Satellite Technology: Principles and Applications

Preface

The word ‘satellite’ is a household name today. It sounds very familiar to all of us irrespective of our educational and professional background. It is no longer the prerogative of a few select nations and is not a topic of research and discussion that is confined to the premises of big academic institutes and research organizations. Today, it is not only one of the main subjects taught at undergraduate, graduate and postgraduate level; it is the bread and butter for a large percentage of electronics, communications and IT professionals working for academic institutes, science and technology organizations and industry. Most of the books on satellite technology and its applications cover only communications-related applications of satellites, with either occasional or no reference to other important applications, which include remote sensing, weather forecasting, scientific, navigational and military applications. Also, space encyclopedias mainly cover the satellite missions and their applications with not much information on the technological aspects.

Satellite Technology: Principles and Applications is a concise and yet comprehensive reference book on the subject of satellite technology and its applications, covering in one volume both communications as well as non-communication applications. The second edition has an additional chapter on Earth stations. The chapter on military satellites has been comprehensively revised by including several new topics, notably space weapons. A number of new topics have been included in other chapters as well to make the book more comprehensive and up-to-date covering all the developmental technologies and trends in the field of satellites. The intended audience for this book includes undergraduate and graduate level students and electronics, telecommunications and IT professionals looking for a compact and comprehensive reference book on satellite technology and its applications.

The book is logically divided into two parts, namely satellite technology fundamentals covered in Chapters 1 to 8, followed by satellite applications in Chapters 9 to 14. The first introductory chapter begins with a brief account of the historical evolution of satellite technology, different types of satellite missions and areas of application of satellite technology. The next two chapters focus on orbital dynamics and related topics. The study of orbits and trajectories of satellites and satellite launch vehicles is the most fundamental topic of the subject of satellite technology and also perhaps the most important one. It is important because it gives an insight into the operational aspects of this wonderful piece of technology. An understanding of the orbital dynamics would put us on a sound footing to address issues like types of orbits and their suitability for a given application, orbit stabilization, orbit correction and station-keeping, launch requirements and typical launch trajectories for various orbits, Earth coverage and so on. These two chapters are well supported by the required mathematics and design illustrations.

After addressing the fundamental issues related to the operational principle of satellites, the dynamics of the satellite orbits, the launch procedures and various in-orbit operations, the focus in Chapter 4 is on satellite hardware, irrespective of its intended application. Different subsystems of a typical satellite and issues like the major functions performed by each one of these subsystems along with a brief discussion of their operational considerations are covered in this chapter.

After an introduction to the evolution of satellites, satellite orbital dynamics and hardware in the first four chapters, the focus shifts to topics that relate mainly to communication satellites in the three chapters thereafter. The topics covered in the first of the three chapters, Chapter 5, mainly include communication fundamentals with particular reference to satellite communication followed by multiple access techniques in the next chapter. Chapter 7 focuses on satellite link design related aspects.

Satellite applications are in the second part of the book in Chapters 9 to 14. Based on the intended applications, the satellites are broadly classified as communication satellites, navigation satellites, weather forecasting satellites, Earth observation satellites, scientific satellites and military satellites. We intend to focus on this ever-expanding vast arena of satellite applications. The emphasis is on the underlying principles, the application potential, their contemporary status and future trends.

Chapter 8 is on Earth station design and discusses the different types of Earth stations used for varied applications, Earth station architecture and design considerations, key performance parameters of an Earth station, Earth station testing, and some representative Earth stations.

Communication satellites account for more than 80% of the total number of satellites in operation. This is one of the most widely exploited applications of satellites. The first chapter on satellite applications covers all the communication-related applications of satellites, which mainly include satellite telephony, satellite radio, satellite television and data broadcasting services. Major international communication satellite missions have also been described at length. The future trends in the field of communication satellites are also highlighted at the end of the chapter.

Remote sensing is a technology used for obtaining information about the characteristics of an object through an analysis of the data acquired from it at a distance. Satellites play an important role in remote sensing. In Chapter 10, various topics related to remote sensing satellites are covered, including their principle of operation, payloads on board these satellites and their use to acquire images, processing and analysis of these images using various digital imaging techniques, and finally interpreting these images for studying various features of Earth for varied applications. We also introduce some of the major remote sensing satellite systems used for the purpose and the recent trends in the field towards the end of the chapter.

The use of satellites for weather forecasting and prediction of related phenomena has become indispensable. There is a permanent demand from the media with the requirement of short term weather forecasts for the general public, reliable prediction of the movements of tropical cyclones to allow re-routing of shipping and a preventive action in zones through which hurricanes pass. Meteorological information is also of considerable importance for the conduct of military operations such as reconnaissance missions. In Chapter 11, we take a closer look at various aspects related to evolution, operation and use of weather satellites. Some of the major weather satellite missions are covered towards the end of the chapter. Like previous chapters on satellite applications, this chapter also contains a large number of illustrative photographs.

Navigation is the art of determining the position of a platform or an object at any specified time. Satellite-based navigation systems represent a breakthrough in this field, which has revolutionized the very concept and application potential of navigation. These systems have grown from a relatively humble beginning as a support technology to that of a critical player used in the vast array of economic, scientific, civilian and military applications. Chapter 12 gives a brief outline of the development of satellite-based navigation systems and a descriptive view of the fundamentals underlying the operation of the GPS and the GLONASS navigation systems, their functioning and applications. The GALILEO navigation system and other developmental trends are also covered in the chapter.

The use of satellites for scientific research has removed the constraints like attenuation and blocking of radiation by the Earth’s atmosphere, gravitational effects on measurements and difficulty in making in situ studies imposed by the Earth-based observations. Moreover, space-based scientific research is global by nature and helps to give an understanding of the various phenomena at a global level. Chapter 13 focuses on the scientific applications of satellites covering in detail the contributions made by these satellites to Earth sciences, solar physics, astronomy and astrophysics.

Military systems of today rely heavily on the use of satellites both during war as well as in peacetime. Many of the military satellites perform roles similar to their civilian counterparts, mainly including telecommunication services, weather forecasting, navigation and Earth observation applications. Though some satellite missions are exclusively military in nature, many contemporary satellite systems are dual-use satellites that are used both for military and civilian applications. In the concluding chapter of the book, we deliberate on various facets of military satellites related to their development and application potential. We begin the chapter with an overview of military satellites, followed by a description of various types of military satellites depending upon their intended application and a detailed discussion on space weapons.

