A document describes a suite that provides four simultaneous ion and neutral-atom measurements as a function of altitude, with variable sensitivity for neutral atmospheric species. The variable sensitivity makes it possible to extend the measurements over the altitude range of 100 to more than 700 km. The four instruments in the suite are (1) a neutral wind-temperature spectrometer (WTS), (2) an ion-drift iontemperature spectrometer (IDTS), (3) a neutral mass spectrometer (NMS), and (4) an ion mass spectrometer (IMS).
The instrument suite has four sensors consisting of two different types of analyzers. The first two are energyangle spectrometers: WTS for the wind-temperature-O/N2 ratio and IDTS for the ion drift-temperaturedensity ratios. The other two use a mass analyzer that allows two spectrometers to be combined into a single rectangular package, one-half for ions (IMS), the other for neutrals (NMS). The high payload velocity enables measurement of non-Maxwellian energy distributions, and also the separation of O from internal ion source products.
All instruments point in the same direction and require their common axis to point within 5° of the payload velocity vector to achieve the desired performance. In their simplest mode of operation, WTS and IDTS derive the component of the wind and iondrift that is perpendicular to them. This is obtained from the angle of the peak of the neutral (ion) flux passing the entrance aperture. The angular distribution of the particle flux appears on the detector plane. The line passing the aperture from outside represents the total velocity vector, the vector sum of the wind, and the payload velocity. Knowledge of the payload velocity coupled with precise knowledge of the peak plus the pointing of the WTS (IDTS) axis then yields the wind vector.
This work was done by Federico Herrero and Hollis Jones of Goddard Space Flight Center, and Theodore Finne and Andrew Nicholas of the Naval Research Laboratory. GSC-15964-1