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Satellites

 

Satellites

This article is about artificial satellites. For natural satellites, also known as moons, see Natural satellite.
For other uses, see Satellite (disambiguation).

File:NASA Earth-observing Fleet June 2012.ogv


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

The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union in 1957. Since then, thousands of satellites have been launched into orbit around the Earth. Some satellites, notably space stations, have been launched in parts and assembled in orbit. Artificial satellites originate from more than 50 countries and have used the satellite launching capabilities of ten nations. A few hundred satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Vesta, Eros, and the Sun.

Satellites are used for a large number of purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.

As per the latest estimates, the total number of artificial satellites orbiting the Earth today is around 8,300. Of these, about 3,000 are not operational having lived out their useful life and are part of the space debris.

Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.

History

Early conceptions

"Newton's cannonball", presented as a "thought experiment" in A Treatise of the System of the World, was the first published mathematical study of the possibility of an artificial satellite.

The first fictional depiction of a satellite being launched into orbit is a short story by Edward Everett Hale, The Brick Moon. The story is serialized in The Atlantic Monthly, starting in 1869.[1][2] The idea surfaces again in Jules Verne's The Begum's Fortune (1879).
In 1903, Konstantin Tsiolkovsky (1857–1935) published Means of Reaction Devices (in Russian: Исследование мировых пространств реактивными приборами), 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.

In 1928 Slovenian Herman Potočnik (1892–1929) published his sole book, The Problem of Space Travel — The Rocket Motor (German: Das Problem der Befahrung des Weltraums — der Raketen-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 (1917–2008) described in detail the possible use of communications satellites for mass communications.[3] 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.

The US military studied the idea of what was referred to as the earth satellite vehicle when Secretary of Defense, James Forrestal, made a public announcement on December 29, 1948 that his office was coordinating that project between the various services.[4]

History of artificial satellites

The first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4, 1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer (there is a crater on the lunar far side which bears his name). This in turn triggered the Space Race between the Soviet Union and the United States.

Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere. The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War.

Sputnik 2 was launched on November 3, 1957 and carried the first living passenger into orbit, a dog named Laika.[5]

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."[6] 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."[7]

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 Army and Navy were working on Project Orbiter, two competing programs: the army's which involved using a Jupiter C rocket, and the civilian/Navy Vanguard Rocket, to launch a satellite. At first, they failed: initial preference was given to the Vanguard program, whose first attempt at orbiting a satellite resulted in the explosion of the launch vehicle on national television. But finally, three months after Sputnik 2, the project succeeded; Explorer 1 became the United States' first artificial satellite on January 31, 1958.[8]

In June 1961, three-and-a-half years after the launch of Sputnik 1, the Air Force used resources of the United States Space Surveillance Network to catalog 115 Earth-orbiting satellites.[9]

Early satellites were constructed as "one-off" designs. With growth in geosynchronous (GEO) satellite communication, multiple satellites began to be built on single model platforms called satellite buses. The first standardized satellite bus design was the HS-333 GEO commsat, launched in 1972.

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


Space Surveillance Network

The United States Space Surveillance Network (SSN), a division of The United States Strategic Command, has been tracking objects in Earth's orbit 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 objects. The SSN currently tracks more than 8,000 man-made orbiting objects. The rest have re-entered Earth's atmosphere and disintegrated, or survived re-entry and impacted the Earth. The SSN tracks objects that are 10 centimeters in diameter or larger; those now orbiting Earth range from satellites weighing several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent are operational satellites (i.e. ~560 satellites), the rest are space debris.[10] The United States Strategic Command is primarily interested in the active satellites, but also tracks space debris which upon reentry might otherwise be mistaken for incoming missiles.

A search of the NSSDC Master Catalog at the end of October 2010 listed 6,578 satellites launched into orbit since 1957, the latest being Chang'e 2, on 1 October 2010.[11]

Non-military satellite services

There are three basic categories of non-military satellite services:[12]

Fixed satellite services

Fixed satellite services handle hundreds of billions of voice, data, and video transmission tasks across all countries and continents between certain points on the Earth's surface.

