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Passage 1:
Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle (PSLV) is an expendable medium-lift launch vehicle designed and operated by the Indian Space Research Organisation (ISRO). It was developed to allow India to launch its Indian Remote Sensing (IRS) satellites into sun-synchronous orbits, a service that was, until the advent of the PSLV in 1993, only commercially available from Russia. PSLV can also launch small size satellites into Geostationary Transfer Orbit (GTO).Some notable payloads launched by PSLV include India's first lunar probe Chandrayaan-1, India's first interplanetary mission, Mars Orbiter Mission (Mangalyaan) and India's first space observatory, Astrosat.PSLV has gained credibility as a leading provider of rideshare services for small satellites, owing to its numerous multi-satellite deployment campaigns with auxiliary payloads, usually ride-sharing along with an Indian primary payload. As of June 2022, PSLV has launched 345 foreign satellites from 36 countries. Most notable among these was the launch of PSLV-C37 on 15 February 2017, successfully deploying 104 satellites in sun-synchronous orbit, tripling the previous record held by Russia for the highest number of satellites sent to space on a single launch, until 24 January 2021, when SpaceX launched the Transporter-1 mission on a Falcon 9 rocket carrying 143 satellites into orbit.Payloads can be integrated in tandem configuration employing a Dual Launch Adapter. Smaller payloads are also placed on equipment deck and customized payload adapters.

Development
Studies by the PSLV Planning group under S Srinivasan to develop a vehicle capable of delivering a 600 kg payload to a 550 km sun-synchronous orbit from SHAR began in 1978. Among 35 proposed configurations, four were picked; by November 1980, a vehicle configuration with two strap-ons on a core booster (S80) with 80 tonne solid propellant loading each, a liquid stage with 30 tonne propellant load (L30), and an upper stage called the Perigee-Apogee System (PAS) was being considered.By 1981, confidence grew in remote sensing spacecraft development with the launch of Bhaskara-1, and the PSLV project objectives were upgraded to have the vehicle deliver a 1000 kg payload into a 900 km SSO. As technology transfer of Viking rocket engine firmed up, a new lighter configuration with the inclusion of a liquid powered stage was selected. Funding was approved in July 1982 for the finalized design, employing a single large S125 solid core as first stage with six 9 tonne strap-ons (S9) derived from the SLV-3 first stage, liquid fueled second stage (L33), and two solid upper stages (S7 and S2.) This configuration needed further improvement to meet the orbital injection accuracy requirements of IRS satellites, and hence, the solid terminal stage (S2) was replaced with a pressure fed liquid fueled stage (L1.8 or LUS) powered by twin engines derived from roll control engines of the first stage. Apart from increasing precision, liquid upper stage also absorbed any deviation in performance of solid third stage. The final configuration of PSLV-D1 to fly in 1993 was (6 × S9 + S125) + L37.5 + S7 + L2.The inertial navigation systems are developed by ISRO Inertial Systems Unit (IISU) at Thiruvananthapuram. The liquid propulsion for the second and fourth stages of the PSLV as well as the Reaction control systems (RCS) are developed by the Liquid Propulsion Systems Centre (LPSC) at Valiamala near Thiruvananthapuram, kerala. The solid propellant motors are processed at Satish Dhawan Space Centre (SHAR) at Sriharikota, Andhra Pradesh, which also carries out launch operations.
The PSLV was first launched on 20 September 1993. The first and second stages performed as expected, but an attitude control problem led to the collision of the second and third stages at separation, and the payload failed to reach orbit. After this initial setback, the PSLV successfully completed its second mission in 1994. The fourth launch of PSLV suffered a partial failure in 1997, leaving its payload in a lower than planned orbit. In November 2014, the PSLV had launched 34 times with no further failures. (Although launch 41: August 2017 PSLV-C39 was unsuccessful.)
PSLV continues to support Indian and foreign satellite launches especially for low Earth orbit (LEO) satellites. It has undergone several improvements with each subsequent version, especially those involving thrust, efficiency as well as weight. In November 2013, it was used to launch the Mars Orbiter Mission, India's first interplanetary probe.In June 2018, the Union Cabinet approved ₹6,131 crore (equivalent to ₹72 billion or US$900 million in 2023) for 30 operational flights of the PSLV scheduled to take place between 2019 and 2024.ISRO is working towards handing over the production and operation of PSLV to private industry through a joint venture. On 16 August 2019, NewSpace India Limited issued an invitation to tender for manufacturing PSLV entirely by private industries. On 5 September 2022, NewSpace India Limited signed a contract with Hindustan Aeronautics Limited and Larsen & Toubro led conglomerate for the production of five PSLV-XL launch vehicles after they won competitive bidding. Under this contract, they have to deliver their first PSLV-XL within 24 months and the remaining four vehicles every six months.

Vehicle description
The PSLV has four stages, using solid and liquid propulsion systems alternately.

First stage (PS1)
The first stage, one of the largest solid rocket boosters in the world, carries 138 t (136 long tons; 152 short tons) of hydroxyl-terminated polybutadiene-bound (HTPB) propellant and develops a maximum thrust of about 4,800 kN (1,100,000 lbf). The 2.8 m (9 ft 2 in) diameter motor case is made of maraging steel and has an empty mass of 30,200 kg (66,600 lb).Pitch and yaw control during first stage flight is provided by the Secondary Injection Thrust Vector Control (SITVC) System, which injects an aqueous solution of strontium perchlorate into the S139 exhaust divergent from a ring of 24 injection ports to produce asymmetric thrust. The solution is stored in two cylindrical aluminium tanks strapped to the core solid rocket motor and pressurised with nitrogen. Underneath these two SITVC tanks, Roll Control Thruster (RCT) modules with small bi-propellant (MMH/MON) liquid engine are also attached.On the PSLV-G and PSLV-XL, first stage thrust is augmented by six strap-on solid boosters. Four boosters are ground-lit and the remaining two ignite 25 seconds after launch. The solid boosters carry 9 t (8.9 long tons; 9.9 short tons) or 12 t (12 long tons; 13 short tons) (for PSLV-XL configuration) propellant and produce 510 kN (110,000 lbf) and 719 kN (162,000 lbf) thrust respectively. Two strap-on boosters are equipped with SITVC for additional attitude control. The PSLV-CA uses no strap-on boosters.
First stage separation is aided by four pairs of retro-rockets installed on inter-stage (1/2L). During staging, these eight rockets help push away the spent stage away from second stage.

Second stage (PS2)
The second stage is powered by a single Vikas engine and carries 41.5 t (40.8 long tons; 45.7 short tons) of Earth store-able liquid propellant – unsymmetrical dimethylhydrazine (UDMH) as fuel and nitrogen tetroxide (N2O4) as oxidiser in two tanks separated by a common bulkhead. It generates a maximum thrust of 800 kN (180,000 lbf). The engine is gimbaled (±4°) in two planes to provide pitch and yaw control by two actuators, while roll control is provided by a Hot gas Reaction Control Motor (HRCM) that ejects hot gases diverted from gas generator of Vikas engine.On inter-stage (1/2U) of PS2  there are two pairs of ullage rockets to maintain positive acceleration during PS1/PS2 staging and also two pairs of retro-rockets to help push away spent stage during PS2/PS3 staging.Second stage also carries some quantity of water in a toroidal tank at its bottom. Water spray is used to cool hot gases from Vikas' gas generator to about 600 °C before entering turbopump. Propellant and water tanks of second stage are pressurized by Helium.

