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Neutron Spectrometer System (NSS)


Mission Name: Peregrine Mission 1 (Astrobotic)
Principal Investigator:Dr. Richard C. Elphic


The Neutron Spectrometer System (NSS) will measure the amount of hydrogen-bearing materials near the surface at the landing site to determine the potential for water ice. It is also designed to determine the bulk composition of the regolith. The instrument works by making measurements to determine the local thermal (<0.3 eV) and epithermal (0.3 eV to 1 keV) neutron flux, which can be used to determine the local hydrogen content.

The instrument comprises two gas-proportional counter (GPC) sensors. Both are filled with helium-3 at 15 atmospheres pressure, one is bare, so it is sensitive to both thermal and epithermal neutrons. The other GPC is wrapped in a 0.63 mm thick layer of cadmium, which absorbs neutrons with energy under 0.3 eV, so that it measures only epithermal neutrons. This measurement, when subtracted from the first GPC reading, gives the thermal neutron flux. The sensors, mounted on the electronics unit, make up the sensor module, including a high-voltage power supply and pre-amplifiers. A separate data processing module controls the sensors and data processing. The instrument has a mass of 1.6 kg and uses 1.5 W power. The sensor module is 21.3 x 32.1 x 6.8 cm, the data processing module is 13.9 x 18.0 x 3.0 cm.

Each sensor produces a 32-channel (1-byte deep) spectrum, once per second. Not all neutron events produce the full energy (e.g. due to some energy being lost to the wall of the sensor), and some energy is produced by gamma-ray background, the energy spectrum captures these. NMLS can measure concentrations as low as 0.5 wt% water-equivalent hydrogen at spatial scales on the order of tens of centimeters.

Alternate Names

  • PeregrineMission1/NeutronSpectrometerSystem(NSS)

Facts in Brief

Mass: 1.6 kg
Power (avg): 1.5 W


  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Richard C. ElphicPrincipal InvestigatorNASA Ames Research
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