The novel idea and technical progress of lunar in-situ condition preserved coring

The moon is rich in material resources, lunar-based sampling is the foundation for an in-depth understanding of lunar material resources endowment characteristics, exploring the evolution of lunar geological structure, and realizing lunar material resources exploitation. This paper briefly introduces the lunar sampling work represented by the Apollo program of the United States, the Luna program of the former Soviet Union, and China’s Chang’E-5 lunar exploration mission, a total of 10 times of successful coring were performed, with a maximum coring depth of 305 cm and a maximum sampling of 110.5 kg. It presents an in-depth analysis of the inadequacy of the existing lunar coring principles and technologies. This paper expounds on the critical strategic significance and scientific value of lunar in-situ condition preserved coring (ICP-Coring). Simultaneously, this paper firstly refines the scientific concept of lunar ICP-Coring in the field of deep space material resources exploitation as the "four preservations" coring (preservation of composition, vacuum storage, stratification/bedding, and compactness)—the "4 Ps" coring, puts forward the fundamental principles, conception, breakthrough theory, and critical core technology of the "4 Ps" lunar ICP-Coring. It explains the latest research progress, including core drilling machinery, film-forming mechanism while drilling, and a platform for fidelity coring testing and analysis under a simulated lunar environment. The research results provide theoretical and technical support for lunar ICP-Coring and resource exploration.

of 305 cm and a maximum sampling of 110.5 kg. It presents an in-depth analysis of the inadequacy of the existing lunar coring principles and technologies. This paper expounds on the critical strategic significance and scientific value of lunar in-situ condition preserved coring (ICP-Coring). Simultaneously, this paper firstly refines the scientific concept of lunar ICP-Coring in the field of deep space material resources exploitation as the ''four preservations'' coring (preservation of composition, vacuum storage, stratification/bedding, and compactness)-the ''4 Ps'' coring, puts forward the fundamental principles, conception, breakthrough theory, and critical core technology of the ''4 Ps'' lunar ICP-Coring. It explains the latest research progress, including core drilling machinery, film-forming mechanism while drilling, and a platform for fidelity coring testing and analysis under a simulated lunar environment. The research results provide theoretical and technical support for lunar ICP-Coring and resource exploration.
Article Highlights This paper expounds on the critical strategic significance and scientific value of lunar in-situ condition preserved coring (ICP-Coring), refines the scientific concept of lunar ICP-Coring in the field of deep space material resources exploitation as the ''four preservations'' coring, and puts forward the fundamental principles, conception, breakthrough theory, and critical core technology of the ''4 Ps'' lunar ICP-Coring.
Keywords Lunar Á Moon Á In-situ condition preserved coring Á Sampling Á Drilling tools

Introduction
Space is an inexhaustible treasure house of resources for humanity. Humankind has carried out space exploration activities for hundreds of years. As the only natural satellite of the earth, the moon's unique material resources (rare earth, radioactive resource uranium, nuclear fusion raw material helium 3, etc.) can become an effective supplement and reserve to the earth's resources providing long-term and practical support for the sustainable development of human society. The exploitation of strategic lunar resources and the establishment of a lunar scientific research base are the inevitable trend and competitive focus of deep space exploration, which will have a far-reaching impact on the sustainable development of human society (Ouyang 2005). Hence, NASA of the United States, ESA of Europe, JAXA of Japan, China National Space Administration, and other national space agencies have launched a new round of lunar exploration programs (Han 2019;Wu et al. 2017), focusing on the exploration of special substances such as lunar mineral resources, water ice resources, volatiles, etc., to uncover the mysteries of lunar evolution and life science and initiate the future process of human exploitation of lunar resources.
The most direct technical method of lunar resource exploration is core drilling. Core drilling is an essential means to an in-depth study of lunar geological information and evaluating mineral resources (Ranjith et al. 2017;Cai et al. 2017). It is an important technical guarantee for the exploitation of lunar resources and the construction of a lunar base. The Luna series of explorers of the former Soviet Union was the first to achieve unmanned automatic coring and sampling; the Apollo series manned lunar landing program of the United States retrieved about 382 kg of lunar soil by manual coring (Ouyang 2003). China completed its lunar surface sampling and drilling sampling in the Chang'E-5 lunar exploration mission in the third phase of its lunar exploration program in 2020 (Leslie 2021). However, the samples obtained from lunar exploration activities to date generally come from areas near the moon's equator, and the maximum depth of drilling and coring is only three meters. Consequently, it is impossible to obtain complete scientific information about lunar bedrocks, limiting humanity's comprehensive understanding of the evolution mechanism of lunar geology and material resources.
