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Neutral Mass Spectrometer (NMS)

NSSDC ID: 1998-041A-02
Mission Name: Nozomi
Principal Investigator: Dr. Hasso B. Niemann


The Planet-B Neutral Mass Spectrometer (NMS) will make in-situ measurements of the elemental and isotopic composition of the upper atmosphere of Mars. The primary scientific objectives of the investigation are to determine the variation of the neutral composition with altitude, season, local solar time, and solar activity; to study the composition, temperature, evolution and dynamics of the upper atmosphere and the effects of lower atmosphere dust storms on the upper atmosphere; and to study the formation of the ionosphere. NMS will also be used as a resource for other studies of the upper atmosphere, ionosphere, and solar wind interactions. 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 130 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 cylindrical with a 15.0 cm diameter and a length of 26.75 cm. It is mounted on the same side of the spacecraft body as the magnetometer. The aperture is at one end of the cylinder, pointing normal to the spacecraft panel, and is covered with a metal-ceramic breakoff cap which seals the instrument and is pyrotechnically removed after Mars orbit insertion. NMS uses a dual frequency quadrupole mass analyzer with a mass range from 1 to 60 AMU (atomic mass units), two off-axis secondary electron multipliers, and a retarding potential ion source which is collinear with the analyzer. The ion source will be operated alternately in "closed source" and "open source" (molecular beaming) modes to increase measurement accuracy, the closed source to measure non-surface reactive neutral species and the open source to measure direct beaming chemically surface active species.

The ion source is an electron gun which uses a heated filament. The mass analyzer consists of four mounted hyperbolic rods with an applied AC and DC potential to create a dynamic electrostatic field. A radio frequency generator drives the quadrupole at two frequencies (3.25 and 4.85 MHz). The two secondary electron multipliers differ in sensitivity by a factor of roughly 2000 and detect ions exiting the analyzer. They are of the continuous channel type and are 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 maximum spatial resolution of the instrument is 55 meters along the spacecraft track. Peak power is 11.8 W and standby is 6.3 W. NMS measurements will take place in a 20 minute time span centered on the near-equatorial periapsis.

Alternate Names

  • NMS

Facts in Brief

Mass: 2.54 kg
Power (avg): 7.4 W

Funding Agency

  • National Aeronautics and Space Administration (United States)


  • Planetary Science: Atmospheres

Additional Information

Questions or comments about this experiment can be directed to: Dr. David R. Williams.



NameRoleOriginal AffiliationE-mail
Dr. Hasso B. NiemannPrincipal InvestigatorNASA Goddard Space Flight Center 

Selected References

Bougher, S. W., and H. Shinagawa, The Mars thermosphere-ionosphere: Predictions for the arrival of Planet-B, Earth Planets Space, 50, No. 3, 247-257, 1998.

Niemann, H. B., et al., The Planet-B neutral gas mass spectrometer, Earth Planets Space, 50, No. 9, 785-792, 1998.

Image of the Neutral Mass Spectrometer (NMS) experiment

Neutral Mass Spectrometer (NMS)

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