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In the context of spaceflight, a satellite is an object that has been intentionally placed into orbit. These objects are called artificial satellites to distinguish them from natural satellites such as Earth's Moon. On 4 October 1957 the Soviet Union launched the world's first artificial satellite, Sputnik 1. Since then, about 8,900 satellites from more than 40 countries have been launched. According to a 2018 estimate, some 5,000 remain in orbit. Of those about 1,900 were operational, while the rest have lived out their useful lives and become space debris. Approximately 63% of operational satellites are in low Earth orbit, 6% are in medium-Earth orbit (at 20,000 km), 29% are in geostationary orbit (at 36,000 km) and the remaining 2% are in elliptic orbit. In terms of countries with the most satellites the USA significantly leads the way with 859 satellites, China is second with 250, and Russia third with 146. These are then followed by India (118), Japan (72) and the UK (5...

The first published mathematical study of the possibility of an artificial satellite was Newton's cannonball, a thought experiment in A Treatise of the System of the World by Isaac Newton (1687). The first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale, The Brick Moon . The idea surfaced again in Jules Verne's The Begum's Fortune (1879). In 1903, Konstantin Tsiolkovsky (1857–1935) published Exploring Space Using Jet Propulsion Devices , which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the orbital speed required for a minimal orbit, and that a multi-stage rocket fueled by liquid propellants could achieve this. In 1928, Herman Potočnik (1892–1929) published his sole book, The Problem of Space Travel – The Rocket Motor . He described the use of orbiting spacecraft for observation of the ground and described how the special conditions of space could be useful for scientific ex...

Satellites can be tracked from Earth stations and also from other satellites. Space Surveillance Network edit The United States Space Surveillance Network (SSN), a division of the United States Strategic Command, has been tracking objects in Earth's orbit since 1957 when the Soviet Union opened the Space Age with the launch of Sputnik I. Since then, the SSN has tracked more than 26,000 objects. The SSN currently tracks more than 8,000-artificial orbiting objects. The rest have re-entered Earth's atmosphere and disintegrated, or survived re-entry and impacted the Earth. The SSN tracks objects that are 10 centimeters in diameter or larger; those now orbiting Earth range from satellites weighing several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent are operational satellites (i.e. ~560 satellites), the rest are space debris. The United States Strategic Command is primarily interested in the active satellites, but also tracks space debris which ...

There are three basic categories of (non-military) satellite services: Fixed satellite services edit Fixed satellite services handle hundreds of billions of voice, data, and video transmission tasks across all countries and continents between certain points on the Earth's surface. Mobile satellite systems edit Mobile satellite systems help connect remote regions, vehicles, ships, people and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems. Scientific research satellites (commercial and noncommercial) edit Scientific research satellites provide meteorological information, land survey data (e.g. remote sensing), Amateur (HAM) Radio, and other different scientific research applications such as earth science, marine science, and atmospheric research.

Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects. Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation. Communication satellites are satellites stationed in space for the purpose of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or Low Earth orbits. Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.) Navigational satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between the satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few mete...

The first satellite, Sputnik 1, was put into orbit around Earth and was therefore in geocentric orbit. This is the most common type of orbit by far, with approximately 2,787 active artificial satellites orbiting the Earth. Geocentric orbits may be further classified by their altitude, inclination and eccentricity. The commonly used altitude classifications of geocentric orbit are Low Earth orbit (LEO), Medium Earth orbit (MEO) and High Earth orbit (HEO). Low Earth orbit is any orbit below 2,000 km. Medium Earth orbit is any orbit between 2,000 and 35,786 km. High Earth orbit is any orbit higher than 35,786 km. Centric classifications edit Galactocentric orbit : An orbit around the centre of a galaxy. The Sun follows this type of orbit about the galactic centre of the Milky Way. Geocentric orbit : An orbit around the planet Earth, such as the Moon or artificial satellites. Currently there are over 2,787 active artificial satellites orbiting the Earth. Heliocentric orbit : An orbit aro...

The satellite's functional versatility is embedded within its technical components and its operations characteristics. Looking at the "anatomy" of a typical satellite, one discovers two modules. Note that some novel architectural concepts such as Fractionated spacecraft somewhat upset this taxonomy. Spacecraft bus or service module edit The bus module consists of the following subsystems: Structural subsystem edit The structural subsystem provides the mechanical base structure with adequate stiffness to withstand stress and vibrations experienced during launch, maintain structural integrity and stability while on station in orbit, and shields the satellite from extreme temperature changes and micro-meteorite damage. Telemetry subsystem edit The telemetry subsystem (aka Command and Data Handling, C&DH) monitors the on-board equipment operations, transmits equipment operation data to the earth control station, and receives the earth control station's commands to per...

