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Scientific Instruments

Neutral Mass Spectrometer (NMS)

The Planet-B NMS is a virtual copy (with minor modifications) of the Pioneer Venus Orbiting Neutral Mass Spectrometer. Vertical and horizontal density variations of the major neutral constituents in the upper atmosphere of Mars will be detected and measured to determine the existing dynamic, chemical and thermal state. The Venus and Mars density measurement regimes are very similar and the highly elliptical orbit is designed to probe both the low altitude atmosphere and ionosphere as well as the solar wind interaction regions with an equatorial orbit rather than a polar orbit, as used in the Pioneer Venus mission.

A quadrupole mass spectrometer with a mass range from 1 to 60 AMU (atomic mass units) equipped with a retarding potential ion source will be used to obtain accurate data pertaining to the chemically active and inactive species. The ion source will be operated alternately in "closed source" and "open source" modes to increase measurement accuracy. Density distributions of neutrals, 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. 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 ion transmission efficiency (sensitivity) of the ion source and ion detection technology have been further improved since the Pioneer Venus mission through computer studies and extensive laboratory tests for optimum bias of the electron beam gun and lens elements. The sensitivity is approximately 50 times higher than in the ONMS.

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.

The electronics system is changed to reflect the current state of technology and parts availability applied in more recently developed space flight instruments by the team. Hybrid electronic circuits were used to reduce volume and weight requirements of the electronics.

The experiment mass is 2.7 kg and its average power consumption is 8 watts.


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