Ionospheric Limitations on Attainable Satellite Potential

Artificial satellites orbiting in the ionosphere normally tend to acquire a slight negative charge due to the high velocity of the electrons relative to the ion and satellite velocities. (At very high altitudes where the ionospheric electron concentrations are small, and in the presence of solar radiation, satellites tend to have a small positive charge due to the photo-electric effect, which in this case predominates over the ionospheric effect.) If the attempt is made to change the potential of a satellite by ejecting energetic beams of electrons or positive ions, the ionosphere provides some rather stringent limitations on the potential that can be achieved, for a substantial potential on a satellite causes appreciable currents to flow between the satellite and the ionosphere, which is a highly conducting medium containing a large reservoir of charge. The physics of the ionospheric limitation on satellite charge is investigated, and it is shown how the satellite charge and potential depend on injection currents and ambient charge density for both intermittent and continuous injection currents.