Solar Activity and Space Radiation Environment

The Sun’s activity varies with time and location on the Sun, as well as characterized by an 11-year cycle that can be divided into solar minimum and maximum phases. Other solar indices such as sunspots and solar radio flux are seen as key indicators of the solar activity cycle. It is a temporary phenomenon that appears as dark spots against a photospheric bright background. Observations over the past two centuries have shown that the number of sunspots changes periodically and moves from minimum to maximum approximately every 11 years. The most recent solar cycle (cycle 24) peaked around 2014. As solar activity is on the decline, it is projected to reach a minimum in late 2019 or 2020, but the solar maximum is expected to occur between 2023 and 2026.
Solar Activity and Space Radiation EnvironmentSolar energy events such as high velocity solar wind currents, solar flares and coronal mass eruptions that cause solar particle events and geomagnetic storms that affect the space environment during solar maximum occur more frequently. Therefore, the effects on atmosphere and air-based technology at this stage of the cycle are expected to be higher than the decreasing or minimum stage. Solar events and related phenomena contribute, in addition to the galactic cosmic ray from space, trapped and transient energetic particles in near space that make up the space radiation environment.

Particles Captured

When charged particles from the solar wind meet and interact with the Earth’s magnetic field, they compress it towards the sun, forming the magnetosphere. This scenario creates a supersonic shock wave known as a spring shock. The solar wind drives the night side of the inner magnetosphere, and this extension is known as the magneto tail. Although the magnetosphere is constantly bombarded by charged particles, they change direction and cannot easily enter the area. However, some particles enter the polar region and are trapped in the Earth’s magnetic field. The trapped particles are found in one of the two annular magnetic rings surrounding the Earth, called the Van Allen radiation belts. The inner belt is a highly stable proton population with energies exceeding 10 mega-electron voltages, and the outer belt mainly contains electrons with energies of up to 10 mega electron volts.
The charged particles forming the belts travel along the Earth’s magnetic lines of force. These lines of force are known to extend from the area above the equator to the North Pole, to the South Pole and then return to the Equator. There is a portion of the inland Van Allen belt that descends on the south Atlantic Ocean off the coast of Brazil for about 200 km to the upper atmosphere, and this region is known as the South Atlantic Anomaly. The tilt is due to the Earth’s magnetic axis tilting about 11 ° from its rotational axis, and the center of the magnetic field is 280 miles from the Earth’s geographic center. The largest portion of radiation exposure during spaceflight missions was due to the transition through the South Atlantic Anomaly. Low-slope flights typically traverse part of the South Atlantic Anomaly up to six or seven times a day.

Temporary Particles

Transient particles or radiation mediums are composed of particles from solar events such as solar wind, solar flares, coronal mass eruptions, and galactic cosmic radiation in interplanetary and near-Earth space regions. In addition, the solar wind consists of relatively low-energy electrons and protons that can significantly affect spacecraft components mounted outside. Solar flares also make a significant contribution to the overall level of ionizing radiation. A solar flare can emit and accelerate energetic particles or protons that can reach Earth 30 minutes after the peak of the glow in interplanetary space.
Coronal mass eruptions can propagate into the solar wind and trigger shocks, which accelerate solar-powered particles and also deflect galactic cosmic rays entering the heliosphere. Coronal mass eruptions can cause geomagnetic storms and other associated events, leading to large-scale disturbances with negative consequences in the geospace environment that can affect satellite systems.

Galactic Cosmic Radiation

Solar Activity and Space Radiation EnvironmentSince galactic cosmic radiations are not directly connected to the Sun, they come from outside the solar system. Galactic cosmic rays consist of ionized atoms ranging from a single proton to a uranium nucleus. These particles have a very low flux level. On the other hand, they produce intense ionization as they pass through matter, as they move at a speed very close to the speed of light and some of them are made up of very heavy elements such as iron. The energy of cosmic rays is usually measured in units of mega-electron volts or giga electron volts. Most galactic cosmic rays have energies between 100 mega-electron volts and 10 giga electron volts. Cosmic rays contain essentially all the elements in the periodic table i.e. about 85% protons, 14% alpha particles and 1% heavy nuclei.
Earth’s magnetic field provides natural protection against both cosmic and solar particles, primarily depending on the inclination and secondarily on altitude. A satellite is out of the protection of the geomagnetic field lines when the slope reaches the polar regions. Intense energetic electron flows, known as precipitating electrons in polar orbits, propagate along magnetic field lines to form the aurora, and as the height increases, exposure to these particles increases.

The Effect of Space Radiation Environment on the Operation of Satellites Near Earth

Understanding the dynamics of the space radiation environment and related effects is critical for satellite design and operation in the ionospheric plasma environment in which satellites are designed to operate. However, there are documented cases or evidence of satellite anomalies associated with space air or space radiation environment. The link between the majority of spacecraft anomalies and space weather distortions has been measured and verified by Lucci and his team. Over a period of 23 years between 1971 and 1994, a large database of approximately 5700 anomalies recorded by 220 satellites in different orbits was compiled. These collection findings are linked to very dense fluxes with anomalies recorded by satellites at high altitude and near polar orbits, and to a much smaller extent with anomalies in fixed orbits.
It has also been reported that energetic electron fluxes are> 10 8 cm high. -2 d -1 sr -1 satellite anomalies are considered as Geostationary Operational Environmental Satellites (GOES) on days occurring in geostationary and low altitude. An intense solar event occurred on March 22 and 23, 1991, resulting in intense geomagnetic storms. This strong solar flash event with high energy solar radiation caused interruption in high latitude point-to-point communication and solar panel failure on GOES-6 and -7 satellites. It is also estimated that GOES-7 reduces its life expectancy of up to 3 years. During the event, high-energy solar particles also increased the frequency of single-event disruptions recorded by spacecraft. Up to six fixed satellites, tracking and data transmission satellites -1, including GOES-6 and -7, had approximately 37 reported single-event crash cases during the main phase of the event.
Solar Activity and Space Radiation EnvironmentIn September 2009, it was reported that SumbandilaSat (in low Earth orbit) in South Africa experienced a radiation-induced power distribution failure shortly after launch, rendering the Z and Y-axis impeller permanently inoperative. However, the satellite continued to operate as a technology demonstrator until August 25, 2011, when it failed completely. Its failure was again attributed to the solar storm, which caused the satellite’s on-board computer to stop responding to commands from the ground station. On April 5, 2010, it was reported that the Galaxy 15 spacecraft (at geosynchronous altitudes) experienced an anomaly that caused it to stop responding to any ground commands. The fault has been reported to cause a built-in electrostatic discharge in the field within the spacecraft baseband communication unit, which caused the programmable gate array to lock. The interaction of the spacecraft with energetic particles injected into the sub-storm caused electrostatic discharge after the spacecraft experienced surface and deep dielectric charge. A brief documentation of many other satellite anomalies and loss cases attributed to space weather is available in several literature.


Author: Ozlem Guvenc Agaoglu

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