Science: Rapid Transit

The compass, the chronometer, the sextant gradually changed navigation from an art to a science, made mere curiosities of such seafaring geniuses as the early Polynesians—who, according to legend, could smell land far beyond the horizon and head their boats accordingly. In 1960, man's most accurate substitute for weather-dependent celestial navigation is World War II's loran (for long-range aid to navigation), a system of cross-monitored radio signals that is highly expensive and covers only the more frequently traveled parts of the earth. Last week loran seemed destined for obsolescence, as an experimental Navy satellite called Transit I-B blasted into space from Florida's Cape Canaveral.

Transit I-B (an attempt to send Transit I-A into orbit failed last September) is only the first basic step in a process that is expected to take two years to develop. Many of the first press stories excitedly treated it as though it were already an operational system. It is not—however dramatic its promise for the future.

By Doppler Effect. Lofted by an Air Force Thor-Able-Star rocket. Transit I-B slanted around the world from 51° N. to 51° S. and settled into an elliptical orbit (apogee, 475 miles; perigee, 235 miles), sending radio signals from the moment it left the pad. From Texas to Hampshire, England, tracking stations sent information to a computing center near Washington, D.C. In future models, orbit-predicting data will be quickly rebroadcast to the satellite, which will remember its daily itinerary on magnetic tape, constantly announce it from space (the day-to-day orbital variations are minuscule, but would be vital to navigators).

The key to the navigation system is a common phenomenon first articulated scientifically little more than 100 years ago, when Austrian Physicist Johann Christian Doppler noted that sound waves coming from a moving object increase in frequency as the source of the sound approaches an observer, decrease as it moves away. Thus, in what has become the standard example of the Doppler effect, a train whistle seems to rise and fall in pitch as the train goes by. Similarly, the signals from a satellite increase in frequency as they move nearer to a receiver on earth, diminish as they move on. By measuring the rate of change of these frequencies, a navigator can determine his exact distance from the satellite's path. And since Transit will also announce just where it will be on its path at any given moment, a computer on shipboard will be able to tell the navigator where he is.

Scrounged Parts. Only one satellite is needed for an accurate navigational fix, but when the Navy's system is operational in 1962, four satellites will crisscross in a synchronization planned to serve all quarters of the earth. The advantage to commercial shipping will be slight, since present methods are more than adequate. But the military significance is great, may solve the major problem of missile shots from submarines: determining the exact distance and direction from the sub to the target. Cruising underwater far off the beaten track and out of loran's range, a nuclear submarine will be able to poke a whip antenna above the surface, take a fix on the nearest Transit satellite, and blaze away with lethal accuracy.