Instrument Information
IDENTIFIER urn:nasa:pds:context:instrument:pvmp.lp.lnms::1.3
NAME Neutral Mass Spectrometer for Pioneer Venus Large Probe
TYPE Mass Spectrometer
DESCRIPTION The Large Probe Neutral Mass Spectrometer (LNMS) of Pioneer Venus has a mass of 10.9 kg, a volume of 10650 cubic cm, and uses 14 W power. The instrument comprises a miniature magnetic sector-field mass analyzer, a gas inlet and pumping system, and an electronics (microprocessor) package all mounted on a 31 x 36 cm baseplate. It also had a noble gas enrichment cell, the Isotope Ratio Measurement Cell (IRMC), which collected an atmospheric sample at the beginning of instrument operation at around 62 km altitude. This sample was purged of carbon dioxide using sorption and getter pumping during the descent to enrich the inert gases in the cell, and then introduced the into the mass spectrometer just before parachute jettison. The inlet system consisted of a primary microleak (conductance of 0.0001 cubic mm per second) and a secondary microleak (0.001 cubic mm per second), which was only used in the upper atmosphere where the pressure was lower. The single focusing magnetic sector-field mass spectrometer consisted of the electron bombardment ion source, with selectable electron energies of 70 eV, 30 eV, or 22 eV, a magnetic momentum analyzer and a detector system, which had two electron multiplier-counter channels, one covering 1 - 16 amu and the other covering 15 - 208 amu. It also had two calibration gases containing 136Xe+, 136Xe++, and CH3+ producing peaks at 135.907, 67.954, and 15.035 amu.
MODEL IDENTIFIER
NAIF INSTRUMENT IDENTIFIER
SERIAL NUMBER not applicable
REFERENCES Hoffman, J. H., et al., Pioneer Venus sounder probe neutral gas mass spectrometer, IEEE Trans. Geosci. Rem. Sens., GE-18, No. 1, 80-84, doi:10.1109/TGRS.1980.350286, Jan 1980.

Hoffman, J. H., et al., Composition of the Venus lower atmosphere from the Pioneer Venus mass spectrometer, J. Geophys. Res., 85, No. A13, 7882-7890, doi:10.1029/JA085iA13p07882, Dec. 1980.