Biomimetics for innovative and future-oriented space applications - A review

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• 2.1 Defenses against the extreme space environment As mentioned above, the space environment presents multiple extreme characteristics fatal to living beings on Earth. Nevertheless, mechanisms can be found that show promising performances in the protection of organisms to cope with ionization radiation, extreme temperatures, electromagnetic interference, micro asteroids and space debris. In humans and other living beings as well as some fungi and bacteria, the biopolymer Melanin is found in cells and is mainly responsible to protect the cell from UV or ionizing radiation. Therefore, synthetic Melanin was produced and investigated for its wavelength absorbing and radiation protection potential with applications in aerospace engineering and other industries (Turick et al., 2011; Li W. et al., 2020; Vasileiou and Summerer, 2020). Another biological mechanism to deal with high levels of radiation can be found in bdelloid rotifers. They display a very effective DNA repair mechanism to restore ionization radiation damage (Gladyshev and Meselson, 2008; Wiles and Schurko, 2020), which may be transferrable or adaptable in the future to produce radiation-tolerant coatings and materials. Especially for manned missions, the protection against UV radiation is vital for the health and survival of humans spending extended periods of time in space (Williams, 2022). Due to the highly fluctuating temperatures within the space environment and, therefore, the enormous range of extremes, heat flow as well as temperature management and control are crucial steps to maintain the integrity of space systems. By incorporating a circulatory systems inspired by biological organisms into solar panels, experiments have demonstrated the potential for a symbiotic use of a single structure for a component’s structural efficiency as well as thermal management (Williams et al., 2007). Furthermore, bio-inspired porous carbon ablators were assessed regarding their thermal protection of spacecrafts during the re-entry process into planetary atmospheres, showing promising results to produce enhanced thermal protection even at high temperatures (Poloni et al., 2022). On the other side of the temperature spectrum, many biological organisms can be found with distinctly evolved mechanisms to protect against freezing temperatures and the subsequent formation of ice crystals in their cells and tissue. Examples for this are ice-binding proteins or antifreeze proteins and glycolipids, which are currently applied within the fields of agriculture, cryobiology and food technology, but also hold great promise for material technology and therefore, aerospace engineering by preventing metals from frost formation and liquid materials from freezing (Bredow and Walker, 2017; Li and Guo, 2018; Zhou et al., 2019; Białkowska et al., 2020; Xiang et al., 2020). Recently, researchers have taken first strides into developing lightweight and flexible materials for the protection of structures and equipment against electromagnetic radiation. Experiments show that electromagnetic interference can be successfully shielded by substituting conventional metal shields with ones inspired by cellular architecture with tiny pores mimicking cell walls as aerogels shown in Figure 3 (Liu et al., 2018; Zeng et al., 2020). Figure 3 FIGURE 3. (A) Diagram how the electromagnetic interference shielding works with aerogels and a graphical representation of different sample performances throughout literature. Reproduced from Zhou et al (2021), with permission from Elsevier, (B) Photograph of the microstructure in the longitudinal (g)) and transverse (h)) planes of a MXene/CNF hybrid aerogels with 17wt% ultrathin cellulose nanofibrils content. Reproduced under CC-BY-4.0, Zeng et al. (2020). While micrometeoroids have been a threat to space systems since the beginning of space flight, the likelihood of a collision with one is rather small compared to the ever-increasing quantity of anthropogenic space debris circulating Earth's orbits. Hence, collisions with such debris become an ever more likely problem. Two options are available for dealing with space debris in orbit: avoidance maneuvers or shielding against collisions. Shielding is very expensive, only possible to a certain degree (dependent on size and velocity of debris) and adds to the mass of the system, inadvertently reducing payload capabilities. Avoidance maneuvers are often an alternative, sometimes, however, a must to escape collisions with large debris. While maneuvers are not only fuel-costly, they also require knowledge and tracking of existing debris (OECD, 2020). Until 2020, the International Space Station (ISS), continuously home to a crew of astronauts since 1999, was forced to conduct 27 collision avoidance maneuvers. Another four instances occurred, where debris was not detected in time, demanding an emergency evacuation by the crew (Johnson, 2012; ODPO, 2020). Other unoccupied space systems such as CubeSats, which are usually not equipped with their own propulsion system, are not capable of performing debris evading maneuvers. Besides