The Dynamics Explorer wind and the temperature spectrometer

The Wind and Temperature Spectrometer (WATS) is designed to measure the concentration, kinetic temperature and motions (3 mutually perpendicular components of the wind) of the neutral particles. In addition, measurements of the concentration and velocity of the ambient thermal ions are possible. Two of the three wind components, the temperature and the concentration of the dominant constituent, can be measured to an altitude of about 650 km, the third wind component to about 375 km (estimated). Ion measurements can be made throughout the orbit. A quadrupole mass spectrometer is the basic sensor for the instrument. Measurements of the zonal and vertical components of the wind are made through interpretation of the modulation of the particle stream entering the mass spectrometer, induced by baffles that scan slowly (one vertically and one horizontally) in front of the entrance port of the mass spectrometer. The third component, horizontal, in the orbit plane, is obtained by evaluating the potential required to decelerate ions the quadrupole analyzer. The instrument affords measurement accuracies approximately as follows: concentration of neutral particles, 20%; their temperature, 5 K; and neutral winds by the baffle technique, 10-12 ms-1; neutral wind component by RPA technique estimated about 50 ms-1, with experimental confirmation of the latter to be obtained in orbit. (orig.)