C H A P T E R
N ° 7
Space Weather and Medium Earth Orbit (MEO)
In the previous article; ‘Space Weather and Low Earth Orbit (LEO)’, SR Hoplon introduced the first orbital class that agencies most commonly launched satellites into. Similar to that article, today’s article will introduce the second orbital class: Medium Earth Orbit (MEO), and the relation between space weather, the Van Allen Belts, and this orbital class.
The Medium Earth Orbit (MEO) and, thus, the second orbital class agencies commonly launch satellites into, is located in the ‘slot’ region (i.e., the ‘safe’ region) between the inner and outer Van Allen radiation belt. Here, satellites get an orbital period of ~6 hours and are, similarly to Low Earth Orbit (LEO) satellites, not restricted to one path around Earth.
Image Credit: Communications, Space & Technology Commission (GST).
Advantages and disadvantageous of Medium Earth Orbit (MEO)
The Medium Earth Orbit (MEO) provides better coverage and less latencies than that of Geosynchronous Orbit (GEO) (i.e. the 3’rd orbital class), whilst staying in view for longer period of times and having a lower fuel consumption than that of Low Earth Orbit (LEO). The Medium Earth Orbit (MEO) is, thus, known to offer a compromise between challenges from the Geosynchronous Orbit (GEO) and Low Earth Orbit (LEO). This makes Medium Earth Orbit (MEO) ideal for commercial, military, and scientific satellites. An example of a satellite/satellite constellation in Medium Earth Orbit (MEO) is the Global Navigation Satellite System (GNSS) – the Global Positioning System (GPS) being a part of that.
The potential disadvantage of this orbital class is, however, the limited coverage of areas, causing a need for satellite constellations in order to enable global coverage, and to minimize latencies and propagation delays. Additionally, it requires higher launch and maintenance costs, and has limited capacity for user terminals. Furthermore, satellites within this orbital class are susceptible to space debris, provide limited satellite redundancy (i.e., limited backup system if a device fails), and the quality of the signals from the satellites are weather-dependent.
Space Weather and Medium Earth Orbit (MEO)
The Medium Earth Orbit (MEO) located in the slot region of the Van Allen Belts is a complex region primarily dominated by electrons. The slot region is argued to have the minimum amount of radiation effects, but is still susceptible to space weather impact. Since the 1950’s, this region was known by scientists as the ‘safe’ region, and the Van Allen Belts were depicted as two zones with a smaller inner radiation belt, a slot region, and a larger outer belt. Of the two belts, the outer belt was argued to be the most dynamic. However, data from NASA’s Van Allen Probes (formerly known as the Radiation Belt Storm Probes (RBSP)) launched in 2012 to study the radiation belts revealed a completely different story. A story much more complex.
In contrast to the old depiction of the radiation belts, this new data revealed that the shape of the radiation belts can vary from a single continues belt with no slot region, to a larger inner belt with a smaller outer belt, to no inner belt at all. Data from the Van Allen Probe showed that the location of the slot region depends on the energy level of the electrons within the Van Allen Belts. Lower energies cause a bigger inner belt and a smaller outer belt with a slot region further from Earth, whereas higher energies cause a smaller inner belt and a bigger outer belt with a slot region closer to Earth.
During Geomagnetic Storms, the outer belt often seems to expand inwards toward the inner belt and, thus, completely fills in the slot region with lower-energy electrons, consequently creating one huge radiation belt. This means that, whereas the satellites located in Medium Earth Orbit (MEO) would usually be within the ‘safe region’, this is not the case during certain space weather events.
The intensity level of Galactic Cosmic Rays (GCRs) surrounding Earth is dependent on the Sun’s 11-year solar cycle. When the activity on the Sun is the highest (i.e., during solar maximum) enhanced number of particles and complex interplanetary magnetic fields interact with the already present Galactic Cosmic Rays (GCRs) in the near-Earth space environment and, thus, within the Van Allen Belts. During this process, the Solar Energetic Particles (SEPs) enhances the overall energy level of the particles within this region. This can produce momentarily high radiation levels and exposure lasting from hours to several days, making the space environment in Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) more hazardous. However, as the magnetosphere surrounding Earth gets weaker the further away an object is to the planet, satellites in Medium Earth Orbit (MEO) are more vulnerable to space weather impact and generally space radiation than satellites within Low Earth Orbit (LEO). Agencies and companies creating and launching satellites and CubeSats into this orbital class should, therefore, be more aware of the risk and the implementation of correct shielding propertise in order to increase resilience to space weather impact.
Image Credit: ESA: Showing the Galileo constellation located within Medium Earth Orbit (MEO).
Sources
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