Chapter One History of Communication Satellites
In the United States today, powerful direct broadcast satellites (DBS) transmit more than 200 audio/video services directly into homes through small, 18-inch-diameter antennas. In the next few years, the number of services surely will exceed 500 and coverage will be extended to many more countries.
The powerful satellites that provide these services are the result of a natural evolution that includes:
• Visionary concepts
• Engineering genius
• Technology continuing to build on itself
This chapter describes the history of this evolution.
1.1 Background
From the dawn of electronic communication in the early twentieth century until the advent of the communication satellite, long-distance communication was limited at best. The electromagnetic waves that implement electronic communication travel in a straight line; the Earth is curved and cannot be penetrated by these waves. Thus, relays in one form or another are required if points wishing to communicate are more than a few hundred miles apart.
One such relay technique is to bounce the signal off the Earth’s ionosphere—a shell of charged particles that surrounds the Earth and reflects the longer wavelength radio waves back to Earth. Since the frequency of an electromagnetic signal and its wavelength are inversely related, lower-frequency signals are reflected. Even long wavelength communications are erratic and subject to outages because of atmospheric conditions.
Perhaps nothing emphasizes the lack of reliability of previous relay techniques, and the problems such a lack of reliability causes, than the story of what happened on the morning of December 7, 1941. U.S. codebreakers in Washington, DC, had broken the Japanese codes and were sure that an attack on the U.S. Naval base in Honolulu, Hawaii, was imminent. They tried to warn the armed forces there by using radio circuits from San Francisco to Hawaii; however, they were down because of atmospheric conditions. As we are aware from history, the message sent to attempt to warn U.S. forces using commercial Western Union services arrived too late.
The technique of reflecting electromagnetic waves off of the ionosphere does not work at all for the shorter wavelengths that pass through the ionosphere and, consequently, are not reflected back to Earth. Since the shorter wavelength-higher frequency carriers are required to carry wideband signals, such as for television, long-distance communication for these wideband services is worse. Across terrestrial distances, a sequence of very expensive relay towers has been used. This was (and is) done to distribute television signals across the United States. However, nothing reasonable was able to solve the situation for communication across the oceans.
As soon as it became possible to place artificial Earth satellites into orbit, communication engineers began to develop communication satellites to solve this problem. In the early 1960s, there were a number of proposals as to how to best achieve this goal. Passive satellites, where ground transmission is just reflected off them, are very simple, but require large and powerful Earth stations. Active satellites receive the signal from Earth and reamplify it for transmission back to Earth. Although active satellites are more complicated electronically than passive satellites, they permit smaller and less powerful Earth stations. Currently all operational communication satellites are active.
Within the class of active satellites, the next consideration is the orbit. Low Earth Orbit (LEO) satellites generally can be lower powered and simpler than higher orbit satellites. Also, smaller boosters can be used to put them into orbit. Alternatively, multiple LEO satellites can be launched with a more powerful rocket. However, LEOs require a large number of satellites to achieve full Earth coverage and Earth station antennas must track each satellite across the sky and then switch to the next satellite coming over the horizon. Thus, LEOs have costly space segments and need Earth stations with costly antenna and control systems.
In October 1945, a brilliant science and science fiction writer, Arthur Clarke, wrote that there was a single, 24-hour-period orbit. A satellite in this orbit would appear stationary to an Earth observer—thus the term geostationary. This orbit at 22,300 miles above the Earth’s surface was so high that three such satellites could cover almost the entire Earth. In the early 1960s, when many of the ideas about communication satellites were being developed, most of the scientists and engineers in the field believed that a geostationary satellite was many years in the future. SYNCOM 1 proved the naysayers wrong and today all operational communication satellites are geostationary.
This happened because a gifted trio of inventors (Dr. Harold Rosen, Thomas Hudspeth, and Donald Williams) at Hughes Aircraft Company conceived an elegantly simple spinning satellite that could be boosted to geostationary orbit by the rockets available at the time. Hughes funded the early developments, including a demonstration model of a geostationary satellite. After a considerable period of trying to interest customers in the project, Hughes was about to cancel the project. At that time, Donald Williams, one of the inventors of the concept, went to the office of Lawrence (Pat) Hyland, then the General Manager of Hughes Aircraft Company, and placed a cashier’s check for $10,000 on Pat’s desk. He told Mr. Hyland that the $10,000 was his life savings and that he wanted to contribute it to continuing the project. The Hughes Policy Board decided to continue the project and the rest is history.
