One of the biggest hazards faced by astronauts as they go above the surface of the Earth is exposure to radiation. Radiation is energy or matter moving through space, and there are many different types of radiation. For example, all visible light, infrared light, ultraviolet light, radio waves, microwaves, and X-rays are all forms of “electromagnetic radiation. “ We are exposed to all forms of radiation on Earth, but the ozone layer filters out most of the more dangerous ultraviolet rays, which have the potential to damage our skin (for example, excessive exposure causes sunburns and can lead to cancer).
The electromagnetic spectrum (Source: Wikipedia)
Another form of radiation is “cosmic rays” which are mostly protons, some helium, and rarely certain other particles. The particles are moving extremely fast, near the speed of light, and are extremely energetic. It is not entirely clear where cosmic rays come from, but it is likely that some of them come from the very energetic area around black holes and supernova. It is still unknown whether cosmic rays originate in the galaxy or from elsewhere in the universe.
Supernova, thought to be source of cosmic rays (Source: Wikipedia)
Another, more local effect is the Van Allen Belts. The Earth has a magnetic field which effects charged particles, forcing them to go in one of two loops. The belts are mostly made of charged particles from the sun, but cosmic rays can also be captured in the Van Allen Loop. Keeping track of the Van Allen loop is incredibly important because they are regions of high radiation, which are very threatening both to astronauts and satellites orbiting in space.
Earth’s Van Allen Belts (Source: Wikipedia)
Radiation is dangerous because intense, energetic particles can penetrate deep into the human body and damage some of the cells that make up the body. This damage can cause a cell to become cancerous, multiple uncontrollably, and create illness in the individual. However, humans are generally exposed to radiation in their everyday life and usually do not get cancer as a result. There are many misconceptions on how what amount of radioactivity is safe and it is not well known that a certain level of exposure to radiation is normal.
Some background: Radiation is measured in units called roentgen equivalent in man (rem for short), which is a measure of how much radiation energy is deposited in the body. Over the course of a year, humans are expected to be exposed to 1 rem coming naturally from the environment. Eating a banana exposes someone to 0.00001 rem from the potassium (although that is controversial). There is evidence that exposure to 1 rem gives a person about an addition .05% chance of getting cancer. This means that if 2000 are each exposed to 1 rem each, there should be one excess cancer in the entire population as a result.
Radiation in the Van Allen belt can be as much as 0.05 rem per second, which means that an astronaut going through that area would be exposed, in 20 seconds, to as much radiation as the average person on Earth is exposed to during the year. In deep space, the exposure is not as bad, but vastly higher than on Earth. Astronauts unshielded would receive close to 100 rem per year, 100 times the annual exposure, and a significant cancer risk. NASA has developed annual and career exposure limits for astronauts of 50 rem per year about 300-400 rem over a career. In contrast, the US sets radiation limits for nuclear plant workers at 5 rem annually.
It is clear that limiting exposure to radiation is a key part of planning future space travel.