Although the space beyond Earth’s atmosphere is vast, human-made satellites are typically located in one of three popular orbital regimes: low Earth orbit (LEO), medium Earth orbit (MEO), and geosynchronous orbit (GEO).
Low Earth Orbit (LEO)
Low Earth Orbit satellites, improving latency What is LEO? Low Earth Orbit satellites circle the earth at a distance of about 1000km, your typical satellites are either Geostationary Earth Orbit (GEO) satellites located at a distance of 36,000km or your mid range satellites MEO located at about 8,000km. A low Earth orbit (LEO) is, as the name suggests, an orbit that is relatively close to Earth’s surface. It is normally at an altitude of less than 1000 km but could be as low as 160 km above Earth – which is low compared to other orbits, but still very far above Earth’s surface. Telesat’s first Low Earth Orbit (LEO) satellite was launched in January, 2018 and is now supporting live demonstrations across a variety of markets and applications. Live demonstrations allow Telesat customers and LEO hardware vendors test low-latency, high throughput performance, satellite tracking and Doppler compensation. With Low Earth Orbit extending from 200 km to 1200 km it means that it is relatively low in altitude, although well above anything that a conventional aircraft can reach. However LEO is still very close to the Earth, especially when compared to other forms of satellite orbit including geostationary orbit.
The majority of satellites orbiting the Earth do so at altitudes between 160 and 2,000 kilometers. This orbital regime is called low Earth orbit, or LEO, due to the satellites’ relative closeness to the Earth. Satellites in LEO typically take between 90 minutes and 2 hours to complete one full orbit around the Earth. Low altitudes in combination with short orbital periods make LEO satellites ideally situated for remote sensing missions, including Earth observation and reconnaissance.
Fifty-five percent of all operational satellites are in LEO.
Polar Orbits
Some LEO satellites orbit such that they pass over (or nearly pass over) both of the Earth’s poles during orbit. This highly-inclined, low-altitude orientation is called a polar orbit. Due to the rotation of the Earth, satellites in polar orbit pass over a different vertical swath of the planet’s surface on each revolution. Using a polar orbital regime, a single satellite could observe every point on Earth twice in one 24-hour day.
Satellite Constellations
Although a single satellite in polar orbit can eventually observe every point on Earth’s surface, it is not able to create a snapshot of the Earth; that is, a composite image of every inch of the planet’s surface at a single moment. Such a capability can only be completed in low Earth orbit by a large collection of satellites, or a satellite constellation. Satellite constellations can be utilized for personal communications, early missile-warning, and space-based weapons systems.
Key Examples
With the exception of the Apollo missions, all human space activity
has occurred in low Earth orbit. The International Space Station, which currently hosts six astronauts, has an average altitude of about 350 kilometers.The Iridium satellite constellation is a 66-satellite full-coverage constellation orbiting at about 780 kilometers. Iridium provides personal communication services through satellite phones.
Medium Earth Orbit (MEO)
Although over 90 percent of all satellites are situated in LEO (below 2,000 kilometers) and GEO (near 36,000 kilometers), the space between the two most popular orbital regimes can be an ideal environment for a smaller subset of satellite systems. Satellites in this middle-of-the-road region, appropriately named medium Earth orbit, have larger footprints than LEO satellites (meaning they can see more of the Earth’s surface at a time) and lower transmission times time than GEO satellites (meaning they have a shorter signal delay because they aren’t as far away).
Van Allen Radiation Belt
One reason there are fewer satellites in MEO than LEO or GEO is the presence of the
Van Allen belts. The Van Allen belts are two doughnut shaped regions surrounding the Earth, centered on its polar axis, where the Earth’s magnetic field traps charged particles from solar winds and cosmic rays, which can damage satellites’ onboard electronic systems. High radiation environments in general can also damage solar arrays, which convert energy to electricity to power satellites after they have achieved their desired orbit.The inner belt extends from roughly 500 km to 5,500 km at the equator and the outer belt extends from 12,000 km to 22,000 km. Satellites in these regions can be outfitted with shielding to lower the risk of damage during their operational lifetime.
Highly Elliptical Orbits (HEO)
Although many of the orbits previously discussed assume a circular or nearly circular path around the Earth, some satellites are situated such that they orbit the Earth in an oblong elliptical path, called highly elliptical orbit, or HEO. While, a satellite in an inclined circular orbit spends an equal amount of time in the northern and southern hemispheres, satellite in inclined HEO spends a significantly greater portion of its orbit over one hemisphere than the other, due to Kepler’s second law of planetary motion.
