8 _The equipment is now ready for communications signals to be sent from the two-kilowatt ground transmitter to the satellite._ 9 _The satellite receives the signals and converts them down to a frequency of 90 megacycles; they are amplified in transistor circuits and converted up to a new frequency of 4170 megacycles._ 10 _The signals are amplified again by the traveling-wave tube—for a total amplification of as much as ten billion times—to get a radiated power of 2¼ watts._ 11 _The 4170-megacycle signals are now transmitted in all directions by the satellite’s equatorial antenna._ 12 _These signals can be picked up at Andover or at any other ground station equipped with a suitable antenna that is within line of sight of the satellite._ 13 _At Andover, the received signals are amplified by means of a solid-state maser and a frequency-modulation-with-feedback circuit._ 14 _They can now be relayed via regular land lines to their destination._ 15 _Near the end of a pass, the command tracker turns off the communications circuits and telemetry in the satellite._ 16 _The satellite drops below the horizon._ Some Big Problems in Satellite Communications 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_.