Satellite communications

“ General Problems of a Satellite Communications System What jobs could a communications satellite do best? Should it be used for television? Should it carry telephone messages? How many? Would it be more valuable for data transmission? Facsimile? What parts of the world should be covered? Can all the problems of international cooperation be solved? Would a satellite that could broadcast directly to home receivers be possible? What military uses could a communications satellite system serve? Would a passive satellite—one that reflects signals without amplifying them—be worth developing? ”

“ In 1945, of course, the very idea of getting a satellite out into space seemed utterly fantastic, and satellite communications could only be classified as science fiction. Ten years later, although Sputnik I had not yet been launched, artificial satellites were close to reality. At that time, John R. Pierce of Bell Telephone Laboratories made 14 the first serious study of what would have to be done to build a working satellite communication system—assuming it ever became possible to put satellites into orbit. And Bell Laboratories has been interested in satellite communications ever since. ”

“ They are not necessarily the most important ones, but they seem to us to be typical of what engineers and scientists working in the satellite communications program actually have to do. These are the six problems we will be talking about at length:
How do we calculate a satellite’s orbit? What color should a satellite be? How can we make optical measurements on a satellite? How do we keep solar cell power plants working in space? Would time delay be a problem in using a synchronous satellite? How can we repair an orbiting satellite? ”

“ Satellite communications is one field in which, as far as we know, American engineering and science have been well in the lead—so we have an even greater incentive to press on in this direction as hard and as fast as we can. ”

“ But perhaps more important than the prestige it would give our country is a second reason for our great interest in satellite communications: We need it. The world today is going through one of its great periods of change. This has caused many complications, and one of the most important is the need for much better communications between nations and peoples. By “communications” we mean all the various ways of sending information from one place to another: mail, telephone calls, business data, radio, television. ”

“ Further in the future, studies are going on of a proposed Intermediate Altitude Communications Satellite for military use in the 6,000- to 10,000-mile-high range (beyond that of Telstar and Relay) and Advanced Syncom, a synchronous satellite of increased capacity. Work is also continuing to acquire new technical knowledge that will be needed in the future—such as various methods of keeping satellites stabilized in space and new ways of supplying power, including improved solar cells and the use of radioisotopes. ”

“ Industrial and governmental communications satellites appear practical and economically sound. Communication satellites will provide high quality and inexpensive telephone and general communication service between most parts of the earth. A by- product of a communication satellite will almost surely be an international television relay system linking all the nations of the world. On a longer time scale it should be feasible to provide radio and television broadcasting service via satellite-mounted transmitters. ”

“ We will also extend the integrated application of remote-sensing satellite data on land, ocean and meteorology, advance the construction of infrastructure for integrated application of the BeiDou Navigation Satellite System, satellite communications, and the ground communications network, and improve our capacity to tailor and refine professional services. ”

“ We hope the last few pages haven’t given you a wrong impression of satellite communications. It is easy to assume, when we list the orderly, step-by-step progress from purely theoretical ideas to a working satellite such as Telstar, that everything has gone like clockwork. ”

“ One of the attractive things about using a satellite is that it doesn’t require a revolutionary breakthrough in technical knowledge. It can employ a satisfactory means of communicating that is already available: the microwave radio relay. Today, this kind of transmission is used on a routine basis to send thousands of telephone calls and television programs across long distances. It gives high-quality performance and has a large message capacity. ”

“ Fortunately, modern technology—given a boost by the world’s interest in rockets, missiles, and the exploration of space—has shown us one answer to this problem: the communications satellite. The conventional pathways for long-distance communication have led along the earth’s surface, under the oceans, and through the lower atmosphere. ”

“ Communications satellites can be grouped into two broad categories. Passive vehicles reflect signals from one ground station to another. Active satellites accept ground signals and either amplify and rebroadcast them immediately or record messages for later transmission.
The Echo satellite balloons typified the passive category of communications spacecraft. These satellites “bounced” radio signals from one ground station to another. Uninflated Echo payloads were carried into orbit packed in special storage containers. ”

“ Within the white aluminum-oxide outer shell of the satellite is crammed a complicated array of electronic equipment. Surprisingly, most of this gear has to do not with Telstar’s prime function—communications—but with its command and telemetry systems. The reason is that the satellite is an experimental device, not just a spectacular way to relay television programs. Altogether, the satellite’s various electronic circuits contain more than a thousand transistors and almost 1500 semiconductor diodes, plus a single electron tube—a traveling-wave tube used in the communications amplifier. ”

“ Relay satellite superimposed on artist's conception of space. Within five years, advances in space technology may create an operational communications satellite system that will vastly increase intercontinental telephone, telegraph, and data exchange channels and make possible transocean television. Contributing to progress toward this new communications era is NASA's Relay satellite program. ”

“ In this section we will go into some detail about Project Telstar. We do this because much of what we learned from this project applies to the general field of satellite communications. The problems that were faced and solved are typical of the challenges that working engineers and scientists must meet today. And there is, of course, another reason to put this much emphasis on Telstar: The six case histories in Part II of our book were written by men who were involved with that project. ”