Impressed by the vision of the Hughes prototype and encouraged by the U.S. Department of Defense (DoD), the National Aeronautics and Space Administration (NASA) awarded Hughes a contract to develop the SYNCOM series of satellites. The SYNCOM name is a derivation of ‘synchronous communication.’ And yes, Mr. Hyland did get Don Williams to take his check back.
In July 1963, SYNCOM 2, the first geosynchronous satellite, was successfully placed into geosynchronous orbit some 22,300 miles above the surface of the Earth, thus revolutionizing the field of communications. Later, its sister satellite, SYNCOM 3, became the first geostationary satellite (the distinction between geostationary and geosynchronous is explained in the next section of this chapter). SYNCOM 3 gained a great deal of attention by televising the Tokyo Olympics from Japan to the west coast of the United States.
Today, more than 35 years since the launch of SYNCOM 2, powerful satellites broadcast hundreds of digital television channels directly to the homes of consumers through an 18-inch receiver dish. These satellites are the direct descendants of the SYNCOM satellites.
Throughout most of the years from the first SYNCOM until the debut of the first Direct Broadcast Satellite (DBS) service, DIRECTV™ from Hughes Electronics, the signals going through the commercial communication satellites were analog. DBS brought the first wide-scale use of compressed digital audio visual services.
The DBS communication system takes advantage of parallel developments in a number of technologies. On the satellite side are more powerful transponders and shaped reflector antennas. On the content side, the Moving Pictures Experts Group (MPEG), a subunit of the International Standards Organization (ISO), created compression standards for audio and video compression, without which DBS would not have been technically or economically feasible.
In June 1994, DIRECTV launched a DBS service in the United States to provide customers with an alternative to traditional cable television networks, while at the same time eliminating the expense and inconvenience of traditional satellite television. In the 12 months that followed the initial DIRECTV subscription service, the satellite receiver became the number one best-selling consumer product of all time. In its first year, DIRECTV surpassed first-year VCR sales by a factor of 25! Within a year, over one million homes subscribed to DIRECTV’s digital DBS service.
Personal Note: There at the Creation Back in 1963, as a 26-year-old engineer working at Hughes Aircraft Company, I was assigned to design the Command Decoder System for the SYNCOM satellites and to be a part of the SYNCOM 1 launch team at Cape Canaveral. I was also fortunate to be involved in the development of DBS, particularly the MPEG standards.
From July 1990 until August 1997, I was head of the Hughes delegation to MPEG and was able to help evolve the MPEG 1 and MPEG 2 standards so that they meet generic objectives and are directly applicable to DBS. Thus, I have had the incredible good fortune to be there at the creation of both the geostationary satellite business and its progeny—DBS.
1.2 Arthur C. Clarke’s Vision
It is instructive to review how Arthur C. Clarke arrived at his geostationary concept—EXTRA-TERRESTRIAL RELAYS. Astronomers have studied the heavens for thousands of years. It wasn’t until 1609 to 1611, however, that the German astronomer Johannes Kepler published his three laws of orbital motion. These laws can be used to calculate the altitude and orbital period for any satellite orbit, whether it is that of the Earth around the sun, or a DBS around the Earth.
Kepler’s laws can be used to show the period of a satellite orbiting a body:
where a is the semimajor axis (the radius for a circular orbit) and M is the gravitational constant. For Earth,
Because the only two variables in (1.1) are a and T, every orbital period has a unique orbital height. Thus, there is one orbital height in which the orbital period is 24 hours. In this orbit, a satellite at this altitude will appear stationary to an observer on Earth. As a result, this orbit is called geostationary. See the following discussion for the distinction between geosynchronous and geostationary satellites.
Solving (1.1) for a yields
For a geostationary orbit
T = 24 h = 8.64 * 104 sec
Inserting the values for T and M into (1.3) yields
a = 13.86 * 105 ft, or
a = 26,250 miles
from the center of the Earth. Since the radius of the Earth is approximately 4,000 miles, the orbital height above the surface of the Earth is 22,250 miles.
Arthur C. Clarke is certainly the most gifted science-fiction writer of the twentieth century. 2001: A Space Odyssey is perhaps his most famous work, although he wrote many more books. To describe Clarke as a science-fiction writer is misleading, however. While most science fiction describes things that are physically impossible or will never happen, Clarke writes science stories that predict the future. Thus, ‘visionary futurist’ would be a more fitting description of this man.
