contained systems and shore-based systenns. Under each of these 

 general types there are existing aids and those undergoing research 

 and development. All have certain advantages and disadvantages. 

 Let us consider the aids under these two categories. The first are 

 the self-contained systems, which are not dependent upon any sig- 

 nal from the shore. 



The most primitive method of celestial navigation is the time- 

 honored use of a HAND-HELD SEXTANT. Although an experienced 

 navigator can obtain fixed accuracies of about two miles, the use 

 of the sextant is limited to periods when both the real horizon and 

 the celestial body are clearly discernible. 



The usefulness of celestial navigation could be extended by 

 increased telescope power and inertial techniques to determine 

 either horizontal or vertical references. The OPTICAL STAR 

 TRACKER embodies these features. Essentially, it is an optical 

 telescope used in conjunction with a stabilized platfornn and a com- 

 puter. Despite these improvements, the benefits of optical data 

 will continue to be limited to periods when the celestial body is 

 visible. This limitation, coupled with the complexity and cost of 

 the equipment, makes the optical star tracker of questionable va- 

 lue for widespread use in the oceanographic program. 



Because of solar microwave radiation, a method of foul- 

 weather celestial navigation is possible. The RADIO SEXTANT 

 combines the best features of radio, celestial, and inertial 

 techniques. This instrument tracks the sun or moon by sensing 

 the direction of thermal microwave radiation from these bodies. 

 Current evaluation of this system indicates an average accuracy 

 of about two miles. Principal disadvantages of the system are the 

 weakness of radiation from the solar bodies and the restriction to 

 only two sources. Despite these two disadvantages, the radio 

 sextant comes close to attaining the ideal characteristics. It is 

 less expensive than the optical star tracker, on the order of 

 $150, 000 as compared to $600, 000 per unit, and is capable of 

 providing nearly worldwide coverage. Coupled with inertial com- 

 ponents for dead reckoning functions, it could provide almost 

 continuous data. So, although the radio sextant does have limita- 

 tions, it may be the only aid available which will provide coverage 

 in the immediate future over the large ocean areas of the Southern 

 Hemisphere. It should be considered for this area of operation. 



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