The main emissions from the sun are electromagnetic radiation and a flow of charged particles called the solar wind. These particles carry both positive and negative charges, and collectively form what’s called a plasma. Think of it as a diluted gas, but it can behave very differently because the particles are charged. The impact on a satellite and its onboard equipment may be a direct result of exposure to solar wind. However, it is important to understand that this radiation has indirect consequences on a spacecraft a well. For instance, residual oxygen from our atmosphere is ionized by solar radiation and impacts the outside materials of a space craft in LEO through chemical interactions. One way to parse the direct emissions from the sun is to focus on particle charge. This distinction is useful because charged particles interact strongly with matter and can be absorbed quickly (depending on their energy, or speed). The absorption will add a unit of charge to the material and may may trigger secondary emissions which must sometimes be taken into account. Neutral particles and electromagnetic waves can still cause molecular or atomic changes in materials, but they can penetrate deeper into solid materials. Neutrons, for instance, will mostly interact with the nucleus of an atom, which is tiny, dense, and surrounded by a void. Electromagnetic particles (also called photons) must be parsed into bins of different energies. The higher the energy of a photon, the shorter its wavelength and the deeper it penetrates. This is easy to remember when you think of X-rays and UV light. X-Rays can penetrate through our bodies because they have much shorter wavelengths than UV rays. That’s why in the illustration on the left you see some of the wiggles making it through the blue block of material and others not. The ones going deeper have a shorter wavelength. For the purpose of our conversation, the important aspect is how far do the particles penetrate, and how much potential damage will occur over time. The most common effect of electromagnetic radiation (or photon impact) is the Compton effect. High energy photons (UV, X-ray, Gamma-ray) can interact with an electron orbiting an atomic nucleus, and provide it with a boost of energy sufficient to liberate it from its atomic confinement. What remains is an atom with a positive charge and a free electron. The Compton effect impacts the tenuous regions of
This NASA illustration shows that the Low Earth Orbits are relatively well protected below the inner and the outer belts, while GPS satellites and Geosynchronous orbits are on the rims of the outer belts.
American physicist Arthur Compton (1892 – 1962) won the Nobel Prize for his discovery of the Compton Effect, which demonstrated the particle nature of electromagnetic radiation.
QwikConnect • January 2021
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