C H A P T E R
N ° 9
Space Weather and Satellites
In previous articles published by SR Hoplon the three most commonly used orbital classes to launch satellites into by agencies and companies have been discussed followed by a presentation of their advantageous and disadvantageous. These orbital classes are: Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geosynchronous Earth Orbit (GEO). Additionally, the relation between space weather, the Van Allen radiation belts, and the different orbital classes have been discussed in those articles.
In this article, SR Hoplon will introduce some issues caused by space weather to the exterior and interior of satellites. Furthermore, additional risks and consequences of impact on the exterior and interior of satellites will be presented and discussed.
Image Credit: Communications, Space & Technology Commission: showing the location of Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geosynchronous Earth Orbit (GEO).
Depending on what orbital class a satellite is launched into, the radiation exposure levels and, thus, the impact may differ. This can be due to the location of the orbital class compared to the Van Allen Belts and/or the Sun’s 11-year solar cycle. Modern commercial satellites often share some similar features. This means, that agencies and companies repeatedly see the same type of impact on different satellites.
The near-Earth space radiation environment is mostly dominated by Galactic Cosmic Rays (GCRs) originating from supernova. These can cause multiple issues to satellites. However, space weather can shorten the time frame wherefrom these issues can occur and, additionally, their likelihood/the risk of them occurring. Issues often seen caused by space weather are: performance issues, blackouts, and complete shutdowns.
Surface charging
When Solar Energetic Particles (SEPs) and Galactic Cosmic Rays (GCRs) hit the atoms that make up a satellite, they knock out electrons. This causes an electric charge to build up within the materials used on the surface of the satellite, especially if the material is a dielectric. If a material is dielectric, it means that it has the property of transmitting electric force without conduction. The charge builds up static electricity until it reaches a high enough voltage to ‘spark’ across the dielectric, which causes current to flow to places it is not supposed to. This consequently deposits heat and damages components. Surface charging is, thus, the result of a complex interaction between the spacecraft and the outer space radiation environment. When the term ‘surface charging’ is used, it is generally used to imply that the effect is caused by the lower energy part of the electron and ion spectra.
The Earth’s magnetosphere provides less protection from space radiation the further away an object is from the planet. Due to this, the outer Van Allen belt is dominated by Solar Energetic Particles (SEPs) originating from the Sun. This means, that Geosynchronous Earth Orbit (GEO) and the outer Van Allen belt are the first to encounter the effects of solar activities if they are Earth-directed. Objects located within the outer radiation belt and, thus, Geosynchronous Earth Orbit (GEO), are, therefore, the most susceptible of the three most commonly used orbital classes to space weather impact. This includes both internal and external effects and, thus, surface charging. When surface discharges occur on satellites it is, however, mostly seen on the satellite’s solar panels.
Internal charging
Internal charging refers to the build-up of electric charge, caused by penetrating radiation, anywhere within the satellite structure except on its surface. It implies the relevance of the higher energy part of the electron spectrum, with an electron energy of approximately 100 KeV and above. This build-up of electric charge eventually causes heat damage on the internal components.
Interior charging is much harder to control compared to surface charging. This is because the interior is composed of computers that are made of plastic, semiconductors, and metals. Effective shielding properties require semi-dense or thick materials.
The only current engineering-based solution to stop internal charging is by locating all the sensitive parts of the satellite in the middle of its interior and create a distance between the components that has very different charging properties. Additional mitigation measures can be: 1) choosing the correct orbital class to launch the satellites into, 2) good design of internal components, and 3) awareness and good operations of the spacecraft. The latter could for example be by turning off the computer within the satellites when the risk of internal charging is high.
Computer malfunctions:
A risk and consequence caused by internal charging is computer malfunctions. When Solar Energetic Particles (SEPs) composed of protons, electrons, and heavy ions interact with a satellite, the heavy ions can pass through a its computer and cause ‘Single Event Upset (SEU)’ in its microelectronics (processor, memory chips etc.). This can cause a challenge for the ability of the electronics to process commands and store data, consequently leading the computer to crash.
Single Event Upset (SEU) is the most common hazard to electronics posed by space weather, but the least damaging to the hardware. It is, therefore, not often seen for a satellite computer to completely shut down. Satellites can, however, experience performance issues or shut down momentarily. In a case like that, it would require fault correction software in order to manage the satellite.
To mitigate against impact on a satellite’s computer, electronic chips can be designed to be radiation hardened if made with materials resistant to radiation, and with increased shielding on the computer chip.
Radio blackouts
Radio blackouts are caused by higher electron densities in the lower ionosphere of Earth’s atmosphere. The ionosphere is a region located within the ‘thermosphere’ which is an atmospheric region spanning from an altitude of approximately 85 km to 500 km. In order for the radio waves from a satellite in outer space to reach the antenna on Earth and provide data to ground stations, it has to travel through this atmospheric layer. However, as the radio waves travel through it, the enhanced electron density causes the radio waves to lose more energy than normal. This consequently prevents them from reaching layers that refract the radio signals back down to Earth.