As an extra resource, the companion website for our book contains a complete compendium of the features and facilities of satellites and satellite launch vehicles from past, present and planned futuristic satellite missions for various applications. Please go to www.wiley.com/go/maini. Colour versions of some of the figures within the book are also available.

The motivation to write this book, and the selection of topics covered, lay in the absence of any other book which in one volume covers all the important aspects of satellite technology and its applications. There are space encyclopaedias that provide detailed information and technical data on the satellites launched by various countries for various applications, but contain virtually no information on the principles of satellite technology. There are a host of books on satellite communications, which discuss satellite technology with a focus on communications-related applications. We have made an honest attempt to offer to our intended audience, mainly electronics, telecommunication and IT professionals, a concise yet comprehensive reference book covering in one volume both the technology as well as the application-related aspects of satellites.

Anil K. Maini

Varsha Agrawal

Laser Science and Technology Centre

India

Part I

Satellite Technology

1

Introduction to Satellites and their Applications

The word ‘Satellite’ is a household name today. It sounds so familiar to everyone irrespective of educational and professional background. It is no longer the prerogative of a few select nations and not a topic of research and discussion that is confined to the premises of big academic institutes and research organizations. It is a subject of interest and discussion not only to electronics and communication engineers, scientists and technocrats; it fascinates hobbyists, electronics enthusiasts and to a large extent, everyone.

In the present chapter, the different stages of evolution of satellites and satellite launch vehicles will be briefly discussed, beginning with the days of hot air balloons and sounding rockets of the late 1940s/early 1950s to the contemporary status in the beginning of the 21st century.

1.1 Ever-expanding Application Spectrum

What has made this dramatic transformation possible is the manifold increase in the application areas where the satellites have been put to use. The horizon of satellite applications has extended far beyond providing intercontinental communication services and satellite television. Some of the most significant and talked about applications of satellites are in the fields of remote sensing and Earth observation. Atmospheric monitoring and space exploration are the other major frontiers where satellite usage has been exploited a great deal. Then there are the host of defence related applications, which include secure communications, navigation, spying and so on.

The areas of application are multiplying and so is the quantum of applications in each of those areas. For instance, in the field of communication related applications, it is not only the long distance telephony and video and facsimile services that are important; satellites are playing an increasing role in newer communication services such as data communication, mobile communication, etc. Today, in addition to enabling someone to talk to another person thousands of miles away from the comfort of home or bringing live on television screens cultural, sporting or political events from all over the globe, satellites have made it possible for all to talk to anyone anywhere in the world, with both people being able to talk while being mobile. Video conferencing, where different people at different locations, no matter how far the distance is between these locations, can hold meetings in real time to exchange ideas or take important decisions, is a reality today in big establishments. The Internet and the revolutionary services it has brought are known to all of us. Satellites are the backbone of all these happenings.

A satellite is often referred to as an ‘orbiting radio star’ for reasons that can be easily appreciated. These so-called orbiting radio stars assist ships and aircraft to navigate safely in all weather conditions. It is interesting to learn that even some categories of medium to long range ballistic and cruise missiles need the assistance of a satellite to hit their intended targets precisely. The satellite-based global positioning system (GPS) is used as an aid to navigate safely and securely in unknown territories.

Earth observation and remote sensing satellites give information about the weather, ocean conditions, volcanic eruptions, earthquakes, pollution and health of agricultural crops and forests. Another class of satellites keeps watch on military activity around the world and helps to some extent in enforcing or policing arms control agreements.

Although mankind is yet to travel beyond the moon, satellites have crossed the solar system to investigate all planets. These satellites for astrophysical applications have giant telescopes on board and have sent data that has led to many new discoveries, throwing new light on the universe. It is for this reason that almost all developed nations including the United States, the United Kingdom, France, Japan, Germany, Russia and major developing countries like India have a full fledged and heavily funded space programme, managed by organizations with massive scientific and technical manpower and infrastructure.

1.2 What is a Satellite?

A satellite in general is any natural or artificial body moving around a celestial body such as planets and stars. In the present context, reference is made only to artificial satellites orbiting the planet Earth. These satellites are put into the desired orbit and have payloads depending upon the intended application.

The idea of a geostationary satellite originated from a paper published by Arthur C. Clarke, a science fiction writer, in the Wireless World magazine in the year 1945. In that proposal, he emphasized the importance of this orbit whose radius from the centre of Earth was such that the orbital period equalled the time taken by Earth to complete one rotation around its axis. He also highlighted the importance of an artificial satellite in this orbit having the required instrumentation to provide intercontinental communication services because such a satellite would appear to be stationary with respect to an observer on the surface of Earth. Though the idea of a satellite originated from the desire to put an object in space that would appear to be stationary with respect to Earth’s surface, thus making possible a host of communication services, there are many other varieties of satellites where they need not be stationary with respect to an observer on Earth to perform the intended function.

A satellite while in the orbit performs its designated role throughout its lifetime. A communication satellite (Figure 1.1) is a kind of repeater station that receives signals from ground, processes them and then retransmits them back to Earth. An Earth observation satellite (Figure 1.2) is a photographer that takes pictures of regions of interest during its periodic motion. A weather forecasting satellite (Figure 1.3) takes photographs of clouds and monitors other atmospheric parameters, thus assisting the weatherman in making timely and accurate forecasts.

A satellite could effectively do the job of a spy in the case of some military satellites (Figure 1.4) meant for the purpose or of an explorer when suitably equipped and launched for astrophysical applications (Figure 1.5).

Figure 1.1 Communication satellite

Figure 1.2 Earth observation satellite

Figure 1.3 Weather forecasting satellite (Courtesy: NOAA and NASA)

Figure 1.4 Military satellite (Courtesy: Lockheed Martin)

Figure 1.5 Scientific satellite (Courtesy: NASA and STScl)

1.3 History of the Evolution of Satellites

It all began with an article by Arthur C. Clarke published in October 1945 issue of Wireless World, which theoretically proposed the feasibility of establishing a communication satellite in a geostationary orbit. In that article, he discussed how a geostationary orbit satellite would look static to an observer on Earth within the satellite’s coverage, thus providing an uninterrupted communication service across the globe. This marked the beginning of the satellite era. The scientists and technologists started to look seriously at such a possibility and the revolution it was likely to bring along with it.

