Positive Ion Probe

A gridded sphere with a -6 V negatively biased collector surrounded by a grid at the payload potential. It measures a current proportional to the density of positive ions, the rocket velocity, and the probe’s cross section. On the upleg the height resolution depends on the sampling rate, on the downleg the highest value in each spin period represents the undisturbed ion density. Absolute values are obtained by normalization to the electron densities above say 90 km.