these obvious challenges, more costs associated with space debris are related to the repair or replacement of spacecrafts, space situational awareness activities, data-blackouts when evading maneuvers are conducted, and insurance costs for operational space systems (OECD, 2020). Hence, finding cost-efficient and effective ways for debris detection and tracking can have enormous economic benefits and make space travel even safer. In nature, several concepts can be found that deal with similar problems as well. Dragonflies, for example, are able to pursue their prey within a turbulent environment and distracting stimuli, yet still manage to capture a selected target with a 97% success rate. They do so by using so-called small target motion detector neurons, which are very sensitive to target contrast. Hence, they present an efficient and highly adaptable visual processing system to prevent collisions with their surrounding, which has already been modified and transferred into tracking algorithms (Bagheri et al., 2017; Colonnier et al., 2019). Investigations by Bagheri et al. (2017) showed that their dragonfly-inspired algorithm presented a higher average success (47.6%) in tracking small targets within a natural scene compared to conventional algorithms (maximum average success: 41.9%). Likewise, locusts demonstrate an attractive mechanism to avoid collisions using their lobula giant movement detector neurons. Those enable locusts to recognize approaching obstacles even in low-contrast conditions or textured backgrounds in motion. Once a collision alert is triggered, the locust can adapt its behavior mid-flight to alter its trajectory and avoid the collision. Since this collision avoidance mechanisms seems very promising, it has already been considered for the implementation of smart vehicle technology and robotic navigation with obstacle avoidance (Yue et al., 2006; Keil et al., 2018; Wang et al., 2021b). Therefore, it shows potential for application within the context of aerospace engineering and space exploration. 2.2 Vibration dissipation, fracture prevention and self-healing Space systems designated for the exploration of extra-terrestrial bodies face an immense challenge right at the beginning of their mission. The landing of unmanned spacecrafts on the surface of another planet is oftentimes violent and associated with enormous impact forces. Therefore, several actions and measures have been taken to protect sensitive equipment and payloads against those forces. Likewise, nature too deals with great impact forces and has spent millions of years of evolutionary development cycles to evolve perfectly matched strategies and extraordinarily sophisticated systems to deal with the existing challenges such as great impacts. Thus, space technologies that have only been developed over the course of a few decades could highly benefit by learning from nature. The seeds of trees fall from great heights to reach the bottom and have therefore developed multiple different protection mechanisms for the valuable payload of DNA contained within. The seeds of the plant Tragopogon dubius, for example, are attached to stalked parachutes, which have evolved to increase the aerodynamic drag of the seed and therefore slow its descent, which not only allows the seed to survive but also increase the distance travelled during its descent from the tree in order to propagate the species as far as possible (Pandolfi et al., 2012). While parachutes are the conventional solution for slowing the descent of space systems, velocity reduction may be optimized using parachutes of plants that have evolved over centuries. In contrast to slowing the seed and thereby reducing the negative effects of hitting the ground, many species of nuts have evolved differently. Instead, they produce a rigid layer of protective shell around their seed, designated to protect it during impact (Islam et al., 2021). Likewise, insects form very stiff cuticles to protect against predators. These cuticles consist of hard composite structures formed with chitin fibers arranged in distinct patterns, which enable insects to cope with extensive amounts of strain and load. The composite structure is able to adapt to external forces and change its thickness, stiffness and orientation of fibers accordingly (Jullien et al., 2020; Stamm et al., 2021). This bio-material on its own has shown to produce a tensile strength of 130 MPa and an elastic modulus of 2,900 MPa, which can further be increased through combination with other materials such as polymers or resins (Gadgey and Bahekar, 2017; Hou et al., 2021). Marine species like mollusk shells, too, make use of a multilayered structure called nacre to build their own homes and as protection, which demonstrates a composite architecture of impressive mechanical characteristics (Yaraghi and Kisailus, 2018). Different species of shells produce different types of nacre some of which present a Young’s modulus of 60–70 GPa and a tensile strength of 70–100 MPa. (Barthelat et al., 2016; Jiao et al., 2019; Askarinejad et al., 2021). Nacre is also known for its great fracture propagation and deflection properties based on their high stiffness and fracture