Problems of Reliability _How long will the satellite remain active?_ _What factors will affect its service life?_ _Should its equipment be made redundant?_ _What kinds of components will be most reliable in space?_ _What is the best way to test its equipment before the satellite is launched?_ _What effects will radiation in space have on the satellite?_ _How can its components be protected from these radiation effects?_ _How can it be insulated from extremes of temperature?_ _What can be done to protect the satellite from the shock and vibration of launching?_ _Will it be possible to repair an orbiting satellite?_ _Could a satellite be brought back from orbit to be repaired or salvaged?_ Types of Satellite Orbits Circular 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_. part 2 Satellite Communications Case Histories [Illustration: Title image] Six Typical Problems The questions we listed in Part I cover a very broad area of science and technology. Their answers involve, more than anything else, physics, electrical engineering, and mechanical engineering. Some, however, also require that the men who work on them know chemistry, metallurgy, mathematics, and occasionally even biology, psychology, geography, and economics. We obviously can’t show you how all the problems in Part I can be solved. Rather, we have picked six of them as examples. 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?_