C H A P T E R
N ° 8
Space Weather and Geosynchronous Earth Orbit (GEO)
In previous articles, SR Hoplon has introduced the first and second orbital class satellites can be launched into. In today’s article SR Hoplon will, therefore, introduce the third, and last, orbital class commonly used: Geosynchronous Earth Orbit (GEO).
Image Credit: ESA: Showing Geosynchronous Earth Orbit (GEO) and altitude.
Geosynchronous Earth Orbit (GEO) is located within the outer Van Allen belt and has an orbital period of ~23 hours 56 minutes and 4 seconds, and an altitude of ~35.786 km above Earth. Its orbital path is around the equator of Earth, consequently making satellites launched into this orbital class travel at the same rate as the planet. From Earth, this makes satellites in this orbital class appear to be stationary over a fixed position.
Advantages and disadvantageous
The Geosynchronous Earth Orbit (GEO) is known to be a reliable orbit that provides variety of services such as voice-, data-, and video-based services for designated regions which makes them ideal for telecommunication satellites. The orbit is easy to use as the satellites remain in the same relative position throughout the day. This means that ground antennas do not have to turn to track the position of the satellites. The fixed position gives a more stable bandwidth and internet connection enabling continues observation of specific areas.
Furthermore, the satellites within Geosynchronous Earth Orbit (GEO) have navigational capabilities offering tracking of objects on the ground with great accuracy. This makes them ideal for navigational and remote sensing purposes. Additionally, they provide real-time global imaging that makes them good for weather monitoring satellites, and they have a long lifecycle compared to satellites in other orbits. They remain up to ~15-20 years, whereas satellites in other orbits lasts ~7-10 years.
Disadvantages of Geosynchronous Earth Orbit (GEO) are the limited numbers of satellites that can be launched into this orbital class. The orbital zone for geostationary satellites is a narrow ring. This increases the risk of satellites colliding with other satellites, consequently causing the loss of satellites, and an increase of space contamination in the form of space debris. Due to this, there is a restriction of the number of allowed satellites within this orbital class. Furthermore, compared to other satellites, geostationary satellites have a higher financial demand in order to be launched into orbit. This is due to their high altitudes which requires more fuel and energy during takeoff. Moreover, the distance can make them more expensive to maintain over their lifecycle.
Satellites in Geosynchronous Earth Orbit (GEO), additionally, provide a limited coverage of Earth’s surface. This is because they have to remain stationary relative to one point on the planet’s rotation axis, and they do not move relative to the ground. Agencies will, therefore, need a minimum of three satellites – creating a satellite constellation – in order to gain global coverage. Furthermore, the signal to and from a satellite in Geosynchronous Earth Orbit (GEO) has a travelling distance of ~36.000 km. This distance causes signal delays which is an issue for services requiring low latency, such as long-distance voice- and video conferencing. This distance, additionally, causes difficulties to repair or replace satellites, and require specialized equipment.
Lastly, satellites located in Geosynchronous Earth Orbit (GEO) can experience disturbances and positioning issues. Satellites must be located at a predetermined position and altitude to accomplish specific tasks. However, due to the orbits distance to Earth, many disturbing forces can make this difficult and, thus, requires extra control. An example is when a satellite gets close to the Sun. Here, the Sun can increase background ‘noise’ (i.e., interference), consequently affecting the satellite’s output. This interference is often experienced once a day for a few minutes during equinoxes (i.e., around March 20 and September 23). Equinox happens two times a year when the Sun is exactly above Earth’s equator and day and night are of equal length. Furthermore, the exact position of geostationary satellites relative to Earth varies slightly over each 24-hour period. This is due to gravitational interactions between the satellite, the Sun, and other celestial bodies. These interactions cause the satellites to wander within a rectangular region in the sky when viewed from Earth, which to a small degree limits the sharpness of the directional pattern and the effectiveness of Earth-based antennas.
Space Weather and Geosynchronous Earth Orbit (GEO)
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 the Geosynchronous Earth Orbit (GEO) and the outer Van Allen belt are the first of the different orbital classes and the two radiation belts to encounter the effects of solar activities if Earth-directed. Objects located within the outer radiation belt and, thus, Geosynchronous Earth Orbit (GEO), are, thus, the most susceptible of the three most commonly used orbital classes to space weather impact.
Video Credit: NASA: Animation of the Solar Wind.
The outer Van Allen belt is dominated by Solar Energetic Particles (SEPs) originating from the Solar Wind. The Solar Wind is a continues flow of plasma and, thus, charged particles from the Sun into the outer space environment. The speed, pressure, and magnetic field of the Solar Wind can change rapidly depending on solar activity. The ‘wind’ is created by the outward expansion of plasma from the Sun’s corona (i.e., its outermost atmosphere). This plasma is continually heated to a point where the gravity of the Sun no longer can hold it down and eventually releases it, consequently creating the constant stream of ‘wind’ into the Solar System. As the magnetic field lines furthest away from Earth are weaker compared to those closer to the planet, it enables Solar Energetic Particles (SEPs) to directly interact and affect satellites in Geosynchronous Earth Orbit (GEO).
During solar activities such as solar flares and Coronal Mass Ejections (CMEs), particles are, however, accelerated to much higher energy levels than that found in the Solar Wind – This is not to be confused with High-Speed Solar Wind Steams (HSS). When Earth-directed, these particles interact with the outer radiation belt, causing the particles within this belt to have a higher average energy level. As a consequence, the space radiation environment in Geosynchronous Earth Orbit (GEO) gets more hazardous. This increases the risk of certain types of impact on satellites within this orbital class that otherwise would not occur.
Image Credit: NASA: Cartoon of the Van Allen Belts and orbital satellite classes.
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