In 1945, Clarke wrote an article in Wireless World magazine that pointed out that three communication satellites (Clarke called them EXTRATERRESTRIAL RELAYS) in geostationary orbit and separated by 120° longitude could provide ubiquitous communications to almost every place in the world [Clarke45]. Clarke later wistfully noted in his book Voices from the Sky that he had mixed feelings about originating one of the most commercially viable ideas of the twentieth century and selling it for just $40 [Clarke65].
Clarke never patented his idea because he felt it would be well into the next century before these satellites could be built and the technology realized. In reality, it took less than 20 years to build the prototype. Clarke has said that if he had not conceived and published his ideas about the geostationary satellite, someone else would have within ten years. Although such projections are always speculative, I believe the combined genius of Clarke and Dr. Harold A. Rosen, who led the group that developed the first geostationary satellite, advanced the realization of the first geostationary satellite by at least several decades. Historic justice has been served in that these two giants became friends in their later years and Dr. Rosen won the Arthur C. Clarke Award for contribution to space science three times.
Sometimes the words geosynchronous and geostationary are used synonymously, but this is incorrect. If a satellite is in a 24-hour orbit, it is said to be geosynchronous; however, if the orbital plane and the equatorial plane of the earth are not the same, the satellite will not appear stationary to an observer on Earth. A satellite so placed traverses a trajectory on the Earth in the shape of a figure eight every 24 hours. Thus, it is exactly on the equator at only two points in time each day. If, however, the plane of the orbit and the equatorial plane are identical, the satellite is said to be geostationary, and, indeed, it appears stationary to an observer on Earth. It is important to have the DBS satellites geostationary so that no antenna movement is required to keep the satellite within the Earth station beam.
1.3 The Early Days of Satellite Communications
The rockets developed by Germany during World War II were not powerful enough to launch an object into orbit around the Earth, much less into geostationary orbit, but it was clear that improvements in these rockets would enable them to do so. This was the reason there was such competition between the USSR and the United States to “obtain” the German rocket scientists at the end of the war. It also was clear that an artificial Earth satellite could be used as EXTRA-TERRESTRIAL RELAYS, to use Clarke’s term. The ability to orbit such satellites became evident when the former USSR shocked the world by orbiting the Sputnik satellite in 1957.
During the period from 1945 to 1957 and beyond, the United States, with Werner von Braun and other expatriate German rocket scientists, was working desperately to develop satellites and the rockets to launch them. The USSR was the first to orbit a man-made satellite and to put a man in orbit, however. In those early days there were several competing ideas of what a communication satellite should be. One of the first considerations was it should be passive or active.
The idea behind the passive satellite was to orbit a relatively large reflector that could be used to reflect the ground-transmitted signal back to the Earth. The passive reflector satellite requires a minimum of electronics but it creates a number of problems. Perhaps the most serious is that the signal needs to travel twice as far without amplification. The power density of a radio frequency signal decreases by the square of its distance from the emitter. Thus, doubling the distance reduces the power at the Earth receiver by a factor of four compared with what could be received by an antenna on the satellite. While the Echo satellite program did launch several aluminum-covered balloon satellites, the program did not go further because of the very large, complicated, and powerful ground stations required.
An alternative to passive satellites was active satellites. Active satellites receive a signal from an Earth station, translate the frequency of the signal, amplify it, and retransmit it to Earth. Active communication satellites can be placed in a variety of orbits. New orbital concepts are still being conceived and tried today. The first orbit that was tried for active communication satellites was what is now called a low Earth orbit, or LEO. Referring to Equation (1.1), the lower the orbital altitude, the shorter the orbital period. While the term LEO can cover a variety of orbital altitudes, assume a 100-mile orbital altitude that corresponds to a 90-minute orbital period. Since the satellite traverses 360 degrees in 90 minutes, the rate is four degrees per minute. Thus, it moves fairly rapidly across the sky.
For example, assume that the satellite is mutually visible for an arc of 60 degrees. The duration of this visibility will be only 15 minutes. Note that both the transmitter and the receiver Earth stations must have movable antennas that track the satellite across the sky. Also, to have continuous coverage between stations, a large number of LEO satellites would be required and a complex control scheme would be needed to hand off the transmission from one satellite disappearing over the horizon to the next one coming into view.
In July 1962, AT&T orbited the Telstar satellite, the world’s first active communication satellite. Telstar worked well and proved a number of theories. However, as an LEO, the number of satellites that would be required for a complete-coverage network and the complexity of the ground antennas that were required worked against the Telstar concept, not allowing it to progress very far.
