Accuracy of Langmuir probe measurements and skin potential on satellites

Using a model ionosphere, we deduce realistic values for satellite floating potential for various geographic locations. The deviation in this floating potential is then calculated as one varies a Langmuir probe potential between ±3 volts. Using Theis's reduction program acting on an I-V probe characteristic, we deduce electron density and temperature values, compare these with our input values, and obtain the errors involved. Here we keep our attention on two sources of error: insufficient satellite conducting area, and the uncertainty of how to allow for photoelectric effects in the computer program. We find that the temperature errors can be kept small (less than 5%) by suitable selection of the amount and location of conducting area. The errors in density resulting from photoemission become significant at very low electron concentrations, less than 500 cm−3.