Mobile satellite systems

Mobile satellite systems help connect remote regions, vehicles, ships, people 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 satellites (commercial and noncommercial)

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

Types

  • Space stations are man-made orbital 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. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.

Orbit types

Main article: List of orbits


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

The general structure of a satellite is that it is connected to the earth stations that are present on the ground and connected through terrestrial links.

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 2,000 km (1,200 mi) to just below geosynchronous orbit at 35,786 km (22,236 mi). Also known as an intermediate circular orbit.
  • High Earth orbit (HEO): Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,236 mi).


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

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 (12,600 mi) and an orbital period equal to one-half of the average rotational period (earth's is approximately 12 hours) of the body being orbited
  • Geosynchronous orbit (GSO): Orbits with an altitude of approximately 35,786 km (22,236 mi). Such a satellite would trace an analemma (figure 8) in the sky.
  • 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: A 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

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.
  • 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 subsystems

The satellite's functional versatility is imbedded within its technical components and its operations characteristics. Looking at the "anatomy" of a typical satellite, one discovers two modules.[12] Note that some novel architectural concepts such as Fractionated Spacecraft somewhat upset this taxonomy.

Spacecraft bus or service module

This bus module consist of the following 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 (aka Command and Data Handling, C&DH)

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. Nuclear power sources (Radioisotope thermoelectric generators) have been used in several successful satellite programs including the Nimbus program (1964–1978).[16]

  • 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 (e.g. Optical Solar Reflector)

  • The Attitude and Orbit Control Subsystems
Main article: Attitude control

The attitude and orbit control 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 transponder 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).

End of life

When satellites reach the end of their mission, satellite operators have the option of de-orbiting the satellite, leaving the satellite in its current orbit or moving the satellite to a graveyard orbit. Historically, due to budgetary constraints at the beginning of satellite missions, satellites were rarely designed to be de-orbited. One example of this practice is the satellite Vanguard 1. Launched in 1958, Vanguard 1, the 4th manmade satellite put in Geocentric orbit, was still in orbit as of August 2009.[17]

Instead of being de-orbited, most satellites are either left in their current orbit or moved to a graveyard orbit.[18] As of 2002, the FCC now requires all geostationary satellites to commit to moving to a graveyard orbit at the end of their operational life prior to launch.[19]

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 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
Order Country Date of first launch Rocket Satellite
1  Soviet Union 4 October 1957 Sputnik-PS Sputnik 1
2  United States 1 February 1958 Juno I Explorer 1
3  France 26 November 1965 Diamant-A Astérix
4  Japan 11 February 1970 Lambda-4S Ōsumi
5  China 24 April 1970 Long March 1 Dong Fang Hong I
6  United Kingdom 28 October 1971 Black Arrow Prospero
7  India 18 July 1980 SLV Rohini
8  Israel 19 September 1988 Shavit Ofeq 1
 Russia[1] 21 January 1992 Soyuz-U Kosmos 2175
 Ukraine[1] 13 July 1992 Tsyklon-3 Strela
9  Iran 2 February 2009 Safir-1 Omid
10  North Korea 12 December 2012 Unha-3 Kwangmyŏngsŏng-3 Unit 2
 South Korea 30 January 2013 Naro-1 STSAT-2C

Attempted first launches

  • United States tried in 1957 to launch the first satellite by own launcher before successfully completing a launch in 1958.
  • China tried in 1969 to launch the first satellite by own launcher before successfully completing a launch in 1970.
  • India, after launching the first national satellite by foreign launcher in 1975, tried in 1979 to launch the first satellite by own launcher before succeeding in 1980.
  • Iraq have claimed orbital launch of warhead in 1989, but this claim was later disproved.[23]
  • Brazil, after launch of first national satellite by foreign launcher in 1985, tried to launched the satellites by own VLS 1 launcher three times in 1997, 1999, 2003 but all were unsuccessful.
  • North Korea claimed a launch of Kwangmyŏngsŏng-1 and Kwangmyŏngsŏng-2 satellites in 1998 and 2009, but U.S., Russian and other officials and weapons experts later reported that the rockets failed to send a satellites into orbit, if that was the goal. The United States, Japan and South Korea believe this was actually a ballistic missile test, which is a claim also made after North Korea's 1998 satellite launch, and later rejected.[by whom?] The first (April 2012) launch of Kwangmyŏngsŏng-3 was unsuccessful, a fact publicly recognized by the DPRK. However, the December 2012 launch of the "second version" of Kwangmyŏngsŏng-3 was successful, putting the DPRK's first satellite into orbit.
  • South Korea (Korea Aerospace Research Institute), after launching their first national satellite by foreign launcher in 1992, tried to launch a first KSLV own launcher (created with assistance of Russia) in 2009, 2011 and 2012, but all were unsuccessful.

