In search of hidden treasures – radar campaign in LUNA
The uppermost meter(s) of the lunar subsurface potentially hold significant resources, like water ice, or lava tubes as possible shelters, that are crucial for a sustainable human presence on the Moon. While these depths are accessible to human and robotic exploration, the first step is knowing where to explore. Geophysical methods that can image from the surface what lies beneath provide an important contribution to detecting and locating these “hidden treasures”. During a campaign from November, 18th to 20th, 2024, a team of scientists from the Chair of Radio Frequency and Photonics Engineering at Technical University (TU) Dresden, Germany, applied one of these methods, ground penetrating radar sounding (GPR) in cooperation with DLR’s Microgravity User Support Center (MUSC). TU Dresden plays a leading role in planetary exploration with radar, with experts actively involved in major NASA and ESA radar sounding missions on both rovers and orbiters. These include for example radar experiments on NASA’s Mars 2020 Perseverance Rover, ESA’s Mars Express orbiter, and ESA’s Jupiter Icy Moon Explorer (JUICE).
GPR uses electromagnetic waves, which are reflected e.g. by geologic layers, ice, rocks, or voids, to sound the subsurface. This technique was pioneered for planetary rover exploration by the Chinese Chang’E 3 and 4 missions to the Moon in the late 2010s. Since 2021, GPR “shoots” the first in-situ images ever taken of the Martian shallow subsurface from the Perseverance rover, reaching depths of several 10s of meters. With these forerunner missions in place, the next step is actual resource localization. The GPR tests in LUNA therefore featured various antennas, including a model of the TU Dresden-built antenna of the WISDOM (Water, Ice and Subsurface Deposit Observation on Mars) radar for ESA’s 2028 Rosalind Franklin ExoMars rover, which will help deciding where to drill for samples and provide context for their interpretation. Various measurement strategies were also tested, with the antenna either hanging above ground from the LUNA crane, similar to rover-mounted radar, towed along the surface, or actually mounted on a remote-controlled rover mock-up. Data was then collected along a line of experiments resembling scenarios on both Moon and Mars, deduced from active rover missions. They include buried rocks and voids in the regolith as well as micro impact crater and duricrust phenomena (a hard, mineral-rich top layer). MUSC provided further special targets of interest across the deep floor area such as a lava tube, ice simulant and deep calibration objects. The tests also provide an in-situ characterization of the electromagnetic properties of the regolith simulant in LUNA that allows for comparison with previously obtained lab data and actual lunar regolith.
The collected radar and contextual sensor data will help to improve the interpretation of geologic targets in the regolith of Moon and Mars. Localizing buried resources is deemed highly complex by scientists, yet of equally high potential for lunar exploration. This makes these experiments in LUNA indispensable for future instrument and mission design that endeavours buried resource detection.
