What is the difference between geostationary and geosynchronous satellites?

A geostationary orbit (parking orbit) is where a satellite is circling the earth in the equitorial plane in an orbit concentric (having the same centre) with the earth and in the same direction of rotation and has a time period (time taken to complete one revolution) equal to that of the earth (approx. 24 hours). In simple terms, the satellite stays over the same spot all the time.

A geosynchronous orbit may have a different period, and may be over different spots at different times.

For mathematical analysis, see below:

Suppose a satellite of mass m circling the earth in the equitorial plane is in an orbit concentric with the earth. If the direction of rotation is the same as that of the earth, and at a distance R from the centre of the earth, velovity V is given by:

mV2/R = GMm/R2 (mV2 means m times V squared)
(Newton’s Law of Gravitation)

where M is the mass of the earth.

But GM=gr2

where r is the radius of the earth

therefore,

mv2/R = mgr2/R2

If the period of the satellite in its orbit is T,

Then, V = 2 Pi R/T (speed = circumference of earth/time)

Substituting for V,

4Pi2mR/T2 = mgr2/R2

therefore, T2 = 4Pi2R3/gr2

Using T squared as 24 hours (convert to seconds), the height of the satellite above the surface of the earth (R-r) and the energy can be found.

Geostationary satellites can be used for relay stations, for continuous world-wide communications.

Geostationary is for a satellite to appear to remain perfectly stationary in the sky as seen from earth. In order for this to happen, it's orbital period must perfectly match the earth's 23 hour 56 minute day. As an added qualifier it must also be exactly above the equator (inclination of 0).

Since to keep a satellite perfectly geostationary for a long amount of time would require too much fuel (in compensation for the gravity fields of other nonstationary bodies, the sun and moon) most satellites are geosynchronous, which allows for some deviation.

In other words, geostationary is a perfectly spherical soap bubble and geosynchronous is your best attempt to make a ball out of play dough.

Hello!

I want to be as specific as I can in answering your direct question, so I'll leave out some facts on the general subject of orbits, many of which were covered below (math!) and focus as much as I can on the specifics of what you asked. . .

As a matter of technical definition, a geostationary orbit is a special kind of geosynchronous orbit. The term geosynchronous defines a whole group of potential orbits, and geostationary is just one of the specific orbits from that group.

First, the broader type: A geosynchronous orbit is any orbit that circles the earth in exactly one day or, as the wonks like to say, has an orbital period equal to the earth's rotational period. In this situation "one day" is actually a more complicated definition than the sunrise/sunset one we usually use, called a "sidereal day," but a sidereal day isn't much different from our normal one, at 23 hours, 56 minutes, and 4.091 seconds its length is just a little more specific to account for more factors than just the rotation of the earth.

A geosychronous orbit can technically orbit in any direction around the earth, the only requirement is that it take exactly one sidereal day to go all the way around once. As you can imagine, however, if a satellite's orbit is set to fly over the poles or at, say, a 45 degree angle to the poles, even though it orbits the earth in exactly one day the satellite flies over various parts of the earth throughout that day as it moves around the earth and the earth rotates under it.

Now to the specific type: A satellite in geostationary orbit also circles the earth in exactly one (sidereal) day and is, by definition, geosychronous. But in the case of the geostationary orbit the orbit's angle and direction have been adjusted so that it is directly over the equator and spinning around the earth in the same direction as the earth itself spins. Because the satellite is now turning around the earth's pole just like the earth is and going the same speed and direction as the earth, the satellite and the earth spin together and the satellite stays over the same place all the time.

This "geostationary geosychronous" orbit is 22,300 miles above the equator and is called the Clarke Belt, after science fiction author Arthur C. Clarke who, although he didn't discover it, did a lot to quantify and popularize the idea. By comparison, the Hubble Space Telescope orbits at a height of 375 miles and GPS satellites orbit at 10,900 miles.

Since all geostationary satellites can be in only one North/South position, over the equator, they are positioned East/West according to their intended function. GE-5 is a communications satellite launched to provide voice and video services to North America, and it stays on the equator right over Equador where it has a clear view. Apstar A1 is a communications satellite launched in 1994 by the People's Republic of China and sits just to the North of Papua New Guinea where it's most useful to them.

This orbit is very useful for communications, and even at the speed of light it takes radio signals about a quarter of a second to make the round trip to the satellite and back.

All that said, however, let me just close by saying that in reality the geostationary orbit is by far the most used and important of the geosychronous orbits, so much so that "geosychronous" is frequently used to mean "geostationary." Not technically correct, but if you start correcting people at parties your social life will suffer.

Hope that helps!

Geostationary is for a satellite to appear to remain perfectly stationary in the sky as seen from earth. In order for this to happen, it's orbital period must perfectly match the earth's 23 hour 56 minute day. As an added qualifier it must also be exactly above the equator (inclination of 0).

A geosynchronous orbit may have a different period, and may be over different spots at different times.

geostationery geosynchronous
e=0 e!=0
T=24hrs T=24hrs
angle of angle of inclination!=0
inclination=0
stationery oscillating
equitorial plane not in equitorial plane

Geosynchronous orbit: orbit at an altitude of 36000km which is not in the eauatorial plane and have 24 hr period.
Geostationery orbit: same but in the equatorial plane.

geostationery geosynchronous
e=0 e!=0
T=24hrs T=24hrs
angle of angle of inclination!=0
inclination=0
stationery oscillating
equitorial plane not in equitorial plane