Other notes

  • ^ Russia and Ukraine were parts of the Soviet Union and thus inherited their launch capability without the need to develop it indigenously. Through Soviet Union they also are on the number one position in this list of accomplishments.
  • France, United Kingdom, Ukraine launched their first satellites by own launchers from foreign spaceports.
  • Some countries such as South Africa, Spain, Italy, Germany, Canada, Australia, Argentina, Egypt and private companies such as OTRAG, have developed their own launchers, but have not had a successful launch.
  • Only eight countries from the list above (Russia and Ukraine instead of USSR, also USA, Japan, China, India, Israel and Iran) 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.)
  • Several other countries, including South Korea, Brazil, Pakistan, Romania, Kazakhstan, Taiwan, Indonesia, Australia, New Zealand, Malaysia and Turkey, are at various stages of development of their own small-scale launcher capabilities.

Launch capable private entities

  • Private firm Orbital Sciences Corporation, with launches since 1982, continues very successful launches of its Minotaur, Pegasus, Taurus and Antares rocket programs.
  • On September 28, 2008, late comer and private aerospace firm SpaceX successfully launched its Falcon 1 rocket into orbit. This marked the first time that a privately built liquid-fueled booster was able to reach orbit.[24] The rocket carried a prism shaped 1.5 m (5 ft) long payload mass simulator that was set into orbit. The dummy satellite, known as Ratsat, will remain in orbit for between five and ten years before burning up in the atmosphere.[24]

A few other private companies are capable of sub-orbital launches.

First satellites of countries

Main article: Timeline of first satellites by country
First satellites of countries including launched indigenously or by help of other[25]
Country Year of first launch First satellite Payloads in orbit as of Jan 2013[26]
 Soviet Union
( Russia)
1957
(1992)
Sputnik 1
(Kosmos 2175)
1457
 United States 1958 Explorer 1 1110
 United Kingdom 1962 Ariel 1 0030
 Canada 1962 Alouette 1 0034
 Italy 1964 San Marco 1 0022
 France 1965 Astérix 0057
 Australia 1967 WRESAT 0012
 Germany 1969 Azur 0042
 Japan 1970 Ōsumi 0134
 China 1970 Dong Fang Hong I 0140
 Netherlands 1974 ANS 0004
 Spain 1974 Intasat 0009
 India 1975 Aryabhata 0050
 Indonesia 1976 Palapa A1 0012
 Czechoslovakia 1978 Magion 1 0004
 Bulgaria 1981 Intercosmos Bulgaria 1300 0001
 Saudi Arabia 1985 Arabsat-1A 0012
 Brazil 1985 Brasilsat A1 0013
 Mexico 1985 Morelos 1 0007
 Sweden 1986 Viking 0011
 Israel 1988 Ofeq 1 00011
 Luxembourg 1988 Astra 1A 005
 Argentina 1990 Lusat 009
 Pakistan 1990 Badr-1 0003
 South Korea 1992 Kitsat A 0011
 Portugal 1993 PoSAT-1 0001
 Thailand 1993 Thaicom 1 0007
 Turkey 1994 Turksat 1B 0008
 Ukraine 1995 Sich-1 0006
 Malaysia 1996 MEASAT 0006
 Norway 1997 Thor 2 0003
 Philippines 1997 Mabuhay 1 0002
 Egypt 1998 Nilesat 101 0004
 Chile 1998 FASat-Bravo 0002
 Singapore[27][28] 1998 ST-1 0003
 Taiwan 1999 ROCSAT-1 0008
 Denmark 1999 Ørsted 0004
 South Africa 1999 SUNSAT 0002
 United Arab Emirates 2000 Thuraya 1 0006
 Morocco 2001 Maroc-Tubsat 0001
 Algeria 2002 Alsat 1 0001
 Greece 2003 Hellas Sat 2 0002
 Cyprus 2003 Hellas Sat 2 0002
 Nigeria 2003 Nigeriasat 1 0004
 Iran 2005 Sina-1 0001
 Kazakhstan 2006 KazSat 1 0002
 Colombia 2007 Libertad 1 0001
 Mauritius 2007 Rascom-QAF 1 0002
 Vietnam 2008 Vinasat-1 0003
 Venezuela 2008 Venesat-1 0002
  Switzerland 2009 SwissCube-1[29] 0002
 Poland[30] 2012 PW-Sat 00001
 Hungary 2012 MaSat-1 [31] 0001
 Romania 2012 Goliat [32] 0001
 Belarus 2012 BelKA-2 N/A
 North Korea 2012 Kwangmyŏngsŏng-3 Unit 2 1
 Azerbaijan 2013 Azerspace [33] 1
 Austria 2013 TUGSAT-1/UniBRITE[34][35] 2
 Ecuador 2013 NEE-01 Pegaso 1
 Estonia 2013 ESTCube-1 1
 Jersey 2013 O3b-1,-2,-3,-4 4
 Qatar 2013 Es'hailSat1 1


