NAVIGATION — CANOES TO SPACESHIPS — DRAPER 305 



celestial sphere. The hour angle, star observations, and almanac data 

 are the elements used to find locations on the earth by conventional 

 methods of navigation. 



The geometrical principles associated with the use of a nonterres- 

 trial reference space for the purposes of navigation have been known 

 and applied for centuries. Many techniques for using these princi- 

 ples, difiering in details from the process that has been described, are 

 possible. This fact is not important for the purposes of this paper, 

 which is primarily concerned with describing the place of inertial 

 methods among other ways of locating points on the earth's surface. 

 It will appear that inertial navigation is geometrically analogous to 

 celestial navigation. The essential difference lies in the use by iner- 

 tial systems of gyroscopically controlled, rigid body members to serve 

 the functions of the celestial sphere as a nonterrestrial reference space. 



NAVIGATION BY RADIO AND RADAR 



Navigation by the use of terrestrial landmarks, a very old art, was 

 revolutionized during the first decades of the 20th century by the new 

 science of electronics. This revolution came from applications of 

 radio techniques to maintain radiation links between vehicles and 

 points with known locations on the earth by the use of electromag- 

 netic radiation having wavelengths much longer than those of visi- 

 ble light (fig. 3). Darkness, bad weather, distance, and obstructions 

 that affect visual observations do not interfere with these long- wave- 

 length contacts with landmarks that are radio stations or reflectors. 



Radio direction fhiders are now conunon equipment for aircraft 

 and marine vessels and serve as basic aids to navigation by giving 

 bearings to known stations. Signals set up in the fashion of the "A" 

 and "N" quadrants that are associated with the radio beams of civil 

 airways have been used for several decades to guide airplanes. Higher 

 accuracy and wider coverage in fixes are possible by applying the 



FOG-ENSHROUDED ^~^±^ 

 COASTLINE =.^^^ 



~ SHIPBORNE DIRECTION-FINDING EQUIPMENT DETECTS PORTION OF RADIO SIGNAL BEING 

 _^ EMITTED FROM SHORE STATION ANDDETERMINES DIRECTION FROM WHICH IT COMES. 

 — BEARINGS ON TWO SHORE STATIONS PROVIDE A POSITION FIX. 



Figure 3. — Application of radio techniques to terrestrial navigation. 



