The ISEE Electron Density Experiment

The French electron density experiment aboard the ISEE 1 and 2 satellites really consists of two separate, but complementary, experiments to measure the total electron density by means of radio techniques. Both experiments are new: one flew above the ionosphere for the first time on the satellite GEOS, launched in April 1977, while the other takes advantage of the unique ISEE feature of having two spacecraft which are always relatively close together. The principles and the realization of both experiments are described.