Communication satellites provide the bridges for a number of new, specialized markets in commercial and private telecommunications and create ties between nations. In their more than 40 years existence, they have become fixed satellite communications (FSC). Eventually, mobile satellite communications (MSC), navigation and determination came to serve navies, ground and air forces worldwide and, for economic reasons, also provided commercial MSC. MSC has been used for the past 35 years, particularly because ocean-going vessels have become dependent on mobile satellite services (MSS) for their commercial and safety communications. Although their use in aircraft and land vehicles started before ships, because of many unsuccessful experiments and projects, they have had to follow the evident lead of Inmarsat maritime MSC service and engineering.

The modified ship's mobile Earth stations (MES) are today implemented on land (road or railway) vehicles and aircraft for all civil and military applications, including remote or rural locations and industrial onshore and offshore installations. The GPS, GLONASS and other new global navigation satellite systems (GNSS) provide precise positioning data for vessels, aircraft and land vehicles. Because of the need for enhanced services, these systems will be augmented with satellite communications, navigation and surveillance (CNS) facilities.

Evolution of Satellite Communications
The first known mention of devices resembling rockets is said to have been made by Archytus of Tarentumin, who invented in 426 B.C. a steam-driven reaction jet rocket engine that flew a wooden pigeon around his room. Devices similar to rockets were also used in China during the year 1232. In the meantime, human space travel had to wait almost a millennium, until the time of Sir Isaac Newton, when it was understood how a projectile launched at the right speed could enter the Earth's orbit. Finally, the twentieth century came with its great progress and the historical age of space communications began to unfold. Russian scientist Konstantin Tsiolkovsky (1857ñ1935) published a scientific book on virtually every aspect of space rocketing. He propounded the theoretical basis of liquid propelled rockets, put forward ideas for multi-stage launchers and manned space vehicles, space walks by astronauts and a large platform system that could be assembled in space for normal human habitation. A little later, the American Robert H. Goddard launched in 1926 the first liquid propelled rocket engine.

At the same time, between the two world wars, many Russian and former USSR scientists and military constructors used the experience of Tsiolkovsky to design many models of rockets and to build the first reactive weapons, particularly rockets called "Katyusha," which the Soviet Red Army used against German troops at the beginning of World War II. Thus, towards the end of the Second World War, many German military contractors started experiments to use their series V1 and V2 rockets to attack targets in England. In October 1945, the British radar expert and writer of science fiction books Arthur C. Clarke proposed that only three communications satellites in geostationary earth orbit (GEO) could provide near global coverage for TV broadcasting.


Figure 1 (A) Sputnik 1 and (B) Explorer 1 (Courtesy of Never Beyond Reach (A) and NASA (B)).

The work on rocket techniques in Russia and the former USSR was extended after the Patriotic War. The satellite era began when the Soviet Union shocked the world with the launch of the first artificial satellite, Sputnik I, on 4 October 1957 (see Figure 1). This launch marked the beginning of the use of artificial Earth satellites to extend and enhance the horizon for radio communications, navigation, weather monitoring and remote sensing. That was soon followed on 31 January 1958 by the launch of the US satellite, Explorer I, also shown in the figure. The development of satellite communications and navigation signified the beginning of the space race. The most significant progress in space technology was on 12 April 1961, when Yuri Gagarin, an officer of the former USSR Air Force, lifted off aboard the Vostok I spaceship from Bailout Cosmodrome and made the first historical manned orbital flight in space.

Figure 2 (A) Telstar 1 and (B) Intelsat 1 (courtesy of Satellite Communications).

