dealing with such familiar displays as compass heading, a heading error indi- 

 cator, and an analog speed indicator. Actually, the same data have been pro- 

 vided within the symbolic digital notation at the top of the display screen, 

 but they are much harder for the operator to decipher. The entire display is 

 available to the operator by depression of the "X" key on the console. Graph- 

 ic display of the meters is performed through interaction with the minifloppy 

 disk. 



VEHICLE ROUTINES. The software structure of the vehicle routines which actu- 

 ally operate the vehicle after the umbilical cable is disconnected and the run 

 has begun is shown in figure 13. The microprocessor first compares the pro- 

 grammed values of the heading and depth with the actual sensor readings, 

 sending the appropriate error signals to the thrusters through the appropriate 

 digital-to-analog converter. It then checks a series of emergency conditions 

 such as leaks, overpressure, or low battery voltage. If the emergency status 

 is bad, the processor aborts the mission, turns on an emergency beacon, and 

 comes to the surface. If the status is good, it checks for a possible abort 

 word from the console which might arrive through an acoustics or fiber-optic 

 communication link (to be installed in the future). If all is satisfactory, 

 the vehicle will check a clock chip to determine if it is time to start a new 

 leg. If not, the program will continue to cycle through as before; otherwise, 

 it will input the next leg of data and begin its execution. 



At present, vehicle navigation is done primarily by dead reckoning. How- 

 ever, it would be easy to install a "strap down" inertia! navigation system 

 using this same software structure, as time and funding permit. Items such as an 

 error-generating program for altitude, a current sensor, and doppler naviga- 

 tion would be straightforward additions to the present software structure. 



PERFORMANCE CHARACTERISTICS 



A summary of the performance characteristics for the MOSC free-swimming 

 vehicle is in table 4. 



The mechanical configuration is such that the vehicle can be packaged 

 within a cylindrical fairing in the future to increase its in-water speed from 

 its present 1.8 knots to a projected 5 knots. These figures represent the 

 speed at any depth down to the maximum operating depth of 2200 ft, since there 

 is no cable drag to slow the vehicle as with tethered submersibles. 



Likewise, the current 1-hr run duration can be extended to 4.4 hr by 

 simply replacing the present inexpensive, rechargeable, lead-acid battery pack 

 with a lithium battery pack currently under development. The approximate pay- 

 load capacity of the vehicle is currently 25 lb. This is also flexible in 

 that approximately 25 lb of additional payload can be added for every foot the 

 vehicle is increased in length. 



The configuration of three thrusters allows 3 degrees of freedom in the 

 water. The thrusters are canted 15 deg to allow a shorter turning radius. 

 Turning radii of less than the length of the vehicle (9 ft) were observed 

 during actual tests. 



30 



