LEO vs. MEO vs. GEO Satellites: What's the Difference? | Symmetry Blog

Jun 26, 2018
 

Cobus Heukelman, Technical Marketing Engineer at Symmetry Electronics, explains the difference between LEO, MEO and GEO satellites, and how they can help your application.

 

 

Written by Cobus Heukelman
Technical Marketing Engineer at Symmetry Electronics

 

As the user, we don’t always think about the satellite when choosing a solution, but the satellite plays a crucial part in the communication link. Three categories of satellites - LEO, MEO and GEO - refer to different orbits that a satellite can be placed in.

We’ll break down these different orbits, and what each of them has to offer.

 

LEO vs. MEO vs. GEO

The terms GEO and GSO often cause confusion, partly because one is a special case of the other. The broader term GSO stands for Geosynchronous Orbit, meaning that it takes one day to complete one orbit. To an observer standing still on the earth’s surface, the GSO satellite will return to exactly the same point in the sky after one day. In between, it can rotate in the same direction, or the opposite direction as the earth. GEO, or Geostationary Equatorial Orbit, is a special case of GSO where the satellite always appears stationary above the same point on earth’s surface. The added benefit is that antennas don’t have to turn to track the satellite’s position.

LEO and MEO stand for Low Earth Orbit and Medium Earth Orbit, respectively. (Not sure why they had to throw “Earth” in there, maybe that will be useful once Elon Musk gets his Mars colony established, but I digress.)

As shown in the table below, the orbits differ mainly in the altitude of the satellite above the earth’s surface

 

Abbreviation

Orbit Name

Altitude [km]

LEO

Low Earth Orbit

160 to 2000

MEO

Medium Earth Orbit

2000 to <35786

GSO

Geosynchronous Orbit

35786

GEO

Geostationary Equatorial Orbit

35786

 

Advantages and disadvantages

LEO and GEO/GSO are the two extremes when it comes to altitude. LEO satellites are much smaller and their orbits are much closer to earth, so the rockets needed to launch them are also smaller and cheaper. The downside with LEO satellites is that many are needed to cover any specific geographical area. LEO satellites orbit the Earth many times per day, so as each satellite flies over the coverage area, another one must follow behind it, ready to take over the communication once the first satellite has passed the area. This also adds to the network complexity as many ground stations are needed to communicate with all these satellites and they also need to use different frequencies to avoid interfering with each other’s communication. Compare this with a GEO satellite, which is parked in the sky above the area that needs coverage and it will stay there. While GEO satellites are bigger and more expensive to deploy, the network operator can gradually add to their coverage as their business grows.

So why does a company like Globalstar use LEO satellites? LEO is well suited for connecting mobile devices. With a GEO satellite, the antenna needs to be pointed to the satellite. This works great for a TV antenna fixed to a building, but it’s impractical for a satellite phone that you carry in your pocket. All GEO satellites are in orbit above the equator, so as you move towards higher latitudes in places like Canada or Europe, the angle of the antenna gets smaller and smaller. Having to receive a signal from an angle makes the transmission susceptible to interference from obstacles like tall buildings or mountains. The figure below illustrates this.

In fact, GEO satellites only cover about 42% of the Earth’s surface. Globalstar’s LEO devices can typically see and communicate with multiple satellites at the same time, from multiple angles, making the communication more robust. For applications requiring global mobile communication, like disaster relief or maritime operations, LEO is the technology of choice. Lower altitude means a signal takes much less time to travel to the satellite, resulting in a low latency. This is useful for real-time communication such as making voice calls. If you’ve ever tried to speak to someone over a bad VOIP connection, then you know how frustrating a long delay can be.

You may be thinking, well what about MEO satellites? Wouldn’t that be a happy medium between LEO and GEO? Like LEO, MEO satellites also require a constellation of satellites to provide geographic coverage. MEO satellites are commonly used for positioning information like GPS, GLONASS and Galileo. GPS satellites have an altitude of about 22000km, which gives an orbital period of 12 hours. If you compare that to Globalstar’s altitude of 1414km you can see that you’ll need much more fuel to propel a satellite that far. The satellite will also need to be bigger to transmit a stronger signal, and the communication latency will be higher. These are all tradeoffs that have to be considered when designing a constellation.

 

>>Learn more about Globalstar and their Satellite Communication Solutions

 


 

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