Experiments with Active Communications Satellites
After the launch of Sputnik I, a sustained effort by the US to catch up with the USSR started. This was reflected in the first active communications satellite named SCORE, launched on 18 December 1958 by the US Air Force. The second satellite, Courier, was launched on 4 October 1960 in high-inclined elliptical orbit (HEO) with its perigee at approximately 900 km and its apogee at approximately 1,350 km using solar cells and a frequency of 2 GHz. The maximum emission length was between 10 and 15 min for every successive passage. The third such satellite was Telstar I, designed by Bell Telephone Laboratories experts and launched by NASA on 10 July 1962 in HEO configuration, with its perigee at approximately 100 km and apogee at approximately 6,000 km (see Figure 2). The plane of the orbit was inclined at approximately 45° to the equator and the duration of the orbit was approximately 2.5 hours. Because of the rotation of the Earth, the track of the satellite as seen from the Earth stations appeared to be different on every successive orbit. Thus, over the next two years, Telstar I was joined by Relay I, Telstar II and Relay II. All of these satellites had the same problem: they were visible to widely separated LES for only a few short daily periods, so a number of LES were needed to provide full-time service.

On the other hand, GEO satellites can be seen 24 hours a day from approximately 40 percent of the Earth's surface, providing direct and continuous links between large numbers of widely separated locations. The world's first GEO satellite, Syncom I, was launched by NASA on 14 February 1963, which presented a prerequisite for the development of MSC systems. This satellite failed during launch, but Syncom II and III were successfully placed in orbit on 26 July 1963 and 19 July 1964, respectively. Both satellites used the military band of 7.360 GHz for the uplink and 1.815 GHz for the downlink. Using FM or PSK mode, the transponder could support two carriers at a time for full duplex operation. Syncom II was used for direct TV transmission from the Tokyo Olympic Games in August 1964.

These spacecraft operated successfully until some time after 1965 and marked the end of the experimental period. Technically, all these satellites were being used primarily for fixed satellite service (FSS) experimental communications, which were used only to relay signals from fixed Earth stations (FES) at several locations around the world. Hence, one FES was actually located aboard the large transport vessel USNS Kingsport, anchored in Honolulu, HI. The ship had been modified by the US Navy to carry a 9.1 m parabolic antenna for tracking the Syncom satellites. The antenna dish was protected, like present mobile antennas, from the marine environment by an inflatable Dacron radome, requiring access to the 3-axis antenna through an air lock within the ship.

The Kingsport ship terminal was the world's first true MES and could be considered the first ship Earth station (SES). The ITU authorized special frequencies for Syncom communication experiments at approximately 1.8 GHz for the downlink (space to Earth) and approximately 7.3 GHz for the uplink (Earth to space). This project and trial was an unqualified success, proving only the practicality of the GEO system for satellite communications but, because of the large size of the Kingsport SES antenna, some experts in the 1960s concluded that MSC at sea would never really be practical. However, it was clear that the potential to provide a high quality line-of-sight path from any ship to the land and vice-versa, via the satellite communications transponder, existed at this time.

Intelsat was founded in August 1964 as a global FSS operator. The first commercial GEO satellite was Early Bird (renamed as Intelsat I) developed by Comsat for Intelsat (see Figure 2). It was launched on 6 April 1965 and remained active until 1969. Routing operations between the US and Europe began on 28 June 1965, a date that should be recognized as the birthday of commercial FSS. The satellite had 2 × 25 MHz transponder bandwidths, the first with two Rx uplinks (centered at 6.301 GHz for Europe and 6.390 GHz for the US) and the second with two Tx downlinks (centered at 4.081 GHz for Europe and 4.161 GHz for the US), with a maximum transmission power of 10 W for each Tx. This GEO system used several LES located within the US and Europe; the modern era of satellite communications had begun.

In the meantime, considerable progress in satellite communications had been made by the former USSR, the first of which, the Molniya I (Lightning) satellite, was launched at the same time as Intelsat I on 25 April 1965. These satellites were put into an HEO, very different to those used by the early experiments and were used for voice, fax and video transmission from central FES near Moscow to a large number of relatively small receive only stations. In other words, that time became the era of development of the international and regional FSS with the launch of many communications spacecraft in the USSR, US, UK, France, Italy, China, Japan, Canada and other countries. At first, all satellites were put in GEO, but later HEO and polar Earth orbits (PEO) were proposed, because such orbits would be particularly suitable for use with MES at high latitudes. The next step was the development of MSC for maritime and later for land and aeronautical applications. The last step has to be the development of the non-GEO systems of Little and Big Low Earth Orbits (LEO), HEO and other GEO constellations for new MSS for personal and other applications.

