In the context of space travel , a satellite is an object that has been intentionally placed in orbit. These objects are called artificial satellites to distinguish them from natural satellites such as the Earth's moon .

On October 4, 1956, the Soviet Union launched the world's first artificial satellite, Sputnik 1 . Since then, about 6,900 satellites have been launched from more than 40 countries. According to a 2016 estimate, about 5,000 are still in orbit. Of these, about 1,900 are in operation, but the rest have gone through their lifetimes and become space debris . About 63% of working satellites are in low Earth orbit , 7% in Earth's middle orbit (20,000 km), 29% in Earth orbit (36,000 km) and the remaining 2% in various elliptical orbits.There are. Among the countries with the most satellites, the United States has the most with 759 satellites, followed by China with 220 satellites and Russia with 147 satellites. It is followed by India (116), Japan (72) and the United Kingdom (52). ^[1] International Space Station with a few large space station partially was launched and in orbit were gathered. More than a dozen space probes have been placed in orbit around other objects , including the Moon , Mercury , Venus , Mars , Jupiter , Saturn , a few asteroids , ^[2] a comet.And has become an artificial satellite of the sun .

Artificial satellites are used for a variety of purposes. In a number of applications, artificial satellites can be used to map and map the surface of the planet and to take pictures of the planet on which the satellite was launched. Common types include military and civilian Earth observation satellites , communications satellites , directional satellites , weather satellites and space telescopes . Orbital space stations and spacecraft are also artificial satellites.

Satellites can work on their own or as part of a larger system for a satellite organization or satellite.

The orbits of artificial satellites vary greatly according to the purpose of the satellite and these orbits are classified differently. Well-known classes (overlays) include the lower Earth orbit, the polar orbit, and the terrestrial orbit .

A launch vehicle is a rocket that puts a satellite into orbit. Typically, it moves from a launch pad to the ground. Some are launched from a submarine or a mobile marine platform towards the sea, or on top of an aircraft (launch from the aircraft into orbit).

Artificial satellites are usually semi-standalone computer-controlled systems. Satellite subsystems perform many functions such as power generation, heat control, telemetry, pose control, scientific instruments, communications , and so on.

The first published mathematical study of the possibility of artificial satellites was Newton 's Cannonball , which was published in Isaac Newton's Philosophia Naturalis Principia Mathematica (18) as a thought-provoking study to explain the motion of natural satellites . The first fictional depiction of the launch of an artificial satellite into orbit is a short story by Edward Everett Hall , "The Brick Moon" (189). ^[3] [4] This idea is repeated in Jules Verne's Begum Ratnabhandar ( 189 ).

In 1903, Konstantin Tsiolkovsky (1858-1935) published Exploring Space Using Jet Propulsion Devices , the first textbook on the use of rocketry for spacecraft launches. He calculated the orbital velocity required for the minimum orbit and also calculated the ability of a multistage rocket powered by a liquid propellant to achieve this velocity.

In 1926 , Herman Potonik (1892–1929) published his only book, The Problem of Space Travel - The Rocket Motor . He described the use of orbiting spacecraft for ground observations and how special space conditions could be effective in scientific experiments.

In a 1945 article in Wireless World, English science fiction writer Arthur C. Clarke detailed the possible use of communication satellites for mass communication . ^[5] He suggested that three geostationary satellites would serve the entire planet.

In May 1948, the U.S. Air Force Project RAND released the preliminary design of an experimental world-orbiting spacecraft, stating that "an artificial satellite with suitable equipment could be expected to be one of the most powerful scientific instruments of the twentieth century." ^{[6] The} United States has been considering launching satellites into orbit since 1954 under the auspices of the United States Navy's Aeronautics Bureau. Project Rand finally released the report, but considered the artificial satellite to be a tool of science, politics, and propaganda rather than a possible military weapon. ^[৭]

In 1946, the American theoretical astronomer Lyman Spitzer proposed an orbiting space telescope . ^[৮]

In February 1954, Project Rand published "Scientific Use of Artificial Satellites" by R. R. Carhart. ^[9] It was expanded by the potential scientific use of artificial satellites, and in June 1955 H.K. Coleman and WW. Kellogg's "Scientific Use of Artificial Satellites" was published. ^[10]

In the context of planning activities for the International Year of the Earth (1958–56), the White House announced on July 29, 1955 that the United States planned to launch a satellite by the spring of 1956. It came to be known as the Vanguard Project. On July 31, the Soviets announced that they would launch a satellite by the end of 1957.

The first artificial satellite was Sputnik 1 , launched in 1954 by the Soviet Union under the Sputnik program with Sergei Korolev as chief designer. Sputnik 1 helped detect the density of the upper atmospheric layers by measuring its orbital change and provided information on the distribution of radio-signals in the ionosphere . The unexpected announcement of the success of Sputnik 1 alarmed the Sputnik crisis in the United States and ignited the so-called space competition in the Cold War .

Sputnik 2 was launched on November 3, 1955, and carried the first living astronaut , a dog named Leica , into orbit. ^[11]

In early 1955 , under pressure from the American Rocket Society , the National Science Foundation, and the International Geopolitical Year, the Army and Navy were working on Project Orbiter with two competitive programs. The military used the Jupiter C rocket , while the civilian / naval program used vanguard rockets to launch satellites . On January 31, 1956, Explorer 1 became the first artificial satellite in the United States. ^[12]

In June 1981, three-and-a-half years after the launch of Sputnik 1, the United States Space Surveillance Network compiled a list of 115 artificial satellites orbiting the Earth. ^[13]

The early satellites were built in unique designs. With the advancement in technology, multiple satellites began to be built on a single model platform called satellite bus . The standard satellite bus nakasasampanna jiosinakronasa (jiio) communications satellite HS -333 197 was launched in.

Currently the largest artificial satellite is the International Space Station . ^[14]