Geostationary satellites: Definition, Application, Limitations

Introduction to Geostationary satellites

A geostationary orbit, also known as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 kilometers (22,236 miles) above Earth’s Equator (42,164 kilometers in radius from Earth’s center) that follows Earth’s rotation.

Because an object in such an orbit has an orbital period equal to Earth’s rotational period, one sidereal day, it appears immobile and fixed in the sky to ground observers. In the 1940s, science fiction writer Arthur C. Clarke popularized the concept of a geostationary orbit as a way to revolutionize telecommunications, and the first satellite to be placed in this orbit was launched in 1963.

Geostationary orbits are used by communications satellites so that Earth-based satellite antennas (located on Earth) do not have to spin to follow them and may be directed continually at the position in the sky where they are located. Weather satellites and navigation satellites are also put in this orbit for real-time monitoring and data collection, as well as a known calibration point to improve GPS accuracy.

Geostationary satellites are launched into a slot above a certain point on the Earth’s surface through a transient orbit. To avoid collisions, modern defunct satellites are placed in a higher graveyard orbit, which requires considerable station keeping to maintain its position.

Definition of Geostationary satellite:

To define a geostationary satellite, we can imagine two circles revolving together. A geostationary satellite is an earth-orbiting satellite that rotates in the same direction as the earth. It is placed at an altitude of approximately 35,800 kilometers (22,300 miles) directly over the equator (west to east). One orbit takes 24 hours at this altitude, the same amount of time it takes the earth to rotate once on its axis. The word “geostationary” refers to a satellite that appears practically stationary in the sky when viewed from the ground. Geostationary satellites are used by BGAN, the new global mobile communications network.

A single geostationary satellite has a direct line of sight with roughly 40% of the earth’s surface. With the exception of small circular zones located at the north and south geographic poles, three such satellites separated by 120 degrees longitude can offer coverage of the whole planet. A directional antenna, usually a small dish, aimed at the spot in the sky where the satellite appears to hover, can be used to access a geostationary satellite. The main benefit of this sort of satellite is that an earthbound directional antenna may be targeted and then left in place without needing to be adjusted again. Another benefit is that because highly directional antennas can be utilized, interference from ground-based sources as well as other satellites is reduced.

The many satellites used for various forms of telecommunication, including television, are best known for their geostationary orbits of 36,000km from the Earth’s equator. These satellites can send signals all the way across the planet. Telecommunications must be able to “see” its satellite at all times, hence it must remain stationary in relation to the Earth’s surface.

For remote sensing, a stationary satellite has the benefit of continually viewing the Earth from the same perspective, allowing it to record the same image at short intervals. This setup is especially beneficial for weather observations. One downside of geostationary orbits is the large distance between them and the Earth, which decreases the spatial resolution that can be achieved.

To provide a global picture, a number of weather satellites are uniformly deployed in geostationary orbit all around the planet.

Application of satellites:

Weather forecasting, which uses observations to analyze the current state of the atmosphere, is one of the most common satellite applications. (We can’t anticipate the weather without the help of satellites. Satellites have made the greatest contribution to making weather change predictions by examining various worldwide situations. Several satellites give photographs of the earth using infrared or visible light. Weather forecasting is accomplished by equipping satellites with unique instruments and sophisticated cameras that monitor numerous climate elements such as air pressure, temperature, and humidity, among others. Weather satellites are spacecraft that are used to forecast the weather). Broadcasting services include direct-to-consumer radio and television, as well as mobile broadcasting. Earth observation satellites are used to observe the Earth’s surface, allowing many things not visible from the ground to be seen, even at altitudes where aircraft travel. The Global Positioning System (GPS) is the first and most frequently used satellite navigation system for civilians.