1.3.1 Era of Hot Air Balloons and Sounding Rockets

The execution of the mission began with the advent of hot air balloons and sounding rockets used for the purpose of aerial observation of planet Earth from the upper reaches of Earth’s atmosphere. The 1945–1955 period was dominated by launches of experimental sounding rockets to penetrate increasing heights of the upper reaches of the atmosphere. These rockets carried a variety of instruments to carry out their respective mission objectives.

A-4 (V-2) rockets used extensively during the Second World War for delivering explosive warheads attracted the attention of the users of these rockets for the purpose of scientific investigation of the upper atmosphere by means of a high altitude rocket. With this started the exercise of modifying these rockets so that they could carry scientific instruments. The first of these A-4 rockets to carry scientific instruments to the upper atmosphere was launched in May 1946 (Figure 1.6). The rocket carried an instrument to record cosmic ray flux from an altitude of 112 km. The launch was followed by several more during the same year.

The Soviets, in the meantime, made some major modifications to A-4 rockets to achieve higher performance levels as sounding rockets. The last V-2A rocket (the Soviet version of the modified A-4 rocket), made its appearance in 1949. It carried a payload of 860 kg and attained a height of 212 km.

Figure 1.6 First A-4 rocket to be launched (Courtesy: NASA)

Figure 1.7 Sputnik-1 (Courtesy: NASA)

1.3.2 Launch of Early Artificial Satellites

The United States and Russia were the first two countries to draw plans for artificial satellites in 1955. Both countries announced their proposals to construct and launch artificial satellites. It all happened very quickly. Within a span of just two years, Russians accomplished the feat and the United States followed quickly thereafter.

Sputnik-1 (Figure 1.7) was the first artificial satellite that brought the space age to life. Launched on 4 October 1957 by Soviet R7 ICBM from Baikonur Cosmodrome, it orbited Earth once every 96 minutes in an elliptical orbit of 227 km × 941 km inclined at 65.1° and was designed to provide information on density and temperature of the upper atmosphere. After 92 successful days in orbit, it burned as it fell from orbit into the atmosphere on 4 January 1958.

Sputnik-2 and Sputnik-3 followed Sputnik-1. Sputnik-2 was launched on 3 November 1957 in an elliptical orbit of 212 km × 1660 km inclined at 65.33°. The satellite carried an animal, a female dog named Laika, in flight. Laika was the first living creature to orbit Earth. The mission provided information on the biological effect of the orbital flight. Sputnik-3, launched on 15 May 1958, was a geophysical satellite that provided information on Earth’s ionosphere, magnetic field, cosmic rays and meteoroids. The orbital parameters of Sputnik-3 were 217 km (perigee), 1864 km (apogee) and 65.18° (orbital inclination).

The launches of Sputnik-1 and Sputnik-2 had both surprised and embarrassed the Americans as they had no successful satellite launch to their credit till then. They were more than eager to catch up. Explorer-1 (Figure 1.8) was the first satellite to be successfully launched by the United States. It was launched on 31 January 1958 by Jupiter-C rocket from Cape Canaveral. The satellite orbital parameters were 360 km (perigee), 2534 km (apogee) and 33.24° (orbital inclination). Explorer’s design was pencil-shaped, which allowed it to spin like a bullet as it orbited the Earth. The spinning motion provided stability to the satellite while in orbit. Incidentally, spin stabilization is one of the established techniques of satellite stabilization. During its mission, it discovered that Earth is girdled by a radiation belt trapped by the magnetic field.

Figure 1.8 Explorer-1 (Courtesy: NASA/JPL-Caltech)

Figure 1.9 Vanguard-1 (TV-4) (Courtesy: NASA)

After the successful launch of Explorer-1, there followed in quick succession the launches of Vanguard-1 on 5 February 1958, Explorer-2 on 5 March 1958 and Vanguard-1 (TV-4) on 17 March 1958 (Figure 1.9). The Vanguard-1 and Explorer-2 launches were unsuccessful. The Vanguard-1 (TV-4) launch was successful. It was the first satellite to employ solar cells to charge the batteries. The orbital parameters were 404 km (perigee), 2465 km (apogee) and 34.25° (orbit inclination). The mission carried out geodetic studies and revealed that Earth was pear-shaped.

1.3.3 Satellites for Communications, Meteorology and Scientific Exploration – Early Developments

Soviet experiences with the series of Sputnik launches and American experiences with the launches of the Vanguard and Explorer series of satellites had taken satellite and satellite launch technology to sufficient maturity. The two superpowers by then were busy extending the use of satellites to other possible areas such as communications, weather forecasting, navigation and so on. The 1960–1965 period saw the launches of experimental satellites for the above-mentioned applications. 1960 was a very busy year for the purpose. It saw the successful launches of the first weather satellite in the form of TIROS-1 (television and infrared observation satellite) (Figure 1.10) on 1 April 1960, the first experimental navigation satellite Transit-1B on 13 April 1960, the first experimental infrared surveillance satellite MIDAS-2 on 24 May 1960, the first experimental passive communications satellite Echo-1 (Figure 1.11) on 14 August 1960 and the active repeater communications satellite Courier-1B (Figure 1.12) on 4 October 1960. In addition, that year also saw successful launches of Sputnik-5 and Sputnik-6 satellites in August and December respectively.

While the TIROS-1 satellite with two vidicon cameras on board provided the first pictures of Earth, the Transit series of satellites was designed to provide navigational aids to the US Navy with positional accuracy approaching 160 m. The Echo series of satellites, which were aluminized Mylar balloons acting as passive reflectors to be more precise, established how two distantly located stations on Earth could communicate with each other through a space-borne passive reflector was followed by Courier-1B, which established the active repeater concept. The MIDAS (missile defense alarm system) series early warning satellites established beyond any doubt the importance of surveillance from space-borne platforms to locate and identify the strategic weapon development programme of an adversary. Sputnik-5 and Sputnik-6 satellites further studied the biological effect of orbital flights. Each spacecraft had carried two dog passengers.

