Figure 7-18. Power distribution voltage trade. Consequently, there are two possible high voltage problems to be considered: (1) power loss due to interaction of the space plasma with the solar array and (2) ''sparking." Based on preliminary investigation of solar array power loss caused by plasma interaction, a power loss of 0. 02 percent was predicted for operation at synchronous orbit. It should be cautioned that this is a preliminary estimate based on tentative analytical math models and that flight testing should be undertaken to substantiate power loss prediction methods. For the second concern, solar array sparking, it was postulated by Lewis Research Center [14,15] that sparking might be controlled by insulating all conducting surfaces floating negative with respect to the space plasma. Provisions for insulation were not incorporated into the design of the solar array because of the lack of design data defining the sparking phenomena. Special emphasis studies have been initiated to analyze high voltage effects, but results are not expected for some time. For the second option it was assumed that the operating voltage of the transmitter tubes was increased to 40 kV and the voltage of the solar array and power line was increased correspondingly to 40 kV. By a first order approximation, the mass of the conductors was reduced from 13.6 x 106 kg to 6. 8 x 106 kg. The power loss due to plasma interaction was increased from 0. 02 percent to 0.04 percent. The effect of sparking remained undetermined. Option 2 is the lowest mass option for power distribution that requires the development of a 40 kV transmitter tube and a higher voltage switch gear.
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