II. SUMMARY 



A. LONG-RANGE NAVIGATION SYSTEMS 



Long-range navigation systems (Table II- 1) are defined here as having 

 a position fixing capability at ranges greater than about 400 miles . Celestial, 

 azimuthal, pulse -time, and phase -measuring systems comprise the largest 

 number of navigation systems in this group. Dependent upon requirements 

 satellite systems may use combinations of these methods to yield accurate 

 fixes . Inertial, and acoustic -do ppler systems are essentially highly sophisti- 

 cated dead -reckoning systems with potential world-wide coverage and position 

 indicating capability. Of these only the inertial systems are completely passive 

 and self-contained. 



The inexpensive, hand-held sextant, tables, and chronometer are still 

 the basic tools of the navigator and give him the possibility of a ±3 mile posi- 

 tion fix twice daily. Recently developed star tracker and sun and moon tracker 

 equipment uses gyro -stabilized references, making a horizon unnecessary. 

 Each of these celestial systems is limited by cloud cover or by the geometry of 

 the sun -moon orbits . These factors limit the current world-wide availability 

 of fix by celestial methods to below 50%. Because of their high cost, the auto- 

 matic star and sun-moon tracker systems can usually be justified only for 

 specialized applications . 



Of the several azimuth measurement systems being used, the Consol/ 

 Consolan and the Radio Direction Finder (RDF) systems have gained the widest 

 acceptance . Both systems require simple and inexpensive receiving equipment 

 and have several stations along the coasts of North America and very good 

 coverage throughout most of Europe. The precision of fix is not high by today's 

 standards, and powerful ground stations and good operating conditions are re- 

 quired for the navigator to obtain a fix at ranges beyond about 300-600 miles . 



Pulse-time measurement systems are capable of fixing a ship's posi- 

 tion by the reception and identification of pulses received in a timed sequence 

 from transmitting stations of known position. About 35% of the northern hemi- 

 sphere is effectively covered by Loran-A. The more recent Loran-C equipment 

 makes use of lower frequencies and uses both pulse -time and phase -measuring 

 techniques . Although the coverage is not yet as great as that of the earlier 

 Loran-A, the system is useful to ranges of 1000-2300 miles and is capable of 

 high accuracy . With good operating conditions system accuracy can approach 

 one foot per mile of range . The recent incorporation of microcircuitry into 

 Loran-C receiving equipment will greatly reduce its size, weight, and eventual 

 cost, and make it much more reliable than the present electromechanical equip- 

 ment. 



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