  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. That isn’t the case at all—and in the rest of this book we are going to show you why it isn’t. Many problems had to be solved; many scientific and technological advances had to be made. We touched on a number of the problems of satellite communications in our detailed account of Project Telstar. Most of them are not confined to that project—they are the sorts of questions that any complex advance in satellite communications will run into. We will list some of the more important ones here. Then, in Part II, we will talk about some general methods of solving scientific and technological problems. All this is a rather roundabout—but necessary—way of leading up to our main interest: the accounts by six Bell Laboratories engineers and scientists of their work to solve some typical problems in satellite communications. The many complications of satellite communications can be divided into several groups. First of all, there are the problems involved in fitting satellite communications into an already established world communications system. There are, next, many problems, both small and large, in designing the right kind of satellite. There are the problems of launching a satellite and getting it into the proper orbit. There are the problems in making sure it stays in the right orbit once it gets there. And, finally there are the problems in seeing that it continues to do its job reliably. In these five categories there are a lot of specific questions that must be answered to plan a working satellite communications system. A list of some of them follows. We haven’t attempted to cover everything, but these should give you some idea of the tasks and questions involved in planning an immense project like this.
Types of Satellite OrbitsCircular Orbit—an orbit whose altitude from the earth remains constant; it makes a circle that has the center of the earth as a center. Elliptical Orbit—an orbit whose altitude from the earth varies from one extreme to another; it makes an ellipse with the center of the earth as one focus. The orbit’s lowest altitude is called the perigee, its highest altitude is called the apogee. Equatorial Orbit—an orbit in the plane of the earth’s equator. Polar Orbit—an orbit in a plane formed by the North and South Poles. Synchronous Orbit—an orbit whose period is 24 hours, the same as that of the earth revolving on its axis—so that the satellite’s and the earth’s angular velocities are the same. Although there are many possible kinds of synchronous orbits, each must have an average altitude above the earth’s surface of approximately 22,300 statute miles. Stationary Orbit—an orbit that is circular, equatorial, and synchronous—so that the satellite will appear stationary from any point on the earth. Inclined Synchronous Orbit—an orbit that is synchronous but not stationary, since it does not follow the plane of the equator. From a point on earth, it will appear to follow a figure eight pattern about a line of constant longitude. |
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