Third stage (PS3)
The third stage uses 7.6 t (7.5 long tons; 8.4 short tons) of HTPB solid propellant and produces a maximum thrust of 250 kN (56,000 lbf). Its burn duration is 113.5 seconds. It has a Kevlar-polyamide fibre case and a submerged nozzle equipped with a flex-bearing-seal gimbaled nozzle with ±2° thrust vector for pitch and yaw control. Roll control is provided by the fourth stage reaction control system (RCS) during thrust phase as well as during combined-coasting phase under which burnt-out PS3 remains attached to PS4.

Fourth stage (PS4)
The fourth stage is powered by regeneratively cooled twin engines, burning monomethylhydrazine (MMH) and mixed oxides of nitrogen (MON). Each pressure fed engine generates 7.4 kN (1,700 lbf) thrust and is gimbaled (±3°) to provide pitch, yaw and roll control during powered flight. Coast phase attitude control is provided by six 50N RCS thrusters. The stage is pressurized by Helium and carries up to 2,500 kg (5,500 lb) of propellant in the PSLV and PSLV-XL and 2,100 kg (4,600 lb) in the PSLV-CA.On PSLV-C29/TeLEOS-1 mission, the fourth stage demonstrated re-ignition capability for the first time which was used in many subsequent flights to deploy payloads in multiple orbits on a single campaign.As a space debris mitigation measure, PSLV fourth stage gets passivated by venting pressurant and propellant vapour after achieving main mission objectives. Such passivation prevents any unintentional fragmentation or explosion due to stored internal energy.

PS4 stage as orbital platform
PS4 has carried hosted payloads like AAM on PSLV-C8, Rubin 9.1/Rubin 9.2 on PSLV-C14 and mRESINS on PSLV-C21. But now, PS4 is being augmented to serve as a long duration orbital platform after completion of primary mission. PS4 Orbital Platform (PS4-OP) will have its own power supply, telemetry package, data storage and attitude control for hosted payloads.On PSLV-C37 and PSLV-C38 campaigns, as a demonstration PS4 was kept operational and monitored for over ten orbits after delivering spacecraft.PSLV-C44 was the first campaign where PS4 functioned as independent orbital platform for short duration as there was no on-board power generation capacity. It carried KalamSAT-V2 as a fixed payload, a 1U cubesat by Space Kidz India based on Interorbital Systems kit.On PSLV-C45 campaign, the fourth stage had its own power generation capability as it was augmented with an array of fixed solar cells around PS4 propellant tank. Three payloads hosted on PS4-OP were, Advanced Retarding Potential Analyzer for Ionospheric Studies (ARIS 101F) by IIST, experimental AIS payload by ISRO and AISAT by Satellize. To function as orbital platform, fourth stage was put in spin-stabilized mode using its RCS thrusters.On PSLV-C53 campaign the PS4-OP was referred as PSLV Orbital Experimental Module (POEM) and it hosted six payloads. POEM was first PSLV fourth stage based orbital platform to be actively stabilised using Helium based cold gas thrusters after the primary mission and stage passivization.

Payload fairing
Payload fairing of PSLV, also referred as its "Heatshield" consists of a conical upper section with spherical nose-cap, a cylindrical middle section and a lower boat-tail section. Weighing 1,182 kilograms (2,606 lb), it has 3.2 meter diameter and 8.3 meter height. It has Isogrid construction and is made out of 7075 aluminum alloy with a 3 mm thick steel nose-cap. The two halves of fairing are separated using a pyrotechnic device based jettisoning system consisting horizontal and lateral separation mechanisms. To protect spacecraft from damage due to excessive acoustic loads during launch, the heatshield interior is lined with acoustic blankets.

Variants
ISRO has envisaged a number of variants of PSLV to cater to different mission requirements. There are currently two operational versions of the PSLV — the core-alone (PSLV-CA) without strap-on motors, and the (PSLV-XL) version, with six extended length (XL) strap-on motors carrying 12 tonnes of HTPB based propellant each. These configurations provide wide variations in payload capabilities up to 3,800 kg (8,400 lb) in LEO and 1,800 kg (4,000 lb) in sun-synchronous orbit.

PSLV-G
The standard or "Generic" version of the PSLV, PSLV-G had four stages using solid and liquid propulsion systems alternately and six strap-on motors (PSOM or S9) with 9 tonne propellant loading. It had capability to launch 1,678 kg (3,699 lb) to 622 km (386 mi) into sun-synchronous orbit. PSLV-C35 was the last operational launch of PSLV-G before its discontinuation.

PSLV-CA
The PSLV-CA, CA meaning "Core Alone", model premiered on 23 April 2007. The CA model does not include the six strap-on boosters used by the PSLV standard variant but two SITVC tanks with Roll Control Thruster modules are still attached to the side of the first stage with addition of two cylindrical aerodynamic stabilizers. The fourth stage of the CA variant has 400 kg (880 lb) less propellant when compared to its standard version. It currently has capability to launch 1,100 kg (2,400 lb) to 622 km (386 mi) Sun-synchronous orbit.

PSLV-XL
PSLV-XL is the upgraded version of Polar Satellite Launch Vehicle in its standard configuration boosted by more powerful, stretched strap-on boosters with 12 tonne propellant load. Weighing 320 t (310 long tons; 350 short tons) at lift-off, the vehicle uses larger strap-on motors (PSOM-XL or S12) to achieve higher payload capability. On 29 December 2005, ISRO successfully tested the improved version of strap-on booster for the PSLV. The first use of PSLV-XL was the launch of Chandrayaan-1 by PSLV-C11. The payload capability for this variant is 1,800 kg (4,000 lb) to Sun-synchronous orbit.

PSLV-DL
PSLV-DL variant has only two strap-on boosters with 12 tonne propellant load on them. PSLV-C44 on 24 January 2019 was the first flight to use PSLV-DL variant of Polar Satellite Launch Vehicle. It is capable of launching 1,257 kg (2,771 lb) to 600 km (370 mi) Sun-synchronous orbit.

PSLV-QL
PSLV-QL variant has four ground-lit strap-on boosters, each with 12 tonnes of propellant. PSLV-C45 on 1 April 2019 was the first flight of PSLV-QL. It has the capacity to launch 1,523 kg (3,358 lb) to 600 km (370 mi) Sun-synchronous orbit.

PSLV-3S (concept)
PSLV-3S was conceived as a three-staged version of PSLV with its six strap-on boosters and second liquid stage removed. The total lift-off mass of PSLV-3S was expected to be 175 tonnes with capacity to place 500 kg in 550 km low Earth orbit.

Launch Profile
PSLV - XL:

The PS1 ignites at T+0 providing 4846  kN of thrust.
Within T+1, 4 out of the 6 boosters ignite on ground, each producing 703 kN of thrust. 7658 kN of total thrust is produced by the combined propulsion of the PSOMs and the PS1.
At around T+23/26, the remaining 2 unlit boosters are air-lit bringing the rocket at its maximum thrust capacity.
At T+1:10, the first 4 ground-lit PSOMs have depleted its propellant and now separates and falls down to the  ocean. The remaining 2 PSOMs and the PS1 continue to burn.
At T+1:35, the remaining 2 PSOMs complete its 70 seconds burn and separate, leaving the rocket in a Core- Alone configuration.
At T+1:50, the PS1 has completed its 110-second burn and it separates and the Vikas Engine inside the PS2 ignites.
The second stage burns for around 130 seconds and around T+4 minutes, the second stages shuts off and separates.
The third stage, which is a solid rocket booster, and burns 80 seconds and then coasts for the remainder of time and around T+8/10 minutes, it separates and the 4th stage ignites to give the rocket a final push into the orbit.
This 4th stage burn is highly variable and depends on the mass and number of payloads and usually is around 500 seconds long. The 4th stage may shut off around T+16/18 minutes followed by the Payload Deployment.

