Electrostatic potential of an equatorial satellite

It is noted that a satellite moving in the ionosphere builds up a charge because of the differential rate of impingement of electrons and ions. A determination of the electrostatic potential is important in determining the electromagnetic forces and torques on the satellite and in interpreting the results obtained by on-board instruments; this potential also figures in wake structure studies. A conducting satellite, under steady conditions, becomes an equipotential if the magnetic field of the earth is neglected. In the presence of the earth's magnetic field, the satellite will no longer be an equipotential because of the induced V x B field. The surface electrostatic potential of a low-altitude spherical satellite of radius R is determined analytically. The satellite is moving with a constant velocity V perpendicular to a constant magnetic field B; the effect of ion thermal motion, the photoelectric effect, and the increase in the collection area for ions due to satellite potential are included. It is found that for a satellite having a diameter of 3 m at 1000 km the photoelectric effect can increase the satellite potential by 7% and ion thermal motion by 8%.