Observations of electron currents, space potentials and ionic composition obtained by Langmuir-type probes installed on the DME-A (Explorer 31) satellite, were used to study the dependence of the region of disturbance around the satellite on the ionic composition. The ratio of the electron current in the wake of the satellite to the current ahead of the satellite, [Ie (wake)/Ie (front)], was found to vary strongly with the ionic composition, it has its minimum value at perigee altitudes (500 km), approaching unity at apogee (3000 km). A similar dependence was found for the ratio [φN (wake)/φN (front)] where φN = eφs.p./kTe and φs.p. is the effective space potential. This ratio varies from about 0·55 at perigee altitudes to 0·9 at apogee, indicating the amount of symmetry of the potential around the satellite's surface. The variation of the electron current and satellite potential with the angle between the normal to the probe and the velocity vector (angle of attack) was studied. The results from the Explorer 31 satellite are in complete agreement with earlier observations obtained from the Ariel I satellite. It is shown that the quantitative measurement of the electron depletion in the wake can serve as a diagnostic tool to measure positive ion composition within a reasonable resolution. A brief discussion of the present state of theoretical and experimental studies is given. Our results are compared with other studies. © 1969.
