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Geosynchronous satellite
Geosynchronous satellite
Geosynchronous satellite
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Satellites in geostationary orbit.

A geosynchronous satellite is a satellite in geosynchronous orbit, with an orbital period the same as the Earth's rotation period. Such a satellite returns to the same position in the sky after each sidereal day, and over the course of a day traces out a path in the sky that is typically some form of analemma. A special case of geosynchronous satellite is the geostationary satellite, which has a geostationary orbit – a circular geosynchronous orbit directly above the Earth's equator. Another type of geosynchronous orbit used by satellites is the Tundra elliptical orbit.

Geostationary satellites have the unique property of remaining permanently fixed in exactly the same position in the sky as viewed from any fixed location on Earth, meaning that ground-based antennas do not need to track them but can remain fixed in one direction. Such satellites are often used for communication purposes; a geosynchronous network is a communication network based on communication with or through geosynchronous satellites.

Definition

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The term geosynchronous refers to the satellite's orbital period which enables it to be matched, with the rotation of the Earth ("geo-"). Along with this orbital period requirement, to be geostationary as well, the satellite must be placed in an orbit that puts it in the vicinity over the equator. These two requirements make the satellite appear in an unchanging area of visibility when viewed from the Earth's surface, enabling continuous operation from one point on the ground. The special case of a geostationary orbit is the most common type of orbit for communications satellites.

If a geosynchronous satellite's orbit is not exactly aligned with the Earth's equator, the orbit is known as an inclined orbit. It will appear (when viewed by someone on the ground) to oscillate daily around a fixed point. As the angle between the orbit and the equator decreases, the magnitude of this oscillation becomes smaller; when the orbit lies entirely over the equator in a circular orbit, the satellite remains stationary relative to the Earth's surface – it is said to be geostationary.

Application

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Further information: List of satellites in geosynchronous orbit

As of October 2018, there are approximately 446 active geosynchronous satellites, some of which are not operational.[1][2][3]

A geostationary satellite is in orbit around the Earth at an altitude where it orbits at the same rate as the Earth turns. An observer at any place where the satellite is visible will always see it in exactly the same spot in the sky, unlike stars and planets that move continuously.

Geostationary satellites appear to be fixed over one spot above the equator. Receiving and transmitting antennas on the earth do not need to track such a satellite. These antennas can be fixed in place and are much less expensive than tracking antennas. These satellites have revolutionized global communications, television broadcasting and weather forecasting, and have a number of important defense and intelligence applications.

One disadvantage of geostationary satellites is a result of their high altitude: radio signals take approximately 0.25 of a second to reach and return from the satellite, resulting in a small but significant signal delay. This delay increases the difficulty of telephone conversation and reduces the performance of common network protocols such as TCP/IP, but does not present a problem with non-interactive systems such as satellite television broadcasts. There are a number of proprietary satellite data protocols that are designed to proxy TCP/IP connections over long-delay satellite links—these are marketed as being a partial solution to the poor performance of native TCP over satellite links. TCP presumes that all loss is due to congestion, not errors, and probes link capacity with its "slow start" algorithm, which only sends packets once it is known that earlier packets have been received. Slow start is very slow over a path using a geostationary satellite. RFC 2488, written in 1999, gives several suggestions on this issue.

There are some advantages of geo-stationary satellites:

  • Get high temporal resolution data.
  • Tracking of the satellite by its earth stations is simplified.
  • Satellite always in same position.

A disadvantage of geostationary satellites is the incomplete geographical coverage, since ground stations at higher than roughly 60 degrees latitude have difficulty reliably receiving signals at low elevations. Satellite dishes at such high latitudes would need to be pointed almost directly towards the horizon. The signals would have to pass through the largest amount of atmosphere, and could even be blocked by land topography, vegetation or buildings. In the USSR, a practical solution was developed for this problem with the creation of special Molniya / Orbita inclined path satellite networks with elliptical orbits. Similar elliptical orbits are used for the Sirius Radio satellites.

History

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The concept was first proposed by Herman Potočnik in 1928 and popularised by the science fiction author Arthur C. Clarke in a paper in Wireless World in 1945.[4] Working prior to the advent of solid-state electronics, Clarke envisioned a trio of large, crewed space stations arranged in a triangle around the planet. Modern satellites are numerous, uncrewed, and often no larger than an automobile.

Widely known as the "father of the geosynchronous satellite", Harold Rosen, an engineer at Hughes Aircraft Company, invented the first operational geosynchronous satellite, Syncom 2.[5] It was launched on a Delta rocket B booster from Cape Canaveral July 26, 1963.

The first geostationary communication satellite was Syncom 3, launched on August 19, 1964, with a Delta D launch vehicle from Cape Canaveral. The satellite, in orbit approximately above the International Date Line, was used to telecast the 1964 Summer Olympics in Tokyo to the United States.

