Difference Between Geosynchronous and Geostationary Orbit

Geosynchronous vs Geostationary Orbit

An orbit is a curved path in space, in which celestial objects tend to rotate. The underlying principle of the orbit is closely related to gravity, and it was not clearly explained until newton’s theory of gravity was published.

To understand the principle, consider a ball attached to a string rotated with a constant length of the string. If the ball is rotating at a slower rate, the ball will not complete cycles, but collapse. If the ball is rotating at a very high rate, the string will break, and the ball will snap away. If you are holding the string, you will feel the pull of the ball on the hand. This effort by the ball to move away is countered by the tension of the string by pulling it back, and the ball starts to move in circles. There is a specific rate at which you have to rotate, so these opposing forces are in balance, and when they do, the path of the ball can be considered as an orbit.

This principle behind this simple example can be applied to much larger objects as planets and moons. The gravity acts as the centripetal force and keeps the object, which is trying to move away, in an orbit, the elliptical path in space. Our Sun holds the planets around it, and the planets hold the moons around it in the same manner. The time taken for an object in the orbit to complete one cycle is known as the orbital period. For example, the earth has an orbital period of 365 days.

Geosynchronous orbit is an orbit around the earth with an orbital period of one sidereal day, and geostationary orbit is a special case of geosynchronous orbit where they are placed right above the equator.

More about Geosynchronous Orbit

Consider the ball and the string again. If the length of the string is short, the ball rotates faster, and if the string is longer, it rotates slower. Analogously orbits with smaller diameter have faster orbital velocities and shorter orbital periods. If the diameter is larger, orbital velocity is slower, and the orbital period is longer. For example, the International Space Station, which is in a low earth orbit, has a period of 92 minutes and the moon has an orbital period of 28 days.

In between these extremes, there is a specific distance from the earth where the orbital period is equal to the rotation period of the earth. In other words, the orbital period of an object in this orbit is one sidereal day (roughly 23h 56m), and hence the angular speed of the earth and the object is similar. One interesting result of this is that every day at the same time the satellite will be in the same position. It is synchronized with the earth’s rotation, hence the geosynchronous orbit.

All geosynchronous orbits of earth, whether circular or elliptical, have a semi-major axis of 42,164km.

More about Geostationary Orbit

A geosynchronous orbit in the plane of the earth’s equator is known as a geostationary orbit. Since the orbit is in the plane of the equator, it has an additional property other than being in the same position at the same time. When an object in the orbit moves, the earth also moves parallel to it. Therefore, it appears that the object is always above the same point, always. It is as if the object is fixed right above some point on earth, rather than orbiting it.

Almost all the communication satellites are placed in the geostationary orbit. The concept of using the geostationary orbit for telecommunication was first presented by the sci-fi author Arthur C Clarke, hence sometimes, called the Clarke Orbit. And the collection of satellites in this orbit is known as the Clarke belt. Today it is used for telecommunication transmission throughout the globe.

Geostationary orbit is located 35,786km (22,236 miles) above the mean sea level, and the Clarke orbit is about 265,000km (165,000 miles) long.

What is the difference between Geosynchronous and Geostationary Orbit?

• An orbit with an orbital period of one sidereal day is known as a geosynchronous orbit. An object in this orbit appears at the same position during every cycle. It is synchronized with the rotation of the earth, hence the term geosynchronous orbit.

• A geosynchronous orbit lying in the plane of the earth’s equator is known as the geostationary orbit. An object in a geostationary orbit seems to be fixed right above a point on earth, and it seems to be stationary relative to earth. Therefore. the term geostationary orbit.