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Medium Earth orbit

Medium Earth orbit is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Medium Earth orbit rather than just read about it. In short: A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between 2,000 and 35,786 km (1,243 and 22,236 mi) above sea level. The boundary between MEO and LEO is an arbitrary altitude chosen by accepted convention, whereas the boundary between MEO and HEO is the particular altitude of a geosynchronous orbit, in which a satellite takes 24…

Medium Earth orbit — main illustration
Medium Earth orbit — illustration

Key takeaways

  • Medium Earth orbit belongs to astronomy; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Medium Earth orbit to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Medium Earth orbit from memory before moving on to harder problems.

Reference excerpt

A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between 2,000 and 35,786 km (1,243 and 22,236 mi) above sea level. The boundary between MEO and LEO is an arbitrary altitude chosen by accepted convention, whereas the boundary between MEO and HEO is the particular altitude of a geosynchronous orbit, in which a satellite takes 24 hours to circle the Earth, the same period as the Earth’s own rotation. All satellites in MEO have an orbital period of less than 24 hours, with the minimum period (for a circular orbit at the lowest MEO altitude) about 2 hours. Satellites in MEO orbits are perturbed by solar radiation pressure, which is the dominating non-gravitational perturbing force. Other perturbing forces include: Earth's albedo, navigation antenna thrust, and thermal effects related to heat re-radiation. The MEO region includes the two zones of energetic charged particles above the equator known as the Van Allen radiation belts, which can damage satellites’ electronic systems without special shielding. A medium Earth orbit is sometimes called mid Earth orbit or intermediate circular orbit (ICO).

Applications

Two medium Earth orbits are particularly significant. A satellite in the semi-synchronous orbit at an altitude of approximately 20,200 kilometres (12,600 mi) has an orbital period of 12 hours and passes over the same two spots on the equator every day. This reliably predictable orbit is used by the Global Positioning System (GPS) constellation. Other navigation satellite systems use similar medium Earth orbits including GLONASS (with an altitude of 19,100 kilometres, 11,900 mi), Galileo (with an altitude of 23,222 kilometres, 14,429 mi) and BeiDou (with an altitude of 21,528 kilometres, 13,377 mi). The Molniya orbit has a high inclination of 63.4° and high eccentricity of 0.722 with a period of 12 hours, so a satellite spends most of its orbit above the chosen area in high latitudes. This orbit was used by the (now defunct) North American Sirius Satellite Radio and XM Satellite Radio satellites and the Russian Molniya military communications satellites, after which it is named. Communications satellites in MEO include the O3b and O3b mPOWER constellations for low-latency broadband and data backhaul to maritime, aero and remote locations (with an altitude of 8,063 kilometres, 5,010 mi). Communications satellites to cover the North and South Pole are sometimes placed in MEO. Telstar 1, an experimental communications satellite launched in 1962, orbited in MEO. In May 2022, Kazakh mobile network operator, Kcell, and satellite owner and operator, SES used SES's O3b MEO satellite constellation to demonstrate that MEO satellites could be used to provide high-speed mobile internet to remote regions of Kazakhstan for reliable video calling, conferencing and streaming, and web browsing, with a latency (delay) five times lower than on the existing platform based on geostationary orbit satellites. In September 2023, satellite operator SES announced the first satellite internet service to use satellite constellations in both MEO and Low Earth Orbit (LEO). The SES Cruise mPOWERED + Starlink service will use SES's O3b mPOWER MEO satellites and SpaceX's Starlink LEO system to provide cruise ship passengers with internet, social media and video calls at up to 3 Gbps per ship anywhere in the World. Subsequently, in February 2024, SES announced that Virgin Voyages will be the first cruise line to deploy the service.

Space debris

Space debris in medium Earth orbit stays practically permanently orbiting Earth. Most space debris extends to the lowest high Earth orbits just beyond the edge of medium Earth orbit, where geostationary satellites are and where after their end of use they are parked in similar orbits, so-called graveyard orbits.

See also

Explanatory notes

References

Illustrations

Medium Earth orbit: Clickable image, highlighting medium altitude orbits around Earth,[a] from Low Earth to the lowest High Earth orbit (geostationary orbit and its graveyard orbit, at one ninth of the Moon's orbital distance),[b] with the Van Allen radiation belts and the Earth to scale
Clickable image, highlighting medium altitude orbits around Earth,[a] from Low Earth to the lowest High Earth orbit (geostationary orbit and its graveyard orbit, at one ninth of the Moon's orbital distance),[b] with the Van Allen radiation belts and the Earth to scale
Medium Earth orbit: To-scale diagram of low, medium, and high Earth orbits
To-scale diagram of low, medium, and high Earth orbits
Medium Earth orbit: Space of Medium Earth orbits (MEO) as pink area, with Earth and the distance of the orbit of the Moon for reference and to scale
Space of Medium Earth orbits (MEO) as pink area, with Earth and the distance of the orbit of the Moon for reference and to scale
Medium Earth orbit: A camera photo of Earth from a distance of 29,400 kilometers (18,300 miles), a distance of higher medium Earth orbits (uncropped and unrotated The Blue Marble image, from Apollo 17 during lunar transfer)
A camera photo of Earth from a distance of 29,400 kilometers (18,300 miles), a distance of higher medium Earth orbits (uncropped and unrotated The Blue Marble image, from Apollo 17 during lunar transfer)
Medium Earth orbit: Infographic showing the space debris situation extending from low Earth orbit, across medium Earth orbits, until the lowest high Earth orbits
Infographic showing the space debris situation extending from low Earth orbit, across medium Earth orbits, until the lowest high Earth orbits

Worked examples

Example 1 — a first encounter with Medium Earth orbit

Start with the simplest possible case. Write down what Medium Earth orbit claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Medium Earth orbit before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Medium Earth orbit ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Medium Earth orbit

In research
Medium Earth orbit appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Medium Earth orbit in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Medium Earth orbit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Earth orbits, so understanding it makes those chapters shorter.
In everyday life
Look for Medium Earth orbit outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Medium Earth orbit in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Medium Earth orbit means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Medium Earth orbit out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Medium Earth orbit in simple terms?

A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between 2,000 and 35,786 km (1,243 and 22,236 mi) above sea level. The boundary between MEO and LEO is an arbitrary altitude chosen by accepted convention, where…

Why does Medium Earth orbit matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Medium Earth orbit?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Medium Earth orbit.

Tags

  • Earth orbits

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