Figure 1.10 TIROS-1 (Courtesy: NASA)

Figure 1.11 Echo-1 (Courtesy: NASA)

1.3.4 Non-geosynchronous Communication Satellites: Telstar and Relay Programmes

Having established the concept of passive and active repeater stations to relay communication signals, the next important phase in satellite history was the use of non-geostationary satellites for intercontinental communication services. The process was initiated by the American Telephone and Telegraph (AT&T) seeking permission from the Federal Communications Commission (FCC) to launch an experimental communications satellite. This gave birth to the Telstar series of satellites. The Relay series of satellites that followed the Telstar series also belonged to the same class.

Figure 1.12 Courier-1B (Courtesy: US Army)

Figure 1.13 Telstar-1 (Courtesy: NASA)

In the Telstar series, Telstar-1 (Figure 1.13), the first true communications satellite and also the first commercially funded satellite, was launched on 10 July 1962, followed a year later by Telstar-2 on 7 May 1963. Telstar-2 had a higher orbit to reduce exposure to the damaging effect of the radiation belt. The Telstar-1 with its orbit at 952 km (perigee) and 5632 km (apogee) and an inclination of 44.79° began the revolution in global TV communication from a non-geosynchronous orbit. It linked the United States and Europe.

Telstar-1 was followed by Relay-1 (NASA prototype of an operational communication satellite) launched on 13 December 1962. Relay-2, the next satellite in the series, was launched on 21 January 1964. The orbital parameters of Relay-1 were 1322 km (perigee), 7439 km (apogee) and 47.49° (inclination). The mission objectives were to test the transmissions of television, telephone, facsimile and digital data.

It is worthwhile mentioning here that both the Telstar and Relay series of satellites were experimental vehicles designed to discover the limits of satellite performance and were just a prelude to much bigger events to follow. For instance, through Telstar missions, scientists came to discover how damaging the radiation could be to solar cells. Though the problem has been largely overcome through intense research, it still continues to be the limiting factor on satellite life.

1.3.5 Emergence of Geosynchronous Communication Satellites

The next major milestone in the history of satellite technology was Arthur C. Clarke’s idea becoming a reality. The golden era of geosynchronous satellites began with the advent of the SYNCOM (an acronym for synchronous communication satellite) series of satellites developed by the Hughes Aircraft Company. This compact spin-stabilized satellite was first shown at the Paris Air Show in 1961. SYNCOM-1 was launched in February 1963 but the mission failed shortly. SYNCOM-2 (Figure 1.14), launched on 26 July 1963, became the first operational geosynchronous communication satellite. It was followed by SYNCOM-3, which was placed directly over the equator near the international date line on 19 August 1964. It was used to broadcast live the opening ceremonies of the Tokyo Olympics. That was the first time the world began to see the words ‘live via satellite’ on their television screens.

Figure 1.14 SYNCOM-2 (Courtesy: NASA)

Another significant development during this time was the formation of INTELSAT (International Telecommunications Satellite Organization) in August 1964 with COMSAT (Communication Satellite Corporation) as its operational arm. INTELSAT achieved a major milestone with the launch of the Intelsat-1 satellite, better known as ‘Early Bird’ (Figure 1.15), on 5 April 1965 from Cape Canaveral. Early Bird was the first geostationary communications satellite in commercial service. It went into regular service in June 1965 and provided 240 telephone circuits for connectivity between Europe and North America. Though designed for an expected life span of only 18 months, it remained in service for more than three years.

Figure 1.15 Intelsat-1 (Reproduced by permission of © Intelsat)

Figure 1.16 Molniya series satellite

While the Americans established their capability in launching communications satellites through launches of SYNCOM series of satellites and Early Bird satellite during the 1960– 1965 era, the Soviets did so through their Molniya series of satellites beginning April 1965. The Molniya series of satellites (Figure 1.16) were unique in providing uninterrupted 24 hours a day communications services without being in the conventional geostationary orbit. These satellites pursued highly inclined and elliptical orbits, known as the Molniya orbit (Figure 1.17), with apogee and perigee distances of about 40 000 km and 500 km and orbit inclination of 65°. Two or three such satellites aptly spaced apart in the orbit provided uninterrupted service. Satellites in such an orbit with a 12 hour orbital period remained over the countries of the former Soviet bloc in the northern hemisphere for more than 8 hours. The Molniya-1 series was followed later by the Molniya-2 (in 1971) and the Molniya-3 series (in 1974).

Figure 1.17 Molniya orbit

1.3.6 International Communication Satellite Systems

The Intelsat-1 satellite was followed by the Intelsat-2 series of satellites. Four Intelsat-2 satellites were launched in a span of one year from 1966 to 1967. The next major milestone vis-à-vis communication satellites was achieved with the Intelsat-3 series of satellites (Figure 1.18) be-coming fully operational. The first satellite in the Intelsat-3 series was launched in 1968. These satellites were positioned over three main oceanic regions, namely the Atlantic, the Pacific and the Indian Oceans, and by 1969 they were providing global coverage for the first time. The other new concept tried successfully with these satellites was the use of a de-spun antenna structure, which allowed the use of a highly directional antenna on a spin-stabilized satellite. The satellites in the Intelsat-1 and Intelsat-2 series had used omnidirectional antennas.

Figure 1.18 Intelsat-3 (Reproduced by permission of © Intelsat)

The communication satellites’ capabilities continued to increase with almost every new venture. With the Intelsat-4 satellites (Figure 1.19), the first of which was launched in 1971, the satellite capacity got a big boost. Intelsat-4A series introduced the concept of frequency reuse. The frequency re-use feature was taken to another dimension in the Intelsat-5 series with the use of polarization discrimination. While frequency re-use, i.e. use of the same frequency band, was possible when two footprints were spatially apart, dual polarization allowed the reuse of the same frequency band within the same footprint. The Intelsat-5 satellites (Figure 1.20), the first of which was launched in 1980, used both C band and Ku band transponders and were three-axis stabilized. The satellite transponder capacity has continued to increase through the Intelsat-6, Intelsat-7 and Intelsat-8 series of satellites launched during the 1980s and 1990s. Intelsat-9 and Intelsat-10 series were launched in the first decade of the new millennium.

Figure 1.19 Intelsat-4 (Reproduced by permission of © Intelsat)

The Russians have also continued their march towards development and launching of communication satellites after their success with the Molniya series. The Raduga series (International designation: Statsionar-1), the Ekran series (international designation: Statsionar-T), shown in Figure 1.21, and the Gorizont series (international designation: Horizon) are the latest in communication satellites from the Russians. All three employ the geostationary orbit.