Launch statistics
As of May 22, 2023 the PSLV has made 57 launches, with 54 successfully reaching their planned orbits, two outright failures and one partial failure, yielding a success rate of 94% (or 95% including the partial failure). All launches have occurred from the Satish Dhawan Space Centre, known before 2002 as the Sriharikota Range (SHAR).

Launch system status

Decade-wise summary of PSLV launches:

See also
GSLV Mark II
LVM 3
Comparison of orbital launchers families
Medium-lift launch vehicle, 2,000 to 20,000 kg to LEO
Comparison of orbital rocket engines
Comparison of orbital launch systems
Passage 2:
USA-214
USA-214, also known as Advanced Extremely High Frequency-1 or AEHF-1, is a military communications satellite operated by the United States Air Force. It is the first of six satellites to be launched as part of the Advanced Extremely High Frequency program, which will replace the earlier Milstar system.

Satellite description
The USA-214 satellite was constructed by Lockheed Martin Space, and is based on the A2100 satellite bus. The satellite has a mass of 6,168 kg (13,598 lb) and a design life of 14 years. It will be used to provide super high frequency (SHF) and extremely high frequency (EHF) communications for the United States Armed Forces, as well as those of the United Kingdom, the Netherlands, and Canada.

Launch
Though initially scheduled for launch on 30 July 2010, delays with the launch vehicle pushed flight back to 10 August 2010, and finally to 14 August 2010.USA-214 was launched by United Launch Alliance, aboard an Atlas V 531 flying from Space Launch Complex-41 (SLC-41) at the Cape Canaveral Air Force Station (CCAFS). The launch occurred at 11:07:00 UTC on 14 August 2010, and resulted in the satellite being deployed successfully into a geostationary transfer orbit (GTO) with a perigee of 221 km (137 mi), an apogee of 50,179 km (31,180 mi), and 22.2° Orbital inclination.

Anomaly
The satellite was intended to maneuver from the transfer orbit into which it was launched to its operational geosynchronous orbit by means of a liquid apogee engine (LAE) and several 
Hall-effect thrusters, a process which normally takes 105 days. However, the satellite's Liquid Apogee Engine malfunctioned shortly after ignition on both its first burn on 15 August 2010 and a second attempt on 17 August 2010, and it was declared inoperable.To solve the problem, the perigee altitude was raised to 4,700 km (2,900 mi) using twelve firings of the smaller Reaction Engine Assembly thrusters, originally intended for attitude control during LAE maneuvers. From this altitude, the solar arrays were deployed and the orbit was raised toward the operational orbit over the course of nine months using the 0.27 Newton Hall effect thruster, a form of electric propulsion which is highly efficient, but produces very low thrust and is therefore very slow.
The problem with the liquid apogee engine was later blamed on a piece of cloth accidentally left in a fuel line leading up to the engine while the line was taken apart for repair during the manufacture of the satellite. The cloth was likely placed in the line to prevent impurities from entering the fuel line and did not get removed when the line was put back together.

See also
2010 in spaceflight
Passage 3:
Communications satellite
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications.  Many communications satellites are in geostationary orbit 22,300 miles (35,900 km) above the equator, so that the satellite appears stationary at the same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit, where antennas on the ground have to follow the position of the satellites and switch between satellites frequently.
The high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth.  The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points.  Communications satellites use a wide range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference.

History
Origins
In October 1945, Arthur C. Clarke published an article titled "Extraterrestrial Relays" in the British magazine Wireless World. The article described the fundamentals behind the deployment of artificial satellites in geostationary orbits to relay radio signals. Because of this, Arthur C. Clarke is often quoted as being the inventor of the concept of the communications satellite, and the term 'Clarke Belt' is employed as a description of the orbit.

The first artificial Earth satellite was Sputnik 1 which was put into orbit by the Soviet Union on 4 October 1957. It was developed by Mikhail Tikhonravov and Sergey Korolev, building on work by Konstantin Tsiolkovsky. Sputnik 1 was equipped with an on-board radio transmitter that worked on two frequencies of 20.005 and 40.002 MHz, or 7 and 15 meters wavelength. The satellite was not placed in orbit to send data from one point on Earth to another; the radio transmitter was meant to study the properties of radio wave distribution throughout the ionosphere.  The launch of Sputnik 1 was a major step in the exploration of space and rocket development, and marks the beginning of the Space Age.

Early active and passive satellite experiments
There are two major classes of communications satellites, passive and active. Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, and only a very small amount of the transmitted energy actually reaches the receiver.  Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss, so the signal received on Earth is very, very weak. Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground. Passive satellites were the first communications satellites, but are little used now.
Work that was begun in the field of electrical intelligence gathering at the United States Naval Research Laboratory in 1951 led to a project named Communication Moon Relay. Military planners had long shown considerable interest in secure and reliable communications lines as a tactical necessity, and the ultimate goal of this project was the creation of the longest communications circuit in human history, with the moon, Earth's natural satellite, acting as a passive relay. After achieving the first transoceanic communication between Washington, D.C., and Hawaii on 23 January 1956, this system was publicly inaugurated and put into formal production in January 1960.

The first satellite purpose-built to actively relay communications was Project SCORE,  led by Advanced Research Projects Agency (ARPA) and launched on 18 December 1958, which used a tape recorder to carry a stored voice message, as well as to receive, store, and retransmit messages. It was used to send a Christmas greeting to the world from U.S. President Dwight D. Eisenhower. The satellite also executed several realtime transmissions before the non-rechargeable batteries failed on 30 December 1958 after eight hours of actual operation.The direct successor to SCORE was another ARPA-led project called Courier. Courier 1B was launched on 4 October 1960 to explore whether it would be possible to establish a global military communications network by using "delayed repeater" satellites, which receive and store information until commanded to rebroadcast them. After 17 days, a command system failure ended communications from the satellite.NASA's satellite applications program launched the first artificial satellite used for passive relay communications in Echo 1 on 12 August 1960. Echo 1 was an aluminized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off the satellite from one point on Earth to another. This experiment sought to establish the feasibility of worldwide broadcasts of telephone, radio, and television signals.

More firsts and further experiments
Telstar was the first active, direct relay communications commercial satellite and marked the first transatlantic transmission of television signals. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, and the French National PTT (Post Office) to develop satellite communications, it was launched by NASA from Cape Canaveral on 10 July 1962, in the first privately sponsored space launch.Another passive relay experiment primarily intended for military communications purposes was Project West Ford, which was led by Massachusetts Institute of Technology's Lincoln Laboratory. After an initial failure in 1961, a launch on 9 May 1963 dispersed 350 million copper needle dipoles to create a passive reflecting belt. Even though only about half of the dipoles properly separated from each other, the project was able to successfully experiment and communicate using frequencies in the SHF X band spectrum.An immediate antecedent of the geostationary satellites was the Hughes Aircraft Company's Syncom 2, launched on 26 July 1963. Syncom 2 was the first communications satellite in a geosynchronous orbit. It revolved around the earth once per day at constant speed, but because it still had north–south motion, special equipment was needed to track it. Its successor, Syncom 3, launched on 19 July 1964, was the first geostationary communications satellite. Syncom 3 obtained a geosynchronous orbit, without a north–south motion, making it appear from the ground as a stationary object in the sky.A direct extension of the passive experiments of Project West Ford was the Lincoln Experimental Satellite program, also conducted by the Lincoln Laboratory on behalf of the United States Department of Defense. The LES-1 active communications satellite was launched on 11 February 1965 to explore the feasibility of active solid-state X band long-range military communications. A total of nine satellites were launched between 1965 and 1976 as part of this series.