The latest lunar exploration data Jia et al. 2020) shows that through various research methods such as all lunar neutron spectrum detection, infrared spectrum detection, and impact experiments in the permanent shadow area, human beings speculate that there may be volatile substances such as water, ice, and rare gases that are directly related to major scientific problems such as life and planetary evolution. The new round of lunar exploration programs worldwide focuses on volatile substances like lunar water ice and rare gases. However, most of these substances occur in a specific depth range below the surface of the lunar soil, and the extreme environment of the moon promotes the escape of volatile substances during the sampling process. During the core drilling process of the Apollo and Luna missions, the lunar soil was subjected to intense mechanical and thermal disturbances due to technical limitations, resulting in the loss of the core compositions to varying degrees. As a result, the samples acquired had been seriously distorted, reducing their scientific quality. Hence, they do not truly reflect the in-situ formation structure and physical and mechanical properties of the lunar sphere, severely restricting the accurate evaluation of the exploration data of the occurrence state, material composition, and content of the unique resources such as lunar minerals, water ice, and volatile substances. Therefore, there is an urgent need to put forward a coring principle, technology, and method to maximize the preservation of the in-situ properties of lunar samples under the extreme lunar environment. This paper systematically summarizes the current situation and achievements of lunar sampling and expounds on the critical scientific significance of lunar ICP-Coring. On this basis, the scientific meaning, fundamental principle, and system concept of lunar ICP-Coring are proposed for the first time, with an indepth analysis of the critical technical bottlenecks in fidelity coring in the lunar environment that need to be broken through. The main research progress of the author's research team is introduced in detail, focusing on exploring and developing the principle, technology, and equipment of fidelity coring system in the unique environment of the moon, aiming at acquiring samples that preserve the in-situ environmental information of lunar soil and lunar rock for conducting fidelity storage and testing, thereby forming a technical and theoretical system for the exploration, development, and utilization of space mineral resources to vigorously promote the development of relevant science, technology, and industries, and to ultimately provide new technology and new equipment for China's and even the world's lunar exploration programs. It holds tremendous application prospects and scientific value.

The current research in China and worldwide
Lunar sampling is a systematic project. In addition to the performance of the coring device, which affects the coring result, its adaptability to the lunar space environment (tremendous temperature difference, intense radiation, microgravity, ultra-high vacuum) and the unique physical and mechanical properties of lunar soil and lunar rock are also critical to the success or failure of coring. Lunar sampling began in the 1950s. Representative missions to date include the Apollo manned lunar landing mission of the United States, the Luna lunar exploration mission of the former Soviet Union, and China's lunar exploration program.

The US Apollo lunar sampling operations
The Apollo 11 manned lunar landing mission carried out by the United States in 1969 implemented lunar soil sampling for the first time (Zacny et al. 2008). In the Apollo 11, 12, and 14 moon-landing missions, astronauts used a press-fit lunar coring tube for coring operations, with a maximum sampling depth of 70 cm and a total of 99.2 kg of lunar-based samples were obtained (Glass et al. 2010). Astronauts used the handsupported rotary percussion drill ALSD (Apollo Lunar Surface Drill) to sample the lunar soil in the three lunar landing missions of Apollo 15, 16, and 17, operating a sampling depth range of 250-300 cm. About 282.5 kg of lunar samples were obtained (Gouache et al. 2011). The drill came with a maximum rotation speed of 280 r/min, a maximum impact frequency of 37.8 Hz, and maximum impact energy of 4.4 J/blow (Hong 2001;Stoker et al. 2008). The lunar soil samples obtained by the Apollo lunar landing missions were stored in a sample box or sealed in the coring tube, which cannot maintain the integrity and authenticity of the lunar soil samples (Zhang 2012;Li 2014). In addition, the United States has developed a set of arm-loaded rotary percussion drilling samplers. The mechanical arm supplies the drilling pressure during the drilling process through compression of the energy storage spring between the drilling device and the drill rig. The drilling depth is compensated in real-time by the mechanical arm (Davé et al. 2013;Glass et al. 2014). The sampler uses a drill bit with a diameter of 6 mm. During the drilling process, sand enters the collection chamber through the annulus between the drill bit and the coring tube and is tested by an analyzing device. For asteroid sampling research, the United States has developed an ultrasonic percussion drill (USDC) based on the principle of piezoelectric driving. The drill can convert high-frequency vibration into lowfrequency impact, effectuating the downward drilling of the drill rig. Compared with traditional drill rigs, USDC can drill into rocks of higher hardness with lower drilling pressure, which overcomes the difficultto-operate weakness of conventional drill rigs in a low gravity environment (Zacny et al. 2013a, b, c;Bar-Cohen et al. 2014). NASA has developed a DAME drilling and sampling test platform with fully autonomous drilling control capabilities based on various fault identification methods for future unmanned lunar deep drilling and sampling missions. DAME can accurately identify six types of failures such as ''drill rod stuck'' and ''drill rod tension'' through the closedloop control method and can perform targeted repairs according to the kind of failure (Badescu 2009). Honeybee Robotics of the United States has equipped the DAME lunar or Mars coring system developed by NASA with online real-time monitoring equipment (such as laser vibrometer) and intelligent real-time control software, which can identify extraordinary drilling operational issues such as blocked drills, stuck drills, drill bit mud wraps, bent drill rods, hard rocks (Statham 2011). And the Comet sample collection and transfer system STAM (Zacny 2007) developed by Honeybee Robotics can process samples while they are being collected, making it possible to perform insitu analysis.
It is evident that the sampling operations of the Apollo lunar exploration missions carried out by the United States have ''insufficient depth'' and ''non-fidelity'' issues. The ultimate sampling depth was about three meters, which did not touch the lunar rock layer, and the sampling equipment used a regular coring tube, which failed to maintain the in-situ information of the lunar soil samples; hence it was difficult to accurately analyze the in-situ physical and mechanical properties of lunar soil, compromising the objectivity of lunar resource evaluation.

