Embodiments of the present invention pertain to an apparatus that provides four simultaneous ion and neutral 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 kilometers. The four instruments included in the apparatus are a neutral wind-temperature spectrometer, an ion-drift ion-temperature spectrometer, a neutral mass spectrometer, and an ion mass spectrometer. The neutral wind-temperature spectrometer and ion-drift ion-temperature spectrometer are configured to separate O and N2 and O+ from H+ while the neutral mass spectrometer and the ion mass spectrometer are configured to separate mass with a resolution of one in sixty-four to enable metallic ion identification in the lower thermosphere. The energy analyzer features of the wind-temperature spectrometer and ion-drift ion-temperature spectrometer also enable the measurement of the thermosphere-to-exosphere transition in the Earth's upper atmosphere.