A solar power satellite in geosynchronous orbit can deliver power through a microwave beam to an Earth-surface receiving station for distribution by electric-power utilities. This nonpolluting power is available 24 hours a day. Spacecraft launch cost is predicted to drop from $10000 a pound to $1000 a pound, and the energy-conversion efficiency of the new multi-junction solar cells is approaching 40 percent. These developments can make the solar power satellite an economically competitive source of power. This satellite would be assembled in low-Earth orbit and then boosted to geosynchronous orbit with ion-propulsion rockets. Our tests and analyses show that a substantial leakage current will flow through pinholes in the solar array whenever the high-voltage positively charged portions of the array are in a plasma environment. For example, in passing through the peak plasma zone in the Van Allen belts at 500 km altitude the power loss can be 7.72 percent of the array's output. However, the propulsion engines will need only around one-fourth of the array's output. In geosynchronous orbit the electron density is only 100 electrons per cubic centimeter, and the leakage current will be insignificant during normal operation. However, the ion-propulsion engines, when fired to correct the spacecraft attitude, will release a plasma that could carry away 56 kA of current from a 40 kV solar array. Capturing the electrons from the plasma with a 20 volt shield before they drift into the solar array's high-voltage zone is one solution to this problem.