Geostationary Orbit

Saturday, September 5th, 2009

This type of orbit is named the “Clarke Orbit” after the visionary science fiction writer Arthur C. Clarke who, in 1945, first described its use for orbiting communication stations. The geostationary orbit is a special type of geosynchronous orbit. This orbit is at 22,300 miles from the surface of the earth. The satellites in this orbit are positioned very close together and the orbit inclination is near zero. The orbit is as circular as possible, therefore eccentricity is near zero.


The geostationary orbit has become the world’s standard for most communications satellites with hundreds of satellites following each other. This orbit is highly controlled to prevent overcrowding of the orbit, space debris, and unauthorized use of resources.

Molniya Orbit

Saturday, August 15th, 2009

The Molniya orbit is a high elliptical type of orbit first used by Russia. A satellite in such an orbit is semi- synchronous, spending about six to eight hours of every 24 hours over a particular region of the earth. This is ideal for communications satellites used to provide coverage in the extreme northern latitudes where access to geostationary satellites can be difficult. There are systems of other satellites in Molniya orbits in which ground systems switch among three or four such satellites in order to receive continuous coverage.

Low Earth Orbit (LEO)

Wednesday, August 5th, 2009

 A satellite in a low earth orbit is generally considered to have an apogee of no more than approximately 530 miles. Most low earth orbits are nearly circular. LEO satellites travel very fast and need to use frequent propulsion to keep them at the proper altitude. LEO satellites tend to be slowed down by the thin atmosphere that remains at LEO altitudes. Without propulsion, the life span of a LEO satellite is about one year. The earliest communications satellites used LEO’s, mainly because of limited launching capability. Today, LEO’s are still used because they have some very attractive features. They have the advantage that they pass relatively close to areas on the earth. As payloads onboard LEO satellites, earth imaging systems get higher resolution because of lower altitude, and radio systems require less transmitter power because of the shorter signal path to earth. Shorter signal path also mean smaller signal delays, which can lend advantage for the responsiveness of services such as cellular telephone or two-way interactive paging systems.

The use of such mobile services in urban areas is further enhanced by LEO satellites’, appearing higher in the sky such that tall structures are less of an obstruction to small terminals that communicate directly via the satellite. LEO systems are commonly used for observation, environmental monitoring, small communications satellites, and scientific payloads. A disadvantage of LEO is that the satellite is in view within any given portion of its ground trace for only a short period of time before it passes quickly out of view. Satellites in LEO do not provide continuous coverage for a specific location on earth. NASA’s Space Shuttle travels in low earth orbit.

Communications Satellites

Friday, August 1st, 2008

Our daily lives are affected regularly by communications satellites. Communications satellites provide an effective way to connect people and business from the most remote areas of the world to civilization. Many forms of business use communications satellites, like newspapers, gas stations, Internet service providers and even emergency management officials.

What makes communications satellites so useful is the frequency range at which these systems operate. Communications satellites operate near or in the microwave frequency range. This frequency range is optimum for carry large quantities of data. They are also best suited for line of sight (LOS) communications. LOS means the antennas have to see each other for the signal to be received. These frequencies are not reflected or absorbed by the Earth’s atmosphere like in the case of HF signals reflected by the ionosphere.