It was generally acknowledged that if Clarke’s vision of geostationary satellites could be realized, it would be the ideal solution. However, virtually all of the scientists and engineers of the time believed that a geostationary system was so complicated it would take years before one could be orbited. That was not to be the case. Led by Rosen, a small group of engineers at Hughes Aircraft Company developed a prototype geostationary satellite. Impressed by the vision of this prototype and encouraged by the DoD, the National Aeronautics and Space Administration (NASA) awarded Hughes a contract to develop the SYNCOM series of satellites.
1.4 SYNCOM
As noted, the engineers and scientists involved in the early development of communication satellites were almost unanimous in their belief that geosynchronous/geostationary satellites were far in the future. What was it about SYNCOM that made them all wrong? The following sections give a general overview of the SYNCOM satellites.
1.4.1 Stabilization
The SYNCOM satellites were the shape of a cylinder and were stabilized by spinning the satellite about the cylindrical axis. If the satellite had an orientation in inertial space, conservation of angular momentum required that it retain that orientation unless acted upon by a force.
1.4.2 Attitude Control and Orbital Positioning
For a satellite in the form of a spinning cylinder, all of the attitude control and orbital positioning can be achieved by two thrusters:
Thruster 1 is parallel to the spin axis but offset from it
Thruster 2 is orthogonal to the spin axis and thrusting through the satellite center of gravity
This form of control was invented by Don Williams and is the basis for the famous “Williams patents.”
On the SYNCOM satellites, the thrusters were provided by nitrogen compressed to very high pressure and stored in small tanks. Small jets released the nitrogen to provide the thrust.
1.4.3 Power
Power for the satellites was provided by solar cells that covered the outside of the satellite. A bluish color comes from the satellite’s solar cells. Batteries provided the power when the satellites suffered from solar eclipses.
An added benefit of the spin stabilization was the fact that the solar cells could cool off when they were on the side of the satellite away from the sun. Solar cell efficiency was high because the solar cells never became too hot.
1.4.4 Orbital Injection
The three-stage Delta booster could launch the SYNCOM satellites into a highly elliptical orbit. When the satellite reached its apogee of this elliptical orbit (22,300 miles) an integral fourth stage was fired, circularizing the orbit.
1.4.5 Communication Antenna
The communication antenna was a simple dipole located coaxially with the satellite spin axis. The radiation pattern, orthogonal to the spin axis, is in the shape of a doughnut. Since the Earth subtends an angle of about 18 degrees from geostationary orbit, only 18/360, or 5 percent, of the radiated power hits the Earth.
Although inefficient, the dipole was simplicity itself. The whole story of the evolution of satellite antennas is one of relentless progress (see Chapter 4). Figure 1.1 is a photograph of an actual SYNCOM satellite.
Figure 1.1 Photograph of a SYNCOM Satellite
Source: Reproduced from Vectors, XXX(3): Cover, 1988, Copyright © 1988 Hughes Aircraft Co. All rights reserved. Used with permission.
SYNCOM 1 was launched February 14,1963, and was lost five hours after launch when its apogee motor firing caused a complete failure. The exact cause of the SYNCOM 1 failure probably will never be known. Certainly it was an on-board explosion: either the integral fourth stage exploded or one of the nitrogen tanks was scratched, turning it into a lethal projectile.
Optical telescope images seemed to indicate the satellite was in a higher orbit than was planned. This would mean the satellite lost mass during fourth stage burn, which would point to the nitrogen tanks as the cause of the explosion.
Regardless, the SYNCOM 1 experience showed there was nothing fundamentally wrong with the SYNCOM design. After the initial failure, certain engineering changes were made to the next flight satellite but nothing fundamental was changed. SYNCOM 2 was launched on July 26,1963, and became the first successful geosynchronous satellite.
It probably is difficult for most people, who now take for granted having satellite TV beamed into their homes, to appreciate the significance of this event. It changed the world forever. A strong argument can be made that it ultimately helped lead to the defeat of Communism. Try as they might the Communist rulers could not stop their citizens from receiving satellite TV. When people in Communist countries saw what life was like in other parts of the world, they demanded the same freedoms.
In Section 1.1, I explained the unreliability of long-distance communication. The dramatic and immediate improvement permitted by geosynchronous satellite communication is illustrated by an event that took place shortly after the SYNCOM 2 launch. In 1963, the USS Kingsport, stationed in Lagos Harbor, Nigeria, conversed with the U.S. Navy base at Lakehurst, New Jersey. It was the first voice message ever transmitted between continents by a synchronous satellite. Later came the highly publicized telephone conversation between U.S. President John F. Kennedy and Nigerian Prime Minister Abubakar Balewa. It should be noted that at that time, all the normal voice circuits were down because of atmospheric conditions but the satellite circuit worked perfectly! [Roddy96]
SYNCOM 2 later was repositioned over the Pacific, where it provided extensive communications capability during the war in Vietnam.
