Highly Elliptical Satellite Orbits

- notes and details about satellite elliptical orbits often referred to as the Highly Elliptical Orbit, HEO: their advantages and key points..

While circular orbits may be the obvious solution for many satellites, elliptical orbits have many advantages for certain applications.

The elliptical orbit is often called the Highly Elliptical Orbit, HEO.

As a result of this many satellites are placed in elliptical orbits, especially where certain attributes are required. For example it does not require the orbits to be equatorial like the geostationary orbit. This means that polar and high latitude areas can be covered with highly elliptical orbits, HEO.

The satellite elliptical orbit gives a number of coverage options that are not available when circular orbits are used.


Highly elliptical orbit, HEO, basics

As the name implies, an elliptical orbit or as it is more commonly known the highly elliptical orbit, HEO, follows the curve of an ellipse. However one of the key features of an elliptical orbit is that the satellite in an elliptical orbit about Earth moves much faster when it is close to Earth than when it is further away.

For any ellipse, there are two focal points, and one of these is the geo-centre of the Earth. Another feature of an elliptical orbit is that there are two other major points. One is where the satellite is furthest from the Earth. This point is known as the apogee - this is where the satellite moves at its slowest as the gravitational pull from the earth is lower. The point where it is closest to the Earth is known as the perigee - this is where the satellite moves at its fastest.

Elliptical satellite orbit
Highly elliptical satellite orbit, HEO

If the satellite orbit is very elliptical, the satellite will spend most of its time near apogee where it moves very slowly. This means that the satellite can be in view over its operational area for most of the time, and falling out of view when the satellite comes closer to the Earth and passes over the blind side of the Earth. By placing a number of satellites in the same orbit, but equally spaced apart, permanent coverage can be achieved.

The plane of a satellite orbit is also important. Some may orbit around the equator, whereas others may have different orbits. The angle of inclination of a satellite orbit is shown below. It is the angle between a line perpendicular to the plane of the orbit and a line passing through the poles. This means that an orbit directly above the equator will have an inclination of 0° (or 180°), and one passing over the poles will have an angle of 90°.

Angle of inclination of a satellite orbit
Angle of inclination of a satellite orbit

Those orbits above the equator are generally called equatorial obits, whilst those above the poles are called polar orbits.


Highly elliptical orbit, HEO, applications

The highly elliptical satellite orbit can be used to provide coverage over any point on the globe. The HEO is not limited to equatorial orbits like the geostationary orbit and the resulting lack of high latitude and polar coverage.

As a result it ability to provide high latitude and polar coverage, countries such as Russia which need coverage over polar and near polar areas make significant use of highly elliptical orbits, HEO.

With two satellites in any orbit, they are able to provide continuous coverage. The main disadvantage is that the satellite position from a point on the Earth does not remain the same.

By Ian Poole


<< Previous   |   Next >>


Share this page


Want more like this? Register for our newsletter






What to consider when incorporating an intelligent touch screen display into your product Markku Rihonnen | 4D Systems
What to consider when incorporating an intelligent touch screen display into your product
Gone are the days of rotary switches, push buttons and seven segment displays. Incorporating touch screen displays into embedded designs is the trend, accelerated of course by consumer adoption of the smartphone.
Training
Online - Fundamentals of Modern RF and Wireless Communications Engineering
This on-line course enables you to quickly get up-to-speed & understand key concepts of modern radio frequency, RF & wireless communications systems

More training courses










Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy