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Robotic measurements of heat flow planned in Mare Crisium (2024) and the Schrödinger basin (2025) of the Moon

Presentation #319.06 in the session Future Missions, Instrumentations and Facilities - Part 2 (Oral Presentation)

Published onOct 23, 2023
Robotic measurements of heat flow planned in Mare Crisium (2024) and the Schrödinger basin (2025) of the Moon

Plans for deploying heat flow probes on the Moon from robotic landers are now in the works. Under NASA’s Commercial Lunar Payload Services (CLPS) program, a heat flow probe, along with several other instruments, will be delivered to Mare Crisium in 2024 and another to the Schrödinger basin in 2025. They would be the first attempts to measure heat flow on the Moon since Apollo 17 in 1972. In the last 5 decades, relying mostly on the Apollo findings and the later orbital observations, we have gained greater knowledge on the thermal evolution of the Moon, but we need additional in-situ heat flow measurements for testing various hypotheses.

Heat flow is obtained as a product of two separate measurements of thermal gradient and thermal conductivity of the regolith depth interval penetrated by a probe. The challenge here is to penetrate the probe deep enough to avoid the influence of the insolation and measure the Moon’s endogenic heat flow. The Apollo 17 astronauts used a rotary-percussive drill to excavate 2.4-m deep holes for installing their probes, and the depth was more than sufficient for the purpose. On robotic missions, however, such a drilling operation is difficult to implement.

The two CLPS missions will deploy identical heat flow probes which integrate thermal sensors with a regolith excavation system: LISTER (Lunar Instrumentations for Subsurface Thermal Exploration with Rapidity). LISTER is designed to penetrate up to 3 m into the regolith and make temperature and thermal conductivity measurements at multiple depths. LISTER emplaces its thermal sensors to the subsurface by spooling out a 6.4 mm in diameter stainless-steel tube. The sensors are contained in a ~20-mm long, 2-mm diameter needle probe, attached to the leading end of the tube. The tube also emits a jet of Nitrogen gas from its leading end, which removes the regolith out of its downward path. When LISTER reaches a target depth, it stops blowing gas and pushes the needle into the bottom-hole regolith to conduct thermal measurements. Upon completing the measurement (a few hours later) the probe continues to the next target depth.

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