toughness. Gao et al. (2017) compared the mechanical properties of the natural nacre produced by the species Cristaria plicata and artificial composite materials, demonstrating higher flexural strength (267 MPa) and similar fracture toughness (1.9 MPa/m2) for the artificial material compared to natural nacre (172 MPa, 2.4 MPa/m2, respectively). Other mechanical parameters of the artificial biomaterial like ultimate stiffness and elastic modulus reached values of 18.6 GPa (Gao et al., 2017) and 11 GPa (Raj et al., 2020), respectively. A third option of dealing with high impact forces is demonstrated by the peel of the pomelo fruit. Instead of evolving hard materials capable of preventing fractures of the plant’s fruit or slowing its descent, the peel of the pomelo fruit demonstrates a thick layer with open cell foam structure of varying pore size as depicted in Figure 4A), which protects the fruit inside from damage when falling from trees of up to 10 m in height. Experiments have uncovered a dissipation of up to 90% of the impact energy while testing on free falling pomelo fruits. They therefore present excellent impact damping and energy dissipating capabilities (Ortiz et al., 2018). More recently, the beneficial features of the pomelo’s peel have been recognized by the scientific community and several articles have been published studying and modelling the foam-like structure (Thielen et al., 2013; Bührig-Polaczek et al., 2016; Ortiz et al., 2018; Li T.-T. et al., 2019). Hence, artificial versions of the foam may be applicable to dampen the effects of vibrations and reduce oscillations of space systems as well. Figure 4 FIGURE 4. Pomelo peel as dampener, (A) Photographs of the honey pomelo’s peel. Reproduced from Pixabay, and a view under a digital microscope taken at different regions of the peel at 150-times magnification (ⓒ E. Banken), (B) Photograph of an Aluminium foam sample with branched Al2O3-fibre bundles and a magnified view of a fibre reinforced Aluminium-alloy foam sample showing the connection between the fibre bundle and the foam matrix, Reproduced from Bührig-Polaczek et al. (2016), with permission IOP Publishing. While some animals protect vital organs through fluid immersion, which absorbs the shock rather than transferring it to the valuable payload, the woodpeckers and Australian cassowary are two types of birds that have evolved different features to protecting their brains from high impact forces. The woodpecker uses its elongated and pointed beak to penetrate the bark of trees and find insects to feed on. It achieves the penetration through high percussive speeds of up to 22 times per second, accomplishing frequencies between 20–25 Hz and an acceleration between 600 g—1,000 g (Bian and Jing, 2014). Hence, to protect its brain, the skull has formed so that the brain is tightly held in its position, while its tongue reaches from its beak all the way around the brain along the back of the skull. Hence, even under extensive stress, the brain is protected and does not get damaged in the process (Hollin, 2021). Likewise, the Australian cassowary uses its head to ram it into tree trunks in order to knock down fruits. It has a hollow fin-shaped protrusion of keratin on its head connected to its skull that is filled with a soft, rubber-like matrix. This protrusion can protect the bird from impact velocities up to 50 km/h and absorbs the shock (Widholm and Jawaharlal, 2016). Bio-inspired concepts like these are heavily researched for applications on earth, such as the prevention of brain injuries, as well as for the protection for sensitive equipment in engineering, and thus, present valuable insights for the protection of space systems, too. In contrast, an example for damage forestalling and injury prevention is the natural principles of load flux dependent design. Trees and bones demonstrate the ability to direct and redistribute cell growth and therefore structural reinforcement in areas experiencing high amounts of stress (Menon et al., 2007). Conch shells, on the other hand, present curved lamellae that can increase fracture resistance by about 30% compared to straight ones (Li and Li, 2019). Self-reinforcing materials like these could significantly contribute to extending the lifespan of space systems and react to unforeseen internal and external system stressors. Apart from high impact forces, space systems are also exposed to brutal vibrations upon launch of the carrier rocket and need to be securely fastened to prevent damages. Furthermore, moving parts in spacecrafts are usually avoided to prevent the creation of unwanted oscillations and rotational forces. Oftentimes, components are added designated to counteract persisting vibrations and associated negative impacts (Menon et al., 2007; Garcia-Perez et al., 2019; Guo et al., 2019). Yet, these measures limit functionalities and influence the system design. Even under consideration of major precautions, micro-vibrations can be created during a spacecraft’s operation due to faulty calculations or external impacts. Thus, mechanisms to reduce oscillations and dampen the effect of vibrations find a broad range of application within the space sector (Kamesh et al., 2010; Yu et al., 