Early Progress in Mobile Satellite Communications and Navigation
The first successful experiments were carried out in aeronautical MSC. The Pan Am airlines and NASA program, in 1964, succeeded in achieving aeronautical satellite links, using the Syncom III GEO spacecraft. The frequencies used for experiments were the VHF band (117.9 to 136 MHz), which had been allocated for aeronautical MSC (AMSC). The first satellite navigation system, called Transit, was developed by the US Navy and became operational in 1964. The great majority of the satellite navigation receivers has worked with this system since 1967 and has already attracted about 100,000 mobile and fixed users worldwide. The former USSR equivalent of the Transit was the Cicada system developed almost at the same time.

Following the first AMSC experiments, the Radiocommunications Subcommittee of the Intergovernmental Maritime Consultative Organization (IMCO), as early as 1966, discussed the applicability of an MSC system to improve maritime radiocommunications. This led to further discussions at the 1967 ITU WARC for the maritime MSC (MMSC), where it was recommended that a detailed plan and study be undertaken of the operational requirements and technical aspects of systems by the IMCO and CCIR administrations.

A little while later, the International Civil Aviation Organization (ICAO) performed a similar role to that of IMCO (described earlier), by the fostering interest in AMSS for air traffic control (ATC) purposes. The majority of the early work was carried out by the applications of space technology to the requirement of aviation (Astra) technical panel. This panel considered the operational requirements for and the design of suitable systems and much time was spent considering the choice of the frequency band. At the 1971 WARC, 2 × 14 MHz of spectrum, contiguous with the MMSC spectrum, was allocated at L-band for safety use. Hence, the work of the Astra panel led to the definition of the Aerosat project, which aimed to provide an independent and near global AMSC, navigation and surveillance system for ATC and airline operational control (AOC) purposes.

The Aerosat project unfortunately failed because, whereas both the ICAO authority and world airlines of the International Air Transport Association (IATA) agreed on the operational benefits to be provided by such a system, there was disagreement concerning the scale, the form and potential cost to the airlines. Finally, around 1969, the project failed for economic reasons.

The first experiment with Land MSC (LMSC) started in 1970 with the MUSAT regional satellite program in Canada for the North American continent. However, in the meantime, it appeared that the costs would be too high for individual countries and that some sort of international cooperation was necessary to make MSS globally available. In 1971, the ICAO recommended an international program of research, development and system evaluation. Before all, L-band was allocated for distress and safety satellite communications and 2 × 4 MHz of frequency spectrum for MMSS and AMSS needs, by the WARC held in 1971. According to the recommendations, Canada, FAA of the US and ESA signed a memorandum of understanding in 1974 to develop the Aerosat system, which would be operated in the VHF and L-bands. Although Aerosat was scheduled to be launched in 1979, the program was cancelled in 1982 because of financial problems. The first truly global MSC system started with the launch of the three Marisat satellites in 1976 by Comsat General. Marisat was a GEO spacecraft, containing a hybrid payload: one transponder for US Navy ship's terminals operating on a government UHF frequency band and another one for commercial merchant fleets utilizing newly-allocated MMSC frequencies. The first official mobile satellite telephone call in the world was established between the vessel-oil platform "Deep Sea Explorer," which was operated close to the coast of Madagascar, and the Phillips Petroleum Co. in Bartlesville, OK, on 9 July 1976, using AOR CES and GEO of the Marisat system.

