Questions and Answers
What sensors were tested for detecting water ice on the Moon? Researchers used ground-penetrating radar, distributed acoustic sensing with fiber-optic cables, a seismic source, a multispectral stereo panoramic camera, and a laser-induced breakdown spectroscopy instrument.
How do these sensors work together to identify subsurface ice? Radar reveals dielectric contrasts, seismic and fiber-optic measurements map layers through vibration signatures, the panoramic camera provides mineral and terrain data, and LIBS detects hydrogen in rock samples.
How do these technologies compare to other lunar water-detection methods? Orbital sensors can estimate surface composition, but the LUNA campaign focused on rovers and in-situ sensing that can directly characterize subsurface structure and verify the presence and location of ice.
COLOGNE, Germany - Researchers at the German Aerospace Center (DLR) in Cologne are evaluating a suite of sensing and signal-processing technologies designed to locate and map water ice in permanently shadowed regions of the Moon. Tests at the DLR–European Space Agency (ESA) LUNA Analog Facility used robotic rovers, ground-penetrating instruments, and fiber-optic sensing networks to characterize how future missions could detect water frozen within lunar regolith.
The LUNA site contains a 700-square-meter testbed filled with simulated lunar soil for evaluating payloads and mobility systems. Nicole Schmitz, a planetary scientist at the DLR Institute of Space Research, said large-area mobility and multi-sensor integration are essential for surface exploration.
Multimodal sensing for water-ice detection
Engineers buried acrylic structures in the three-meter-deep regolith bed to mimic the radar contrast of subsurface ice. LRU1, a lightweight robotic rover, towed a ground-penetrating radar package to scan beneath the surface. The radar data was merged with terrain information from LRU1’s multispectral stereo panoramic camera, which collects image data across wide wavelength bands to estimate mineral composition and build 3D elevation models for autonomous navigation.
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A second sensing method used a seismic source called the Portable Active Seismic Source, or PASS. The device introduced vibrations into the simulated lunar surface, which were recorded by fiber-optic cables laid across the testbed. The system used distributed acoustic sensing, in which minute changes in the fiber indicate ground motion and reveal subsurface layering. This approach could be deployed on the Moon because fiber cables can be rolled out quickly and operate passively over long distances.
Spectroscopy for hydrogen detection
To analyze hydrogen in rock samples, DLR researchers used laser-induced breakdown spectroscopy. The LIBS instrument fires a pulsed laser to generate plasma on the target and measures the emitted light to determine elemental content. The sensor is mounted in a payload box manipulated by the robotic arm of LRU2, which can position the instrument directly against rock surfaces.
LRU2 also carries tools for autonomous sample handling and onboard computation, enabling greater independence for future robotic missions.
Simulated mission operations
Researchers combined radar, camera, seismic, fiber-optic, and LIBS data to generate a three-dimensional view of the surface and subsurface. This multichannel approach helped locate and map simulated water ice deposits. In a flight mission, these sensors would be integrated directly into the rover's structure rather than carried on trailers.
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The campaign supports a mission concept proposed by DLR teams to the ESA for deployment on the Argonaut lander, which is under development to carry payloads and support surface operations. Schmitz said the campaign demonstrated that all mission elements are operational and compatible.
Field-proven robotic systems
The LRU1 and LRU2 rovers previously operated during field trials on Mount Etna in Italy as part of the ARCHES campaign, where they performed autonomous navigation, sampling, and multi-robot cooperation. At LUNA, they demonstrated obstacle avoidance and reliable operation under low-angle simulated polar lighting conditions produced by a dedicated Sun simulator.
"All of our goals in the Polar Explorer campaign were achieved," said Martin Görner of the DLR Institute of Robotics and Mechatronics.