1.3.7 Domestic Communication Satellite Systems

Beginning in 1965, the Molniya series of satellites established the usefulness of a domestic communications satellite system when it provided communications connectivity to a large number of republics spread over the enormous land-mass of the former Soviet Union. Such a system was particularly attractive to countries having a vast territory. Canada was the first non-Soviet country to have a dedicated domestic satellite system with the launch of the Anik-A series of satellites (Figure 1.22), beginning in 1972. The capabilities of these satellites were subsequently augmented with the successive series of Anik satellites, named Anik-B (beginning 1978), Anik-C (beginning 1982), Anik-D (also beginning 1982), Anik-E (beginning 1991) and Anik-F (beginning 2000).

Figure 1.20 Intelsat-5 (Reproduced by permission of © Intelsat)

Figure 1.21 Ekran series

The United States began its campaign for development of domestic satellite communication systems with the launch of Westar satellite in 1974, Satcom satellite in 1975 and Comstar satellite in 1976. Satcom was also incidentally the first three-axis body-stabilized geostationary satellite. These were followed by many more ventures. Europe began with the European communications satellite (ECS series) and followed it with the Eutelsat-II series (Figure 1.23) and Eutelsat-W series of satellites.

Indonesia was the first developing nation to recognize the potential of a domestic communication satellite system and had the first of the Palapa satellites placed in orbit in 1977 to link her scattered island nation. The Palapa series of satellites have so far seen three generations named Palapa-A (beginning 1977), Palapa-B (beginning 1984) and Palapa-C (beginning 1991).

India, China, Saudi Arabia, Brazil, Mexico and Japan followed suit with their respective domestic communication satellite systems. India began with the INSAT-1 series of satellites in 1981 and has already entered the fourth generation of satellites with the INSAT-4 series. INSAT-4CR (Figure 1.24), the latest in the series, was launched in September 2007. Arabsat, which links the countries of the Arab League, has also entered the third generation with the Arabsat-3 series of satellites.

Figure 1.22 Anik-A (Courtesy: Telesat Canada)

Figure 1.23 Eutelsat-II (Reproduced by permission of © Eutelsat)

1.3.8 Satellites for other Applications also made Rapid Progress

The intention to use satellites for applications other than communications was very evident, even in the early stages of development of satellites. A large number of satellites were launched mainly by the former Soviet Union and the United States for meteorological studies, navigation, surveillance and Earth observation during the 1960s.

Figure 1.24 INSAT-4A (Courtesy: ISRO)

Making a modest beginning with the TIROS series, meteorological satellites have come a long way both in terms of the number of satellites launched for the purpose and also advances in the technology of sensors used on these satellites. Both low Earth as well as geostationary orbits have been utilized in the case of satellites launched for weather forecasting applications. Major non-geostationary weather satellite systems that have evolved over the years include the TIROS (television and infrared observation satellite) series and the Nimbus series beginning around 1960, the ESSA (Environmental Science Service Administration) series (Figure 1.25) beginning in 1966, the NOAA (National Oceanic and Atmospheric Administration) series beginning in 1970, the DMSP (Defense Meteorological Satellite Program) series initiated in 1965 (all from the United States), the Meteor series beginning in 1969 from Russia and the Feng Yun series (FY-1 and FY-3) beginning 1988 from China. Major meteorological satellites in the geostationary category include the GMS (geostationary meteorological satellite) series from Japan since 1977, the GOES (geostationary operational environmental satellite) series from the United States (Figure 1.26) since 1975, the METEOSAT (meteorological satellite) series from Europe since 1977 (Figure 1.27), the INSAT (Indian satellite) series from India since 1982 (Figure 1.28) and the Feng Yun series (FY-2) from China since 1997.

Figure 1.25 ESSA satellites (Courtesy: NASA)

Figure 1.26 GOES satellite (Courtesy: NOAA and NASA)

Sensors used on these satellites have also seen many technological advances, both in types and numbers of sensors used as well as in their performance levels. While early TIROS series satellites used only television cameras, a modern weather forecasting satellite has a variety of sensors with each one having a dedicated function to perform. These satellites provide very high resolution images of cloud cover and Earth in visible and infrared parts of the spectrum and thus help generate data on cloud formation, tropical storms, hurricanes, likelihood of forest fires, temperature profiles, snow cover and so on.

Remote sensing satellites have also come a long way since the early 1970s with the launch of the first of the series of Landsat satellites that gave detailed attention to various aspects of observing the planet Earth from a spaced platform. In fact, the initial ideas of having satellites for this purpose came from the black and white television images of Earth beneath the cloud cover as sent by the TIROS weather satellite back in 1960, followed by stunning observations revealed by Astronaut Gordon Cooper during his flight in a Mercury capsule in 1963 when he claimed to have seen roads, buildings and even smoke coming out of chimneys from an altitude of more than 160 km. His claims were subsequently verified during successive exploratory space missions.

Figure 1.27 METEOSAT series (Reproduced by permission of © EUMETSAT)

Figure 1.28 INSAT series (Courtesy: ISRO)

Over the years, with significant advances in various technologies, the application spectrum of Earth observation or remote sensing satellites has expanded very rapidly from just terrain mapping called cartography to forecasting agricultural crop yield, forestry, oceanography, pollution monitoring, ice reconnaissance and so on. The Landsat series from the United States, the SPOT (satellite pour l’observation de la terre) series from France and the IRS (Indian remote sensing satellite) series from India are some of the major Earth observation satellites. The Landsat programme, beginning with Landsat-I in 1972, has at the time of writing this book progressed to Landsat-7 (Figure 1.29) as the latest in the series, which was launched in 1999. The SPOT series has also come a long way, beginning with SPOT-1 in 1986 to SPOT-5 (Figure 1.30) launched 2002. IRS series launches began in 1988 with the launch of IRS-1A and the most recent satellites launched in the series are IRS-P6 called Resourcesat 1 (Figure 1.31) launched in 2003 and IRS-P5 called Cartosat 1 launched in 2005. Cartosat 2 and Cartosat 2A launched in 2007 and 2008 respectively are other remote sensing satellites of India. Sensors on board modern Earth observation satellites include high resolution TV cameras, multispectral scanners (MSS), very high resolution radiometers (VHRR), thematic mappers (TM), and synthetic aperture radar (SAR).

