Intervals Between Periods of No Service in Certain Satellite Communication Systems -- Analogy with a Traffic System

Several typos of communication systems have been proposed which would use repeaters orbiting the earth as artificial satellites. The problem considered in this paper arises in systems employing a number of satellites at altitudes of several thousand miles. Typically, the orbit altitude might be of the order of ;',00() miles with a period of revolution of about f) hours. The companion paper by Rinehart and Robbins 1 discusses the conditions under which a particular satellite will be visible to a given pair of ground stations. For the orbit altitudes considered here, the satellite will be visible intermittently. Conceivably the relative positions of the satellites could be maintained so that at least one satellite is mutually visible from (he two ground stations at all times. However, at least for some of the early systems proposed, it is of interest to consider the case 1671 1 ( V 7 G T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , S E P T E M B E R 1902 in which small differences in orbital period cause the relative positions of the satellites to vary with time. Attention is therefore directed to the statistical characteristics of satellite visibility. We are especially interested in those periods during which 110 satellite is available for communication between a given pair of ground stations. F o r convenience these events are called outages although, as pointed out by Rinehart and Robbins, these occurrences need not imply an interruption of calls in progress. By analogy the intervals between outages are called innages.