International commercial satellite projects
In the United States, 1962 saw the creation of the Communications Satellite Corporation (COMSAT) private corporation, which was subject to instruction by the US Government on matters of national policy. Over the next two years, international negotiations led to the Intelsat Agreements, which in turn led to the launch of Intelsat 1, also known as Early Bird, on 6 April 1965, and which was the first commercial communications satellite to be placed in geosynchronous orbit. Subsequent Intelsat launches in the 1960s provided multi-destination service and video, audio, and data service to ships at sea (Intelsat 2 in 1966–67), and the completion of a fully global network with Intelsat 3 in 1969–70. By the 1980s, with significant expansions in commercial satellite capacity, Intelsat was on its way to become part of the competitive private telecommunications industry, and had started to get competition from the likes of PanAmSat in the United States, which, ironically, was then bought by its archrival in 2005.When Intelsat was launched, the United States was the only launch source outside of the Soviet Union, who did not participate in the Intelsat agreements. The Soviet Union launched its first communications satellite on 23 April 1965 as part of the Molniya program. This program was also unique at the time for its use of what then became known as the Molniya orbit, which describes a highly elliptical orbit, with two high apogees daily over the northern hemisphere. This orbit provides a long dwell time over Russian territory as well as over Canada at higher latitudes than geostationary orbits over the equator.

Satellite orbits
Communications satellites usually have one of three primary types of orbit, while other orbital classifications are used to further specify orbital details. MEO and LEO are non-geostationary orbit (NGSO).

Geostationary satellites have a geostationary orbit (GEO), which is 22,236 miles (35,785 km) from Earth's surface. This orbit has the special characteristic that the apparent position of the satellite in the sky when viewed by a ground observer does not change, the satellite appears to "stand still" in the sky.  This is because the satellite's orbital period is the same as the rotation rate of the Earth.  The advantage of this orbit is that ground antennas do not have to track the satellite across the sky, they can be fixed to point at the location in the sky the satellite appears.
Medium Earth orbit (MEO) satellites are closer to Earth. Orbital altitudes range from 2,000 to 36,000 kilometres (1,200 to 22,400 mi) above Earth.
The region below medium orbits is referred to as low Earth orbit (LEO), and is about 160 to 2,000 kilometres (99 to 1,243 mi) above Earth.As satellites in MEO and LEO orbit the Earth faster, they do not remain visible in the sky to a fixed point on Earth continually like a geostationary satellite, but appear to a ground observer to cross the sky and "set" when they go behind the Earth beyond the visible horizon. Therefore, to provide continuous communications capability with these lower orbits requires a larger number of satellites, so that one of these satellites will always be visible in the sky for transmission of communication signals.  However, due to their closer distance to the Earth, LEO or MEO satellites can communicate to ground with reduced latency and at lower power than would be required from a geosynchronous orbit.

Low Earth orbit (LEO)
A low Earth orbit (LEO) typically is a circular orbit about 160 to 2,000 kilometres (99 to 1,243 mi) above the earth's surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes.Because of their low altitude, these satellites are only visible from within a radius of roughly 1,000 kilometres (620 mi) from the sub-satellite point. In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, many satellites are needed if the mission requires uninterrupted connectivity.
Low-Earth-orbiting satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to the ground, do not require as high signal strength (signal strength falls off as the square of the distance from the source, so the effect is considerable). Thus there is a trade off between the number of satellites and their cost.
In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions.

Satellite constellation
A group of satellites working in concert is known as a satellite constellation. Two such constellations, intended to provide satellite phone and low-speed data services, primarily to remote areas, are the Iridium and Globalstar systems. The Iridium system has 66 satellites, which orbital inclination of 86.4° and inter-satellite links provide service availability over the entire surface of Earth. Starlink is a satellite internet constellation operated by SpaceX, that aims for global satellite Internet access coverage.
It is also possible to offer discontinuous coverage using a low-Earth-orbit satellite capable of storing data received while passing over one part of Earth and transmitting it later while passing over another part.  This will be the case with the CASCADE system of Canada's CASSIOPE communications satellite. Another system using this store and forward method is Orbcomm.

Medium Earth orbit (MEO)
A medium Earth orbit is a satellite in orbit somewhere between 2,000 and 35,786 kilometres (1,243 and 22,236 mi) above the earth's surface.  MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 and 8 hours. MEO satellites have a larger coverage area than LEO satellites. A MEO satellite's longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. One disadvantage is that a MEO satellite's distance gives it a longer time delay and weaker signal than a LEO satellite, although these limitations are not as severe as those of a GEO satellite.
Like LEOs, these satellites do not maintain a stationary distance from the earth.  This is in contrast to the geostationary orbit, where satellites are always 35,786 kilometres (22,236 mi) from the earth.
Typically the orbit of a medium earth orbit satellite is about 16,000 kilometres (10,000 mi) above earth. In various patterns, these satellites make the trip around earth in anywhere from 2 to 8 hours.

Examples of MEO
In 1962, the communications satellite, Telstar, was launched. It was a medium earth orbit satellite designed to help facilitate high-speed telephone signals. Although it was the first practical way to transmit signals over the horizon, its major drawback was soon realised. Because its orbital period of about 2.5 hours did not match the Earth's rotational period of 24 hours, continuous coverage was impossible. It was apparent that multiple MEOs needed to be used in order to provide continuous coverage.
In 2013, the first four of a constellation of 20 MEO satellites was launched. The O3b satellites provide broadband internet services, in particular to remote locations and maritime and in-flight use, and orbit at an altitude of 8,063 kilometres (5,010 mi)).

Geostationary orbit (GEO)
To an observer on Earth, a satellite in a geostationary orbit appears motionless, in a fixed position in the sky.  This is because it revolves around the Earth at Earth's own angular velocity (one revolution per sidereal day, in an equatorial orbit).
A geostationary orbit is useful for communications because ground antennas can be aimed at the satellite without their having to track the satellite's motion. This is relatively inexpensive.
In applications that require many ground antennas, such as DirecTV distribution, the savings in ground equipment can more than outweigh the cost and complexity of placing a satellite into orbit.

Examples of GEO
The first geostationary satellite was Syncom 3, launched on 19 August 1964, and used for communication across the Pacific starting with television coverage of the 1964 Summer Olympics. Shortly after Syncom 3, Intelsat I, aka Early Bird, was launched on 6 April 1965 and placed in orbit at 28° west longitude. It was the first geostationary satellite for telecommunications over the Atlantic Ocean.
On 9 November 1972, Canada's first geostationary satellite serving the continent, Anik A1, was launched by Telesat Canada, with the United States following suit with the launch of Westar 1 by Western Union on 13 April 1974.
On 30 May 1974, the first geostationary communications satellite in the world to be three-axis stabilized was launched: the experimental satellite ATS-6 built for NASA.
After the launches of the Telstar through Westar 1 satellites, RCA Americom (later GE Americom, now SES) launched Satcom 1 in 1975.  It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now TBS), HBO, CBN (now Freeform) and The Weather Channel become successful, because these channels distributed their programming to all of the local cable TV headends using the satellite.  Additionally, it was the first satellite used by broadcast television networks in the United States, like ABC, NBC, and CBS, to distribute programming to their local affiliate stations.  Satcom 1 was widely used because it had twice the communications capacity of the competing Westar 1 in America (24 transponders as opposed to the 12 of Westar 1), resulting in lower transponder-usage costs. Satellites in later decades tended to have even higher transponder numbers.By 2000, Hughes Space and Communications (now Boeing Satellite Development Center) had built nearly 40 percent of the more than one hundred satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral, Orbital Sciences Corporation with the Star Bus series, Indian Space Research Organisation, Lockheed Martin (owns the former RCA Astro Electronics/GE Astro Space business), Northrop Grumman, Alcatel Space, now Thales Alenia Space, with the Spacebus series, and Astrium.