Figure 1.29 Landsat-7 (Courtesy: NASA)

Figure 1.30 SPOT-5 (Reproduced by permission of © CNES/ill.D.DUCROS, 2002)

Figure 1.31 Resourcesat (Courtesy: ISRO)

1.4 Evolution of Launch Vehicles

Satellite launch vehicles have also seen various stages of evolution in order to meet launch demands of different categories of satellites. Both smaller launch vehicles capable of launching satellites in low Earth orbits and giant sized launch vehicles that can deploy multiple satellites in geostationary transfer orbit have seen improvements in their design over the last four decades of their history. The need to develop launch vehicles by countries like the United States and Russia was in the earlier stages targeted to acquire technological superiority in space technology. This led them to use the missile technology developed during the Second World War era to build launch vehicles. This was followed by their desire to have the capability to launch bigger satellites to higher orbits. The next phase was to innovate and improve the technology to an extent that these vehicles became economically viable, which meant that the attainment of mission objectives justified the costs involved in building the launch vehicle. The technological maturity in launch vehicle design backed by an ever-increasing success rate led to these vehicles being used for offering similar services to other nations who did not possess them.

The situation in different countries involved in developing launch vehicles is different. On the one hand, there are nations keen to become self-reliant and attain a certain level of autonomy in this area; there are others whose commercial activities complement a significant part of their national activity.

Beginning with a one-stage R-7 rocket (named Semyorka) that launched Sputnik-1 into its orbit in 1957, Russia has developed a large number of launch vehicles for various applications. Some of the prominent ones include the Vostok series, the Molniya series (Figure 1.32), the Soyuz series, the Proton series (Figure 1.33), the Zenit series and Energia series (Figure 1.34). Energia is capable of placing a payload of 65 to 200 tonnes in a low Earth orbit.

Figure 1.32 Molniya series (Reproduced by permission of © Mark Wade)

Figure 1.33 Proton series (Courtesy: NASA)

Figure 1.34 Energia series (Reproduced by permission of © Mark Wade)

Important launch vehicles developed by the United States include the Delta series (Figure 1.35), the Atlas series, the Titan series (Figure 1.36), the Pegasus series and the re-usable famous Space Shuttle (Figure 1.37). Buran (Figure 1.38) from Russia is another re-usable vehicle similar in design and even dimensions to the American Space Shuttle. The main difference between the two lies in the fact that Buran does not have its own propulsion system and is launched into orbit by Energia launch vehicle. The Ariane launch vehicle from the European Space Agency (ESA) has entered the fifth generation with the Ariane-5 heavy launch vehicle. Ariane-5 ECB (Enhanced Capability-B) (Figure 1.39) has the capacity of launching 12 tonnes to the geostationary transfer orbit.

Figure 1.35 Delta series

Figure 1.36 Titan series (Courtesy: NASA/JPL-Caltech)

Figure 1.37 Space Shuttle (Courtesy: NASA)

Figure 1.38 Buran series

Figure 1.39 Ariane-5ECA (Reproduced by permission of © ESA-D. DUCROS)

Long March (Figure 1.40) from China, the PSLV (polar satellite launch vehicle) and the GSLV (geostationary satellite launch vehicle) (Figure 1.41) from India and the H-2 series from Japan are some of the other operational launch vehicles.

Figure 1.40 Long March

Figure 1.41 GSLV (Courtesy: ISRO)

1.5 Future Trends

The technological advances in the field of satellites will be directed with an aim of reducing the cost and size of the satellites as well as improving the quality of the services provided. One of the main technological trends is to develop satellites with a longer mission life. Smaller satellites are being developed as they can be launched using smaller launchers, thereby cutting the overall mission expenditure.

1.5.1 Communication Satellites

In the case of communication satellites, key technologies include development of large-scale multi-beam antennas to allow intensive reuse of frequencies, USAT terminals to replace VSAT terminals, ground user terminals, development of signal processing algorithms to perform intelligent functions on-board the satellite including signal regeneration, overcoming the signal fading problem due to rain and allowing use of smaller antennas. Flexible cross-link communication between satellites will be developed to allow better distribution of traffic between the satellites. The trend will be to use millimetre or EHF bands of the spectrum to cope with the increased demand for broadband services. This will require the development of technologies to cope with rain-fade problems in these bands. Newer LEO and MEO satellite constellations will be launched mainly for enhancing land-mobile services.

1.5.2 Weather Forecasting Satellites

Future weather forecasting satellites will carry advanced payloads including multispectral imagers, sounders and scatterometers with better resolution. Hyperspectral measurements from newly developed interferometers will be possible in the near future. These instruments will have more than a thousand channels over a wide spectral range. Also, the satellite data download rates are expected to exceed several terabytes per day.

The GOES-R satellite planned to be launched in the year 2015 will carry several sophisticated instruments including the Advanced Baseline Imager (ABI), Space Environment In-Situ Suite (SEISS), Solar Imaging Suite (SIS), Geostationary Lightning Mapper (GLM) and Magnetometer. SEISS further comprises two Magnetospheric Particle Sensors (MPS-HI and MPS-LO), an Energetic Heavy Ion Sensor (EHIS) and a Solar and Galactic Proton Sensor (SGPS). The SIS payload has a Solar Ultraviolet Imager (SUVI), a Solar X-Ray Sensor (XRS) and an Extreme Ultraviolet Sensor (EUVS).

1.5.3 Earth Observation Satellites

For Earth observation satellites, technological advancements will lead to better resolution, increase in observation area and reduction in access time, i.e time taken between the request of an image by the user and its delivery. Plans for future missions and instruments include entirely new types of measurement technology, such as hyper-spectral sensors, cloud radars, lidars and polarimetric sensors that will provide new insights into key parameters of atmospheric temperature and moisture, soil moisture and ocean salinity. Several new gravity field missions aimed at more precise determination of the marine geoid will also be launched in the future. These missions will also focus on disaster management and studies of key Earth System processes – the water cycle, carbon cycle, cryosphere, the role of clouds and aerosols in global climate change and sea level rise.

1.5.4 Navigational Satellites

Satellite based navigation systems are being further modernized so as to provide more accurate and reliable services. The modernization process includes launch of new more powerful satellites, use of new codes, enhancement of ground system, etc. Infact satellite based systems will be integrated with other navigation systems so as to increase their application potential.