• Mineral mining
• Television, telephone, direct relay and radio broadcasting – Satellites provide access to hundreds of TV and radio programming. In many regions, this technology employs cable because it is less expensive to install and, in most situations, there are no additional costs to pay for this service. Satellite dishes in central Europe today have a diameter of 30-40 cm, with slightly higher diameters in northern regions.
• Atmosphere and weather broadcasting 
• Remote sensing and the global positioning system (GPS) – Despite the fact that it was initially primarily utilized for military purposes, the GPS (Global Positioning System) is today well-known and accessible to the general public.

All of our navigation systems, Google maps, and other similar services allow for perfect global localization, and with some extra techniques, the precision can reach a few meters.

GPS is used by almost all planes and ships as a supplement to traditional navigation systems. Many automobiles and vehicles come equipped with GPS receivers. This system is also utilized for truck fleet management and vehicle tracking in the event of theft.

• Operation Search and Rescue
• Military satellites – The use of satellites for espionage is one of the oldest applications of satellites. The majority of communication links are maintained via satellite since they are far less vulnerable to enemy attack.

Limitations:

There are two primary drawbacks of geostationary satellites. For starters, because the orbital zone is a very narrow ring in the plane of the equator, the number of satellites that can be kept in geostationary orbits without colliding is limited. Second, an electromagnetic (EM) signal must travel a minimum of 71,600 kilometers (44,600 miles) to and from a geostationary satellite. When an EM signal travels at 300,000 kilometers per second (186,000 miles per second) from the surface to the satellite and back, a lag of at least 240 milliseconds is added.

Geostationary satellites also have two other, less critical issues. First, due to gravitational interaction between the satellite, the earth, the sun, the moon, and the non-terrestrial planets, the exact position of a geostationary satellite relative to the surface varies slightly throughout the course of each 24-hour period. The satellite travels around the sky in a rectangular zone known as the box, as seen from the ground. Although the box is small, it restricts the sharpness of the directed pattern and thus the power gain that earth-based antennas may achieve. Second, because the sun is a major source of EM radiation, there is a dramatic increase in background EM noise when the satellite approaches the sun as seen from a receiving station on the ground. Solar fade is a concern only a few days before and after the equinoxes in late March and late September. Even so, episodes are only a few minutes long and only happen once a day.

Low-earth-orbit (LEO) satellite systems have become increasingly common in recent years. This system uses a fleet or swarm of satellites, each in a polar orbit at a few hundred kilometers height. Each revolution lasts anything from 90 minutes to several hours. A satellite like this comes within range of every point on the earth’s surface for a certain amount of time during the course of a day. A LEO swarm’s satellites are carefully positioned so that at least one satellite is always visible from any point on the surface. In a worldwide cellular network, the satellites serve as moving repeaters. A LEO satellite system allows for the use of simple, non-directional antennas, lower latency, and avoids solar fade. These are cited as LEO systems’ advantages over geostationary satellites.

Conclusion:

A geosynchronous satellite is one that is in geosynchronous orbit, or one that orbits at the same time as the Earth rotates. Such a satellite returns to the same location in the sky after each sidereal day, sketching out a path in the sky that is often some form of analemma throughout the course of a day. The geostationary satellite, which has a geostationary orbit — a circular geosynchronous orbit precisely over the Earth’s equator – is a specific case of a geosynchronous satellite. The Tundra elliptical orbit is another type of geosynchronous orbit utilized by satellites.

Geostationary satellites have the unique virtue of being continuously fixed in the same position in the sky as viewed from any fixed place on Earth, allowing ground-based antennas to remain fixed in one direction rather than tracking them. Geosynchronous satellites are frequently used for communication; a geosynchronous network is a communication network that uses or communicates with geosynchronous satellites.

Advantages:

• Especially for remote locations or backup links, communications between substations and dispatch centers are essential.
• Using mobile assets for communication (e.g. drones)
• Power lines are being monitored.
• Vegetation monitoring in corridors
• The placement of assets (GPS)
• Electronic equipment synchronization (GPS)
• Forecasting the weather as a tool for operations planning