Westar 1 was America's first domestic and commercially launched geostationary communications satellite, launched by Western Union and NASA on April 13, 1974.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Geosynchronous satellite

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A geosynchronous satellite is an Earth-orbiting spacecraft positioned in a geosynchronous orbit, characterized by an orbital period matching Earth's sidereal day of 23 hours, 56 minutes, and 4 seconds. This orbit, typically at an altitude of approximately 35,786 kilometers above Earth's surface, enables the satellite to appear stationary relative to a fixed longitude on the ground, though non-equatorial inclinations may cause apparent north-south motion. A subset of these, known as geostationary satellites, follow a circular path directly over the equator with zero inclination, remaining fixed over a single point for continuous observation or communication. Geosynchronous satellites are primarily deployed for applications requiring persistent coverage of specific regions, such as telecommunications, where they relay television broadcasts, internet services, and telephone signals across vast areas with minimal need for ground antenna tracking. In meteorology, they support real-time weather monitoring by capturing images of cloud formations, storms, and atmospheric conditions over continents or oceans, as exemplified by NOAA's Geostationary Operational Environmental Satellites (GOES). Additional uses include military surveillance, navigation signal augmentation, and data relay systems, such as ESA's European Data Relay System, which connects low-Earth orbit satellites to ground stations without interruption. The concept of geosynchronous orbits was first proposed by science fiction author Arthur C. Clarke in 1945, envisioning a ring of communication satellites for global broadcasting. The first successful geosynchronous satellite, Syncom 2, was launched by NASA on July 26, 1963, demonstrating spin stabilization and enabling transatlantic television transmission during the 1964 Tokyo Olympics. Today, hundreds of such satellites populate the geosynchronous belt, managed under international regulations by the International Telecommunication Union to prevent interference, though challenges like space debris and orbital congestion persist at this crowded altitude.

Fundamentals

Definition and Terminology

A geosynchronous satellite, also known as a geosynchronous (GSO) satellite, is an -orbiting whose is synchronized with the sidereal period of , approximately 23 hours, 56 minutes, and 4 seconds. This matching period ensures that the completes one full around in the same time it takes for to rotate once relative to the fixed stars, causing the to return to the same position in the sky after each sidereal day. As a result, from 's surface, a geosynchronous appears to hover or move slowly in a predictable pattern relative to the rotating planet, rather than tracing a rapidly changing path like satellites in lower orbits. The term "geosynchronous" broadly describes any orbit with this specific period, derived from "geo" (Earth) and "synchronous" (synchronized with rotation), and it encompasses both equatorial and inclined configurations. In contrast, a geostationary orbit (GEO), or geosynchronous equatorial orbit, is a subset of geosynchronous orbits that is circular, direct (prograde), and lies precisely in the plane of Earth's equator with zero inclination. This equatorial alignment makes GEO satellites appear completely stationary when viewed from the ground at the equator, fixed above a single longitude. Inclined geosynchronous orbits, however, result in the satellite's sub-satellite point tracing a figure-eight or analemma pattern daily due to the tilt relative to the equator. Key related terms include the "sidereal day," defined as Earth's rotation period relative to distant stars (distinct from the solar day of about 24 hours), and the "orbital period," the duration for the satellite to complete one revolution around Earth's center of mass. Visual aids like figure-ground diagrams are essential for illustrating these concepts, often depicting Earth as a rotating globe with the satellite's path overlaid to show apparent motion. For instance, such diagrams highlight how a geostationary satellite maintains a single point on the equatorial ground track, while an inclined geosynchronous satellite's track forms a symmetric loop centered on the equator, emphasizing the role of inclination in perceived stability. These representations aid in understanding the satellite's synchronization without requiring complex computations.

Orbital Mechanics

The orbital mechanics of geosynchronous satellites are fundamentally described by Kepler's laws of planetary motion, with the third law providing the key relationship between the orbital period TT and the semi-major axis aa: T2∝a3T^2 \propto a^3. This law, derived from Newton's law of universal gravitation for a two-body system consisting of the satellite and Earth, takes the precise form T2=4π2μa3T^2 = \frac{4\pi^2}{\mu} a^3, where μ=GM\mu = GM is Earth's standard gravitational parameter, valued at approximately 3.986×10143.986 \times 10^{14} m³/s². For geosynchronous orbits, the period TT is set equal to Earth's sidereal rotation period of 86,164 seconds to achieve synchronization with the planet's rotation. For a circular geosynchronous orbit, the semi-major axis aa equals the orbital radius rr from Earth's center. Solving Kepler's third law for rr yields: r=(μT24π2)1/3r = \left( \frac{\mu T^2}{4\pi^2} \right)^{1/3} Substituting the values of μ\mu and TT gives r≈42,164r \approx 42,164 km, corresponding to an altitude of approximately 35,786 km above Earth's surface (accounting for Earth's mean radius of about 6,378 km). The tangential velocity required to maintain this circular orbit is derived from the balance of gravitational force and centripetal acceleration: v=μr≈3.07v = \sqrt{\frac{\mu}{r}} \approx 3.07
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