Artificial Earth satellites are spacecraft that are launched into the Earth’s orbit and revolve around it in a geocentric orbit. They are intended for solving applied and scientific problems. The first launch of an artificial Earth satellite took place on October 4, 1957 in the USSR. This was the first artificial celestial body that humans created. The event became possible thanks to the results of achievements in many areas of rocket, computer engineering, electronics, celestial mechanics, automatic control and other branches of science. The first satellite made it possible to measure the density of the upper layers of the atmosphere, verify the reliability of theoretical calculations and the main technical solutions that were used to put the satellite into orbit, and study the features of radio signal transmission in the ionosphere.
America launched its first Explorer-1 satellite on February 1, 1958, and then, later, other countries also launched: France, Australia, Japan, China, and Great Britain. In the field of space research , cooperation between countries around the world is widespread.
A spacecraft can be called a satellite only after it has completed more than one revolution around the Earth. Otherwise, it is not registered as a satellite and will be called a missile probe, which took measurements along a ballistic trajectory.
A satellite is considered active if it is equipped with radio transmitters, flash lamps that give light signals, and measuring equipment. Passive artificial Earth satellites are often used for observations from the surface of the planet when performing some scientific tasks. These include balloon satellites with a diameter of up to several tens of meters.
Artificial Earth satellites are divided into applied and research, depending on the tasks they perform. Research designed to conduct research on celestial bodies, the Earth, outer space. These are geodetic and geophysical satellites, astronomical orbital observatories, etc. Applied satellites are communication satellites, navigation satellites, meteorological satellites for Earth resources research, technical and others.
Artificial Earth satellites created for human flight are called "manned satellite ships." The satellites in the circumpolar or polar orbit are called polar, and in the equatorial orbit they are called equatorial. Stationary satellites are satellites launched into the equatorial circular orbit of the satellite, the direction of motion of which coincides with the rotation of the Earth, they motionless hang over a specific point on the planet. Parts that are detached from satellites during orbit, such as head fairings, are secondary orbital objects. Often they are called satellites, although they move along near-Earth orbits, and serve primarily as objects for observation for scientific purposes.
From 1957 to 1962 the name of the space objects indicated the year of launch and the letter of the Greek alphabet corresponding to the serial number of the launch in a particular year, as well as the Arabic numeral - the number of the object, depending on its scientific significance or brightness. But the number of satellites launched rapidly grew, because from January 1, 1963 they began to be indicated by the year of launch, the launch number in the same year and the letter of the Latin alphabet.
Satellites can be different in size, design, weight, composition of onboard equipment, depending on the tasks performed. The power supply of the equipment of almost all satellites is made through solar panels installed on the outer part of the hull.
The satellites are launched into orbit using automatically controlled multi-stage launch vehicles. The movement of artificial Earth satellites is subject to passive (planetary gravity, Earth's atmosphere resistance, etc.) and active (if a jet engine is installed on the satellite ) forces.