Low Earth Orbit and Medium Earth Orbit in Satellite Communications

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  • Low Earth Orbit satellites, situated 500–1,500 km above the surface, are far closer to the planet than GEO satellites.
  • With a Low Earth orbit, the signal-to-noise ratio should be improved.
  • shorter wait times, usually between 1 and 10 ms
  • Low Earth Orbits need to be tracked because of their relative motion to the Earth.
  • LEO satellites are only visible for 15 to 20 minutes during each pass and do not maintain a fixed location concerning the surface.
  • For LEO satellites to be useful, a network of LEO satellites is required.
  • LEO (Low Earth Orbit) satellite systems operate within a defined altitude range, typically between approximately 500 km, where atmospheric drag becomes a limiting factor and an upper limit of around 1500 km.
  • Leo Satellites are also known as Non-Geostationary Orbit Satellites (NGSO).
  • While early LEO (low-Earth orbit) satellites were small, simple, and cost-effective compared to their GEO (geostationary) counterparts, the evolution of satellite technology has led to more complex and costly Low Earth Orbit systems. 
  • Today, deploying and maintaining a constellation of advanced LEO communication satellites requires significant financial investment in design, construction, launch, and ongoing operations.

Benefits of LEO

  • Because a LEO satellite is closer to Earth than a GEO satellite, it has a stronger signal and experiences less latency, making it ideal for point-to-point communication.
  • The reduced coverage area of a low-Earth orbit satellite reduces bandwidth consumption.

Drawbacks of Low Earth Orbit

  • LEO satellite networks are required, albeit they can be expensive.
  • LEO satellites must comprise Doppler shifts brought on by their varying movements.
  • LEO satellites are affected by atmospheric drag, which gradually deteriorates their orbit.

Applications of Low Earth Orbit

  1. Global Broadband Internet: Through LEO satellite constellations like Starlink, SpaceX is pioneering a new era of internet connectivity, offering high-speed broadband to previously unreachable corners of the globe.
  2. Earth Observation and Remote Sensing: LEO satellites offer high-resolution imaging and frequent revisits, making them ideal for Earth observation and remote sensing applications. This data is used for weather forecasting, environmental monitoring, disaster management, and agricultural analysis.
  3. Internet of Things (IoT) Connectivity: LEO satellites are increasingly used to offer access to IoT devices in remote areas, enabling applications like asset tracking, environmental monitoring, and smart agriculture. This expands the reach of IoT technology beyond terrestrial networks.
  4. Navigation and Positioning: GPS primarily relies on Medium Earth Orbit (MEO) satellites, LEO satellites can enhance GNSS accuracy and reliability, especially in urban canyons and other challenging environments. They can also provide independent navigation capabilities.
  5. Scientific Research and Experimentation: LEO provides a platform for scientific research and experimentation in microgravity, enabling studies in biology, materials science, and other fields. LEO satellites also contribute to space weather monitoring and research.
Low Earth Orbit and Medium Earth Orbit

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Medium Earth Orbit (MEO):

  • A Medium Earth Orbit satellite is 8,000–18,000 kilometers above the earth’s crust in orbit.
  • In terms of functioning, MEO satellites are comparable to LEO satellites.
  • Typically visible for two to eight hours, MEO spacecraft are visible for significantly longer periods than LEO satellites.
  • Compared to LEO satellites, MEO satellites have a wider coverage area.
  • MEO (Medium Earth Orbit) satellites typically operate at altitudes between 10,000 and 15,000 km, with a lower bound of around 1,500 km and an upper bound set by the GEO (Geostationary Earth Orbit) altitude of 36,000 km.
  • MEO Satellites are also known as Non-Geostationary Orbit Satellites(NGSO).

Advantages of Medium Earth Orbit

  • In comparison to a LEO network, a MEO network requires fewer satellites due to the MEO satellite’s greater area and longer time of sight.

Disadvantage of MEO

  • Though not as severe as a GEO satellite, a MEO satellite’s distance causes a longer delay and a weaker signal than a LEO satellite.

Applications of MEO

  1. Global Navigation Satellite Systems (GNSS): MEO is the primary orbit for global navigation satellite systems like GPS (United States), GLONASS (Russia), Galileo (Europe), and BeiDou (China). These constellations provide precise positioning, navigation, and timing services worldwide.
  2. Search and Rescue (SAR) Operations: MEO satellites play a crucial role in search and rescue operations by detecting distress signals from emergency beacons carried by ships, aircraft, and individuals. This enables faster response times and improved chances of survival.
  3. Global Communication Services: MEO satellites are used for various communication services, including voice, data, and internet connectivity. They can provide broader coverage and higher throughput relative to geostationary satellites, especially in regions with high latitudes.
  4. Satellite-Based Augmentation Systems (SBAS): MEO satellites are utilized in SBAS like WAAS (United States), EGNOS (Europe), and MSAS (Japan) to enhance the accuracy and integrity of GNSS signals. This is critical for aviation safety and other precision applications.
  5. Remote Sensing and Earth Observation: While not as common as LEO for Earth observation, MEO satellites can still be used for remote sensing applications, such as monitoring large-scale environmental changes, oceanography, and atmospheric studies.

1. What are the main differences between LEO and MEO satellites?

  • LEO satellites orbit closer to Earth (160-2000 km), offering lower latency but requiring more satellites for global coverage. 
  • MEO satellites orbit at medium altitudes (2000-35,786 km), balancing the needs of coverage and latency.

2. What are the advantages of using LEO satellites for communication?

  • In contrast to satellites in higher orbits, LEO satellites boast lower latency, leading to quicker data transmission, stronger signal strength, and cost-effective launches.
  • These advantages make them ideal for high-speed broadband internet and real-time applications.

3. What are the advantages of using MEO satellites for communication?

  • MEO satellites balance the needs of coverage and latency, making them suitable for global navigation systems like GPS and communication services requiring moderate latency. 
  • They also offer longer dwell times over a particular region compared to LEO.

4. What are the challenges of using LEO and MEO satellites?

  • LEO constellations require a large number of satellites and complex ground infrastructure. 
  • MEO satellites face challenges with higher latency compared to LEO and limited capacity compared to GEO. 
  • Both orbits can experience signal interference due to atmospheric conditions.

5. What are the main applications of LEO and MEO satellites?

  • LEO satellites are primarily used for broadband internet, Earth observation, IoT connectivity, and scientific research. 
  • MEO satellites are used for navigation (GPS), search and rescue, communication, and Earth observation applications.

6. What is the future of LEO and MEO satellite communication?

  • The future of LEO and MEO satellite communication is bright. 
  • Technology advancements include smaller, more powerful satellites, reusable launch vehicles, and inter-satellite laser links.
  • Further expand the capabilities and affordability of these systems, revolutionizing global connectivity and services.
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