Where does Space Radiation come From?
Space radiation is a challenging problem for biological cells and electronic circuits. The radiation level is substantially higher in space than on Earth, with stronger negative impacts.
What is Radiation?
Radiation is an energy deposition in material from electromagnetic waves, such as microwaves, or from moving particles, such as electrons and photons like gamma-ray and X-ray. Radiation can be categorized into two groups, depending on its impact:
- Non-ionizing radiation is when its impact does not generate charged ions in the material. This occurs when the radiation impact energy is insufficient to remove electrons orbiting the atoms of the medium and the radiation source is charge neutral like photons. Microwaves, radio waves, sunlight, and mobile phone signals are non-ionizing radiation.
- Ionizing radiation is when a charge imbalance is created. This ionizes the medium and can occur either from the strong collision impact of the radiation with the atoms or molecules of the medium which ejects electrons or from the complete stop of a charged radiation source, like electrons or protons, within the medium. This form of radiation can create permanent damages that can impact the health and function of biological cells and electronic circuitries. Examples of ionizing radiation include gamma-rays, x-rays, and energetic protons, electrons, and neutrons.
Figure 1. Relation between wavelength and the likelihood of ionizing the medium it goes through.
What are space radiation sources?
The space environment contains a significant amount of ionizing radiation sources originating from both within and without our solar system. We can categorise space radiation into three types, depending on their origin:
- Solar Particles (SP) originate from our sun. They are predominantly electrons and protons in equal quantities with a very small amount of heavier elements such as Helium. The amount of solar particles that can hit a satellite is relatively high but their energy is too low to induce much radiation damage. Solar Particle Events (SPE), which include Solar Coronal Mass Ejections and Solar Flares, are rare events that eject large amounts of solar particles with energies orders of magnitude greater than usual and that can impact satellites.
- Trapped Particles (TP) are charged particles or elements that bounce around a planet’s magnetic field poles such as Earth or Jupiter. Those particles are effectively trapped along magnetic field lines and form radiation belts known as Van Allen. They consist mainly of protons and electrons that originate from trapped solar particles or from Earth’s upper atmosphere. The flow rate of trapped particles can vary dramatically depending on the orbit and solar weather conditions. Most importantly, the energy range of trapped particles is orders of magnitude greater than Solar Particles. They are the main source of radiation damage for a satellite orbiting Earth.
- Galactic Cosmic Rays (GCR) originate outside our solar system from cataclysmic events such as a star’s supernova explosion. They are predominantly protons, 90%, and some heavier elements and are found in all space environments. The energy range of GCR is even greater than trapped particles and so can create even more damage per impact. However, those impacts are extremely rare owing to the extreme distance of the origin of GCR’s.
Figure 2. Range of the flux density and energy of the various space radiation.
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