Satellite

For other uses, see Satellite (disambiguation).

A full size model of the Earth observation satellite ERS 2

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.

Contents 1 History 2 History of artificial satellites 3 Space Surveillance Network 4 Non-Military Satellite Services 4.1 Fixed Satellite Service 4.2 Mobile Satellite Systems 4.3 Scientific Research Satellite (commercial and noncommercial) 5 Types 6 Orbit types 6.1 Centric classifications 6.2 Altitude classifications 6.3 Inclination classifications 6.4 Eccentricity classifications 6.5 Synchronous classifications 6.6 Special classifications 6.7 Pseudo-orbit classifications 7 Satellite Modules 7.1 Spacecraft bus or service module 7.2 Communication Payload 8 Launch-capable countries - space powers 9 Satellite Services 10 See also 11 References 12 External links

History

The first known fictional depiction of a satellite being launched into orbit is a short story by Edward Everett Hale, The Brick Moon. The story was serialized in The Atlantic Monthly, starting in 1869. The Brick Moon and Other Stories by Edward Everett Hale. Project Gutenberg. Retrieved on 2008-03-06. Contents - The Atlantic monthly. Volume 24, Issue 141. cornell.edu. Retrieved on 2008-03-06. The idea surfaces again in Jules Verne\'s The Begum\'s Millions (1879).

In 1903 Konstantin Tsiolkovsky (1857–1935) published Исследование мировых пространств реактивными приборами (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 orbital speed required for a minimal orbit around the Earth at 8 km/s, and that a multi-stage rocket fueled by liquid propellants could be used to achieve this. He proposed the use of liquid hydrogen and liquid oxygen, though other combinations can be used. 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 (1892–1929) 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 a 1945 Wireless World article the English science fiction writer Arthur C. Clarke (b. 1917) described in detail the possible use of communications satellites for mass communications.The_1945_Proposal_by_Arthur_C._Clarke_for_Geostationary_Satellite_Communications. lakdiva.org. Retrieved on 2008-03-06. 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 artificial satellites

Main article: Timeline of artificial satellites and space probes

See also: Space Race

The first artificial satellite was Sputnik 1, launched by the Soviet Union on 4 October 1957. This triggered the Space Race between the Soviet Union and the United States.

In May, 1946, Project RAND had 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. Preliminary Design of an Experimental World-Circling Spaceship. RAND. Retrieved on 2008-03-06. The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy. The United States 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."

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.

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 satellite. The project succeeded, and Explorer 1 became the United States\' first satellite on January 31, 1958.News Reel - First US Satellite Launched. webcastr.com. Retrieved on 2008-03-05.

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

Space Surveillance Network

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 weighing 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 space debris.ORBITAL_DEBRIS_EDUCATION_PACKAGE. nasa.gov. Retrieved on 2008-03-06. 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.

Non-Military Satellite Services

There are three basic categories of non-military satellite services:Grant, A.,& Meadows, J. (2004). Satellites Communication. Communication Technology Update (ninth edition). Burlington: Focal Press.

Fixed Satellite Service

Fixed satellite services handle hundreds of millions of voice, data, and video transmission tasks across all continents between fixed points on the earth’s surface

Mobile Satellite Systems

Mobile satellite systems help connect remote regions, vehicles, ships and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems

Scientific Research Satellite (commercial and noncommercial)

Scientific research satellites provide us with meteorological information, land survey data (e.g., remote sensing), and other different scientific research applications such as earth science, marine science, and atmospheric research.

Types

MILSTAR: A communication satellite

• 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.
• 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 satellites stationed in space for the purpose 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.Workshop on the Use of Microsatellite Technologies. United Nations. Retrieved on 2008-03-06. New classifications are used to categorize these satellites: minisatellite (500–200 kg), microsatellite (below 200 kg), nanosatellite (below 10 kg).
• Navigational 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 meters 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.)
• \'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.
• Tether satellites are satellites which are connected to another satellite by a thin cable called a tether.
• Weather satellites are primarily used to monitor Earth\'s weather and climate.Earth_Observations_from_Space_The_First_50_Years_of_Scientific_Achievements. nas.edu. Retrieved on 2008-03-06.

