Objective The planning of lunar bases, represented by the International Lunar Research Station, is advancing lunar exploration into a new phase of “long-term utilization and in-situ resource transformation”. In-situ resource utilization (ISRU) of lunar regolith is crucial for constructing sustainable lunar habitats. However, the extreme lunar environment and manufacturing processes may introduce internal defects into regolith-based components, posing risks to structural integrity. Thus, developing in-situ non-destructive detection techniques is imperative. While infrared thermography offers significant advantages, its conventional excitation sources (e.g., halogen lamps, lasers) rely on external power supplies, presenting limitations for long-term lunar surface operations. To address this problem, this study proposes and investigates a novel in-situ infrared thermographic inspection method utilizing concentrated solar energy as the excitation source.

Methods A three-dimensional finite element model coupling optical excitation with transient heat transfer was established. Four groups of lunar regolith simulant specimens with standardized dimensions (20 mm×15 mm×5 mm) were designed, each containing an array of flat-bottom hole defects at their surface center. These defects varied systematically in diameter (1-4 mm) and burial depth (0.2-0.5 mm). Numerical simulations were conducted under three characteristic scenarios: earth ambient temperature, lunar high-temperature, and lunar low-temperature environment. First, the detection process of a specimen with 1-mm diameter defects was simulated and compared across all three environments. Subsequently, the influence of defect size was analyzed by simulating specimens with defect diameters of 2-4 mm under the lunar low-temperature condition, using a pulsed heating protocol.

Results and Discussions From the temperature distribution at typical times in earth ambient temperature scenario (Fig.5), lunar high-temperature scenario (Fig.6), lunar low-temperature scenario (Fig.7), it can be seen that the optimal detection window universally occurs during the late heating to early cooling phases across all scenarios, as the thermal excitation is sufficiently established while background thermal noise remains non-uniform, maximizing the temperature contrast between defects and the substrate. In the lunar high-temperature scenario, the elevated initial temperature combined with intense heating accelerates thermal diffusion, allowing deeper defects to manifest earlier. However, this advantage is offset by a significantly reduced thermal contrast due to the overall high background temperature, which compromises defect contour clarity and identifiable duration. As shown in temperature distribution of specimens with different defect diameters at typical times (Fig.8), under identical excitation conditions, larger defects produce thermal signals with greater robustness and a longer observable time window.

Conclusions This study establishes a coupled "optical-thermal" 3D finite element simulation model, systematically demonstrating the feasibility of using concentrated solar excited infrared thermography for in-situ defect detection of lunar regolith molten structures. The temperature field evolution trends are generally similar across the three scenarios, with the optimal detection window commonly appearing during the late heating phase to the early cooling phase. The distinction lies in the lunar high-temperature environment, where deeper defects manifest earlier but the excessively high background temperature reduces the recognizability of defect contours. Under identical excitation conditions, larger-sized defects produce thermal signals with stronger robustness and a longer observable time window.