NASA Tool to Scout Water at Moon's South Pole

Neutron Spectrometer System will ride aboard LUPEX rover to hunt for lunar ice

Mar. 25, 2026 at 1:28am

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NASA is providing a water-detecting instrument called the Neutron Spectrometer System (NSS) to the Lunar Polar Exploration (LUPEX) mission led by JAXA and ISRO. The NSS will be installed on LUPEX's lunar rover planned to arrive at the Moon no earlier than 2028. The instrument can detect the presence of hydrogen, a key indicator of water ice, by measuring interactions with neutrons in the lunar soil. This is part of NASA's ongoing effort to identify and characterize lunar water and other materials that could support future human exploration of the Moon.

Why it matters

Water is a critical resource for NASA's plans to develop a sustained human presence on the Moon. By identifying and mapping the location and quantity of lunar water ice, NASA can mark potential landing sites for future astronauts who could use the water for life support, rocket fuel, and other purposes instead of relying solely on resources brought from Earth.

The details

The NSS instrument uses a "gas proportional counter" to detect neutrons bouncing out of the lunar soil. It features two tubes that contain a rare gas called helium-3 that is very sensitive to neutrons. When neutrons strike the helium-3 gas atoms, the gas produces electrical pulses that can be counted to infer the presence and quantity of hydrogen up to three feet underground. This data will help build detailed maps of the location and quantity of lunar water ice.

  • The LUPEX mission with the NSS instrument is planned to arrive at the Moon no earlier than 2028.
  • The first Moon-bound NSS instrument was carried aboard Astrobotic's Peregrine lander, Astrobotic Peregrine Mission One, which launched in January 2024.

The players

JAXA

The Japan Aerospace Exploration Agency, the lead agency for the Lunar Polar Exploration (LUPEX) mission.

ISRO

The Indian Space Research Organisation, a partner agency for the Lunar Polar Exploration (LUPEX) mission.

NASA

The United States National Aeronautics and Space Administration, which is providing the Neutron Spectrometer System (NSS) instrument for the LUPEX mission.

Rick Elphic

The NSS lead at NASA's Ames Research Center in California, where the instrument was developed in collaboration with Lockheed Martin.

Lockheed Martin Advanced Technology Center

The company that collaborated with NASA's Ames Research Center to develop the Neutron Spectrometer System (NSS) instrument.

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What they’re saying

“There is currently a gap in our understanding of how lunar ice is distributed at small scales, from 10s of centimeters up to 10s of kilometers. The only way to understand the 'where' and 'how much' of lunar ice is by exploring on the surface at these scales.”

— Rick Elphic, NSS lead at NASA's Ames Research Center

What’s next

The three upcoming NSS rover expeditions, including NASA's VIPER mission and the MoonRanger "micro rover" developed by Carnegie Mellon University, will provide more detailed information about the location and quantity of lunar water ice to help plan future missions to access and utilize this critical resource.

The takeaway

NASA's provision of the Neutron Spectrometer System instrument to the international LUPEX mission is a key step in the agency's broader effort to map and characterize lunar water resources, which will be essential for supporting a sustainable human presence on the Moon in the coming decades.