Orbit types

Main article: List of orbits

Various earth orbits to scale; cyan represents low earth orbit, yellow represents medium earth orbit, the black dashed line represents geosynchronous orbit, the green dash-dot line the orbit of Global Positioning System (GPS) satellites, and the red dotted line the orbit of the International Space Station (ISS).

The first satellite, Sputnik 1, was put into orbit around Earth and was therefore in geocentric orbit. By far this is the most common type of orbit with approximately 2456 artificial satellites orbiting the Earth. Geocentric orbits may be further classified by their altitude, inclination and eccentricity.

The commonly used altitude classifications are Low Earth Orbit (LEO), Medium Earth Orbit (MEO) and High Earth Orbit (HEO). Low Earth orbit is any orbit below 2000 km, and Medium Earth Orbit is any orbit higher than that but still below the altitude for geosynchronous orbit at 35786 km. High Earth Orbit is any orbit higher than the altitude for geosynchronous orbit.

Centric classifications

• Galactocentric 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.
• Areocentric orbit: An orbit around the planet Mars, such as moons or artificial satellites.

Altitude classifications

• Low Earth Orbit (LEO): Geocentric orbits ranging in altitude from 0–2000 km (0–1240 miles)
• Medium Earth Orbit (MEO): Geocentric orbits ranging in altitude from 2000 km (1240 miles) to just below geosynchronous orbit at 35786 km (22240 miles). Also known as an intermediate circular orbit.
• High Earth Orbit (HEO): Geocentric orbits above the altitude of geosynchronous orbit 35786 km (22240 miles).

Inclination classifications

• Inclined orbit: An orbit whose inclination in reference to the equatorial plane is not zero degrees.
  • Polar orbit: An orbit that passes above or nearly above both poles of the planet on each revolution. Therefore it has an inclination of (or very close to) 90 degrees.
  • Polar sun synchronous orbit: A nearly polar orbit that passes the equator at the same local time on every pass. Useful for image taking satellites because shadows will be nearly the same on every pass.

Eccentricity classifications

• Circular orbit: An orbit that has an eccentricity of 0 and whose path traces a circle.
  • Hohmann transfer orbit: An orbital maneuver that moves a spacecraft from one circular orbit to another using two engine impulses. This maneuver was named after Walter Hohmann.
• Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse.
  • Geosynchronous transfer orbit: An elliptic orbit where the perigee is at the altitude of a Low Earth Orbit (LEO) and the apogee at the altitude of a geosynchronous orbit.
  • Geostationary transfer orbit: An elliptic orbit where the perigee is at the altitude of a Low Earth Orbit (LEO) and the apogee at the altitude of a geostationary orbit.
  • Molniya orbit: A highly elliptic orbit with inclination of 63.4° and orbital period of half of a sidereal day (roughly 12 hours). Such a satellite spends most of its time over a designated area of the planet.
  • Tundra orbit: A highly elliptic orbit with inclination of 63.4° and orbital period of one sidereal day (roughly 24 hours). Such a satellite spends most of its time over a designated area of the planet.
• 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 gravitational 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 gravitational 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.
  • Escape orbit (EO): A high-speed parabolic orbit where the object has escape velocity and is moving away from the planet.
  • Capture orbit: A high-speed parabolic orbit where the object has escape velocity and is moving toward the planet.

