Geostationary orbit

A geostationary orbit is a specialised form of geosynchronous equatorial orbit in which a satellite remains fixed relative to a single point above Earth’s equator. At an altitude of about 35,786 kilometres, a satellite’s orbital period matches Earth’s rotation period (one sidereal day). As a result, the satellite appears motionless in the sky to observers on the ground. This property makes geostationary orbits essential for telecommunications, meteorology, and navigation.
Geostationary satellites occupy an area above the equator known as the Clarke Belt, named after Arthur C. Clarke, who popularised the concept in the 1940s. The first satellite placed into such an orbit was launched in 1964, and since then geostationary orbits have become a backbone of global communications infrastructure.

Historical Background

The idea of placing satellites into geosynchronous positions can be traced back to early twentieth-century theoretical work. In 1929 Herman Potočnik outlined both geosynchronous and specifically geostationary orbits as potential locations for space stations. A fictional but early public appearance of the concept occurred in 1942 in George O. Smith’s Venus Equilateral stories.
Arthur C. Clarke’s 1945 article Extra-Terrestrial Relays explored geostationary satellites as relays for global radio communication, helping to frame the scientific and engineering relevance of the orbit. Clarke later acknowledged the indirect influence of earlier works such as Smith’s.
The first attempts at communications satellites in the early 1960s used low-Earth and medium-Earth orbits because a geostationary orbit was widely considered impractical. Engineers doubted that rockets could deliver the required payload and that such satellites would operate long enough to justify the expense.
Harold Rosen, working at Hughes Aircraft, challenged these assumptions. Drawing inspiration from Sputnik 1, he developed a lightweight spin-stabilised satellite design. After initial setbacks—including the failure of Syncom 1—Syncom 2 successfully entered geosynchronous orbit in 1963. The first true geostationary satellite, Syncom 3, launched in 1964, transmitted live television from the Tokyo Olympics to the United States. These successes established geostationary orbits as a feasible and valuable communications platform.

Characteristics and Operation

A satellite in a geostationary orbit must meet three key conditions:

• It must orbit at a precise altitude of approximately 35,786 kilometres above Earth’s equator.
• It must follow Earth’s direction of rotation.
• It must have an orbital period exactly matching Earth’s rotation.

Such satellites appear stationary relative to the Earth’s surface, allowing fixed ground antennas to maintain continuous contact without repositioning. This contrasts with satellites in low or medium orbits, which require tracking equipment due to rapid relative motion.
Geostationary satellites are usually launched first into a temporary parking orbit before being moved into their final position. To remain fixed over a designated longitude, satellites perform periodic station-keeping manoeuvres. At end-of-life, they are moved into a higher “graveyard orbit” to prevent interference with operational satellites.

Communications Applications

Most commercial communications satellites—including broadcast television satellites and many satellite-based augmentation systems (SBAS)—operate in geostationary orbit. Their fixed position makes them ideal for ground receivers with simple, non-tracking dishes.
A single geostationary satellite can be seen from a large portion of Earth’s surface—approximately 81° in latitude and 77° in longitude from the subsatellite point. However, communication quality decreases at higher latitudes due to atmospheric refraction, lower elevation angles, and obstructions. Above about 81° latitude geostationary satellites become invisible below the horizon, which is why high-latitude countries such as Russia have historically used highly elliptical Molniya and Tundra orbits.
One significant limitation of geostationary communication is latency. A round-trip signal between a ground station at the equator and a geostationary satellite takes roughly 240 milliseconds. This delay affects real-time applications such as voice communication and interactive data services, making geostationary links more suitable for broadcast and non-time-critical uses.

Meteorology and Environmental Monitoring

Operational weather satellites in geostationary orbit provide continuous monitoring of atmospheric conditions across large regions. As of 2019, nineteen such satellites were in service or on standby. Major systems include:

• The United States’ GOES series
• Europe’s Meteosat satellites
• Japan’s Himawari series
• Russia’s Elektro-L satellites
• China’s Fengyun series
• India’s INSAT satellites
• Korea’s Chollian and GEOKOMPSAT-2A mission

These satellites operate in visible and infrared wavelengths, providing imagery with resolutions typically ranging from 0.5 to 4 square kilometres. Their continuous coverage supports cyclone tracking, volcanic ash monitoring, cloud-top temperature measurement, and vegetation analysis. While useful for real-time and short-term forecasting, the lower spatial resolution compared to polar-orbiting satellites limits their use in long-range numerical weather prediction.

Navigation and Positioning

Geostationary satellites play an important role in global navigation augmentation systems. They relay correction data for clock, ephemeris, and atmospheric errors, enhancing the accuracy and reliability of global navigation satellite systems. Satellite-based augmentation systems (SBAS) used in aviation and precision mapping often rely on geostationary platforms to maintain wide coverage areas.

Broader Use and Accessibility

Today hundreds of geostationary satellites support telecommunications, broadcasting, remote sensing, and navigational services. Although most populated regions have access to terrestrial fibre-optic and microwave infrastructure, geostationary satellites remain vital for remote communities, maritime and aviation operations, and disaster-response communication.
Geostationary orbits thus continue to serve as a strategic resource for global information exchange, meteorological observation, and technological connectivity, maintaining their position as one of the most valuable orbital regimes in modern space operations.