The GPS system is being modernized so as to provide more accurate, reliable and integrated services to the users. The first efforts in modernization began with the discontinuation of the selective availability feature, so as to improve the accuracy of the civilian receivers. In continuation of this step, Block IIRM satellites will carry a new civilian code on the L2 frequency. This will help in further improving accuracy by compensating for atmospheric delays and will ensure greater navigation security. Moreover, these satellites will carry a new military code (M-code) on both the L1 and L2 frequencies. This will provide increased resistance to jamming. This new code will be operational by the year 2010. The satellites will also have more accurate clock systems.

Block-IIF satellites (to be launched after the Block II satellites), planned to be launched by the year 2011, will have a third carrier signal, L5, at 1176.45 MHz. They will also have larger design life, fast processors with more memory, and a new civil signal. The GPS-III phase of satellites is at the planning stage. These satellites will employ spot beams. The use of spot beams results in increased signal power, enabling the system to be more reliable and accurate, with system accuracy approaching a metre. As far as the GLONASS system is concerned, efforts are being made to make the complete system operational in order to exploit its true application potential.

Another satellite navigation system that is being developed is the European Galileo system. The first Galileo satellite was launched on 28 December 2005. It is planned to launch another satellite in the near future. These satellites will define the critical technologies of the system. Following this, four operational satellites will be launched to complete the validation of the basic Galileo space segment and its related ground segment. Once this In-Orbit Validation (IOV) phase has been completed, the remaining operational satellites will be placed in orbit so as to reach the full operational capability. The fully operational Galileo system will comprise 30 satellites (27 operational and three active spares), positioned in three circular Medium Earth Orbit (MEO) planes at 23 222 km altitude above the Earth, and with each orbital plane inclined at 56 degrees to the equatorial plane. The system will be operational in the near future. All of these developments will expand the horizon of their applications to new dimensions. In fact, the future of satellite navigation systems is as unlimited as one’s imagination.

Navigation satellite services will improve as the services provided by the three major navigation satellite systems (GPS, GLONASS, and GALILEO) will be integrated and the user will be able to obtain position information with the same receiver from any of the satellites of the three systems.

1.5.5 Military Satellites

The sphere of application of military satellites will expand further to provide a variety of services ranging from communication services to gathering intelligence imagery data, from weather forecasting to early warning applications, from providing navigation information to providing timing data. They have become an integral component of the military planning of various developed countries, especially of the USA and Russia. Developing countries are designing their military satellites so as to protect their territory. The concept of space based lasers is evolving wherein the satellites carrying onboard high power lasers will act as nuclear deterrent. These satellites will destroy the nuclear missile in its boost phase within the country that is launching it.

Further Reading

Labrador, V. and Galace, P. (2005) Heavens Fill with Commerce: A Brief History of the Communications Satellite Industry, Satnews Publishers, California.

Internet Sites

1. http://electronics.howstuffworks.com/satellite.htm/printable

2. http://www.aero.org/publications/gilmore/gilmore-1.xhtml

3. http://www.thetech.org/exhibits events/online/satellite/home.xhtml

4. www.intelsat.com

5. www.isro.org

6. www.nasa.gov

Glossary

Ariane:

European Space Agency’s launch vehicle

Astronaut:

A space traveller, i.e. a person who flies in space either as a crew member or a passenger

Astrophysics:

Study of the physical and chemical nature of celestial bodies and their environments

Buran:

A re-usable launch vehicle, Russian counterpart of a space shuttle

Early Bird:

Other name for Intelsat-1. First geostationary communications satellite in commercial service

Explorer-1:

First successful satellite from the United States

Footprint:

The area of coverage of a satellite

Geostationary orbit:

An equatorial circular orbit in which the satellite moves from west to east with a velocity such that it remains stationary with respect to a point on the Earth. Also known as the Clarke orbit after the name of the science fiction writer who first proposed this orbit

GPS:

An abbreviation for the global positioning system. It is a satellite-based navigation system that allows you to know your position coordinates with the help of a receiver anywhere in the world under any weather condition

GSLV:

Abbreviation for geostationary satellite launch vehicle. Launch vehicle from India

INTELSAT:

Acronym for International Telecommunications Satellite Consortium operating satellites internationally for both domestic and international telecommunication services

Landsat:

First remote sensing satellite series in the world from USA

Molniya orbit:

A highly inclined and elliptical orbit used by Russian satellites with apogee and perigee distances of about 40 000 and 500 km and an orbit inclination of 65°. Two or three such satellites aptly spaced apart in the orbit provide an uninterrupted communication service

Multispectral scanner (MSS):

A multispectral scanning device that uses an oscillating mirror to continuously scan Earth passing beneath the spacecraft

NASA:

National Aeronautics and Space Administration

Palapa:

First domestic communication satellite from a developing country, Indonesia

Payload:

Useful cargo-like satellite being a payload of a launch vehicle

Satellite:

A natural or artificial body moving around a celestial body

Sounding rocket:

A research rocket used to obtain data from the upper atmosphere

Space shuttle:

A re-usable launch vehicle from the United States

Spin-stabilized satellite:

A satellite whose attitude stabilization is achieved by the spinning motion of the satellite. It employs the gyroscopic or spinning top principle

Sputnik-1:

First artificial satellite launched by any country. Launched on 4 October 1957 by erstwhile Soviet Union

Thematic mapper:

A type of scanning sensor used on Earth observation satellites

Three-axis stabilized satellite:

A satellite whose attitude is stabilized by an active control system that applies small forces to the body of the spacecraft to correct any undesired changes in its orientation

TIROS:

First series of weather forecast satellites, launched by United States

Transponder:

A piece of radio equipment that receives a signal from the Earth station at the uplink frequency, amplifies it and then retransmits the same signal at the downlink frequency

Westar:

First domestic communication satellite from the United States

2

Satellite Orbits and Trajectories

The study of orbits and trajectories of satellites and satellite launch vehicles is the most fundamental topic of the subject of satellite technology and perhaps also the most important one. It is important because it gives an insight into the operational aspects of this wonderful piece of technology. An understanding of the orbital dynamics would give a sound footing to address issues like types of orbits and their suitability for a given application, orbit stabilization, orbit correction and station keeping, launch requirements and typical launch trajectories for various orbits, Earth coverage and so on. This chapter and the one after this focus on all these issues and illustrate various concepts with the help of necessary mathematics and a large number of solved problems.

