20 kw-hr for 2 kw lamps 

 10 kw-hr for remaining gear 



Total stored energy will then be about 224 kw-hr. Because of greater 

 efficiency, silver/zinc batteries will be used which have a power density of 

 0.06 kw-hr/lb. The weight of the battery package will then be 

 224/0.06 = 3,740 lb. 



4. Helium Reservoirs. Because of its low density and nonflammable 

 nature, high-pressure helium would be used for displacing water from the 

 ballast tanks. The helium reservoirs will be constructed of HY-130 steel 

 formed into spheres. A trade-off study was conducted to determine the most 

 favorable weight to displacement ratio. The results are shown in table C-1 . 

 The constraints used in the analysis were that: 



1 . The maximum diameter of individual spheres would not exceed 

 6 feet. Large diameter spheres would be too unwieldy. 



2. The maximum thickness of the spherical shell could not exceed 

 3 inches, since thicker sections would create unusually trouble- 

 some welding problems. 



3. Six would be the maximum number of spheres allowed. A 

 greater number would create the need for complex piping and 

 valving and thus afford a greater chance for system failure. 



The near optimum arrangement appears to be five, 6-foot diameter 

 spheres with a wall thickness of 2.0 inches and an operating pressure of 

 7,650 psia. At this pressure, the stress in the spherical shells is one-half of the 

 130 ksi yield strength (safety factor of 2.0). Although this arrangement 

 represents the most favorable weight to displacement ratio, the submerged 

 weight of the sphere array is still 5,920 pounds. In order to insure near 

 neutral buoyancy of the lift vehicle, this weight must be compensated for by 

 the addition of syntactic foam. 



142 



