A Rocket-Borne RF Capacitance Probe for Determining Electron Densities

The design and operational characteristics of a rocket-borne radio frequency (RF) capacitance probe for obtaining electron densities in the 60-100-km altitude are described. The design objective was to provide a simple inexpensive system suitable for synoptic measurements of electron density. Basically the probe consists of a coaxial capacitor which is exposed to the atmosphere. This capacitor is the frequency control element of a 5-MHz oscillator. As the dielectric constant is a function of the electron density within the capacitor dielectric, the oscillator frequency changes are related to electron density. A simple procedure, which ignored sheath effects, was used to calibrate the probes. Despite this calibration deficiency electron densities derived from data obtained during two test flights were reasonable and agreed with results obtained from other experiments in this altitude region.