Show how to find the optimum specific impulse for an electrical propulsion system to be us...

Show how to find the optimum specific impulse for an electrical propulsion system to be used for missions with large payload. Assume that the thrust is constant. Consider the mass of the electrical power generation equipment  to be proportional to the power produced, and all other structural mass to be proportional to the sum of the payload, power plant, and propellant masses. That is,

Show how the results of using these assumptions with β = 0.05 and α = 10 kg/kW compare with the results shown in Fig. 10.11.