Molniya orbit
Geostationary satellites must operate above the equator and therefore appear lower on the horizon as the receiver gets farther from the equator. This will cause problems for extreme northerly latitudes, affecting connectivity and causing multipath interference (caused by signals reflecting off the ground and into the ground antenna).
Thus, for areas close to the North (and South) Pole, a geostationary satellite may appear below the horizon. Therefore, Molniya orbit satellites have been launched, mainly in Russia, to alleviate this problem.
Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected positions during the northern portion of the orbit. (Elevation is the extent of the satellite's position above the horizon. Thus, a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees.)
The Molniya orbit is designed so that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for operation over the targeted region for six to nine hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage.
The first satellite of the Molniya series was launched on 23 April 1965 and was used for experimental transmission of TV signals from a Moscow uplink station to downlink stations located in Siberia and the Russian Far East, in Norilsk, Khabarovsk, Magadan and Vladivostok. In November 1967 Soviet engineers created a unique system of national TV network of satellite television, called Orbita, that was based on Molniya satellites.

Polar orbit
In the United States, the National Polar-orbiting Operational Environmental Satellite System (NPOESS) was established in 1994 to consolidate the polar satellite operations of
NASA (National Aeronautics and Space Administration)
NOAA (National Oceanic and Atmospheric Administration). NPOESS manages a number of satellites for various purposes; for example, METSAT for meteorological satellite, EUMETSAT for the European branch of the program, and METOP for meteorological operations.
These orbits are sun synchronous, meaning that they cross the equator at the same local time each day. For example, the satellites in the NPOESS (civilian) orbit will cross the equator, going from south to north, at times 1:30 P.M., 5:30 P.M., and 9:30 P.M.

Beyond geostationary orbit
There are plans and initiatives to bring dedicated communications satellite beyond geostationary orbits.
NASA proposed LunaNet as a data network aiming to provide a „Lunar Internet for cis-lunar spacecraft and Installations.
The Moonlight Initiative is an equivalent ESA project that is stated to be compatible and providing navigational services for the lunar surface. Both programmes are satellite constellstions of several satellites in various orbits around the Moon.
Other orbits are also planned to be used. Positions in the Earth-Moon-Libration points are also proposed for communication satellites covering the Moon alike communication satellites in geosynchronous orbit cover the Earth. Also, dedicated communication satellites in orbits around Mars supporting different missions on surface and other orbits are considered, such as the Mars Telecommunications Orbiter.

Structure
Communications Satellites are usually composed of the following subsystems:

Communication Payload, normally composed of transponders, antennas, and switching systems
Engines used to bring the satellite to its desired orbit
A station keeping tracking and stabilization subsystem used to keep the satellite in the right orbit, with its antennas pointed in the right direction, and its power system pointed towards the sun
Power subsystem, used to power the Satellite systems, normally composed of solar cells, and batteries that maintain power during solar eclipse
Command and Control subsystem, which maintains communications with ground control stations. The ground control Earth stations monitor the satellite performance and control its functionality during various phases of its life-cycle.The bandwidth available from a satellite depends upon the number of transponders provided by the satellite. Each service (TV, Voice, Internet, radio) requires a different amount of bandwidth for transmission. This is typically known as link budgeting and a network simulator can be used to arrive at the exact value.

Frequency allocation for satellite systems
Allocating frequencies to satellite services is a complicated process which requires international coordination and planning. This is carried out under the auspices of the International Telecommunication Union (ITU).
To facilitate frequency planning, the world is divided into three regions:

Region 1: Europe, Africa, the Middle East, what was formerly the Soviet Union, and Mongolia
Region 2: North and South America and Greenland
Region 3: Asia (excluding region 1 areas), Australia, and the southwest PacificWithin these regions, frequency bands are allocated to various satellite services, although a given service may be allocated different frequency bands in different regions. Some of the services provided by satellites are:

Fixed satellite service (FSS)
Broadcasting satellite service (BSS)
Mobile-satellite service
Radionavigation-satellite service
Meteorological-satellite service

Applications
Telephony
The first and historically most important application for communication satellites was in intercontinental long distance telephony. The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite.  The downlink follows an analogous path.  Improvements in submarine communications cables through the use of fiber-optics caused some decline in the use of satellites for fixed telephony in the late 20th century.
Satellite communications are still used in many applications today. Remote islands such as Ascension Island, Saint Helena, Diego Garcia, and Easter Island, where no submarine cables are in service, need satellite telephones. There are also regions of some continents and countries where landline telecommunications are rare to non existent, for example large regions of South America, Africa, Canada, China, Russia, and Australia. Satellite communications also provide connection to the edges of Antarctica and Greenland. Other land use for satellite phones are rigs at sea, a backup for hospitals, military, and recreation. Ships at sea, as well as planes, often use satellite phones.Satellite phone systems can be accomplished by a number of means. On a large scale, often there will be a local telephone system in an isolated area with a link to the telephone system in a main land area. There are also services that will patch a radio signal to a telephone system. In this example, almost any type of satellite can be used. Satellite phones connect directly to a constellation of either geostationary or low-Earth-orbit satellites. Calls are then forwarded to a satellite teleport connected to the Public Switched Telephone Network .

Television
As television became the main market, its demand for simultaneous delivery of relatively few signals of large bandwidth to many receivers being a more precise match for the capabilities of geosynchronous comsats.  Two satellite types are used for North American television and radio: Direct broadcast satellite (DBS), and Fixed Service Satellite (FSS).
The definitions of FSS and DBS satellites outside of North America, especially in Europe, are a bit more ambiguous. Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America, but use the same linear polarization as FSS-class satellites. Examples of these are the Astra, Eutelsat, and Hotbird spacecraft in orbit over the European continent. Because of this, the terms FSS and DBS are more so used throughout the North American continent, and are uncommon in Europe.
Fixed Service Satellites use the C band, and the lower portions of the Ku band. They are normally used for broadcast feeds to and from television networks and local affiliate stations (such as program feeds for network and syndicated programming, live shots, and backhauls), as well as being used for distance learning by schools and universities, business television (BTV), Videoconferencing, and general commercial telecommunications. FSS satellites are also used to distribute national cable channels to cable television headends.
Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band. The Intelsat Americas 5, Galaxy 10R and AMC 3 satellites over North America provide a quite large amount of FTA channels on their Ku band transponders.
The American Dish Network DBS service has also recently used FSS technology as well for their programming packages requiring their SuperDish antenna, due to Dish Network needing more capacity to carry local television stations per the FCC's "must-carry" regulations, and for more bandwidth to carry HDTV channels.
A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes (usually 18 to 24 inches or 45 to 60 cm in diameter). Direct broadcast satellites generally operate in the upper portion of the microwave Ku band. DBS technology is used for DTH-oriented (Direct-To-Home) satellite TV services, such as DirecTV, DISH Network and Orby TV in the United States, Bell Satellite TV and Shaw Direct in Canada, Freesat and Sky in the UK, Ireland, and New Zealand and DSTV in South Africa.
Operating at lower frequency and lower power than DBS, FSS satellites require a much larger dish for reception (3 to 8 feet (1 to 2.5 m) in diameter for Ku band, and 12 feet (3.6 m) or larger for C band).  They use linear polarization for each of the transponders' RF input and output (as opposed to circular polarization used by DBS satellites), but this is a minor technical difference that users do not notice. FSS satellite technology was also originally used for DTH satellite TV from the late 1970s to the early 1990s in the United States in the form of TVRO (Television Receive Only) receivers and dishes. It was also used in its Ku band form for the now-defunct Primestar satellite TV service.
Some satellites have been launched that have transponders in the Ka band, such as DirecTV's SPACEWAY-1 satellite, and Anik F2. NASA and ISRO have also launched experimental satellites carrying Ka band beacons recently.Some manufacturers have also introduced special antennas for mobile reception of DBS television. Using Global Positioning System (GPS) technology as a reference, these antennas automatically re-aim to the satellite no matter where or how the vehicle (on which the antenna is mounted) is situated.  These mobile satellite antennas are popular with some recreational vehicle owners.  Such mobile DBS antennas are also used by JetBlue Airways for DirecTV (supplied by LiveTV, a subsidiary of JetBlue), which passengers can view on-board on LCD screens mounted in the seats.