2018). Nature has brought forth multiple approaches to protect organisms from large oscillations and vibrations. One method of dealing with vibrations is their isolation as demonstrated by the human middle ear using an auxiliary mass mechanism among others (Kim and Kang, 2019; Wang et al., 2019; Yan et al., 2021). Fish, too, present a natural vibration dissipation through their hierarchical arrangement of scales in a compliant dermal tissue that allows for flexibility. They offer reversible non-linear stiffening and exhibit an interesting locking behaviour that is observed when the tissue is bent or twisted. First experiments show a viscous damping performance and direction-dependent frictional characteristics of the scales that can be adjusted and manipulated through alterations of the scale’s geometry (Ali et al., 2019). In the plant world, oscillation dissipation can be observed as well. Plant roots as well as tree trunks have been shown to provide structural dampening and transfer of vibration energy throughout their branches (Barth, 2008; Kovacic et al., 2018). If the force and experienced stress on single components or parts gets too large, biological organisms and technical systems alike tend to break, fracture, bend and deform. Nevertheless, nature displays various mechanisms to deal with such damages and is able to repair components to restore their mechanical and practical function. Healing capabilities can be found in almost every living being as it is crucial for survival to maintain structural integrity, fluid balance, and function. Self-healing in organisms can take shape in various different approaches, using stored elastic energy, hierarchical structures, self-assembly systems, liquid exchange, cross-linking of proteins and many more (Speck and Speck, 2019). During the wound-closing and healing process, activities such as coagulation, cell proliferation and matrix deposition are deployed to close holes and fissures, restoring the organism back to almost its original state (Aïssa et al., 2019). Bauer and Speck (2012) investigated the healing capabilites of tree bark species and found a 55% restoration after only 30 min of initial external injury. Thus, tissue can be sealed over a short period of time, restoring the parts functionality without repairing its full mechanical properties. Methods to structurally repair any fissures and (partially) restore mechanical properties exist too, however, take much longer (Speck and Speck, 2019). Self-healing and -repairing systems are crucial for space systems as aerospace companies and manufacturers go through enormous efforts to protect components and parts from structural or electrical failure. Furthermore, maintenance operations are either very costly or not existent at all. Hence, systems like self-repairing components can extend the lifetime of spacecrafts and prevent total system failures due to propagating fissures and cracks. Some mechanisms inspired by animal, plant and human tissue have been abstracted and implemented as self-repairing materials, especially for polymer composite materials. Four main methods for repair have been established, and come in either a capsule, particle form or an organized net (filled with fluid or made from wires) that are spread throughout the material and are triggered by internal or external stimuli (Cohades et al., 2018; Aïssa et al., 2019). Liquid-filled fibers or capsules incorporated into materials can excrete a dye for visual detection of damages or a resin-hardener combination that fill any occurring cracks and restore their mechanical properties (Nellesen et al., 2011; Speck and Speck, 2019). 2.3 Planetary exploration and activities In order to learn more about a planet or other extra-terrestrial body, the gathering of as much information as possible is crucial. While sensors and scans using optical and thermal equipment as payload on satellite flyby’s deliver a great deal of data on those bodies, it is vital for a deeper understanding to gather physical evidence and take samples of various materials to be analyzed for mineral content but also for traces of life (Zhang et al., 2022b). Eventually, this information will be used to plan and execute in situ resource utilization to e.g., build a future space base. Other applications include asteroid mining for rare elements and finding life on other planets. One of the most prominent applications for biomimetics within the space industry are drilling processes for planetary exploration and sample acquisition. Thus, multiple concepts exist that have conceptualized bio-inspired methods and procedures to improve and enhance these activities. One well developed biomimetic concept is based on the reciprocating drilling motion of the wood wasp. Wood wasps use their serrated ovipositors as depicted in Figures 5A,B to drill into the bark of trees to deposit their eggs. They can achieve a drilling speed of approximately 1–1.5 mm/min, while its ovipositor is assumed to have a Young’s modulus of about 10 GPa (King and Vincent, 1995). This drilling method exhibits several favorable characteristics like its drilling efficiency and low overhead mass requirements. In addition, it circumvents the major challenge