While Canada was the third country to build a satellite which was launched into space,[36] 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.[37] Australia's launch project (WRESAT) involved a donated U.S. missile and U. S. support staff as well as a joint launch facility with the United Kingdom.[38]

Attempted first satellite

  •  USA tried unsuccessfully to launch its first satellite in 1957; they were successful in 1958.
  •  China tried unsuccessfully to launch its first satellite in 1969; they were successful in 1970.
  •  Iraq under Saddam fulfilled in 1989 an unconfirmed launch of warhead on orbit by developed Iraqi vehicle that intended to put later the 75-kg first national satellite Al-Ta’ir, also developed.[39]
  •  Chile tried unsuccessfully in 1995 to launch its first satellite FASat-Alfa; in 1998 they were successful.†
  •  North Korea has tried in 1998, 2009, 2012 to launch satellites, first successful launch on 12 December 2012.[40]
  •  Belarus tried unsuccessfully in 2006 to launch its first satellite BelKA.†

†-note: Both Chile and Belarus used Russian companies as principal contractors to build their satellites, they used Russian-Ukrainian manufactured rockets and launched either from Russia or Kazakhstan.

Planned first satellites

  •  Afghanistan announced in April 2012 that it is planning to launch its first communications satellite to the orbital slot it has been awarded. The satellite is expected to be launched by a commercial company.[41]
  •  Bangladesh announced in 2009 that it intends to launch its first satellite into space by 2011.[42]
  •  Belgium Its nano-satellite OUFTI-1 within European University program CubeSat QB50 for test radio protocol in space are under construction in University of Liege.[43]
  •  Bolivia New Bolivian Space Agency plans a first satellite to 2012 or later by Chinese help [44]
  •  [3]
  •  Croatia has a goal to construct a satellite by 2013–2014. Launch into Earth orbit would be done by a foreign provider.[45]
  •  [4]. When launched (plan to 2013), it would be the first Finnish satellite.
  • Saddam's  Iraq planned to purchase the first satellite in 2002 but project was not realised.[46] Now Iraqi experimental satellite schedules to launch in 2013[47] prior to ordered abroad for $50 million the first national large communication satellite near 2015.[48][49]
  •  Ireland Team of Dublin Institute of Technology intends to launch the first Irish satellite within European University program CubeSat QB50.[50]
  •  Laos First satellite will be telecommunication and will be built and launched in 2013 for $250 million by China Asia-Pacific Mobile Communications Company (China-APMT) [51]
  •  Latvia The 5 kg nano-satellite Venta-1 is built in Latvia in cooperation with the German engineers. The data received from satellite will be received and processed in Irbene radioastronomical centre (Latvia); satellite will have software defined radio capabilities. "Venta-1" will serve mainly as a means for education in Ventspils University College with additional functions, including an automatic system of identification of the ships of a sailing charter developed by OHB-System AG. The launch of the satellite was planned for the end of 2009 using the Indian carrier rocket. Due to the financial crisis the launch has been postponed until late 2011.[52] Started preparations to produce the next satellite "Venta-2".
  •  Lithuania New national Space Science and Technology Institute [53] plans nano-satellite "Lituanica SAT-1" [54] with space capsules by Russian help [55]
  •  Moldova The remote sensing satellite plans to start in 2013 by Space centre at national Technical University.[56]
  •  Mongolia While National Remote Sensing Center of Mongolia plans to order the communication satellite in Japan, Mongolian Academy of Sciences schedules to launch the first national experimental satellite Mongolsat by US launcher in the first quarter of 2013.[57]
