Satellite

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A satellite is any object that orbits another object (which is known as its primary). All masses that are part of the solar system, including the Earth, are satellites either of the Sun, or satellites of those objects, such as the Moon.

It is not always a simple matter to decide which is the 'satellite' in a pair of bodies. Because all objects exert 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 of the two objects is inside the primary object.

In popular usage, the term satellite normally refers to an artificial satellite, which would be a man-made object that orbits the Earth (or another body). However, scientists may also use the term to refer to natural satellites, or moons. In general word usage, "natural satellite" is the term used to refer to moons. Template:Spaceflight portal

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Artificial satellites

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The first artificial satellite

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

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Early history of the US satellite program

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.Template:Ref 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 Defence 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 and on October 4, 1957 Sputnik I was launched into orbit, which triggered the Space Race between the two nations.

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

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Types of satellites

Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.

Communications satellites are artificial satellites stationed in space for the purposes of telecommunications using radio at microwave frequencies. Most communications satellites use geosynchronous orbits or near-geostationary orbits, although some recent systems use low Earth-orbiting satellites.

Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)

Navigation 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 metres in real time.

Killer Satellites / Anti-Satellite Weapons are satellites designed to destroy "enemy" satellites, other orbital weapons and targets. Some are armed with kinetic rounds, while others use energy and/or particle weapons to destroy satellites, ICBMs, MIRVs. Both the US and the USSR had these satellites. Links discussing "Killer Satellites", ASATS (Anti-Satellite satellite) include USSR Tests ASAT weapon and ASAT Test. See also IMINT

Reconnaissance satellites are Earth observation satellite or communications satellite deployed for military or intelligence applications. Little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.

Solar power satellites are proposed satellites built in high Earth orbit that use microwave power transmission to beam solar power to very large antenna on Earth where it can be used in place of conventional power sources.

Space stations are man-made structures that are designed for human beings to live on in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.

Weather satellites are satellites that primarily are used to monitor the weather and/or climate of the Earth.

Miniaturized satellites are satellites of unusually low weights and small sizes. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).

Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.

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Orbit types

Many times satellites are characterized by their orbit. Although a satellite may orbit at almost any altitude, satellites are commonly categorized by their altitude:


The following orbits are special orbits that are also used to categorize satellites:

  • Molniya orbits
  • Heliosynchronous or sun-synchronous orbit
  • Polar orbit
  • LTO lunar transfer orbit.
  • Hohmann transfer orbit For this particular orbit type, it is more common to identify the satellite as a spacecraft.
  • Supersynchronous orbit or drift orbit — orbit above GEO. Satellites will drift in a westerly direction.
    • (GEO + 235 km + (1000 × CR × A/m) km)
      • where CR is the solar pressure radiation coefficient (typically between 1.2 and 1.5) and A/m is the aspect area [m2] to dry mass [kg] ratio
  • Subsynchronous orbit or drift orbit - orbits close to but below GEO. Used for satellites undergoing station changes in an eastern direction.

Satellites can also orbit libration points.

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Countries with satellite launch capability

Template:Main 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 - which relatively speaking, does not require much economic, scientific and industrial capacity - 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 indiginously, and the date this capability was first demonstrated.

First launch by country
Country Year of first launch First satellite
Template:Flagcountry 1957 Sputnik 1"
Template:Flagcountry 1958 Explorer 1
Template:Flagcountry 1965 Astérix
Template:Flagcountry 1970 Osumi
Template:Flagcountry 1970 Dong Fang Hong I
Template:Flagcountry 1971 Prospero X-3
Template:Flagcountry 1979 Ariane 1
Template:Flagcountry 1980 Rohini
Template:Flagcountry 1988 Ofeq 1

Both North Korea and Iraq have claimed orbital launches but these are unconfirmed. Norway has launched domestic and international satellites from its space center on Andøya. As of 2006, only eight countries, have independently launched satellites into orbit on their own indiginously developed launch vehicles - in chronological order: USSR, USA, France, Japan, China, UK, India and Isreal. The launch capabilties of the United Kingdom and France now fall under the European Union, and the launch capabilities of the Soviet Union fall under Russia, reducing the number of political entities with active satellite launch capabilites to seven - six 'major' space powers: USA, Russia, China, India, EU, Japan - and one 'minor' space power: Israel. Several other countries such as South Korea, Pakistan, Iran and Brazil are in the early stages of developing their own small-scale launch capabilties, and seek to become 'minor' space powers - others may have the scientific and industrial capability, but not the economic or political will.

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See also

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Reference

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External links

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