Learn more about Satellite
A satellite is any object that orbits another object (which is known as its primary). Satellites can be manmade or may be naturally occurring such as moons, comets, asteroids, planets, stars, and even galaxies.
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.
What seems the first fictional depiction of an artificial satellite launched into Earth orbit seems to be 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 Исследование мировых пространств реактивными приборами (The Exploration of Cosmic Space by Means of Reaction Devices), which was arguably the first academic treatise on rocketry. 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 Potočnik (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.<ref>facsimile at http://www.lsi.usp.br/~rbianchi/clarke/ACC.ETRelaysFull.html</ref> 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.
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.<ref>Hess, Wilmot (1968). The Radiation Belt and Magnetosphere.</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. 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.
- Anti-Satellite weapons, sometimes called "Killer satellites" 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 U.S. 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
- 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.
- Communications satellites are an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites typically use geosynchronous orbits, Molniya orbits or low Earth orbits.
- 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).
- 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.
- 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.
- Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc. (See especially Earth Observing System.)
- 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 Earth's weather and climate.
 Orbit types
Low Polar Orbit
 Centric Classifications
- Galacto-centric Orbit - An orbit about the center of a galaxy. Earth's sun follows this type of orbit about the galactic center of the Milky Way.
- Heliocentric Orbit - An orbit around the Sun. In our Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial satellites and pieces of space debris. Moons by contrast are not in a heliocentric orbit but rather orbit their parent planet.
- Geocentric Orbit - An orbit around the planet Earth, such as the Moon or artificial satellites. Currently there are approximately 2465 artificial satellites orbiting the Earth.
 Altitude Classifications
- Medium Earth Orbit (MEO) - Geocentric orbits ranging in altitude from 2,000 km (1,240 miles) - to just below geosynchronous orbit at 35,786 km (22,240 miles). Also known as an intermediate circular orbit.
- High Earth Orbit (HEO) - Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles).
 Inclination Classifications
 Eccentricity Classifications
- Elliptic Orbit - An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse.
- Hyperbolic orbit - An orbit with the eccentricity greater than 1. Such an orbit also has a velocity in excess of the escape velocity and as such, will escape the gravataional pull of the planet and continue to travel infinitely.
- Parabolic Orbit - An orbit with the eccentricity equal to 1. Such an orbit also has a velocity equal to the escape velocity and therefore will escape the gravatational pull of the planet and travel until its velocity relative to the planet is 0. If the speed of such an orbit is increased it will become a hyperbolic orbit.
 Synchronous Classifications
- Synchronous Orbit - An orbit where the satellite has an orbital period equal to the average rotational period (earth's is: 23 hours, 56 minutes, 4.091 seconds) of the body being orbited and in the same direction of rotation as that body. To a ground observer such a satellite would trace an analemma (figure 8) in the sky.
- Semi-Synchronous Orbit (SSO) - An orbit with an altitude of approximately 20,200 km (12544.2 miles ) and an orbital period of approximately 12 hours
- Geosynchronous Orbit (GEO) - Orbits with an altitude of approximately 35,786 km (22,240 miles). Such a satellite would trace an analemma (figure 8) in the sky.
- Subsynchronous orbit - A drift orbit close to but below GSO/GEO. Satellites will drift east.
- Areosynchronous Orbit - A synchronous orbit around the planet Mars with an orbital period equal in length to Mars' sidereal day, 24.6229 hours.
- Areostationary Orbit (ASO) - A circular areosynchronous orbit on the equatorial plane and about 17,000 km(10557 miles) above the surface. To an observer on the ground this satellite would appear as a fixed point in the sky.
- Heliosynchronous Orbit - An heliocentric orbit about the Sun where the satellite's orbital period matches the Sun's period of rotation. These orbits occur at a radius of 24.360 Gm (0.1628 AU) around the Sun, a little less than half of the orbital radius of Mercury.
 Special Classifications
- Sun-synchronous Orbit - An orbit which combines altitude and inclination in such a way that the satellite passes over any given point of the planets's surface at the same local solar time. Such an orbit can place a satellite in constant sunlight and is useful for imaging, spy, and weather satellites.
- Moon Orbit - The orbital characteristics of earth's moon. Average altitude of 384,403 kilometres (238,857 mi), elliptical-inclined orbit.
- Horseshoe Orbit - An orbit that appears to a ground observer to be orbiting a certain planet but is actually in co-orbit with the planet. See asteroids 3753 (Cruithne) and 2002 AA29.
- Exo-orbit - A maneuver where a spacecraft approaches the height of orbit but lacks the velocity to sustain it.
- Lunar transfer orbit (LTO) -
- Prograde Orbit - An orbit with an inclination of less than 90°. Or rather, an orbit that is in the same direction as the rotation of the primary.
- Retrograde orbit - An orbit with an inclination of more than 90°. Or rather, an orbit counter to the direction of rotation of the planet. Almost no satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocity equal to the rotational velocity of the planet at its launch latitude.