The Luna lunar sampling operations of the former Soviet Union
The Luna lunar explorer series of the former Soviet Union was the first to complete unmanned lunar core drilling, sampling and return to the earth (Harvey et al. 2011). The Luna-16 explorer independently drilled lunar soil with the equipped sampler for the first time and ultimately stopped drilling due to excessive load.
Its drilling depth was about 35 cm, and the sample mass acquired was about 101 g (Harvey 2006). The sampling method of the Luna-20 explorer launched later was similar to that of Luna-16, but it encountered strong resistance during drilling, resulting in motor overheating and failure. It was eventually forced to abort drilling at a depth of 25 cm and collected about 55 g of lunar soil (Zacny et al. 2013a). The Luna-24 explorer completed the last lunar surface sampling mission of the former Soviet Union. The impact motor was frequently turned on during drilling, and the alarm went off due to excessive drilling pressure. The final drilling depth was about 225 cm, the total length of the returned sample was about 160 cm with a mass of about 171 g (Zacny et al. 2013b). The Luna-16 and Luna-20 explorers of the former Soviet Union both drilled lunar soil employing an extended manipulator equipped with a sampler (Harvey et al. 2011). The augur drill rod was fitted with a coring barrel inside for sampling. When the sampling drill went into a specified depth, both the sample and the drilling tool were transferred to the collection container above the return module and returned to the earth. Since the lunar soil samples collected in these two times are directly encapsulated in the drill pipe, it was not possible to apply sample fidelity storage technology, resulting in the distortion of the bedding information of the samples acquired. The Luna-24 adopted the improved slide rail deep drilling sampling method, made greater use of the dead weight of the landing module, significantly increasing the drilling pressure (Bar-Cohen et al. 2009). Unlike the previous sampling method, the Luna-24 explorer adopted the independent control method based on the threshold judgment principle and judged the relationship between the drilling pressure and the set threshold with the help of a spring mechanism. The impact motor was started in time to overcome the drilling resistance when the drilling pressure exceeded the set threshold, which significantly improved the operational performance of the sampler ( Van et al. 2005). During the Luna-24 coring process, the soft coring bag gradually wrapped up the lunar soil sample, and there was no slip motion between them. After sampling, the sample was no longer stored in the drilling tool but wound up in the sample barrel and transported back to the earth with the return module, maintaining the in-situ bedding information of lunar soil to a certain extent (Zacny et al. 2013b).
We can see that the lunar exploration missions of the former Soviet Union had limited sampling depth and quality, and the collected lunar samples were of a single type. Thus, although there was some breakthrough in preserving stratigraphic information, insitu condition-preserved lunar samples were not acquired due to technical limitations, resulting in the loss of rich information resources of the samples.

The lunar sampling operations of China's lunar exploration program
The Chang'E-5 lunar explorer launched in the third phase of China's lunar exploration program in 2020 was the explorer that carried out China's first unmanned lunar sampling mission and returned samples to the earth (Che et al. 2021). The mission adopted augur drilling and surface excavation sampling (Ma et al. 2018). The drilling and sampling operation lasted about 3.12 h, during which the drilling movement of the drilling and sampling device was about 1.68 m, the effective travel distance of lunar soil drilling distance was about 1 m, the cover of the sealing packaging device was opened in place in 169 s, and the primary packaging container and drilled samples successfully entered into the sealing and packaging device. The surface sampling operation lasted about 15.82 h, during which two lunar contact sampling operations and sample deposits were performed, and ten noncontact lunar samplings and sample deposits were carried out. The surface sampling primary packaging containers and samples successfully entered the sealed packaging device, and the sealed packaging device completed the lunar surface sealing operation as planned (Deng et al. 2021). The drilling sampling was jointly implemented by the drilling control unit and drilling sampling device. It adopted a footagerotation-percussion coaxial drive. The maximum power of a single machine exceeded 800 W, which successfully achieved effective control of the drilling and coring of the profile lunar soil. The surface sampling was jointly implemented by a surface sampling control unit, a mechanical sampling arm, and a surface sampling primary packaging device. The system was equipped with a robotic arm with multiple degrees of freedom, lightweight and small size, large arm spread, and high load, integrating various functions such as shoveling, digging, suction, receiving, and grasping. The repeated positioning accuracy was better than one mini meter, capable of working in different working modes to obtain multi-point samples from the moon's surface. The sample packaging was jointly implemented by the sealing control unit and the sealing packaging device. A two-stage packaging design including primary and sealing packaging was adopted to ensure that the lunar samples were somewhat differentiated and free from pollution. The drilling and surface primary packages were designed separately to differentiate and isolate the drilling and surface samples, which were then transferred to the sealed packaging device to avoid sample mixing through physical isolation. To minimize the influence of the lunar surface environment on the in-situ properties of the lunar samples, sealing with ultralow leakage rate was achieved by a sealing ring and metal extrusion before the explorer took off so that the lunar samples were in a super-pure environment. The lunar sampling mission of the Chang'E-5 ultimately acquired about 1731 g of profile samples and surface samples in the high latitude region of the moon ). It can be seen that the Lunar sampling mission of Chang 'e-5 achieved low leakage rate sealing and protected the lunar samples in a relatively good manner. However, due to the limited influence of drilling tool power and sampling method, the sampling depth and quality were limited, and the lunar rock samples were not taken, also the sample stratification and compactness were not preserved.
