The Neutral Gas and Ion Mass Spectrometer (NGIMS) measures the composition and isotopes of thermal neutrals and ions.

  Goals:
*Determine structure and variation of neutral atmosphere and ionosphere with altitude over the globe from the homopause to above the exobase where the neutral gas can escape
*Provide a basis for the study of thermospheric energetics, transport, circulation and formation of the ionosphere
*Reveal the effects of lower atmospheric effects on the composition of the upper atmosphere and escape

Observations:
*Basic structure of the upper atmosphere (major species He, N, O, CO, N2, NO, O2, Ar, and CO2) and ionosphere from the homopause to above the exobase
*Stable isotope ratios, and variations

Technical details and heritage:
*Quadrupole Mass Spectrometer with open and closed sources
*Open source: neutrals and ions
*Closed source: non-reactive neutrals
*Mass Range: 2 – 150 Da
*Mass Resolution: 1 Da
*Modes: scan entire spectra or adapt to fixed masses
*Sensitivity: 10-2 (counts/s)/(particles/cm-3)
*Heritage from Galileo GPMS, Pioneer Venus ONMS, CASSINI INMS, Contour NGIMS