SYNCOM 3, the last of the series, was launched on August 19, 1964. By using a more powerful fourth stage, it was possible to make the satellite’s orbital plane the same as the Earth’s equatorial plane. Thus, SYNCOM 3 became the world’s first geostationary satellite. SYNCOM 3 later gained fame by telecasting the Tokyo Olympics across the Pacific. Figure 1.2 shows the 85-foot-diameter antenna used to receive the signal at Point Mugu, California. Note the man on the pedestal next to the antenna. Today’s DBS antenna is smaller in diameter than the length of his arm.
Figure 1.2 Antenna Used to Receive the 1964 Olympic Games from Tokyo
Source: Reproduced from Vectors. XXX(3): 3, 1988. Copyright© 1988 Hughes Aircraft Co. ASI rights reserved. Used with permission.
Once the geostationary satellite concept had been proven, it was clear that this would be the preferred approach. After 30 years, this concept continues to dominate the communication satellite business, particularly for broadcast purposes.
1.5 The Early Commercial Geostationary Earth Orbit Satellites: INTELSAT I and II
In the early 1960s it became apparent that communication satellites would benefit not only the citizens of the United States, but of the world as well.
In 1963 the U.S. Congress formed the Communication Satellite Corporation (COMSAT) as a quasiprivate company to represent the interests of the United States in international communication satellite matters. Dr. Joseph Charyk was appointed the founding president of COMSAT and served with distinction as president, CEO, chairman of the board, and director for 35 years.
Founded in 1964, the International Satellite Consortium (INTELSAT) was the first organization to provide global satellite coverage and connectivity, and continues to be the communications provider with the broadest reach and the most comprehensive range of service.
INTELSAT is an international, not-for-profit cooperative of more than 140 member nations. Owners contribute capital in proportion to their relative use of the system and receive a return on their investment. Users pay a charge for all INTELSAT services, depending on the type, amount, and duration of the service. Any nation may use the INTELSAT system, whether or not it is a member. Most of the decisions that member nations must make regarding the INTELSAT system are accomplished by consensus—a noteworthy achievement for an international organization with such a large and diverse membership. For more information, the reader is referred to INTELSAT’S Web page.
It was important that the fledgling INTELSAT establish a real system as early as possible. COMSAT and INTELSAT made the decision that their first system would be geostationary and contracted with Hughes to build the first commercial communication satellite.
On the twenty-fifth anniversary of the first commercial communication satellite, Charyk noted that he made the historic decision to use geostationary Earth orbit satellites (GEOS) because of Rosen and the Hughes team. This first commercial communication satellite, known officially as INTELSAT 1 and affectionately called Early Bird, was launched on April 6,1965, and provided either 2,400 voice circuits or one two-way television channel between the United States and Europe. During the 1960s and 1970s, message capacity and transmission power of the INTELSAT 2 (Blue Bird), 3, and 4 generations were progressively increased by beaming the satellite power only to Earth and segmenting the broadcast spectrum into transponder units of a certain bandwidth.
1.6 The Evolution of Communication Satellites
In the 33 years since the launch of SYNCOM 1 and 2, rocket science has continued to develop and provide for larger and larger payloads. Perhaps nothing illustrates this more dramatically than Table 1.1, which shows the evolution of satellites from SYNCOM to date. Every subsystem on the satellite has evolved remarkably from where it was 33 years ago. Improvements have been made to the solar cells, batteries, propellants for station keeping, and all of the electronics technologies. The last line of Table 1.1 shows the figures for the HS 702 satellites, which are expected to be placed in service by the end of the decade.
Table 1.1 The Evolution of Communication Satellites
As can be seen from Table 1.1, a new era in satellite size and power began in 1988 with the launch of the OPTUS-B satellite. With this satellite, weight was increased 1,000 pounds and power was almost tripled. The OPTUS-B and DBS satellites are Hughes Electronics’s HS 601 body stabilized models. As shown in Figure 1.3, the solar arrays are 86 feet (26 meters) from tip to tip and generate 4,300 watts of prime power. The solar arrays are connected to a 32-eeli nickel-hydrogen battery for uninterrupted service during eclipses.
