Firing Mechanism 



The firing mechanism (components shown in Figure 2) consists of a 

 weighted touchdown rod with a 2%- inch square base pad, a safe and arm 

 device (S&A) , and a power package with a nickel-cadmium battery supply 

 and the appropriate electronic circuity to sequentially energize two 

 solenoid valves within the safe and arm device. 



The touchdown rod slides freely when frontal force equalling the 

 resistance supplied by \ psi shear strength soil acts upon it. The 

 force required to cause a bearing capacity type failure in h, psi soil 

 is equivalent to a water-drag force on the rod occurring at 17 ft/sec, 

 which is considerably greater than the lowering velocity, 2 ft/sec, 

 thus providing a satisfactory margin of safety. 



The S&A, Figure 9, consists of a cartridge of high pressure (1100 

 psi) nitrogen (N-2) , an inflator, a 1200 psi volt two-way normally 

 closed solenoid valve, a 750 psi 24 volt three-way normally vented to 

 S&A chamber solenoid valve, a 440 psi ±10% gold shear disk, a firing 

 pin piston/cylinder, a MK43 Mod 1 detonator mounted in a spring return 

 out-of-line plunger, a lead cup, and a lead block. These are all con- 

 tained in an aluminum housing. To minimize cost and ensure high 

 reliability, the shear disk, firing pin, detonator, and plunger arrange- 

 ment used is a proven system from the SUS (Signal Underwater Sound) 

 MK59 series of which several hundred thousand units were manufactured 

 and used with very good safety and detonation records . 



As the anchor is lowered, hydrostatic pressure arms both the 

 electronic package and the S&A. The electronic package is armed by a 

 pressure switch, and the S&A is armed by the spring-loaded arming 

 plunger moving into the in-line position. Firing will occur upon 

 touchdown in water depths of 100 feet or more. The electronic package 

 and the S&A remain in this armed condition until touchdown or until 

 being recalled above the arming depth, in which case they both would 

 disarm automatically. 



When the anchor touches the seafloor, a magnet located atop the 

 touchdown rod moves in cloase proximity to the fluke-mounted magnetic 

 switch, momentarily closing it. The power package activates the three- 

 way valve completing the gas flow path to the shear disk. The power 

 package delays 30 msec to ensure that the three-way valve has time to 

 change state, then it activates the two-way valve. The gas passes 

 through both valves and the pressure above the shear disk increases 

 until it ruptures at 400 psi. After rupture the pressure acts on the 

 top of the firing pin pushing it down like a piston until it strikes 

 the detonator. This sets off the detonator which in turn sets off 

 the lead cup (CH-6 and explosive) lead block high order (CH-6) (Figure 

 9). The shock wave set up by the high order detonation travels across 

 the gap between the end of the CH-6 column and cartridge to fire the 

 cartridge's primer. 