“ Project Telstar is actually an extension into space of microwave communications methods that have been thoroughly proved on the ground. For Project Echo and other early experiments in satellite communications, Bell Laboratories built a large antenna of the type known as a horn-reflector in Holmdel, New Jersey. For Project Telstar, a similar but much larger antenna was designed. It was located in a relatively isolated spot at Andover, in the western part of Maine, where it would be close to Europe. ”

“ As you can see, we have picked problems that offer a good deal of variety. Some of them have been satisfactorily solved; for others the solutions are not yet complete. Some deal with basic scientific research; others are much more concerned with the engineering applications of technical knowledge. Some were solved by careful, logical thinking; others were solved almost by accident. Some deal with a particular immediate task (in this case, Project Telstar) ; others are more concerned with general planning for satellite communications. ”

“ On December 31, a check of the satellite revealed that it was functioning satisfactorily except for a small power drain by voltage regulator No.1.
Because of difficulties experienced with the command system of transponder No.1, project managers decided to employ the other transponder. On January 3, 1963, they activated transponder No.2 and carried out a continuing sequence of transatlantic television, telephone, and teletype communication tests. Some difficulty has been encountered with the command system of the satellite. ”

“ When this book was written satellite communications was still a technological infant. It is growing and changing so swiftly that much of what we say may soon be out of date. That can’t be helped, of course, and we ask you—who may be reading it long afterward—to be tolerant. ”

“ If a communications satellite is to go into regular commercial service, it must continue working for several years in space. The Telstar satellite, however, was designed as an experimental project, and we decided that two years would be a reasonable lifetime to plan for. When Project Telstar began, our problem was to develop solar cells that would operate in an environment subject to strong radiation effects—and keep on operating there for two years. ”

“ Now you, who have in your own homes seen pictures transmitted across the ocean by satellite, can learn first hand from the men who worked on hard and varied technical problems just what these problems were and how they were solved. And, by reading you can find out what sort of knowledge, training, and habits you yourself will need if you wish some day to adventure into those undiscovered or unexplored fields of technology which will be new and exciting when Telstar has become old hat. ”

“ It isn’t possible to build an antenna that radiates at exactly the same power in all directions. Telstar’s antennas work very well, but they operate better in the direction of the satellite’s equator than they do towards its poles. This means that if the spin axis is constantly changing transmission will fade in and out—even at times passing through “null” where no transmission at all is possible. No single fixed orientation is perfect for the spin axis, but we decided that the best average position would be to keep it always perpendicular to the plane of the earth’s orbit. ”

“ The exterior of eight-sided Relay is composed of honeycomb aluminum panels studded with 8215 solar cells.
The world’s first commercial communications satellite was called “Early Bird,” or INTELSAT 1. Built a decade ago by Hughes Aircraft Company for Communications Satellite Corporation (COMSAT) , Early Bird could transmit simultaneously on 240 two-way channels for telephone, telegraph, or data transmission. Transatlantic telephone circuit capability increased by 50 percent once Early Bird went into orbit on April 6, 1965. ”

“ Inmarsat - International Maritime Satellite Organization (London) ; provider of global mobile satellite communications for commercial, distress, and safety applications at sea, in the air, and on land. Intelsat - International Telecommunications Satellite Organization (Washington, DC) . Intersputnik - International Organization of Space Communications (Moscow) ; first established in the former Soviet Union and the East European countries, it is now marketing its services worldwide with earth stations in North America, Africa, and East Asia. ”

“ Review of national and defense policy relevant to the requirements for, acquisition of, and use of commercial satellite capabilities, and the relationship with commercial satellite providers. (2) Assessment of the manner in which commercial satellite capabilities are used by the Department of Defense and options for expanding such use or identifying new means to leverage commercial satellite capabilities, such as hosting payloads. (3) Review of military requirements for satellite communications and remote sensing by quantity, quality, timeline, and any other metric considered appropriate. ”

“ A man-made satellite’s position relative to the earth is very like that of the earth in relation to the sun; the earth, after all, is itself a satellite of the sun. And during most of its useful life a satellite will be in thermal equilibrium—it will be losing just as much heat energy by its own radiation into space as it will be gaining from other sources, primarily the sun. Since the total amount of energy it absorbs is equal to the amount of energy it emits, Qbody is equal to Qsun. ”

“ It is hard enough to fix a new piece of scientific equipment when it goes out of order in the laboratory. And when the equipment is sailing around the earth a couple of thousand miles up in the sky a repair job ought to be impossible. But during the last two months of 1962 we found this not to be true at all. That was when the Telstar I satellite began to misbehave and eventually would not obey the commands we sent it from the ground. ”

“ They tell us how fast we must move a precision tracker to follow the satellite through the sky, how much time a satellite will spend above the horizon, and how long will be the time from one chance of seeing it to the next. However, in the Echo project we were not merely concerned with planning our experiments from hour to hour; we also needed to know how the satellite would move for weeks and perhaps months in advance. When you study the motion of a satellite over such a length of time, you discover that its circular orbit will not remain the same as it was at launch. ”