2.1 Definition of an Orbit and a Trajectory

While a trajectory is a path traced by a moving body, an orbit is a trajectory that is periodically repeated. While the path followed by the motion of an artificial satellite around Earth is an orbit, the path followed by a launch vehicle is a trajectory called the launch trajectory. The motion of different planets of the solar system around the sun and the motion of artificial satellites around Earth (Figure 2.1) are examples of orbital motion.

The term ‘trajectory’, on the other hand, is associated with a path that is not periodically revisited. The path followed by a rocket on its way to the right position for a satellite launch (Figure 2.2) or the path followed by orbiting satellites when they move from an intermediate orbit to their final destined orbit (Figure 2.3) are examples of trajectories.

2.2 Orbiting Satellites – Basic Principles

The motion of natural and artificial satellites around Earth is governed by two forces. One of them is the centripetal force directed towards the centre of the Earth due to the gravitational force of attraction of Earth and the other is the centrifugal force that acts outwards from the centre of the Earth (Figure 2.4). It may be mentioned here that the centrifugal force is the force exerted during circular motion, by the moving object upon the other object around which it is moving. In the case of a satellite orbiting Earth, the satellite exerts a centrifugal force. However, the force that is causing the circular motion is the centripetal force. In the absence of this centripetal force, the satellite would have continued to move in a straight line at a constant speed after injection. The centripetal force directed at right angles to the satellite’s velocity towards the centre of the Earth transforms the straight line motion to the circular or elliptical one, depending upon the satellite velocity. Centripetal force further leads to a corresponding acceleration called centripetal acceleration as it causes a change in the direction of the satellite’s velocity vector. The centrifugal force is simply the reaction force exerted by the satellite in a direction opposite to that of the centripetal force. This is in accordance with Newton’s third law of motion, which states that for every action there is an equal and opposite reaction. This implies that there is a centrifugal acceleration acting outwards from the centre of the Earth due to the centripetal acceleration acting towards the centre of the Earth. The only radial force acting on the satellite orbiting Earth is the centripetal force. The centrifugal force is not acting on the satellite; it is only a reaction force exerted by the satellite.

Figure 2.1 Example of orbital motion – satellites revolving around Earth

Figure 2.2 Example of trajectory – path followed by a rocket on its way during satellite launch

Figure 2.3 Example of trajectory – motion of a satellite from the intermediate orbit to the final orbit

Figure 2.4 Gravitational force and the centrifugal force acting on bodies orbiting Earth

The two forces can be explained from Newton’s law of gravitation and Newton’s second law of motion as outlined in the following paragraphs.

2.2.1 Newton’s Law of Gravitation

According to Newton’s law of gravitation, every particle irrespective of its mass attracts every other particle with a gravitational force whose magnitude is directly proportional to the product of the masses of the two particles and inversely proportional to the square of the distance between them and written as

(2.1)     c02e001

m1, m2 = masses of the two particles

r = distance between the two particles

G = gravitational constant = 6.67 × 10–11 m³/kg s²

The force with which the particle with mass m1 attracts the particle with mass m2 equals the force with which particle with mass m2 attracts the particle with mass m1. The forces are equal in magnitude but opposite in direction (Figure 2.5). The acceleration, which is force per unit mass, experienced by the two particles, however, would depend upon their masses. A larger mass experiences lesser acceleration. Newton also explained that although the law strictly applied to particles, it is applicable to real objects as long as their sizes are small compared to the distance between them. He also explained that a uniform spherical shell of matter would behave as if the entire mass of it were concentrated at its centre.

Figure 2.5 Newton’s law of gravitation

2.2.2 Newton’s Second Law of Motion

According to Newton’s second law of motion, the force equals the product of mass and acceleration. In the case of a satellite orbiting Earth, if the orbiting velocity is υ, then the acceleration, called centripetal acceleration, experienced by the satellite at a distance r from the centre of the Earth would be υ²/r. If the mass of satellite is m, it would experience a reaction force of mυ²/r. This is the centrifugal force directed outwards from the centre of the Earth and for a satellite is equal in magnitude to the gravitational force.

If the satellite orbited Earth with a uniform velocity υ, which would be the case when the satellite orbit is a circular one, then equating the two forces mentioned above would lead to an expression for the orbital velocity υ as follows:

(2.2)     c02e002

(2.3)     c02e003

where

m1 = mass of Earth

m2 = mass of the satellite

μ = Gm1 = 3.986013 × 10⁵ km³/s² = 3.986013 × 10¹⁴N m²/kg

The orbital period in such a case can be computed from

(2.4)     c02e004

In the case of an elliptical orbit, the forces governing the motion of the satellite are the same. The velocity at any point on an elliptical orbit at a distance d from the centre of the Earth is given by the formula v

(2.5)     c02e005

where

a = semi-major axis of the elliptical orbit

The orbital period in the case of an elliptical orbit is given by

(2.6)     c02e006

The movement of a satellite in an orbit is governed by three Kepler’s laws, explained below.

2.2.3 Kepler’s Laws

Johannes Kepler, based on his lifetime study, gave a set of three empirical expressions that explained planetary motion. These laws were later vindicated when Newton gave the law of gravitation. Though given for planetary motion, these laws are equally valid for the motion of natural and artificial satellites around Earth or for any body revolving around another body. Here, these laws will be discussed with reference to the motion of artificial satellites around Earth.

2.2.3.1 Kepler’s First Law

The orbit of a satellite around Earth is elliptical with the centre of the Earth lying at one of the foci of the ellipse (Figure 2.6). The elliptical orbit is characterized by its semi-major axis a and eccentricity e. Eccentricity is the ratio of the distance between the centre of the ellipse and either of its foci (= ae) to the semi-major axis of the ellipse a. A circular orbit is a special case of an elliptical orbit where the foci merge together to give a single central point and the eccentricity becomes zero. Other important parameters of an elliptical satellite orbit include its apogee (farthest point of the orbit from the Earth’s centre) and perigee (nearest point of the orbit from the Earth’s centre) distances. These are described in subsequent paragraphs.

Figure 2.6 Kepler’s first law

For any elliptical motion, the law of conservation of energy is valid