## 4 Scientific Load Platform  
The main goal of the EFSOS is to convey scientific payloads to subglacial lakes for data and sample retrieval. The specific scientific payload can be customized according to the intended purpose of the exploration. The SPINDLE and TRIPLE project packages can be integrated into AUV systems, enabling the exploration of subglacial lakes. However, AUV systems add to the size of the system. For instance, the AUV system utilized in an Ice Shuttle project is approximately 4 m in length [26]. Selecting an AUV-type scientific payload would significantly increase the length of the RECAS, presenting challenges in  
Figure 5: Schematic diagram of RECAS detection and control system.  
terms of overall design complexity and implementation risks (including cable management, structural considerations, and thermal management capabilities).  
In the early stages of our project, the scientific loading platform was designed as a fixed-parameter measurement and sampling device (Figure 6). It comprises two CTDs for measuring lake water pressure (0-3500 dbar, \(\pm\)0.05% F.S.), temperature (-5-35 \({}^{\circ}\)C, \(\pm\)0.002 \({}^{\circ}\)C), and conductivity (0-70 mS/cm, \(\pm\)0.005 mS/cm). Moreover, it includes two pH sensors (2-11, \(\pm\)0.05) and two water samplers for collecting lake water samples. The scientific loading platform was installed in the lower section of the RECAS sonde (Figure 4).  
The scientific load platform and the downhole control system were interconnected via watertight cables, utilizing the conventional serial RS485 full-duplex communication protocol. To guarantee system reliability, the scientific load platform was outfitted with a self-testing function. Once normal self-test results are obtained, the platform shifts into a standby state and patiently waits for a start command. Upon receiving the start command, the system reads the calibrated parameters and performs measurements of multiple parameters, including temperature, pressure, conductivity, salinity, and pH. The data collected are then transmitted in real-time to the downhole control system for display and storage. Moreover, the platform is integrated with a real-time monitoring module, enabling the tracking and recording of events, including power-on startup and abnormal data measurements. Such functionality provides essential equipment support for subsequent data processing.  
The sampler, fabricated from titanium alloy, utilized a solenoid valve to control the opening and closing of the sampling mechanism. Each sampling cylinder has a volume of 360 mL. The test results revealed that each sampler could successfully extract 330 mL of water under a water pressure of 5 MPa. Consequently, the two samplers combined were able to obtain 660 mL of subglacial lake water. The suction port of the sampler was strategically positioned above the lower melting tip and close to the bottom of the sonde. This configuration effectively mitigated the influence of residual meltwater within the sonde on the subglacial lake water sampling process. When required, a pump accessory  
Figure 6: Structural diagram of RECAS scientific load platform.  
can be employed to ensure water circulation, thereby further guaranteeing the purity of the water extraction process.