Radio broadcasting
Satellite radio offers audio broadcast services in some countries, notably the United States. Mobile services allow listeners to roam a continent, listening to the same audio programming anywhere.
A satellite radio or subscription radio (SR) is a digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals.

Amateur radio
Amateur radio operators have access to amateur satellites, which have been designed specifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters, and are generally accessed by amateurs equipped with UHF or VHF radio equipment and highly directional antennas such as Yagis or dish antennas. Due to launch costs, most current amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a limited number of brief contacts at any given time. Some satellites also provide data-forwarding services using the X.25 or similar protocols.

Internet access
After the 1990s, satellite communication technology has been used as a means to connect to the Internet via broadband data connections. This can be very useful for users who are located in remote areas, and cannot access a broadband connection, or require high availability of services.

Military
Communications satellites are used for military communications applications, such as Global Command and Control Systems. Examples of military systems that use communication satellites are the MILSTAR, the DSCS, and the FLTSATCOM of the United States, NATO satellites, United Kingdom satellites (for instance Skynet), and satellites of the former Soviet Union. India has launched its first Military Communication satellite GSAT-7, its transponders operate in UHF, F, C and Ku band bands. Typically military satellites operate in the UHF, SHF (also known as X-band) or EHF (also known as Ka band) frequency bands.

Data collection
Near-ground in situ environmental monitoring equipment (such as weather stations, weather buoys, and radiosondes), may use satellites for one-way data transmission or two-way telemetry and telecontrol. It may be based on a secondary payload of a weather satellite (as in the case of GOES and METEOSAT and others in the Argos system) or in dedicated satellites (such as SCD). The data rate is typically much lower than in satellite Internet access.

See also
Passage 4:
ATS-6
ATS-6 (Applications Technology Satellite-6)  was a NASA experimental satellite, built by Fairchild Space and Electronics Division It has been called the world's first educational satellite as well as world's first experimental Direct Broadcast Satellite as part of the Satellite Instructional Television Experiment between NASA and Indian Space Research Organisation (ISRO). It was launched May 30, 1974, and decommissioned July 1979. At the time of launch, it was the most powerful telecommunication satellite in orbit. ATS-6 carried no fewer than 23 different experiments, and introduced several breakthroughs. It was the first 3-axis stabilized spacecraft in geostationary orbit. It was also the first to use experimentally with some success electric propulsion in geostationary orbit. It also carried several particle physics experiments, including the first heavy ion detector in geostationary orbit.
During its five-year life, ATS-6 transmitted connection programming to various countries, including India, the United States and other regions. The vehicle also conducted air traffic control tests, was used to practice satellite-assisted search and rescue techniques, carried an experimental radiometer subsequently carried as a standard instrument aboard weather satellites, and pioneered direct broadcast TV.
ATS-6 was a precursor to many technologies still in use today on geostationary spacecraft: large deployable antenna, 3-axis attitude control with slewing capabilities, antenna pointing through RF sensing, electric propulsion, meteorological radiometer in geostationary orbit, and direct to home broadcasting. It is also possible that ATS-6 was a forerunner of the large ELINT satellites such as Mentor.

Launch
ATS-6 was launched on May 30, 1974, by a Titan III-C launch vehicle. The spacecraft was inserted directly in the geosynchronous orbit. This reduced the on-board fuel requirements to less than 40 kilograms (88 lb) (for a total mass at launch of nearly 1,400 kilograms (3,100 lb)). The highly accurate orbit insertion further lowered the amount of fuel required for final positioning to 9 kilograms (20 lb). This enabled a life extension from the original 2 year to 5 years, even accounting for the premature failure of the electric propulsion subsystem (the station-keeping fuel requirement being around 1.6 kilograms per year (3.5 lb/a)).

Structure, power subsystem and antenna
One of the major innovations of ATS-6 was an in-flight deployable antenna of more than 9 metres (30 ft) in diameter. The antenna reflector was furled during launch under the launch vehicle fairing, and was deployed in orbit much like an umbrella. The antenna reflector was built from 48 aluminum ribs, supporting a metallized Dacron mesh. The antenna feeds (in C, S, L, UHF and VHF bands) were placed on the spacecraft body, facing the antenna reflector, and linked to the antenna and the solar panels masts by a carbon-fiber reinforced plastic (CFRP) truss. The solar panels were rigidly mounted on two deployable masts. They were of hemi-cylinder shape, thus providing a relatively constant power (595 W beginning of life). Electric power was supplied during eclipses by two Nickel cadmium batteries of 15-A·h capacity, powering a regulated 30.5-V bus. The satellite dimensions in orbit were 15.8-metre (52 ft) width by 8.2-metre (27 ft) height.
This deployable antenna parabola was designed and developed by Lockheed Missiles and Space Company (LMSC), now Lockheed Martin, under subcontract to Fairchild Aerospace, after several years of small study contracts at LMSC.  The program manager at LMSC was GKC (Colin) Campbell.  The deployment of the reflector was initiated by pyrotechnically operated SQUIB cable cutters.  Deployment time was on the order of 2.5 seconds producing 3,400 newton-metres (2,500 lb⋅ft) of torque at the spacecraft interface.  The reflector surface was designed for optimal operation at S-Band frequencies. It weighed 83 kilograms (182 lb) at launch and stowed into a toroidal volume (doughnut shaped) approximately 1.8 metres (6 ft) in diameter and 250 millimetres (10 in) thick.  Three models were fabricated, the STM or structural test model, the F reflector and the G reflector.  The STM was destroyed by Fairchild shortly after the program was finished and the F model was launched with the spacecraft in 1972.  The G model sat unprotected in the Farchild parking lot for several years before it was donated to the Smithsonian.  Bill Wade, the assistant program manager and test manager on the program supported The Smithsonian in the restoration by providing a complete set of drawings and specifications and visited the Silver Hill facility to provide technical guidance.At the time of launch it was the largest parabolic surface launched into orbit.

Three-axis stabilisation
ATS-6 has been the first geostationary satellite with three-axis stabilization and pointing., This subsystem was capable of a highly accurate pointing (better than 0.1° through the inertial measurement units, down to 0.002° by using a radio-frequency interferometer.). Furthermore, the satellite was able to follow low earth orbit satellites through slewing, by tracking the low earth-orbit satellite through an S-band RF sensing. The system was also able to perform orbitography of the tracked satellite, and was a precursor to the operational system TDRSS.
This highly advanced (for the time) pointing subsystem used earth and sun sensors, a star tracker pointed to the pole star, Polaris, and three inertial sensors. The sensor measurements were fed to two digital computers (nominal and redundant), as well to a back-up analog computer. It was also possible to orient the satellite by using radio-frequency sensors.  Actuators were three momentum wheels, and hot gas (hydrazine mono-propellant) thrusters. One of the momentum wheels having failed in July 1975, an alternative scheme was developed, allowing station-keeping with the two remaining wheels and thrusters.

