## 8 Discussion  
Through laboratory and lake testing, as well as debugging, the principle feasibility, long-term operational reliability, and drilling cleanliness of the EFSOS system were validated. Inspired by the spinning and reeling behavior of spiders, the RECAS sonde's operational behavior in the ice layer exhibits a \"silk pay out/in\" function, emulates the diving, searching, and return paths of spiders. Consequently, it establishes a connection between biological spider behavior and environmentally friendly drilling processes in engineering systems. All components of the EFSOS system, in collaborative operation with the RECAS sonde, functioned precisely within the expected parameters. Regarding the RECAS sonde, during the downward drilling process, with a heating power of 6-6.5 kW at the melting tip, the penetration rate reached 2.14 m/h, yielding a borehole diameter of approximately 185-195 mm. The lateral power density of 0.129 W/cm\({}^{2}\) ensures safe drilling within the \(-25\)\({}^{\circ}\)C ice layer. The control mode of the inner winch, relying on the WOB and internal tension, effectively maintained the WOB within a range of 20-50 kg, facilitating the orderly retrieval and deployment of cables. Two vacuum-treated water samplers collected approximately 660 mL of lake water in situ. As for the surface system, the RCUPS system was run for over 1000 h. This demonstrated the stable automatic rotation operation of the two generators, along with automatic fuel filling, and automatic maintenance functions, thus guaranteeing an uninterrupted automatic power supply for the RECAS sonde. The primary challenge encountered during the testing phase mainly concerned the safety of the synthetic fiber armored cables. The self-heating of the multilayer cable can readily cause the temperature in the inner layers of the drum to surpass the cable's tolerance limit. In dry holes, the temperature of the fully powered upper melting tip rises rapidly, and the temperature in the central hole poses a risk of cable damage. Although measures  
Figure 12: Variation of drilling parameters with depth during downward drilling of the second borehole. such as installing a circulating water channel on the drum and implementing temperature feedback control for the melting tip have been taken to mitigate these problems, during actual drilling, close attention should be paid to the cable voltage drop (which increases with the cable temperature), tip temperature, and other parameters. This is essential for preventing local cable overheating and ensuring safe cable operation, as these factors directly impact the sustainability of the entire process. In January-February 2022, a RECAS field test was carried out in the blue ice area on the flank of the Dalk Glacier, Antarctica. The test led to the successful drilling of three boreholes, with an aggregate depth of 517 m. Approximately 1800 mL of ice-meltwater was obtained, signifying the first successful deployment of the \"spider and silk\" type sonde in Antarctica [28]. This accomplishment offers valuable insights for subsequent research and the refinement of clean subglacial lake sampling systems. Currently, more detailed field-test data are currently being processed. Looking ahead, two primary directions for optimization and improvement should be considered. First, the RECAS structure needs to be optimized to boost the drilling capacity and reduce its body weight. It is desirable to achieve a smaller cable diameter, a minimum bending radius, greater power supply capacity, smaller volume, and lower power consumption and sonde weight while ensuring sufficient strength and drilling capacity. Thus, ongoing research on flexible cables with small diameters and high strength is of crucial importance, especially in scenarios where similar technologies are proposed for exploring subglacial oceans on extraterrestrial planets. Secondly, the compatibility of the RECAS sonde with other scientific loads should be optimized.