CASE HISTORY NO. 5
Would Time Delay Be a Problem in Using a Synchronous Satellite?
Peter D. Bricker
Psychologist—Member of Staff, Behavioral Research Laboratory
THE PROBLEM
One of the satellite communications systems that has been proposed would make use of stationary synchronous satellites. These would be precisely located above the earth’s equator in orbits 22,300 miles high, where they would circle the earth once every 24 hours, and thus appear to remain stationary over a point on the earth. There are several advantages to this type of system—the most important being that we would need only three satellites for communications between almost all the inhabited regions of the earth.
On the other hand, there are several problems in establishing a synchronous system. Just getting the satellites into exactly the right places and keeping them in position is a formidable one. We also have something of a mystery to contend with, because of the tremendous distances that would be involved. Although we can communicate at speeds close to that of light—186,000 miles per second—we cannot go any faster than that. You might think that 186,000 miles a second was fast enough for us, and most of the time it is. However, if you send signals 22,300 miles up into the sky, transmit them back to earth, perhaps send them up again to a second satellite, and finally bring them 22,300 miles back down to earth, even the speed of light may not be fast enough. The delay will be only about a second or so, but it may—for some kinds of communications—be long enough to cause trouble. How much trouble, we don’t yet know.
For one-way signals such as television, a transmission delay of about one second obviously makes little or no difference. But for two-way conversations on the telephone, where there is rapid back-and-forth talking, even this tiny amount of time delay may be a problem. And then again, it may not be. There have been a lot of experiments to find out something about this delay problem, and these have given us a lot of different answers. Work is still going on, and there is still much to find out. In this chapter, we tell you about one small, early experiment. Its results were not conclusive, but they should give you one example of how to set up and carry out a typical experimental study on human behavior.
Typical circular satellite orbit: r is distance from center of earth to satellite; R is radius of earth.