The IMCO convened an international conference in 1973 to consider the establishment of an international organization to operate the MMSC system. The international conference met in London two years later to set up the structure of the international maritime satellite (Inmarsat) organization. The Inmarsat convention and operating agreements were finalized in 1976 and opened for signature by states wishing to participate. On 16 July 1979, these agreements entered into force and were signed by 29 countries. The Inmarsat officially went into operation on 1 February 1982 with worldwide maritime services in the Pacific, Atlantic and Indian Ocean regions at first, using only Inmarsat-A SES. Moreover, the Marecs-1 B2A satellite was developed by nine European states in 1984 and launched for the experimental MCS system Prodat, serving all mobile applications.

In 1985, the Cospas-Sarsat satellite SAR system was declared operational. Three years later, the international Cospas-Sarsat program agreement was signed by Canada, France, the US and the former USSR. In 1992, the global maritime distress and safety system (GMDSS), developed by the International Maritime Organization (IMO), began its operational phase. Hence, in February 1999, the GMDSS became fully operational as an integration of Radio MF/HF/VHF (DSC), Inmarsat and Cospas-Sarsat LEOSAR and GEOSAR systems.

The Transit system was switched off in 1996 to 2000 after more than 30 years of reliable service. By then, the US Department of Defense was fully converted to the new Global Positioning System (GPS). However, the GPS service could not have the market to itself; the ex-Soviet Union developed a similar system called Global Navigation Satellite System (GLONASS) in 1988. While both the Transit or Cicada system provides intermittent two-dimensional (latitude and longitude when altitude is known) position fixes every 90 minutes on average and was best suited to marine navigation, the GPS or GLONASS system provides continuous position and speed in all three dimensions, equally effective for navigation and tracking at sea, on land and in the air.

The US Federal Communications Commission (FCC) worked toward private development of the radio determination satellite system (RDSS), which would combine position fixing with short messaging. In 1985, Inmarsat developed the Standard-C system and later examined the feasibility of adding navigational capability. The ESA satellite navigation concept, called Navsat, dates back to the 1980s, but the proposed project has received relatively little attention and even less financial support. In 1988, the US-based company Qualcomm established the OmniTRACS service for mobile messaging and tracking. Soon after, Eutelsat promoted a very similar system named EuroTRACS integrated with GPS and the Emsat communications system.

At the beginning of this millennium, three satellite augmentation systems (SAS) were developed for communications, navigation and surveillance (CNS): the American WAAS, Japanese MTSAT and European EGNOS. Those three operable and future projected SAS will augment the two military Global Satellite Navigation Systems (GNSS), the US GPS and the Russian GLONASS and make them suitable for safety critical applications, such as flying aircraft or navigating ships through narrow channels and port approaches. The last project of the European Union is Galileo second generation of GNSS, which should be operational in 2015.

Finally, several interesting projects are developing in Europe, Japan and the US for new mobile and fixed multimedia stratospheric communication platform (SCP) systems powered by fuel or the sun's energy and manned or unmanned aircraft or airships equipped with transponders and antenna systems at an altitude of approximately 20 to 25 km. At the end of this race, a new mobile satellite revolution is coming, whereby anyone can carry a personal handheld telephone using simultaneously satellite or cellular/dual systems at sea, in the car, in the air, on the street, in rural areas, in the desert, that is to say everywhere and in all positions. These integrated systems will soon be implemented, with new stratospheric platform wireless systems using aircraft or airships.


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Stojce Dimov Ilcev received two BEng degrees in mobile radio engineering and maritime navigation from the faculty of Maritime Studies at Kotor of Podgorica University, Montenegro. He also received his BSc Eng (Hons) degree in maritime communications from the Maritime Faculty of Rijeka University, Croatia, and his MSc degree in electrical engineering from the faculty of electrical engineering, telecommunication department of Skopie University, Macedonia, in 1971, 1986 and 1994, respectively. He obtained his PhD degree from the telecommunication department of the faculty of electrical engineering "Nikola Tesla" of Belgrade University, Serbia, in 2000. Prof. Ilcev is currently Director for establishment National Space Institute (NSI) at Durban University of technology (DUT), South Africa. His research concentrated over 45 years on all aspects of Radio and Satellite Communications, Navigation and Surveillance (CNS) systems, networks and technology