Body Stabilized: The spin-stabilized satellites permitted the early development of geostationary communication satellites. However, the basic solar-cell power of a spinning satellite is controlled by the surface area of the cylinder. Satellite development reached the point where this area was not large enough for the demands of more powerful satellites.
The solution has been the body-stabilized satellite. The solar cells are located on large paddles that can be continuously adjusted to maximize the power output from the sun (see Figure 1.3). Attitude stabilization is achieved by a flywheel in the body of the satellite. Thus, in some sense, spin stabilization lives on.
Figure 1.3 The Hughes DBS Satellites
Source: Reproduced from Hughes Space & Communications DBS brochure (HSC95D1Q4/1500/4-95X 1996. Used with permission.
1.7 The Hughes Direct Broadcast Satellites
On December 17, 1993, an Ariane 4 rocket launched DBS-1 from Kourou, French Guiana, ushering in a new era in satellite communications. On August 3,1994, DBS-2 was launched, and on June 10, 1995, DBS-3 was lauoched. All are located at 101° W longitude.
Figure 1.4 shows the DBS-1 satellite in its stowed position (solar panels and antennas folded in), and Figure 1.5 shows the actual liftoff. The HS 601 body is composed of two main modules: the bus module and the payload module. The bus module is the primary structure that carries launch vehicle loads and also carries the propulsion, attitude control, and electrical power subsystems. The payload module is a honeycomb structure that contains the payload electronics, telemetry, command, and ranging subsystems. The HS 601 transmit-and-receive antenna reflectors are eight feet in diameter. They are constructed with a composite graphite material and weigh only 20 pounds each. Both are fed from their own feedhorn. For more on this innovative antenna design, see section 4.2 in Chapter 4.
Figure 1.4 DBS-1 in Stowed Position
Source: Reproduced from Hughes Space & Communications DBS brochure (HSC95D104/1500/4-95), 1995. Used with permission.
Figure 1.5 DBS Liftoff
Source: Reproduced from Hughes Space & Communications DBS brochure (HSC95D104/1500/4-95), 1995, Used with permission.
1.8 Frequency Bands
The frequency bands for communication satellites certainly have some of the most confusing nomenclature in modern science. The bands are designated by alpha characters, which have their origins in World War II secrecy considerations and have become so embedded in the language that they are still used. Table 1.2 shows band designations and their corresponding frequency range.
Table 1.2 Band Designation
Most of the early communication satellites were C-Band, with an uplink at 6 GHz and a downlink at 4 GHz. Even today the mainstay of communication satellite distribution of television and the corresponding backyard dish products are in the C-Band. C-Band has a number of highly desirable attributes, including the fact that it has very little attenuation because of rain and the componentry is inexpensive. However, the world is running out of space on the C-Band spectrum. The satellites in geosynchronous orbit can be placed only so close to each other without causing undesirable interference. Thus, many of the new services, including DBS, are provided in the Ku-Band. Most of this book will discuss the communication system in Ku-Band; however, Chapter 12 discusses the move to Ka-Band.
1.9 Summary
A large number of technological capabilities came together at the right time to make DBS economically viable. Certainly the satellite size and prime power-enabling high-power transponders were essential, and the creation of the MPEG 1 and MPEG 2 compression standards could not have come at a better time.
Gordon Moore, chairman of Intel, made the prediction more than 20 years ago that every two years the cost of semiconductors for the same function would halve; that is, one would get twice the functionality for the same price. This certainly must rank as one of the most remarkable predictions of all time. Much of our technology today is made possible by affordable integrated circuits. The inexorable march of Moore’s law made the cost of the DBS settop unit affordable.
A number of other design decisions vital to the success of DBS had to be made, however. These are explored in Chapters 3 through 9.[Clarke65] Clarke, Arthur C., Voices From the Sky, New York: Harper & Row, 1965/
References
[Clarke45] Clarke, Arthur C., ‘EXTRA-TERRESTRIAL RELAYS,’ Wireless World, 51(10):305-308, October 1945.
[Clarke65] Clarke, Arthur C., Voices From the Sky, New York: Harper & Row, 1965.
[Hughes88] Hughes Electronics, Vectors, XXX(3): Cover, 2-8, Hughes Aircraft Company, Torrance, CA, 1993.
[Hughes95] Hughes Space & Communications, DBS Brochure (HSC950104/1500/4-95), Hughes Aircraft Company, April 1995.
[Roddy95] Roddy, Dennis, Satellite Communications, 2nd ed., New York: McGraw-Hill, 1996.