was installed on the vehicle and Is shown to illustrate the 

 type of construction. The structural members are all of 

 606I-T6 aluminum. The round stock is I-I/2" solid bar. 

 The rest is 2" x 2" x 3/8" angle except for the 8" channel 

 belt at the tow point. An electronic light source is mounted 

 at each end with two cameras Just aft the tow point, approx- 

 imately half way between the two lights. The telemetry 

 system, battery, transponder, and other equipment are mounted 

 in the space between the cameras and the two lights. Not 

 shown in the figure are the boom which supports the magnetome- 

 ter head approximately four feet behind the rear light source, 

 and the side-looking sonar transducers which are mounted on 

 the sides of the vehicle. The open construction is used to 

 allow modification of the sensor package in order to fit the 

 job at hand. Since the unit is towed at speeds of about one 

 knot, the added drag resulting from this type of construc- 

 tion is not significant when compared to the drag of the 

 cable . 



MAGNETOMETER 



As in the THRESHER search, the magnetometer was the most 

 useful non-optical sensor used in locating the SCORPION. The 

 NRL designed proton precession type unit has a toroidal head. 

 This head reduces noise due to stray electrical fields and 

 eliminates the null that results when the polarized field is 

 parallel to the ambient field. The problem of winding a hollow 

 toroidal coil was solved by using a wax form. After the head 

 was wound, it was impregnated with epoxy and then heated so 

 the melted wax could be poured out. Recently, we have found 

 an easier method which uses hollow plastic cores obtained from 

 an inexpensive Infant's toy called "Rock-a-stack" . 



During most of the search, the magnetometer head was mounted 

 on a boom approximately four feet aft of the rear electronic 

 light source. The pressure housings for the flash and most of 

 the other instruments are made of 17-^PH stainless steel. This 

 material is very strong but also ferromagnetic. The bottles 

 therefore distort the earth's magnetic field. As a result 

 variations in the "fish" heading introduce fluctuations in 

 magnetic intensity. The level of these fluctuations varied 

 considerably as a function of heading, speed, and other 

 variables. Levels higher than 100 gamma were measured, a 

 small portion of the time. Since the size of the centerwell 

 precludes lengthening the boom, we experimented with towing 

 the head below the "fish", and this significantly reduced the 

 fluctuations . 



Unlike the THRESHER area which was fairly uniform as far 

 as magnetic measurements were concerned, the SCORPION area 

 contained a large number of natural magnetic anomalies. 



43 