In summary, many innovative studies and sampling missions have been carried out in China and worldwide for lunar coring exploration (Table 1). Countries have obtained lunar samples of different depths and weights through various sampling equipment. However, the lunar coring operations that have been carried out were ''regular coring.'' Preservation of the in-situ lunar environment was absent in the coring process, resulting in the loss of critical in-situ information such as water, ice, and rare gases in the core samples, substantially compromising the authenticity and scientificity of samples and seriously restricting the accurate exploration of lunar-based material resources. Thus, there is a pressing need to refine the scientific concept of lunar ICP-Coring, propose the lunar ICP-Coring concept and improve the weakness of coring technology, explore the fundamental principle and technical device of lunar ICP-Coring, obtain lunar samples with the in-situ environmental information preserved, and promote the long-term development of deep space strategy.

The scientific concept and fundamental principle of ICP-Coring of lunar material resources
The regular lunar soil and rock samples obtained by lunar sampling are separated from the lunar in-situ environment, so they can not accurately convey the information such as in-situ geological composition and occurrence state or provide accurate scientific data limiting the depth and breadth of lunar research. Therefore, the study on lunar ICP-Coring is of great significance for acquiring lunar in-situ information and material resources in future lunar explorations. Lunar ICP-Coring is a new scientific concept and engineering practice. Its comprehensive and effective development requires the intersection and integration of multiple disciplines and fields. Based on the extreme environment of the moon (great temperature difference up to 313°C, microgravity only 1/6 g, high vacuum up to 1.01 9 10 -12 Pa), the unique physical and mechanical properties of lunar soil and rock and the operational characteristics of space mechanism, etc., the scientific concept and fundamental principle of lunar ICP-Coring were refined, which mainly involves preserving in-situ properties of lunar samples in four aspects: composition, vacuum, bedding and compactness.
3.1 The principle of core drilling with in-situ material composition preservation in the lunar environment (composition preservation coring) The actual sample composition in the lunar in-situ environment includes mineral composition, water ice resources, and volatile substances. Their physicochemical properties are the basis for studying the composition of lunar materials and are of enormous significance for exploring the formation and evolution of the moon. External factors such as mechanical disturbance and temperature rise during core drilling will result in destructive impacts on in-situ samples at different depths of the moon, for instance, water ice evaporation, escape of volatile elements, and changes in chemical properties of minerals, which will seriously hinder the research on lunar water content distribution, resource occurrence state, the proportion of volatiles, mineral crystallization characteristics and other scarce elements (Gao et al. 2020a(Gao et al. , 2021a. Hence, the coring process in the lunar in-situ environment needs to preserve the fidelity of in-situ material compositions to ensure the authenticity and reliability of the in-situ data of lunar samples to facilitate the accurate analysis of lunar material resources and provide a guarantee for lunar scientific research. 3.2 The principle of core drilling with in-situ vacuum preservation in the lunar environment (vacuum preservation coring) Since the lunar surface vacuum degree is as high as 1.01 9 10 -12 Pa, the lunar soil and rock are completely isolated from air in an extreme vacuum environment (Ouyang 2005). In the ultra-high vacuum environment, the particle spacing of samples is much smaller than that of the ground, which results in the prominent influence of van der Waals force between grains, and the weak cohesion and tensile strength between grains of lunar soil (Zhou et al. 2019). In addition to changes in mechanical properties, physical and chemical reactions such as oxidation may also occur if the sample leaves the vacuum environment, leading to qualitative changes in its original mineral and microbial compositions. Consequently, such changes will affect the scientific judgment of the existence of trace elements and water ice, and the sample will lose its scientific research value, which has adverse effects on humanity's endeavor in revealing the laws of the moon's evolution. Thus, in the process of in-situ condition-preserved core drilling, storage, and transfer, preserving the vacuum degree of the lunar soil and rock storage environment can avoid the loss of water content and other volatile substances in the sample and fill the gap in the field of lunar water ice detection. 3.3 The principle of core drilling with preservation of the structural characteristics of the in-situ strata in the lunar environment (bedding preservation coring) In the normal geological sequence of the moon bedrock layer, the first rock layer formation is located in the deep part of the moon bed. The rock layer formed later is located relatively close to the moon's surface. The geological sequence analysis utilizes time sequence to analyze the spatial distribution law of the geological body and the depositional environment changes. It truly reflects the regional structural characteristics and evolution process (Gao et al. 2018). Conventional coring loosens the original bedding surface of lunar rock due to the disturbance of drilling power and drilling speed, causing disorder in the rock formation, affecting its spatial structure and in-situ geological sequence (Gao et al. 2020b(Gao et al. , 2022. The study of the lunar in-situ environment and geological sequence contributes to determining rock formation time and composition according to the superimposed relationship of the spatial geometric position of the moon rock layer, leading to accurate classification, comparison, and analysis of the sequence strata in the sample cores, which provides valuable theoretical and measured data for the zoning of lunar sedimentary facies, lithofacies paleogeography reconstruction, and paleogeography evolution. Preserving the in-situ bedding sequence of lunar rock samples is also necessary for studying the morphological characteristics, interrelationships, temporal and spatial distribution patterns, and structural changes of the lunar rock stratigraphic units in the insitu state, restoring the actual lunar geological structural features, and analyzing the evolutionary history and the current status of the moon, leading to the accurate evaluation of the material resource endowment features at different depths. 3.4 The principle of core drilling with in-situ material compactness preservation in the lunar environment (compactness preservation coring) Lunar ICP-Coring is essentially a core drilling operation in the unique environment of the moon. A certain degree of stress release will occur when the core leaves its in-situ environment, destroying its initial compactness and enlarging its pores. That is when changes happen in the real particle bonding and cementation state, density, number of pores, and volume of the core, which will affect the core's physical and mechanical properties such as cohesion, internal friction angle, and strength (Gao et al. 2021b(Gao et al. , 2021c. Therefore, lunar ICP-Coring has exceptionally demanding requirements for preserving the compactness of lunar soil and lunar rock. The compactness of sample cores genuinely reveals the characteristics of the in-situ state of lunar soil and rock and reflect the occlusion between lunar soil and lunar rock particles, which can prove the in-situ physical and mechanical properties of the lunar soil and rock and provide reliable data for the exploration and research of lunar-based mineral resources. Preserving the compactness of lunar soil and rock during the coring process in the lunar in-situ environment is also conducive to quantitatively describing the changing laws of the sedimentary environment, inverting the lunar structure process, and exploring the reconstruction of the sedimentary environment within a short time span.