Satellites can also orbit Lagrangian Points.
 Launch capable countries
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 indigenously, and the date this capability was first demonstrated. Does not include consortium satellites or multi-national satellites.
|Country||Year of first launch||First satellite||Payloads in orbit in 2006|
|Image:Flag of the Soviet Union.svg USSR||1957||Sputnik 1||1390|
|Image:Flag of the United States.svg United States||1958||Explorer 1||999|
|Image:Flag of Australia.svg Australia||1964||Blue Streak||9|
|Image:Flag of France.svg France||1965||Astérix||43|
|Image:Flag of Japan (bordered).svg Japan||1970||Osumi||102|
|Image:Flag of the People's Republic of China.svg China||1970||Dong Fang Hong I||53|
|Image:Flag of the United Kingdom.svg United Kingdom||1971||Prospero X-3||23|
|Image:Flag of India.svg India||1979||Rohini-1||31|
|Image:Flag of Israel (bordered).svg Israel||1988||Ofeq 1||6|
|Image:Flag of North Korea.svg North Korea||1998||Kwangmyongsong||Unknown|
Both North Korea and Iraq have claimed orbital launches but these are unconfirmed. As of 2006, only ten countries have independently launched satellites into orbit on their own indigenously developed launch vehicles - in chronological order: USSR, USA, Canada, France, Australia, Japan, China, UK, India and Israel. It should be noted that while Kazakhstan did launch their satellite independently, it was built by the Russians, and the rocket was not independently designed. While Canada was the third country into Space, it has since retired its launch capabilities, and depends upon USA, Russia or the EU for its launches. Australia's launch project may have involved some input from the United Kingdom, although they are still considered an independent launch nation (see Australian Space Research Institute. The launch capabilities 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 capabilities to seven - six 'major' space powers: USA, Russia, China, India, EU, Japan, and Israel.
Several other countries such as South Korea, Pakistan, Iran and Brazil are in the early stages of developing their own small-scale launch capabilities, and seek to become 'minor' space powers - others may have the scientific and industrial capability, but not the economic or political will. The first Italian satellite was San Marco 1, launched from Wallops Island (USA) on 15 December, 1964 on a scout launcher. Italy used a modified Scout launcher and never developed her own launcher: Italian satellites use Soyuz or Ariane (ESA) launchers.
The (artificial, though this is not stated in the blazon) satellite appears as a charge in the arms of Arthur Maxwell House.<ref>http://heraldry.ca/arms/h/house.htm</ref> This is in addition to numerous appearances of the natural satellite the moon, and the moons of the planets Jupiter and Saturn (with those planets) in the arms of Pierre-Simon LaPlace.
 See also
- Communications satellite
- Timeline of artificial satellites and space probes
- List of Earth observation satellites
- International Designator
- Satellite Catalog Number
- Satellites (sorted by launch date):
- Satellite Services:
- Anti-satellite weapon
- GoldenEye (fictional satellite weapon)
- Tether satellite
Anemometer | Barograph | Barometer | Ceiling balloon | Ceiling projector | Ceilometer | Dark adaptor goggles | Disdrometer | Field mill | Hygrometer | Ice Accretion Indicator | LIDAR | Lightning detector | Nephelometer | Nephoscope | Radiosonde | Rain gauge | Satellite | Snow gauge | SODAR | Sounding rocket | Stevenson screen | Sunshine recorders | Thermograph | Thermometer | Weather balloon | Weather radar | Weather satellite | Weather vane | Windsock | Wind profiler
 External links
- 'Eyes in the Sky' Freeview video by the Vega Science Trust and the BBC/OUSatallites and their implications over the last 50 years.
- How Stuff Works.com How satellites work
- UCS Satellite Database Lists operational satellites currently in orbit around the Earth. Updated quarterly.
- Free web based satellite tracker
- Edusat project
- Facsimile of Arthur C. Clarke's 1945 paper on communication satellites
- J-Pass NASA site for satellite-watching
- GPS Satellites
- heavens-above.com site for satellite-watching
- Orbitron - Satellite Tracking System Free satellite tracking software
- UN Office for Outer Space Affairs ensures all countries benefit from satellites
- Satellite Internet: Beam contour maps Worldwide satellite mapping showing service area coverages in each region, plus independent advice and forum on two-way VSAT terminal operation for voice, data and internet access
- Satellite Service Providers Compare and review on top satellite tv, radio and internet service providers]
- CBC Digital Archives - Launching the Digital Age: Canadian Satellites
- http://scienceworld.wolfram.com/physics/RetrogradeOrbit.html Retrograde Orbit
- BusinessCom Internet via Satellite - worldwide Internet access and VoIP provider
- BNLsat - Satellite Internet access in Middle East
- BNLsat-Africa - Satellite Internet access in Africa
- Satellite VSAT Providerar:قمر اصطناعي
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