  •  [5]
  •  [11]
  •  Peru developed its space satellite with the National Engineering University, called Chasqui 1. The nano-satellite planning to launch into orbit in 2012 or later with an expected 60-day lifespan. Payload includes two small VGA cameras with NIR filter(s).
  •  Serbia Nongovermental organisations designed, developed and assembled the first Serbian satellite Tesla-1 in 2009 but it still remains unlaunched.
  •  Sri Lanka has a goal to construct two satellites beside of rent the national SupremeSAT payload in Chinese satellites. Sri Lankan Telecommunications Regulatory Commission has signed an agreement with Surrey Satellite Technology Ltd to get relevant help and resources. Launch into Earth orbit would be done by a foreign provider.[58][59]
  •  Tunisia is developing its first satellite, ERPSat01. Consisting of a CubeSat of 1 kg mass, it will be developed by the Sfax School of Engineering. ERPSat satellite is planned to be launched into orbit in 2013.[60]
  •  Turkmenistan New National Space Agency plans a first satellite by help of SpaceX to 2014 [61]
  •  Uruguay's Aeronautics and Space Research and Diffusion Center, University of Engineering of Uruguay and state company for telecommunications ANTEL plans to launch its first satellite by 2013.[62]
  •  [13]
  •  Qatar Qatar will launch its first communication satellite Es'hailSat1 in August 2013, and it is planning to launch Es'hailSat2 between 2016 and 2017

[63]

Attacks on satellites

In recent timesTemplate:Clarify timeframe satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.[64][65]

For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from earth. Russia, the United States and China have demonstrated the ability to eliminate satellites.[66] In 2007 the Chinese military shot down an aging weather satellite,[66] followed by the US Navy shooting down a defunct spy satellite in February 2008.[67]

Jamming

Due to the low received signal strength of satellite transmissions, they are prone to jamming by land-based transmitters. Such jamming is limited to the geographical area within the transmitter's range. GPS satellites are potential targets for jamming,[68][69] but satellite phone and television signals have also been subjected to jamming.[70][71]

Also, it is trivial to transmit a carrier radio signal to a geostationary satellite and thus interfere with the legitimate uses of the satellite's transponder. It is common for Earth stations to transmit at the wrong time or on the wrong frequency in commercial satellite space, and dual-illuminate the transponder, rendering the frequency unusable. Satellite operators now have sophisticated monitoring that enables them to pinpoint the source of any carrier and manage the transponder space effectively.

Satellite services

See also

Spaceflight portal

References

External links

  • DMOZ
  • Satellite Ground Tracks Real time satellite tracks (Full catalog of satellite orbit). (English) (German) (Spanish) (French) (Italian) (Portuguese) (Chinese)
  • Real Time Satellite Tracking provides real-time tracks for about 17000 satellites, as well as 5-day predicitions of visibility
  • Heavens Above provides 10-day predictions of satellite visibility
  • Satflare tracks in real time all the satellites orbiting the Earth
  • 'Eyes in the Sky' Free video by the Vega Science Trust and the BBC/OU Satellites and their implications over the last 50 years.
  • UCS Satellite Database Lists operational satellites currently in orbit around the Earth. Updated quarterly.
  • Current and Historical Launch Calendar
  • Satellite launch schedule
  • http://www.youtube.com/ The making of an SES satellite -- ASTRA 2F
  • The 1945 Proposal by Arthur C. Clarke for Geostationary Satellite Communications

ast:Satélite (dixebra)

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