The conception and research progress of crucial technologies of ICP-Coring system in a simulated lunar environment
Based on the scientific connotation and fundamental principles of lunar ICP-Coring, considering the impact of extreme environments such as high vacuum, microgravity, and extreme temperature differences on the moon, and thoroughly absorbing and utilizing previous research results and technical advantages in China and abroad, the essential technical conception of the lunar ICP-Coring system was proposed. We conducted many studies, including developing a core drilling robot, the ICP-Coring film-forming-whiledrilling technology, research on in-situ packaging and storage technology, and constructing an ICP-Coring testing and analysis platform in a simulated lunar environment.

The development of unmanned self-adaptive drilling devices for the extreme lunar environment
Lunar ICP-Coring operates in extreme environments such as lunar microgravity, high vacuum, drastic temperature difference, and intense radiation. There are challenges such as complex conditions in the deep part of the lunar base, unknown hardness of the lunar rock, lack of visualization in the drilling process, and the difficulty of heat dissipation. Under such circumstances, employing existing drilling tools in lunar coring operations will encounter problems such as poor environmental adaptability, excessive tool wear, and mission termination. There is an urgent need for innovative designs of drill bits and coring tools for the unknown lunar geological environment (Xie et al. 2020).
(1) Retractable and flexible self-coring drill bit Aiming at addressing the problems of unknown lunar rock hardness and non-visualization of the drilling process in the extreme lunar environment, an unmanned, retractable, and flexible self-coring drill bit for the lunar environment was designed; the blade posture of the drill bit can adapt to the unknown lunar geological environment through variation, thereby improving the efficiency of coring. When the coring process is complete, during the lifting process, the drill bit can retract the drill minimizing the damage to the coring hole, the demand for lifting force, the possibility of a drill jam, and improving the coring process's continuity. The design of the flexible coring bit is shown in Fig. 1. It comprises retractable blades, a drill bit, a spring, a core barrel, and a positioning pin. Among them, the retractable blades can freely adjust the feed. In addition, its posture can be controlled through the drill bit rotation to adapt to different geological environments. The retractable blades can freely rotate around the rotating hinge, and its position is determined by the shape of the drill and the positioning device. The drill bit shape, stop position, and the various operating modes of the retractable blades are shown in Fig. 2. The positioning device limits the rotational movement of the retractable blades, controlling their fastening via drilling pressure. The positioning device contains components such as screws, springs, pressure plates, and positioning pins. As shown in Fig. 3, where the screw is connected to the drill bit and floats with the core barrel, the spring remains compressed during the entire operating process so that the positioning device does not connect with the drill bit in the absence of drilling pressure.
(2) Universal joint coring robot To cope with the unclear target of lunar core drilling operations and solve the emergent situation where high-strength lunar rock may cause a screeching halt to the coring operation during the coring process, we have designed a universal joint coring robot capable of direction adjustment during the lunar coring process. Thus, the coring robot can change its drilling direction to avoid high-strength rocks that are difficult to drill in the unknown lunar geological environment. The design of the universal joint coring robot is shown in Fig. 4, which is composed of an actuator, a universal joint, a servo motor, a rotary frame, bellows, and other components.
Among the components, the bellows mainly prevent impurities such as lunar soil and rock debris from falling into the actuator system to ensure its normal operation. The actuator is responsible for transmitting the power of the servo motor to the rotary frame to control the rotation angle of the universal joint. It includes a plurality of gears and a transmission shaft. The bevel gear cooperates to convert the rotation in the horizontal direction into the rotation in the vertical direction. The spur gear set prevents interference of the transmission structure and increases the torque. The driveshaft is responsible for transmitting the power of the gear to the rotary frame causing it to rotate. The supporting shaft is responsible for supporting the rotary frame in the universal joint to ensure that the virtual shaft in the rotary frame is in a crisscross shape; both the driveshaft and the support shaft can rotate freely at the groove of the universal joint. The specific structure of the transmission components and the schematic diagram of the universal joint robot after rotation are shown in Fig. 5. The operating process of the universal joint coring robot is as follows: when encountering rocks that are difficult to drill into, the propulsion unit of the coring device is retracted, and then a direction change is achieved through the universal joint robot so that the coring robot avoids the hard rock and continue its sampling operation (Fig. 6). Given the nature of unequal velocity of a single cross-axis universal joint, that is, the angular velocities at both ends of the universal joint are not identical, and the rotation direction of a single universal joint robot gives the corer only the option to obtain samples in the oblique direction in the subsequent coring operation, uniform velocity sample coring in a vertical direction is achieved through the combination of two universal joint robots.

