Satellites

A satellite is any object that orbits another object (which is known as its primary). Satellites can be spacecraft manufactured on Earth and sent into orbit on a launch vehicle, they may be naturally occurring such as moons, comets, asteroids, planets, stars, and even galaxies, or they may be space debris.

It is not always a simple matter to decide which is the "satellite" in a pair of bodies. Because all objects with mass are affected by gravity, the motion of the primary object is also affected by the satellite. If two objects are sufficiently similar in mass, they are generally referred to as a binary system rather than a primary object and satellite; an extreme example is the 'double asteroid' 90 Antiope. The general criterion for an object to be a satellite is that the center of mass (known as the Barycenter) of the two objects is inside the primary object. Another, perhaps better known, example is the dwarf planet Pluto and its companion, Charon. While many consider Charon to be a satellite of Pluto, this can be debated, as their masses are similar to the point where their barycenter is not within either object. Accordingly, some consider Pluto and Charon to be the two members of a double planet system.

The first known fictional depiction of an artificial satellite launched into orbit around the Earth is a short story by Edward Everett Hale, The Brick Moon. The story was serialized in the Atlantic Monthly, starting in 1869. The object named in the title is intended as a navigational aid, but is accidentally launched with people aboard. The idea surfaces again in Jules Verne's The Begum's Millions (1879). In this book, however, this is a completely unintentional result of the book's villain building an enormous artillery piece in order to destroy his enemies, and imparting to the shell a greater velocity than intended.

In 1903 Konstantin Tsiolkovsky (1857–1935) published (The Exploration of Cosmic Space by Means of Reaction Devices), which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the escape velocity from Earth into orbit at 8 km/second and that a multi-stage rocket fueled by liquid oxygen and liquid hydrogen would be required. During his lifetime he published over 500 works on space travel and related subjects, including science fiction novels. Among his works are designs for rockets with steering thrusters, multi-stage boosters, space stations, airlocks for exiting a spaceship into the vacuum of space, and closed cycle biological systems to provide food and oxygen for space colonies. He also delved into theories of heavier-than-air flying machines, independently working through many of the same calculations that the Wright brothers were performing at about the same time.

In 1928 Herman Potocnik (1898–1929) published his sole book, Das Problem der Befahrung des Weltraums - der Raketen-motor (The Problem of Space Travel - The Rocket Motor), a plan for a breakthrough into space and a permanent human presence there. He conceived of a space station in detail and calculated its geostationary orbit. He described the use of orbiting spacecraft for detailed peaceful and military observation of the ground and described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.

In 1945 the English science fiction writer Arthur C. Clarke (b. 1917) conceived of the possibility for mass artificial communication satellites in his Wireless World article. Clarke examined the logistics of satellite launch, possible orbits and other aspects of the creation of a network of world-circling satellites, pointing to the benefits of high-speed global communications. He also suggested that three geostationary satellites would provide coverage over the entire planet.

History Of Artifical Satellites

The first artificial satellite was Sputnik 1 launched by Soviet Union on 4 October 1957.

In May, 1946, Project RAND released the Preliminary Design of an Experimental World-Circling Spaceship, which stated, "A satellite vehicle with appropriate instrumentation can be expected to be one of the most potent scientific tools of the Twentieth Century. The achievement of a satellite craft would produce repercussions comparable to the explosion of the atomic bomb…"

The space age began in 1946, as scientists began using captured German V-2 rockets to make measurements in the upper atmosphere. Before this period, scientists used balloons that went up to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere research was conducted using V-2s and Aerobee rockets. This allowed measurements of atmospheric pressure, density, and temperature up to 200 km. (see also: magnetosphere, Van Allen radiation belt)

The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The Air Force's Project RAND eventually released the above report, but did not believe that the satellite was a potential military weapon; rather they considered it to be a tool for science, politics, and propaganda. In 1954, the Secretary of Defense stated, "I know of no American satellite program."

Following pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, military interest picked up and in early 1955 the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to launch a small satellite called Explorer 1 on January 31, 1958.

On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that they intended to launch a satellite by the fall of 1957. On October 4, 1957 Sputnik 1 was launched into orbit, which triggered the Space Race between the two already adversarial nations.

The largest artificial satellite currently orbiting the Earth is the International Space Station.

The United States Space Surveillance Network (SSN) has been tracking space objects since 1957 when the Soviets opened the space age with the launch of Sputnik I. Since then, the SSN has tracked more than 26,000 space objects orbiting Earth. The SSN currently tracks more than 8,000 man-made orbiting objects. The rest have re-entered Earth's turbulent atmosphere and disintegrated, or survived re-entry and impacted the Earth. The space objects now orbiting Earth range from satellites weighting several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent of the space objects are operational satellites (i.e. - ~560 satellites), the rest are debris. USSTRATCOM is primarily interested in the active satellites, but also tracks space debris which upon reentry might otherwise be mistaken for incoming missiles. The SSN tracks space objects that are 10 centimeters in diameter (baseball size) or larger.

Telecommunication satellite is a kind of satellite (later explained) that’s very close to our daily life. Arthur C. Clarke was one of the pioneers of this field; he fostered the idea of a worldwide satellite system. Echo I is a passive communication satellite launched in 1960. It was not equipped with a two-way system yet, and it was rather functioned as a reflector. Not very long after then, the Telstar I, an active communication satellite, was launched in 1962, with receiving and transmitting equipment, and was an active participant in the reception-transmission process. Telstar created the world’s first international television link. Therefore, Mirabito & Morgernstern in their book, The New Communication Technologies: Applications, Policy, and Impact, 5th edition, said that Telstar had paved the way for today’s communication spacecraft