Satellites rely on radio communication with ground stations in order to control operations and for most primary functions (e.g., telecommunications). Continuing radio contact is necessary in order to control and maintain a satellite. Without it, the risk of satellites colliding with other satellites, debris, and other space objects tremendously increases as satellite maneuvers cannot be made. Thus, losing the ability to communicate with a satellite increases the risk of losing the satellite itself.
Furthermore, by losing a satellite in outer space it becomes part of the space debris environment. This furtherly contaminates the already contaminated near-Earth space environment and adds to the issue of space debris and satellite collisions. A loss of control of a satellite is often difficult to recover. The loss of radio link is, thus, very severe. Despite the risks and issues caused by radio blackouts, this type of impact is the most common one caused by space weather events.
Atmospheric drag:
A risk and consequence caused by radio blackout is atmospheric drag and, thus, re-entry of satellites into Earth. Atmospheric drag is the force put on an object by the atmosphere surrounding it. Satellites launched into Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) can experience significant atmospheric drag. Atmospheric drag depends on the density of the thermosphere, the surface area of the satellite, and its speed. The drag slows down the satellite, which then decreases its orbital radius. Once a satellite gets below ~300 km altitude, the risk of re-entry to Earth and collision with the terrestrial environment is said to be only a matter of a few weeks.
Most satellites cannot operate effectively at altitudes and orbits other than those they were designed for. This means, uncontrolled orbital changes are highly undesirable. A satellite below for example an altitude of 800 km requires regular orbital maneuvers and a lot more fuel to remain in place. Space weather events causing radio blackouts, therefore, increases the risk of satellites re-entering Earth. This is because the mission control center cannot perform the maneuvers needed, due to the loss of radio link.
Furthermore, at certain times, when the Sun is active, the drag force on satellites increases. This is because Earth-directed solar activities causing space weather events add additional energy to the atmosphere of Earth. This makes the low density layers of air around Low Earth Orbit (LEO) to rise, causing them to be replaced by higher density layers that were previously at lower altitudes. As a result, the satellite will travel through the higher density layer and experience a stronger drag force. When the Sun is quiet, satellites in Low Earth Orbit (LEO) have to boost their orbits about four times per year to make up for the atmospheric drag. When solar activity is at its greatest over the 11-year solar cycle (i.e. during solar maximum), satellites may have to be maneuvered every 2-3 weeks to maintain their orbital path.
Furthermore, interactions between the solar wind and the Earth’s magnetic field during space weather events such as geomagnetic storms can produce large short-term increases in the temperature and density of the upper atmosphere, which consequently increases the drag on satellites and the risk of changes to their orbital path. This means, that after a severe or extreme space weather event, space and defence departments, companies etc. like for example the North American Aerospace Defense Command (NORAD) has to re-identify hundreds of objects and record their new orbital pathways.
An example where a satellite experienced atmospheric drag due to a space weather event was during the March 1989 geomagnetic storm. Here, the NASA's Solar Maximum Mission (SMM) satellite was reported to have "dropped as if it hit a brick wall" due to the increased atmospheric drag caused by two Earth-directed Coronal Mass Ejection (CME). Space weather, thus, plays a significant role in the discussion of space sustainability and space debris.
Image Credit: X2NSat.
A Technology Dependent World
Today’s modern society no longer rely on the telegraph networks to communicate compared to the society in 1859 during the Carrington Event. However, as discussed, our communication technologies are still vulnerable to space weather impact and the general hazardous space radiation environment.
In a world that becomes increasingly more dependent on technology withinand, thus, all forms of satellites and CubeSats, it is important to increase the awareness of space weather impact on critical space infrastructure and the terrestrial infrastructures relying on it. The creation and implementation of innovative mitigation measures have never been more vital and will increasingly be so. This is especially when discussing the future of technology, critical infrastructures, space sustainability, and the safety of living beings on Earth when for example discussing the re-entrance of satellites.
Sources
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James P. McCollough et al. (2022): “Space-to-space very low frequency radio transmission in the magnetosphere using the DSX and Arase satellites”. Earth Planets Space 74. Article No. 64. DOI: https://doi.org/10.1186/s40623-022-01605-6
Krausmann, Elisabeth; Andersson, Emmelie; Gibbs, Mark; Murtagh, William (2016): Space Weather & Critical Infrastructures: Findings and Outlook. JRC Science for Policy Report. DOI: 10.2788/152877
Baker, D.N; Daly, Eamonn; Daglis, Ioannis; Kappenman, John G; Panasyuk, Makhail (2004): Effect of Space Weather on Technology Infrastructure. AGU Vol. 2, Issue 2. DOI: https://doi.org/10.1029/2003SW000044
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