Film-forming while drilling, and in-situ packaging storage technologies ICP-Coring
Lunar microgravity, high vacuum, extreme temperature difference, and other extreme environments have seriously impacted the preservation of in-situ information of samples during traditional core drilling. The film-forming while drilling ICP-Coring and in-situ packaging and storage technologies to address such issues were proposed. The in-situ information of the samples is preserved through the innovatively designed core storage device during the core drilling and sample storage stage. It also explains the central mechanism of realizing ICP-Coring.  (1) Film-forming while drilling technology ICP-Coring The ultimate challenge in lunar ICP-Coring lies in how to achieve real-time packing and in-situ sealing of the sample core in the limited space of the core barrel during the dynamic coring process under the harsh lunar environment such as high vacuum and extreme temperature difference, thereby maintaining the in-situ bedding, compactness, and composition of cores, and protecting the in-situ occurrence state of material resources, and accurately determining the in-situ material abundance. In response to the challenge, the viscoelastic in-situ self-healing sealing principle and technology, enabling self-triggered film-forming and real-time sealing in a low-temperature vacuum environment and limited space were innovatively developed. The principle and technology are based on the viscoelasticity theory and the dynamic reversibility principle of supramolecular structure, combined with the creep and self-healing properties of viscoelastic bodies. They are developed to achieve the formation of a sealing film on the surface of the core during core drilling in a low temperature and vacuum environment and completely seal and cover the core to obtain the most authentic composition, properties, and state of the lunar core. As shown in Fig. 7a, we imagine that a selfhealing elastic body is preset inside the coring tube. When the core starts to enter the coring tube and comes into contact with the viscoelastic body, dynamic bond dissociation occurs in Fig. 5 The structure of the transmission components and the universal joint robot after rotation Fig. 6 Operating process of single-double universal joint coring robots the molecular bonds of the elastic body. As a result, self-healing viscoelastic bodies consolidate at the bottom of the core after the core is fully inserted, self-healing through dynamic bonding such as hydrogen bonding and dynamically seals to completely wrap around the core to achieve ICP-Coring (as shown in Fig. 7b).
In order to implement the principle and process conception mentioned above in the unique environment of the moon, this study innovatively designed and developed a polyborosiloxane sealing film composed of montmorillonite nano-networks, which has the advantages of self-forming, effective self-healing, molecular barrier, and being pollution-free. The reversible dissociation and association between B and O atoms give the sealing film excellent viscoelasticity and self-forming properties, ensuring that the film material adaptively coats the core during the dynamic coring Fig. 7 Schematic diagrams of film-forming while drilling. a Coring process b Sealing process at the bottom of the core Fig. 8 Diagram of the mechanism of the fidelity preservation film. a Diagram of the synthesis mechanism of the fidelity preservation film. b Diagram of the dynamic bond dissociation and reconstruction mechanism of the fidelity preservation film process and maintains the bedding structure and density of the core (Fig. 8a). The rheological properties are shown in Fig. 9a; the storage modulus curve and loss modulus curve intersect at 1.4 Hz (G 0 ¼ G 00 ). The storage modulus of the film material is lower than the loss modulus when the frequency is less than 1.4 Hz, indicating that the material has a flow molding property like ''liquid.'' Further, the dynamic molding experiment results show that the film material can conform to the core surface and cover it in a narrow space at room temperature (Fig. 9b). The film material was further stretch tested under a simulated lunar environment with low-temperature conditions (-20°C) (Fig. 9c). It was found still to creep slowly, demonstrating the excellent self-forming properties of the sealing film. The sealing film has excellent self-healing properties because of weak intermolecular cross-linking (formed by unreacted -OH in PDMS) and dynamic coordination bond (formed between B and O in the polymer), which enables real-time sealing at the bottom of the sample core while preventing the impact, collision, tearing and other external forces in the coring process from destroying the integrity of the film material (Fig. 8b). Figure 10a reveals Fig. 9 Self-forming performance of sealing film. a Rheological test diagram of self-healing sealing film. b Self-forming simulation experiment. c Low temperature creep experiment of self-healing sealing film Fig. 10 Self-healing performance of sealing film. a Self-healing behavior experiment at room temperature. b Self-healing behavior experiment in low temperature. c Healing efficiency of sealing film the highly effective self-healing capability of the film material. The test results show that the film sections were lightly attached after being cut, and it self-healed in 30 s and did not break off even with twisting. The quantitative characterization of the healing efficiency of the film (Fig. 10c) indicated that the material's selfhealing efficiency was as high as 99%. The damage-healing test was also carried out under simulated low-temperature lunar conditions (-20°C). The results showed that the material healed itself and could be stretched within 15 min (Fig. 10b), showing the superior lowtemperature healing capability of the sealing film, which is suitable for the extreme lunar environment.
