of radiation are not significant health hazards because the Earth's atmosphere and magnetic field protect us from most of the radiation from space. Astronauts in low Earth orbit still receive some protection from the Earth's atmosphere and magnetic field, but radiation becomes a much bigger problem when they travel to places outside these protective barriers, like the moon or mars.

The Effects of Radiation on the Human Body

Space Radiation is one of the main health hazards of spaceflight. It is dangerous because it has sufficient energy to change or break DNA molecules, which can damage or kill a cell. This can lead to health problems ranging from acute effects to long term effects.

Acute effects such as changes to the blood, diarrhea, nausea, and vomiting are mild and recoverable. Other effects of acute radiation exposure are much more severe such as central nervous system damage or even death. Acute effects are not expected to result from exposure to space radiation, except if an astronaut is exposed to a large solar particle event, such as a solar flare, which produces a high dose of radiation.

The major concern about space radiation is the long term effects on astronauts. Long term effects can include cataracts, increased chance of cancer, and sterility. Some health effects can skip a generation and appear in the descendants of the exposed individual, being passed on by mutated genes.

The types of health problems that occur are determined by the extent of exposure to radiation, an astronaut's vulnerability to radiation and other variables. Exposure to radiation depends on:

  • Altitude of the spacecraft
  • Amount of shielding from the spacecraft or spacesuit,
  • Length of mission,
  • Duration and intensity of exposure,
  • Type of radiation.

Vulnerability to radiation includes individual sensitivity to radiation and differences in age, sex, or health status. In addition, variables such as weightlessness or body temperature can weaken the human immune system and affect how body tissues and organs respond to radiation.

Space Radiation Exposure Limits for Astronauts

An international panel dealing with medical issues concerning International Space Station (ISS) astronauts, the ISS Multilateral Medical Operations Panel (ISS MMOP) and its Radiation Health Working Group (RHWG), are responsible for setting exposure limits for ISS astronauts. The standards are based on the recommendations of the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurement (NCRP). After exceeding the set career limit, there is a greater probability that astronauts will develop harmful health effects, and so they are no longer allowed to participate in space flight. The career limit for Canadian astronauts is the same as what is recommended for national workers in the radiation field, such as x-ray technicians. The exposure limits for 30 days and 1 year are to prevent acute effects of radiation exposure and career limits are to prevent long term effects.

Organ Specific Exposure Limits for Canadian Space Agency (CSA) Astronauts (Sv)
Exposure Interval Blood Forming Organs Eye Skin
30 Days 0.25 1.00 1.50
Annual 0.50 2.00 3.00
Career 1.00 4.00 6.00

Overexposure Prevention Methods

Flight surgeons and scientists continuously monitor astronauts' exposures to ensure that the astronauts do not exceed the set radiation exposure limits. When in space, astronauts are monitored 24 hours per day by the Space Radiation Analysis Group (SRAG) from NASA's Mission Control Center in Houston, Texas. The SRAG carefully analyzes the exposure data from radiation detectors on the ISS and passes the results on to the medical team responsible for the health and safety of astronauts. This data and "radiation weather" forecasts obtained from the National Oceanic and Atmospheric Administration (NOAA) are used by mission planners to schedule potentially high radiation exposure activities, such as spacewalks, for times when cosmic radiation levels are the lowest. The ultimate goal is to keep radiation exposure below the limits; therefore the ALARA principle is followed to make sure that exposures are always As Low As Reasonably Achievable.

The CSA is supporting the development of the new Canadian radiation detectors called Bubble Detectors and MOSFET Dosimeters to better monitor and assess astronauts' radiation exposures and doses.

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