When satellites reach the end of their mission (this normally occurs within 3 or 4 years after launch), satellite operators have the option of de-orbiting the satellite, leaving the satellite in its current orbit or moving the satellite to a graveyard orbit. Historically, due to budgetary constraints at the beginning of satellite missions, satellites were rarely designed to be de-orbited. One example of this practice is the satellite Vanguard 1. Launched in 1958, Vanguard 1, the 4th artificial satellite to be put in Geocentric orbit, was still in orbit as of March 2015update, as well as the upper stage of its launch rocket. Instead of being de-orbited, most satellites are either left in their current orbit or moved to a graveyard orbit. As of 2002, the FCC requires all geostationary satellites to commit to moving to a graveyard orbit at the end of their operational life prior to launch. In cases of uncontrolled de-orbiting, the major variable is the solar flux, and the minor variables ...

This list includes countries with an independent capability to place satellites in orbit, including production of the necessary launch vehicle. Note: many more countries have the capability to design and build satellites but are unable to launch them, instead relying on foreign launch services. This list does not consider those numerous countries, but only lists those capable of launching satellites indigenously, and the date this capability was first demonstrated. The list does not include the European Space Agency, a multi-national state organization, nor private consortiums. First launch by country Order Country Date of first launch Rocket Satellite(s) 1 Soviet Union 4 October 1957 Sputnik-PS Sputnik 1 2 United States 1 February 1958 Juno I Explorer 1 3 France 26 November 1965 Diamant-A Astérix 4 Japan 11 February 1970 Lambda-4S Ohsumi 5 China 24 April 1970 Long March 1 Dong Fang Hong I 6 United Kingdom 28 October 1971 Black Arrow Prospero...

First satellites of countries including those launched indigenously or with the help of others Country Year of first launch First satellite Operational payloads in orbit as of April 2020 Soviet Union (Russia) 1957 (1992) Sputnik 1 (Kosmos 2175) 1524 United States 1958 Explorer 1 1914 China 1970 Dong Fang Hong I 0 391 Japan 1970 Ohsumi 0 181 India 1975 Aryabhata 00 96 France 1965 Astérix 00 73 Germany 1969 Azur 00 67 Canada 1962 Alouette 1 00 54 United Kingdom 1962 Ariel 1 00 54 Italy 1964 San Marco 1 00 29 South Korea 1992 Kitsat A 23 Spain 1974 Intasat 000 27 Australia 1967 WRESAT 00 22 Brazil 1985 Brasilsat-A1 00 21 Argentina 1990 Lusat 20 Israel 1988 Ofeq 1 000 20 Indonesia 1976 Palapa A1 18 Turkey 1994 Turksat 1B 13 Saudi Arabia 1985 Arabsat-1A 00 15 Mexico 1985 Morelos 1 13 Sweden 1986 Viking 00 11 Singapore 1998 ST-1 11 Netherlands 1974 ANS 000 8 Czechoslo...

Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks. For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from earth. Russia, United States, China and India have demonstrated the ability to eliminate satellites. In 2007 the Chinese military shot down an aging weather satellite, followed by the US Navy shooting down a defunct spy satellite in February 2008. On 27 March 2019 India shot down a live test satellite at 300 km altitude in 3 minutes. India became the fourth country to have the capability to destroy live satellites. Jamming edit Due to the low received signal strength of satellite transmissions, they are prone to jamming by land-based transmitters. Such jamming is limited to the geographical area within the transmitter's range. GPS satellites are potential targets for jamming, but satellite phone and telev...

During the last five decades, space agencies have sent thousands of space crafts, space capsules, or satellites to the universe. In fact, weather forecasters make predictions on the weather and natural calamities based on observations from these satellites. The National Aeronautics and Space Administration (NASA) requested the National Academies to publish a report entitled, Earth Observations from Space; The First 50 Years of Scientific Achievements in 2008. It described how the capability to view the whole globe simultaneously from satellite observations revolutionized studies about the planet Earth. This development brought about a new age of combined Earth sciences. The National Academies report concluded that continuing Earth observations from the galaxy are necessary to resolve scientific and social challenges in the future. NASA edit The NASA introduced an Earth Observing System (EOS) composed of several satellites, science component, and data system described as the Earth Obser...

Generally liability has been covered by the Liability Convention. Issues like space debris, radio and light pollution are increasing in magnitude and at the same time lack progress in national or international regulation. With future increase in numbers of satellite constellations, like SpaceX Starlink, it is feared especially by the astronomical community, such as the IAU, that orbital pollution will increase significantly. A report from the SATCON1 workshop in 2020 concluded that the effects of large satellite constellations can severely affect some astronomical research efforts and lists six ways to mitigate harm to astronomy. Some notable satellite failures that polluted and dispersed radioactive materials are Kosmos 954, Kosmos 1402 and the Transit 5-BN-3.