The composite of nano-composite fillers constructs a three-dimensional barrier network, which further boosts the film's protection of the material information inside the sample core. We constructed the film material's excellent molecular barrier capability using the threedimensional nano-barrier network technology. As shown in Fig. 11a, when 10 wt% filler was added, the barrier performance of the film material reached 4.74 9 10 -11 gÁm/(m 2 ÁsÁpa); the healing barrier performance is shown in Fig. 11b. The initial water vapor permeability coefficient of the film material was 5.19 9 10 -11 gÁm/(m 2 ÁsÁpa), and four damagehealing tests were performed. The recorded water vapor permeability coefficients of the film material were 5.20 9 10 -11 , 5.34 9 10 -11 , 5.54 9 10 -11 , and 5.75 9 10 -11 gÁm/(m 2 ÁsÁpa). The performance of the film material remained consistent and exhibited sound barrier and healing capability, capable of constant longterm preservation of the material information in the core. The moon is still an unmanned planet waiting to be developed, and complete protection of the lunar environment needs to be considered for lunar exploration missions. The main chemical components of lunar soil/rock are SiO 2 , Al 2 O 3 , FeO, MgO, CaO, etc. (Xu 1985), which do not have mutual chemical interactions with polyborosiloxane and montmorillonite nano lamellar fillers; hence no chemical reaction and erosion will occur. We conducted simulation experiments using rock cores from the earth whose main composition includes SiO2, FeO, etc. The XRD spectrum shows (Fig. 12) that there is no significant change in the core composition before and after the sealing film is coated, which proves that the material does not change the composition properties of the rock formation and is pollution-free.
(2) In-situ packaging and storage technology for condition-preserved coring In addition to the film-forming-while-drilling technology, in-situ packaging and storage of lunar in-situ condition-preserved cores is also the key to lunar ICP- Fig. 11 Barrier performance of sealing film. a Variation of water vapor permeability coefficient with different filler content. b Change of water vapor permeability coefficient of sealing film after healing from multiple damages Coring. Therefore, storage and transportation with insitu environment preservation after core drilling necessitate focusing on overcoming technologies for preserving the in-situ information of samples from different depths in extreme environments and longterm storage in an in-situ environment to achieve lasting and highly accurate preservation of in-situ information of lunar samples.
In terms of preserving the in-situ compactness of lunar samples, 'we have proposed a technique and method for pressure detection between lunar rock and soil based on the combination of depth calculation and precision sensing. Based on the pressure data between the lunar rock and soil, the in-situ condition-preserved chamber can be filled with an inert gas of the same pressure without destroying the fidelity film and keeping the vacuum of the sample, to help maintain the in-situ compactness of the lunar sample. A multitube lunar in-situ condition-preserved storage chamber is designed to preserve the in-situ environmental information of lunar samples at different depths. The sealed lunar samples will be stored in the coring device. Upon returning to the lunar surface, the coring device will be positioned and stored in the tube of the sample in-situ condition-preserved chamber. Each tube independently stores the lunar-based samples from different depths and does not interfere with each other. Simultaneously, with the help of in-situ environmental information sensing and feedback control technology in the coring process, the exact reconstructed environment identical to the in-situ environment is provided in each tube of the in-situ condition-preserved chamber to maintain its in-situ properties meeting the in-situ environment preservation requirements of lunar samples from different depths. We also designed an in-situ condition-preserved sample storage device based on the principle of magnetism, which is composed of a coring tube, an outer barrel, a rotating inner tube, a magnet, rockbreaking parts, sealing parts, and other parts. The structural design is shown in Fig. 13. Its operating principle is that the collected lunar rock sample drives the impact magnet to move to the upper part of the coring tube until it reaches the coring designed height. At this point, the receiving magnet attracts the impact magnet, thereby accelerating its movement towards the receiving magnet. Concurrently, the impact magnet will break the weakened lever and release the synchronization card. The synchronization card synchronizes the rotary inner tube with the outer coring barrel. The inner coring tube remains non-rotary, creating a rotation speed difference between the rotary inner tube and the inner coring tube. The sealing cloth can be twisted and deformed by utilizing this speed difference, causing the lunar rock to be cut off, completing the sealing operation. The same speed difference can be used to drive the rock-breaking slider to slide out along the slide rail so that the pointed tip of the rock-breaking slider pushes into the lunar rock, aided by the impact force of the impact module, causing the lunar rock to be cut off. A specific volume of debris holding space is reserved on the upper part of Fig. 12 XRD spectrum of rock samples before and after sealing film coating the storage module to provide a temporary storage location for the rock debris/lunar soil that needs to be discharged during the drilling process to keep it from affecting the subsequent drilling and coring process.

