TECHNICAL BARRIER: VEHICLE BOTTOM NAVIGATION 



The vehicle botton navigation technical barrier has two parts: 

 Operational Navigation and Precision Bottom Navigation. 



OPERATIONAL NAVIGATION 



Operational Navigation is knowing the location of the CURV vehicle 

 with respect to the support vessel accurately enough to allow the vehicle 

 to operate within the radius of the buoyed portion of the cable or "whip. " 

 If the vehicle attempts to move beyond the length of the whip cable, it 

 begins to pull a catenary in the main cable, which hangs vertically from 

 the support vessel. The vehicle does not have enough power to do this, 

 and the vehicle loses all maneuverability. In fact, if the support vessel 

 happens to be drifting in the other direction, the vehicle will be pulled off 

 the bottom and out of the work area. To prevent this, the location of the 

 vehicle with respect to the support ship must be known, so if the vehicle 

 begins to utilize all of the whip cable, it can be determined how far and 

 in what direction to move the support vessel to give the vehicle added 

 cable for maneuvering. 



Present CURV systems utiHze a directional hydrophone which is 

 lowered over the side of the support vessel to track the vehicle. This 

 hydrophone can be trained in azimuth or tilted. The hydrophone listens 

 for a 37.5 kc pulse which is being emitted from the vehicle. 



This technique for determining vehicle location is definitely limited 

 to shallow water work since the angle between the support ship vertical 

 reference and the vehicle becomes very small as the depth increases. 

 For example, at 20,000 feet with a 600-foot whip, the angle is only 1.5°. 



It is anticipated that an operational navigation system can be installed 

 on the CURV IV support vessel, but at present no system is in operation 

 which meets the CURV needs. There are, however, equipments which 

 probably could be modified, installed, and evaluated to meet the 20,000- 

 foot CURV needs. A short base-line system, one in which several 

 hydrophones are mounted on the support vessel, as opposed to a 

 long base-line system, one consisting of transponders or beacons 

 forming a grid on the bottom, appears most desirable for a CURV opera- 

 tional navigation system, since it is undesirable to have to drop, calibrate, 

 and recover bottom-moimted equipment during typical CURV operations. 

 There are three basic types of short base line systems which may be used 



164 



