Neutral Mass Spectrometer (NMS)
The Planet-B
Neutral Mass Spectrometer (NMS) will measure the elemental and isotopic composition of the
upper atmosphere of Mars. Vertical and horizontal density distributions of the major
neutral constituents, including hydrogen, helium, atomic and molecular nitrogen, atomic
and molecular oxygen, nitrous oxide, carbon monoxide, carbon dioxide, and argon will be
obtained, as well as elemental isotopic ratios. Neutral temperature profiles will be
determined from approximately 500 km to 150 km above the surface. These data will be used
to determine the existing dynamic, chemical and thermal state of the upper atmosphere.
The NMS is a virtual copy (with minor modifications) of the Pioneer Venus Orbiting Neutral Mass Spectrometer. The instrument is a quadrupole mass spectrometer with a mass range from 1 to 60 AMU (atomic mass units) equipped with a retarding potential ion source, a high resolution quadrupole mass filter, and an off-axis secondary electron multiplier. The ion source will be operated alternately in "closed source" and "open source" modes to increase measurement accuracy. The secondary electron multiplier ion detector is of the continuous channel type and it is similar to those used in the Galileo Probe Mass Spectrometer, the Cassini INMS and Huygens GC-MS instruments. A commandable unit mass or fractional mass scan format for selected masses or the full spectrum is used to optimize data return. Other operating modes can be selected by ground command for specific scientific investigations. The highly elliptical equatorial orbit is designed to probe both the low altitude atmosphere and ionosphere as well as the solar wind interaction regions.