Key Examples
The Global Positioning System (GPS) is a 24-satellite constellation, with each satellite in circular MEO with an altitude of about 20,000 km. The constellation is oriented such that at any given moment, every point on Earth has access to four GPS satellites.One example of a highly elliptical orbit is a Molniya orbit. Molniya orbits have an inclination of 63.4 degrees, an apogee of about 40,000 km and a perigee of about 1,000 km. For the majority of their periods, satellites in Molniya orbit are primarily observing the northern hemisphere of the Earth. Since both the United States and Russia are in the northern hemisphere, Molniya orbits were ideal for reconnaissance in the Cold War Era.
Leo Low Earth Orbit Time
Geosynchronous Earth Orbit (GEO)
The period of a satellite, or how long it takes to orbit the Earth one time, is dependent on its orbital altitude. Satellites in LEO, like the International Space Station, take about 90 minutes to orbit the Earth. Satellites in MEO take about 12 hours to do the same.
Satellites orbiting at 35,786 km have a period precisely equal to one day. Satellites in this orbit, known as geosynchronous Earth orbit, or GEO, observe the Earth as if it were not rotating. Because of this property, satellites in GEO are constantly in the field of view for approximately one-third the planet’s surface.
While about 55 percent of all operational satellites are in LEO, another 35 percent are in GEO, making it the second most popular orbital regime.
Geostationary Orbit
Low Orbit Satellite System
Transmission Time
Key Examples
Other Orbits
Some orbits have special properties that make them ideal for specific satellite missions. Only a small fraction of operational satellites fall into this category.
Sun-Synchronous Orbit
Lagrange Points
Lagrange points are special locations in the Earth-Sun orbital plane in which satellites orbit the Sun while maintaining a fixed position relative to Earth’s center of gravity. Lagrange points are caused by the balance between the gravitational fields of two large bodies; equilibria between two pulling forces. Of the five Lagrange points in the Earth-Sun system, three are unstable (L1, L2, and L3), meaning they require periodic orbital adjustments to maintain their position, and two are stable (L4 and L5), meaning no adjustments are required.Lagrange points, especially L2, are particularly well situated for scientific studies of the universe, including NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and European Space Agency’s Planck mission.
Advantages of LEO Orbit | disadvantages of LEO Orbit
This page covers advantages and disadvantages of LEO Orbit. It mentions LEO Orbit advantages and LEO Orbit disadvantages.LEO stands for Low Earth Orbit.
There are three main types of orbits viz. LEO, MEO and GEO based on distances from lowest to the highestfrom the Earth.There are orbits around the earth where satellites are installedafter their launch.Following are the features of LEO orbit.
• Orbit period: 10 to 40 minutes
• Orbit height from Earth: 500 to 1500 Km
• Life of satellite in the orbit: Short
• Propagation loss in the orbit: Least
• Number of satellites to cover entireregions on Earth: 40 to 80
The figure-1 depicts LEO (Low Earth Orbit).
LEO vs MEO vs GEO andsatellite basics for more information.
Advantages of LEO orbit
Following are the advantages of LEO orbit:
➨As it is near to the earth, LEO satelliteslaunced in LEO orbit provides better signal strength. Henceless power (about 1 watt) is needed for transmission.
➨It has least propagation delay (about 10ms) compare toother orbits due to closeness to the Earth.Due to lower latency, it can be used for realtime time criticalapplications.
➨It eliminates need for bulky receiver equipments due tohigher C/N signal ratio.
➨Low price satellite equipments are sufficient forground stations.
➨Better frequency reuse can be achieved due to smaller footprints.
➨It provides high elevation for polar regions of the Earth.Hence better global coverage can be achieved.
Disadvantages of LEO orbit
Following are the disadvantages of LEO orbit:
➨As it is at lesser distance above the Earth,it covers less region of the earth. Hencelarge number of satellites are needed to cover the entireregion of the Earth. Hence the installation of such LEObased system is costly.
➨As LEO satellites move constantly and hence service is beinghanded off by each satellite to the next one inthe constellation. Hence succession of satellites are required tocover any region on the Earth.
➨Atmospheric effects are more and hence willcause gradual orbital dis-orientation of the satellites.This requires regular maintenance of satellites to keepthem on track in the LEO orbit.
➨It is only visible for 15 to 20 minutes fromparticular area of the Earth. Hence there is lesstime available for testing and troubleshooting activities.
➨Efficiency to serve populated region is less compare to GEO satellites.
➨Ground station is very complex as it requires to handle frequent handoffsbetween LEO satellites.
➨The complete deployment of LEO constellation is essential tostart the service to the customers. Hence it requires more time to providethe satellite service & mass adoption by the users compare to GEO.
➨LEO satellites have shorter life span (about 5 to 8 years)compare to GEO satellites (about 10 years).
Also refer advantages and disadvantages of MEO >> and GEO >>.
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