Electric propulsion
ATS-6 was equipped with two electric thrusters based on the acceleration of cesium ions, that were to be used for North-South Station Keeping. This subsystem development followed earlier failed attempts on the previous ATS spacecraft. Each of the thrusters had a mass of 16 kilograms (35 lb), used 150 W of electric power, and produced a thrust of 4 newton-metres (3.0 lbf⋅ft), with a specific impulse of 2500s. The on-board supply of cesium would have been sufficient for 4400 hours of thrust. Unfortunately, both thrusters failed prematurely, one after 1 hour of operation, one after 95 hours. However, some of the experiments objectives could be met, such as the measurement of the effective thrust, the absence of any interference with the radio-frequency payloads (from 150 MHz to 6 GHz), no cesium redeposition on the critical parts of the payload (such as the radiometer), and the correct neutralisation of the spacecraft versus its environment.

Payload
Radiometer
A radiometer was on board ATS-6, mounted on the earth-facing panel. This instrument was (for the time) of very high resolution. It operated on two channels: infra-red (10.5 to 12.5 µm) and visible light (0.55 to 0.75 µm). Images taken with the radiometer covered the whole earth disk, with a resolution of 1,200 lines of 2,400 pixels each (11-kilometre (6.8 mi) square pixel in infra-red, and 5.5-kilometre (3.4 mi) square in visible light). The IR detector was passively cooled at 115K, and the visible light detector maintained at 300K. A complete image of earth's disk was transmitted to ground every 25 minutes. Several hundreds images were taken and transmitted, until a mechanical component of the radiometer failed, two and a half months after launch.

Telecommunication experiments
The main mission of ATS-6 was to demonstrate the feasibility of direct-to-home (DTH) television broadcasting. To this end, in addition to the high-gain antenna, the spacecraft payload was able to receive in any of the VHF, C, S and L-bands, and to transmit in S-band (2 GHz) through a 20-W solid state transmitter, in L-band (1650 MHz) at 40W, in UHF (860 MHz) at 80W (which was used for the Satellite Instructional Television Experiment (SITE)), and with a TWTA-based transmitter of 20 W in C-band (4 GHz). The antenna produced two spots on earth of 400,000 square kilometres (150,000 sq mi) each, in which the TV broadcast could be received with 3 metres (9.8 ft) diameter antennas. This payload was first used over the United States for tele-education and tele-medicine experiments, from August 1974 to May 1975 as part of the HET, or Health, Education, Telecommunications experiment developed jointly by NASA and the US Department of Health, Education, & Welfare (now DHHS). The spacecraft was then moved over the geo-stationary arc from 94 °W to 35 °E, in collaboration with the Indian Space Agency (ISRO), who had deployed in India more than 2500 receive ground stations. The move of the satellite from 94 degrees West to 35 degrees East, a journey of 12,800 kilometres (8,000 mi), was actioned from the ground station at Rosman North Carolina  This relocation involved 2 rocket burns of the onboard rocket motor. The 2nd burn lasting 5 hours 37 minutes and 17 seconds. The longest burn ever done by a chemical rocket in space at that time. A tele-education programme was started – Satellite Instructional Television Experiment or SITE – and run for one year. During the experiment, a receive station was offered by the Indian Government to Arthur C. Clarke, who was living in Sri Lanka. This experiment was highly successful, and encouraged ISRO to start building an operational program, with the Indian spacecraft  INSAT IB (launched 1983). After the SITE experiment, the satellite was brought back over the United States, and served notably as a data-relay and tracking satellite for low-orbit spacecraft such as Nimbus 6, and for the Apollo-Soyuz flight.

Particle physics experiments
Several particle physics experiments were on board ATS-6. The most significant measured low energy protons (from 25 keV to 3.6 MeV), as well as detected heavy ions (up to 6 MeV). This latter experiment allowed to detect the first heavy ions (Z > 6) with an energy  E > 4 MeV, in geostationary orbit.

Propagation experiments
Finally, ATS-6 embarked several radio beacons, which allowed to measure electromagnetic propagation properties of the atmosphere at 13, 18, 20 and 30 GHz.

Decommissioning
By June 30, 1979, only one of the four ATS-6 station keeping thrusters was working, and was showing signs of unreliability. This thruster was used to move ATS-6 out of geostationary orbit to an orbit several hundred kilometers higher. This was to vacate the geostationary slot for the next satellite.

See also
1974 in spaceflight
Applications Technology Satellite
Passage 5:
FedSat
FedSat (Australia's 'Federation Satellite'; sometimes FedSat 1; COSPAR 2002-056B, SATCAT 27598) was an Australian scientific research satellite launched from Tanegashima Space Center, Japan by a NASDA H-IIA launch vehicle  on 14 December 2002 (NASDA is now merged with JAXA). The satellite was developed by the Cooperative Research Centre for Satellite Systems, a cooperative made up of several universities, commercial organisations and government bodies. The ground station was at the Institute for Telecommunications Research, part of the University of South Australia, near Adelaide. Since 2005 it was operated by the Australian Department of Defence.

Payloads
The satellite had six payloads, as given below:

Communications Payload: A collection of three components (UHF transponder, Ka-band transponder and base-band processor) used to perform several experiments in satellite communications.
High Performance Computing Experiment: A reconfigurable computer based on a Xilinx XQR4062 FPGA, the first of its kind to be used in space.
GPS Payload: A Global Positioning System receiver built by NASA. Conceived especially for ionospheric studies between GPS constellation levels and FedSat orbit.
NewMag Payload: A magnetometer built by the University of Newcastle, Australia, used to take measurements of the Earth's magnetic field near its poles.
Star Camera: An experimental star camera built by the University of Stellenbosch, used to determine the position of the satellite in space by analysing images of surrounding stars.
Compact Disk: A nickel "master" disk "cultural time capsule" with tracks including Paul Kelly's performance of the song he co-wrote with Kev Carmody, "From Little Things, Big Things Grow", and recorded statements from several hundred Australian school children about how they imagined a future Australia and its place in the Asia-Pacific.The satellite platform, comprising the structural/thermal components, power system, attitude control system, onboard computer and groundlink, was originally developed in the United Kingdom by Space Innovations Limited. It was later completed along with integration of payloads in Canberra, Australia.

Declared Dead
The spacecraft's battery failed in May 2007 and the mission has been terminated, after lasting 18 months longer than expected.
Passage 6:
NOAA-4
NOAA-4, also known as ITOS-G was a weather satellite operated by the National Oceanic and Atmospheric Administration (NOAA). It was part of a series of satellites called ITOS, or improved TIROS. NOAA-4 was launched on a Delta rocket on November 15, 1974. The launch carried two other satellites: AMSAT-OSCAR 7 and Intasat. It remained operational for 1463 days until it was deactivated by NOAA on November 18, 1978.
Passage 7:
Hans K. Ziegler
Hans K. Ziegler (March 1, 1911, Munich, Germany – December 11, 1999 Colts Neck Township, New Jersey, United States) was a pioneer in the field of communication satellites and the use of photovoltaic solar cells as a power source for satellites.

