Some ionospheric measurements with satellite-borne ion traps

Two ion traps with plane geometry were flown in polar-orbiting oriented satellites, one in October 1961 and one in April 1962. Several results from these flights are at variance with our present understanding of the ionosphere. The measurements were confined to the altitude region from 200 to 500 km, and on the second flight data were obtained over many complete orbital paths. The measured ion concentrations varied from about 106 ions/cm3 to less than 2×103 ions/cm3 and the vehicle potential varied from less than one volt negative to twenty volts negative. In general the negative potential of the satellite was high when the ion concentration was low, although many exceptions to this occurred. At high latitudes, the data on occasion indicate large horizontal gradients, the ion concentration sometimes changing by factors greater than 2 in a few kilometers, and on one occasion it appeared to change by a factor of at least 50 in a horizontal distance of about 200 km. The temperature of the ions obtained from the ion trap data tends to be higher than that expected from present models of the ionosphere.