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 20200 km (12544.2 miles) and an orbital period of approximately 12 hours
• Geosynchronous orbit (GEO): Orbits with an altitude of approximately 35786 km (22240 miles). Such a satellite would trace an analemma (figure 8) in the sky.
  • Geostationary orbit (GSO): A geosynchronous orbit with an inclination of zero. To an observer on the ground this satellite would appear as a fixed point in the sky.PEARL HARBOR IN SPACE. jamesoberg.com. Retrieved on 2008-03-06.
    • Clarke orbit: Another name for a geostationary orbit. Named after the writer Arthur C. Clarke.
  • Supersynchronous orbit: A disposal / storage orbit above GSO/GEO. Satellites will drift west. Also a synonym for Disposal orbit.
  • Subsynchronous orbit: A drift orbit close to but below GSO/GEO. Satellites will drift east.
  • Graveyard orbit: An orbit a few hundred kilometers above geosynchronous that satellites are moved into at the end of their operation.
    • Disposal orbit: A synonym for graveyard orbit.
    • Junk orbit: A synonym for graveyard orbit.
• 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 17000 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 384403 kilometres (238857 mi), elliptical-inclined orbit.

Pseudo-orbit classifications

• 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.
  • Orbital spaceflight: A synonym for exo-orbit.
• 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. Apart from those in sun-synchronous orbit, few 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.
• Halo orbit and Lissajous orbit: Orbits "around" Lagrangian points.

Satellite Modules

The satellite’s functional versatility is imbedded within its technical components and its operations characteristics. Looking at the “anatomy” of a satellite, one discovers two modules.

Spacecraft bus or service module

This first module consist of five subsystems:

• The Structural Subsystems

The structural subsystem provides the mechanical base structure, shields the satellite from extreme temperature changes and micro-meteorite damage, and controls the satellite’s spin functions.

• The Telemetry Subsystems

The telemetry subsystem monitors the on-board equipment operations, transmits equipment operation data to the earth control station, and receives the earth control station’s commands to perform equipment operation adjustments.

• The Power Subsystems

The power subsystem consists of solar panels and backup batteries that generate power when the satellite passes into the earth’s shadow.

• The Thermal Control Subsystems

The thermal control subsystem helps protect electronic equipment from extreme temperatures due to intense sunlight or the lack of sun exposure on different sides of the satellite’s body

• The Altitude and Orbit Controlled Control Subsystems

The altitude and orbit controlled subsystem consists of small rocket thrusters that keep the satellite in the correct orbital position and keep antennas positioning in the right directions.

Communication Payload

The second major module is the communication payload, which is made up of transponders. A transponders is capable of :

• Receiving uplinked radio signals from earth satellite transmission stations (antennas).
• Amplifying received radio signals
• Sorting the input signals and directing the output signals through input/output signal multiplexers to the proper downlink antennas for retransmission to earth satellite receiving stations (antennas).

Launch-capable countries - space powers

Main article: Timeline of first orbital launches by nationality

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.

First launch by country

Country	Year of first launch	First satellite
Soviet Union	1957	Sputnik 1
United States	1958	Explorer 1
France	1965	Astérix
Denmark	1999	Ørsted
Japan	1970	Osumi
China	1970	Dong Fang Hong I
United Kingdom	1971	Prospero X-3
India	1981	Rohini
Israel	1988	Ofeq 1

Both North Korea (1998) and Iraq (1989) have claimed orbital launches (satellite and warhead accordingly), but these claims are unconfirmed.

In addition to the above, countries such as South Africa, Spain, Italy, West Germany, Canada, Australia, Argentina, Egypt and private companies such as OTRAG, have developed their own launchers, but have not had a successful launch.

As of 2008, only seven countries from list above ( Russia and Ukraine instead of USSR, also USA, Japan, China, India, and Israel) and one regional organization (the European Space Agency, ESA) have independently launched satellites on their own indigenously developed launch vehicles. (The launch capabilities of the United Kingdom and France now fall under the ESA.)

Also, one international private company (Sea Launch) demonstrates launch capability through their purchase of Ukrainian–Russian launchers. Some of other companies plans to begin operate the launchers and launch systems in near future.

Several other countries, including South Korea, Iran, Brazil, Pakistan, Romania, Kazakhstan, Australia, Malaysia and Turkey, are at various stages of development of their own small-scale launcher capabilities, and seek membership in the club of space powers.

It is schedules that in early 2008 South Korea is launching KSLV rocket (created with assistance of Russia) and become the next space power. Iran already has successfully tested its own space launch vehicle (Kavoshgar 1) and is scheduled to put its first domestic satellite (Omid 1) into orbit within a year from February 4 2008. It is expects that Brazil and Pakistan to be follows in nearest future.