of rotary motion associated with conventional planetary drill designs. Several prototypes exist that have been tested intensively in a wide range of substrates ranging from fine regolith simulants to icy substrates as the one shown in Figure 5C. Sakes et al. (2020) developed a wood wasp inspired micro-drill prototype for minimal invasive surgery capable of achieving a stroke velocity of 4–8.77 mm/s and a transportation rate of up to 5.82 mg/s. Still, a wood-wasp inspired drills for aerospace applications have yet to be deployed and tested within the space environment (Gao et al., 2006; Gouache et al., 2010; Pitcher et al., 2020; Alkalla et al., 2021). Figure 5 FIGURE 5. Wood wasp reciprocating drill, (A) Photograph of a wood wasp, (B) magnified view of its ovipositor consisting of two serrated valves, Reproduced from King and Vincent (1995), with permission from the authors, (C) schematic picture of a micro drill for aerospace applications. Reproduced under CC-BY-4.0, Pitcher et al. (2020). A similar concepts is demonstrated by the locust digging into the soil to deposit their eggs by pulling their abdomen into the hole while simultaneously clearing the debris out of the digging path (Gao et al., 2007). Other biomimetic concepts exist based on the earthworm or mole and operate with a similar approach (Kubota et al., 2007; Lee et al., 2019). Other organisms besides earth-dwelling animals have proven effective ways to drill into substrates, too. Plants heavily rely on their roots to form a secure and permanent attachment to the soil and the distribution of water and nutrients to enable the development of a seedling able to outcompete its competitors and go on to grow into a mature plant. Hence, roots of different plants have developed various ways to achieve effective anchoring. One great example is displayed by the seeds of the plant Erodium cicutarium, which bury themselves into substrates. This mechanism is thought to have developed improving the seed dispersion process of the plant. Its fruits develop a seed with an elongated and spirally twisted tail that, once in contact with the ground, is humidity driven and causes the seed to autonomously bury itself into the material (Pandolfi et al., 2012; Mancuso et al., 2014). Developing such a passive drilling mechanism dependent on abiotic conditions in the surrounding environment could provide a very useful, resource-saving and energy efficient mechanism to allow probes to bury themselves into the surface material of planets. Furthermore, the formation of complex networks of smaller and bigger roots may offer great possibilities for underground pathfinding and mapping of structures under the surface, which can help to determine geological compositions, traces of water and other valuable resources (Menon et al., 2006; Seidl et al., 2008). In order to transport different probes or scientific equipment across planetary surfaces from one interesting spot to another, autonomous or remote-controlled robotic systems are required. Extra-terrestrial terrains are often found to be difficult with many obstacles and rough surface textures, which frequently display challenges and limitations to conventional wheeled robotic systems (Armour et al., 2007). Many bio-inspired concepts exist and present different characteristics dependent on the local demands and requirements. Limbed robots, for example, are useful for rough terrain with large obstacles and are often designed to mimic multi-legged organisms such as spiders due to their high stability, range of motion and surface adhesion (Gasparetto et al., 2008; Dürr et al., 2019; Lopez-Arreguin and Montenegro, 2020). Other concepts are based on the jumping mechanisms of locusts, frogs, kangaroos and shrimps dismissing the highly complex control systems and the maximum height of obstacles (Armour et al., 2007). After the success of the first-ever human-made flying object on Mars, the Ingenuity Mars Helicopter has paved the way for a new level of extra-planetary exploration (Balaram et al., 2018). Hence, flying drones and other flight systems have become of more interest for the exploration and investigation of foreign bodies throughout the Universe. On Mars, one of the most significant challenges is the thin atmosphere, which makes the generation of sufficient lift and thrust necessary to get a system airborne difficult. Nature offers a range of locomotion types for different media, and therefore provides a large pool of propulsion systems to get inspired by. Babu Mannam et al. (2020), for example, investigated several biological examples of flapping wings for their potential use in light atmosphere environments and summarized a design methodology and relevant hydrodynamic aspects to evaluate bio-inspired concepts for their application to different environmental conditions found on planets. Eventually, the long-term goal of many space enthusiasts is to create manned habitats on other planetary bodies, elevating humanity from a single planet-based species to one that wonders the Universe. Hence, biomimetic concepts involved in the creation of habitats and continuously sustaining life under adverse environmental conditions will eventually become of much more interest. And