Life
Hans Ziegler was born in Munich, Germany. There, he studied at the Technische Hochschule, which is today the Technische Universität München (TUM), and began his career as Wissenschaftlicher Assistant (Scientific Assistant). Following that, he was a researcher in German industry for ten years. During the Second World War, he worked for the company Rosental Selb in Bavaria on high tension porcelain.
In 1947, he came to the US with Wernher von Braun under Operation Paperclip, by means of which the USA gained Nazi engineers and scientists. He went to the US Army Signal Corps' Laboratories in Fort Monmouth, New Jersey, and became a US citizen in 1954.
Ziegler's work in the US was very influential in the development of military electronics, especially in the electronics for the early phases of the US space program. During the thirty years he worked as an engineer in the field of electronics and electrical engineering in the research and development department of the U.S. Army in Fort Monmouth, N.J. (from 1947 to 1976), he held the top position of Chief Scientist for 12 years. In Fort Monmouth, he worked as a Scientific Consultant, Assistant Director of Research, Director of the Astro-Electronics Division and Chief Scientist (1959). After the Army was restructured, he became Deputy for Science and Chief Scientist of the US Army Electronics Command in 1963 and Director of the US Army Electronics Technology & Devices Laboratory from 1971 until his retirement.
In May 1954, after examining the solar cells of Daryl Chapin, Calvin Fuller and Gerald Pearson at Bell Laboratories, Ziegler wrote, "Future development [of the silicon solar cell] may well render it into an important source of electrical power [as] the roofs of all our buildings in cities and towns equipped with solar [cells] would be sufficient to produce this country's entire demand for electrical power."Referring to silicon solar cells, he said to the head of the U. S. Signal Corps, General James O'Connell, at a meeting in September 1955, "In fact, in the long run, mankind has no choice but to turn to the sun if it wants to survive."He and his team produced a report on the prospects for application of this technique in the field of communication and they named the supply of energy for artificial satellites as the most important application. He knew that he was not the first to suggest this application. For example, the science fiction author, Arthur C. Clarke had already made this suggestion in 1945, but without having a concrete technology for it at that time.
Ziegler participated in the development of the first planned satellites. The first satellite,
Explorer 1, still went into space without solar cells, since it was a quick, less-than-ideal solution after the start of the Sputnik to show the American public that America's scientists could also start a satellite. The actual scheduled satellite project, Project Vanguard, successfully put a satellite named Vanguard I in orbit around Earth on March 17, 1958.
Over the objections of the Navy, which still thought that solar cells were not a mature technology, this satellite had four solar cells on its outer hull, due to the persistent work of Ziegler, which powered the instruments and performed their duties reliably for more than seven years. After this success, solar cells were established as the energy supply for satellites. He was also involved with the development of the first communication satellite in the world, SCORE, which was started in 1958.
He was awarded the Meritorious Civilian Service Award by the US Department of Defense in 1963 as a " world pioneer in communications satellites and solar energy systems to power satellites". When he retired in 1977, he was decorated with the highest award of the Army for "exceptional civilian service".
Ziegler was the author of many technical papers, a member of the IEEE, and represented the US, in military and civilian matters, in many national and international committees. In 1958, he was a member of the US delegation to the International Geophysical Year in Moscow, USSR, and in 1964, he gave advice on the scientific activities in Antarctica and at the South Pole, under the direction of the US National Science Foundation.
Ziegler's wife Friederike died in 1996. He last lived in Colts Neck Township, New Jersey and died at the age of 88 on December 11, 1999. He was survived by his daughters, Christine Griffith and Friederike Meindl, and his son, Hans.

See also
Solar power
Solar panel
Active solar
Photovoltaic components, projects and howtos
Passage 8:
TDRS-6
TDRS-6, known before launch as TDRS-F, is an American communications satellite, of first generation, which is operated by NASA as part of the Tracking and Data Relay Satellite System. It was constructed by TRW, and is based on a custom satellite bus which was used for all seven first generation TDRS satellites.

History
TDRS-F was deployed from Space Shuttle Endeavour during the STS-54 mission in 1993. Endeavour was launched from Launch Complex 39B at the Kennedy Space Center, at 13:59:30 UTC on 13 January 1993. TDRS-F was deployed from Endeavour around six hours after launch, and was raised to geosynchronous orbit by means of an Inertial Upper Stage.

Deployment
The two-stage solid-propellent Inertial Upper Stage made two burns. The first stage burn occurred shortly after deployment from Endeavour, and placed the satellite into a geosynchronous transfer orbit (GTO). At 02:26 UTC on 14 January 1993, it reached apogee, and the second stage fired, placing TDRS-F into geosynchronous orbit. At this point, it received its operational designation, TDRS-6.

Operation
In 1994, it was placed at a longitude 46.0° West of the Greenwich Meridian, to serve as an on-orbit spare. In 1996, it was moved to 47.0° West, where it remained until 2005, when it was repositioned to 174.0° West, where, as of August 2009, it was used to provide communications with spacecraft in Earth orbit, such as the International Space Station (ISS) and spacecraft bringing astronauts to the ISS.

See also
List of TDRS satellites
Passage 9:
GSAT-7
GSAT-7 or INSAT-4F is a multi-band military communications satellite developed by the Indian Space Research Organisation. The Indian Navy is the user of the multi-band communication spacecraft, which has been operational since September 2013. According to defense experts, the satellite will enable the navy to extend its blue water capabilities and stop relying on foreign satellites like Inmarsat, which provide communication services to its ships.

Satellite
GSAT-7, the multi-band communication satellite named Rukmini carries the payloads in UHF, C band and Ku band. It is the first dedicated military communication satellite (unlike earlier dual use satellites) built by ISRO that will provide services to the Indian Armed Forces with the main user being the Indian Navy. Its procured launch cost has been put at ₹480 crore, with the satellite costing ₹185 crore. Cost of whole project per Memorandum of Understanding with ISRO was ₹950 crores.The multiple-band spacecraft will be used exclusively by the Navy to shore up secure, real-time communications among its warships, submarines, aircraft and land systems. GSAT-7/ INSAT-4F is said to significantly improve the country's naval operations around the world. 
GSAT 7 satellite carrying payloads operating in UHF, S, C and Ku bands, had a lift-off mass of 2,650 kilograms (5,840 lb) and is based on ISRO's 2,000 kilograms (4,400 lb) class satellite bus I-2K with some new technological elements, including the antennae. After a flight of almost 34 minutes, the satellite was injected into a geosynchronous transfer orbit (GTO) of 249-kilometre (155 mi) perigee, 35,929-kilometre (22,325 mi) apogee and an inclination of 3.5 degree with respect to the equator.ISRO launched a second satellite, GSAT-7A for Indian Air Force on 19 December 2018 on its Geosynchronous Satellite Launch Vehicle (GSLV-F11).

Launch
The satellite was launched early on 30 August 2013 atop an Ariane 5 ECA rocket from Kourou, French Guiana.India's first dedicated military satellite was put into a geosynchronous orbit, about 36,000 kilometres (22,000 mi) above Earth, five days after it was launched after three orbit-raising manoeuvres from ISRO's Master Control Facility at Hassan in Karnataka. The 2.5-tonne spacecraft's antennae, including the ultra high frequency Helix antenna were deployed before it was stabilised on its three-axis in the orbit. All of the on-board transponders were switched on successfully on September 18, 2013

Capability
Rukmini will provide networking capabilities to various Indian Naval assets. During Theater-level Readiness and Operational Exercise (Tropex) in the Bay of Bengal in 2014, Rukmini was able to network about 60 ships and 75 aircraft seamlessly. Rukmini has a nearly 2,000 nautical mile 'footprint' over the Indian Ocean Region.

Replacement
The Indian Navy placed an order for GSAT-7R on June 11, 2019. GSAT-7R is expected to eventually replace GSAT-7.

See also
Indian military satellites
GSAT-7A
GSAT
Indian National Satellite System
List of Indian satellites

Answer the question based on the given passages. Only give me the answer and do not output any other words.

Question: What is the experimental satellite which was the forerunner to the communication satellite of the operator of GSAT-7 called?



Answer: ATS - 6 (Applications Technology Satellite - 6) ATS-6