First launch by country including help of other partiesFirst time in History. tbs-satellite.com. Retrieved on 2008-03-06.

Country	Year of first launch	First satellite	Payloads in orbit in 2008SATCAT Boxscore. celestrak.com. Retrieved on 2008-03-05.
Soviet Union	1957	Sputnik 1	1398
United States	1958	Explorer 1	1042
Canada	1962	Alouette 1	25
Italy	1964	San Marco 1	14
France	1965	Astérix	44
Australia	1967	WRESAT	11
Germany	1969	Azur	27
Japan	1970	Osumi	111
China	1970	Dong Fang Hong I	64
United Kingdom	1971	Prospero X-3	25
Poland	1973	Intercosmos Kopernikus 500	?
Netherlands	1974	ANS	5
Spain	1974	Intasat	9
India	1975	Aryabhata	34
Indonesia	1976	Palapa A1	10
Czechoslovakia	1978	Magion 1	5
Bulgaria	1981	Intercosmos 22
Brazil	1985	Brasilsat A1	11
Mexico	1985	Morelos 1	7
Sweden	1986	Viking	11
Israel	1988	Ofeq 1	7
Luxembourg	1988	Astra 1A	15
Argentina	1990	Lusat	10
Pakistan	1990	Badr-1	5
South Korea	1992	Kitsat A	10
Portugal	1993	PoSAT-1	1
Thailand	1993	Thaicom 1	6
Turkey	1994	Turksat 1B	5
Chile	1995	FASat-Alfa	1
Malaysia	1996	MEASAT	4
Norway	1997	Thor 2	3
Philippines	1997	Mabuhay 1	2
Egypt	1998	Nilesat 101	3
Denmark	1999	Ørsted	3
South Africa	1999	SUNSAT	1
Saudi Arabia	2000	Saudisat 1A	12
United Arab Emirates	2000	Thuraya 1	3
Algeria	2002	Alsat 1	1
Greece	2003	Hellas Sat 2	2
Nigeria	2003	Nigeriasat 1	2
Iran	2005	Sina-1	1
Kazakhstan	2006	KazSat 1	1
Colombia	2007	Libertad 1	1

While Canada was the third country to build a satellite which was launched into space,Canada\'s Churchill Spaceport. spacetoday.org. Retrieved on 2008-03-06. it was launched aboard a U.S. rocket from a U.S. spaceport. The same goes for Australia, who launched on-board a donated Redstone rocket. The first Italian-launched was San Marco 1, launched on 15 December, 1964 on a U.S. Scout rocket from Wallops Island (VA,USA) with an Italian Launch Team trained by NASA.San Marco 1. nasa.gov. Retrieved on 2008-03-05. Australia\'s launch project, in November 1967, involved a donated U.S. missile and U. S. support staff as well as a joint launch facility with the United Kingdom.WRESAT_Australia\'s_First_Satellite. powerup.com.au. Retrieved on 2008-03-05. Kazakhstan claimed to have made their satellite independently, but the satellite was built with Russian help, like Polish and Bulgarian ones earlier.

Satellite Services

• Satellite Internet
• Satellite phone
• Satellite radio
• Satellite television
• Weather satellite
• Satellite navigation

See also

Spaceflight Portal

• Footprint (satellite)
• GoldenEye (fictional satellite weapon)
• International Designator
• List of Earth observation satellites
• Satellite Catalog Number
• Satellite formation flying
• Smallsat
• IMINT

References

External links

• J-Track 3D A 3-dimensional display of all active satellites orbiting planet Earth.
• Satellite Ground Tracks Real time satellite\'s tracks (Full catalog of satellite orbit). (English) (German) (Spanish) (French) (Italian) (Portuguese) (Chinese)
• \'Eyes in the Sky\' Free video by the Vega Science Trust and the BBC/OU Satellites 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.
• Satellite launch schedule

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