Development of an ICP-Coring testing and analysis platform in a simulated lunar environment
In the lunar coring equipment development and equipment ground experiment, NASA and the Center for Astrobiology have jointly developed the MARTE extraterrestrial sampling System, which has a power of 150 W, a diameter of 48 mm, and a core length of 200 mm (Stoker et al. 2008). Harbin Institute of Technology has developed a series of conventional drilling and sampling test platforms for lunar soil, such as 2, 1, and 0.5-m bionic coring apparatus, and carried out relevant experiments, but the extreme lunar occurrence environment was not considered (Zhang et al. 2015). Beijing University of Aeronautics and Astronautics developed a lunar surface drilling vacuum environment simulation device with a load vacuum of 10 Pa. The temperature range is -40°C to ? 80°C, and the effective drilling depth is 2000 mm (Ding et al. 2016). In summary, the existing development of lunar coring equipment has the disadvantages of low power, low torque and limited coring depth, which cannot realize the simulation of extreme temperature difference and high vacuum degree in lunar extreme environment. Carrying out ICP-Coring tests in a simulated lunar environment is a prerequisite for exploring and exploiting lunar geological resources. Therefore, establishing an ICP-Coring testing and analysis platform in a simulated lunar environment will be conducive to exploring efficient rock-breaking principles and testing lunar ICP-Coring technology. Moreover, full-scale drilling tests based on lunar soil and rock simulants can be carried out to simulate and test an entire multi-parameter coupling ICP-Coring process at different depths and perform real-time monitoring and recording of changes in the coring environmental vacuum, temperature, coring torque, and drilling pressure, etc., thereby providing a testing platform and technical support for the manufacturing technology of a lunar ICP-Coring robot.
(1) Overview of the experimental platform To study the process of core drilling and coring in a simulated lunar environment, we developed an ICP-Coring testing and analysis platform in a lunar-based simulated environment (Fig. 14), which can perform relevant tests on the environmental suitability and reliability under the single or multiple coupling effects of different occurrence depths, vacuum, high and low temperatures of the moon. The lunar environmental vacuum degree is 1.01 9 10 -12 Pa, the highest temperature reaches 130°C, while the lowest temperature can be -183°C, with a maximum temperature difference of 313°C, and there is no apparent magnetic field. To simulate drilling operations under such an environment, the ICP-Coring testing and analysis platform in the simulated lunar environment comprises a drilling system, a lunar environment simulation system, and a testing and analysis system. The drilling system includes a rotary motor, an impact motor, and a footage motor, the lunar environment simulation system includes a (2) Lunar environment simulation system of the platform The lunar environment simulation system ( Fig. 15) is the key to simulating the lunar environment's high vacuum and extreme temperature difference on the experimental platform. It adopts the tight sealing technology of customized magnetic fluid leveraging magnetic fluid colloidal solution properties such as nonprecipitation, non-coagulation, non-decomposition, high saturation magnetization, leading to advantages such as lasting service life, wearfree, high reliability, and excellent adaptability. The achievable ultimate vacuum of the system under a no-load state is 1 9 10 -2 Pa, and the leakage rate is 1 9 10 -12 Pa.m 3 /sec. In addition, it adopts an electric heating plate heating system and uses direct liquid nitrogen evaporation for cooling, and the test chamber is equipped with temperature and vacuum degree sensors.
(3) Related design parameters of the experimental platform In subsurface drilling on extraterrestrial celestial bodies, the rotation speed of drill pipes is generally limited to 500 r/min due to environmental and technical constraints. For example, the rated speed of the ALSD system in the Apollo mission was 280 r/min, and its impact frequency was 37.8 Hz; the maximum impact work was 4.4 J (Haggerty 1978). Some scholars used numerical simulation software to establish a mechanical model of the lunar soil and drilling tools to dynamically simulate the process of the drilling tools drilling into the lunar soil. The recorded drilling resistance was about 300 N, and the drilling resistance torque was 7.5 NÁm (Wang et al. 2016). The design parameters of the fidelity coring testing and analysis platform in a simulated environment can be planned as shown in Table 2, by referencing the drilling parameter planning of lunar surface sampling institutions that has been carried out, considering the needs of experimenting and researching drilling under a simulated environment, and combining with the lunar drilling capacity design and analysis of simulated lunar rock surface drilling load test.

Conclusion
Deep space exploration is of great significance to exploiting space resources and promoting cuttingedge science and technology. It is a complete manifestation of a country's capabilities in cutting-edge science and technology. The moon has become the first choice for deep space exploration because of its unique spatial location and abundance of scarce natural resources.
(1) The lunar sampling represented by the US Apollo program, the Luna program of the former Soviet Union, and China's Chang'e-5 lunar mission are all ''ordinary sampling'', ignoring the preservation of the lunar in-situ environment, and there is an issue of sampling depth and fidelity. The problem is that essential in-situ information such as volatile gas, compactness, and stratigraphic sequence in the obtained core samples is lost, restricting research on major issues such as lunar resource exploration, the origin of life, and the evolution of geological structures.
(2) Lunar ICP-Coring is a new scientific concept and engineering practice. Its comprehensive and practical development requires the intersection and integration of multiple disciplines and fields. The ''4 Ps'' coring (preservation of composition, vacuum, bedding, compactness) has been proposed as the central scientific concept of ICP-Coring based on the extreme lunar environment (extreme temperature difference, intense radiation, microgravity, ultra-high vacuum), the unique physical and mechanical properties of lunar rock and the operating characteristics of space institutions, etc. (3) Based on the scientific meaning and fundamental principles of lunar ICP-Coring, the critical technical conception of the lunar ICP-Coring system was proposed. Numerous research and development have been carried out, including developing a drilling and coring robot and filmforming while drilling technology for ICP-Coring, in-situ packaging, and storage technology research, and establishing an ICP-Coring testing and analysis platform in a simulated lunar environment. The research results provide a theoretical and practical foundation for the development of lunar exploration and ICP-Coring robots, as well as research ideas and technical references for the ICP-Coring on other extraterrestrial objects in the future.