their subsequent manning, maintenance, and operation. Significant savings without loss of 

 effectiveness could be achieved by substituting remotely controlled unmanned craft for 

 manned surface vessels and aircraft. By powering these robots with solar cells their cost of 

 operation would be low and their stationkeeping ability or range virtually unlimited. 



The unmanned surface patrol vessel can be conceived as a narrow, long submarine 

 sufficiently ballasted with lead batteries to have its flat deck continuously awash. The solar 

 cells mounted on the flat deck would provide sufficient power to keep the vessel on a preset 

 location or course during day and night regardless of wind, wave, or current conditions. The 

 unmanned patrol submarine would be equipped with passive sonar, active radar, television 

 cameras, IR imaging systems, and associated radio and video transceivers. The passive sonar 

 would be either mounted on the hull of the vessel or towed behind on a long cable. The other 

 systems, however, would be mounted on a hydrodynamically streamlined sensor mast to keep 

 them above the water spray generated by waves breaking on deck. 



To conserve power, only few sensors would be activated at all times. Other systems 

 would become only activated when triggered by an appropriate signal from the sonar indicat- 

 ing the presence of a surface target in the near vicinity of the patrol vessel. If needed, the 

 patrol vessel would depart from its assigned location and steer an intercept course for positive 

 identification of a suspicious surface or submerged target. If eminent danger exists that the 

 patrol vessel may be rammed or seized by a hostile target, it would emit a radio distress signal 

 and dive to a predetermined depth for cover. In some cases it may also submerge to obtain a 

 better signal-to-noise ratio of a submerged vessel transiting through its patrol area. Upon 

 surfacing, the gathered information would be transmitted by radio to the central monitor. 



The patrol functions of the surface vessel would be augmented and complemented 

 during day by a solar-cell-powered drone aircraft equipped with television transceivers. The 

 drone would cruise above the surface patrol vessel at such an altitude that two neighboring 

 surface patrol vessels would be visible at all times. 



The patrolling activity of the surface vessel and aircraft would be coordinated by a 

 satellite or family of solar-powered satellites orbiting overhead and relaying all information 

 gathered by patrolling craft to a central command post. Since solar-cell-powered aircraft 

 drones have already been built and experimentally flown with success, there is no technological 

 barrier to implementing the concept of remotely controlled, solar-cell-powered patrol aircraft. 



CONCLUSION 



Solar cells have been found to perform successfully underwater, although their power 

 output is significantly reduced with increasing depth of submersion. As a result of this power 

 output decrease, the ultimate visual contrast limit depth, which varies from 2.5 to 95 ft 

 depending on the type of water and location, is considered to be the practical limit for the 

 depth of the solar cell submersion. At this depth, the power output of solar cells has already 

 decreased by 95 percent from the value measured above water surface. 



The power output density of submerged solar cells located in the depth range between 

 the ultimate visual contrast limit depth and the water surface is considered to be adequate for 



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