with it, all of the biomimetic concepts already widely applied throughout many industries nowadays on Earth. This includes radiation protection, nutrition, waste management, as well as medical care (Jemison and Olabisi, 2021). ESA’s Advanced Concepts Team even investigated the possibility of mimicking the hibernation behavior of mammalians (e.g., Spermophilus tridecemlinneatus) to achieve human hypometabolic state for long duration journeys (Menon et al., 2007). One example with great potential are the water-living lotus plants, which have developed superhydrophobic surfaces that cause water droplets to simply roll off, naturally keeping the leaf clean and continously guaranteeing access to oxygen in the surrounding air. Another water-living plant species is Salvinia molesta, which is able to trap air on the leaf’s surface and therefore can retain an air layer on top of their leaves in times where the leaves are temporarily fully submerged in water (Barthlott et al., 2016; Gobalakrishnan et al., 2020). Those mechanisms have been abstracted and applied throughout multiple industries but also hold merit for aerospace engineering. In fact, they have been proposed to prevent icing in small airplanes (Piscitelli et al., 2020) and water retention in a human life support system in spacecrafts (Rasheed and Weislogel, 2019). More importantly, such surfaces have been conceptualized for reducing dust and ice on solar panels on Earth (Wu et al., 2022), which is also of relevance for orbiting systems. Likewise, animals, too, have self-cleaning abilities similar to plants. The toe pads of geckos and tree frogs (Crawford et al., 2012; Hawkes et al., 2015) or the rigid forewings of dung beetles (Sun et al., 2012) present interesting methods keeping water from settling onto the surface of functional body parts. Mechanisms like these have been proposed for their implementation for anti-reflection, anti-fogging, micro-manipulators and self-healing in space systems (Xu et al., 2016), and are especially useful for things like lenses and visors, sensitive instruments such as batteries and power systems (Williams, 2022). 3 Biomimetics for space debris removal 3.1 Existing bio-inspired debris removal concepts Space debris has become a major topic of concern, as defunct satellites, rocket upper stages and fragments are starting to threaten the operation of functional satellites, thereby endangering satellite communication, weather observations, and climate monitoring on earth (Sannigrahi, 2017; ESA, 2019; OECD, 2020). Hence, recent efforts have concentrated on space debris removal and mitigation measures (Ansdell, 2010), and options for more sustainable mission design as well as the establishment of mitigation guidelines have been proposed. These guidelines include provisions for incorporating removal systems such as drag sails into spacecraft design prior to launch for their eventual end-of-life (United Nations, 2010; Stokes et al., 2019). Especially drag sails have already been discussed within the scope of biomimetic design in terms of efficient folding and storage mechanisms, and several alternatives have been proposed, mimicking seeds and their dispersal mechanisms (Pandolfi et al., 2012; Pandolfi and Izzo, 2013) or tree and plant leaves (de Focatiis and Guest, 2002; Jasim and Taheri, 2018). While space agencies and companies have focused on space debris capture and developing removal missions, to date no such mission has ever been performed. The first-ever operation simulating debris removal was conducted during the controlled activities of the RemoveDEBRIS mission in 2019, where a harpoon and a net were deployed to capture a previously released and well-known target body (Aglietti et al., 2020; Forshaw et al., 2020). In a joined venture of ESA and Cleanspace, the first debris removal mission Cleanspace-1 is scheduled to perform the first debris removal service of a VEGA secondary payload adapter as early as 2025 (Biesbroek et al., 2021). While these efforts displays a huge leap in space debris removal and tests showed promising results, harpoons are still associated with high risks of additional debris production due to the forces required to penetrate the target’s surface material while preventing a large impulse generation and thus pushing the target from its current course. Furthermore, complex rope dynamics between chaser and target have not been investigated in this mission and present a technical challenge (Zhang et al., 2021). Both, nets and harpoons offer great opportunities for their adaptation by using biological models as inspiration. Nets have frequently been under investigation in biomimetic research ranging from textiles (Blamires et al., 2020; Gu et al., 2020) to optical fibers (Tow et al., 2018). Harpoons, too, have been studied extensively and concepts have been proposed for surgical tools, modelling tips and shafts after the bee’s stingers (Sahlabadi and Hutapea, 2018) and mosquito’s probiscis (Li A. D. R. et al., 2020), among others. One of the most prominent and probably furthest developed biomimetic example for space applications is the gecko tape. The tape exhibits a specifically structured surface modelled after the example of a gecko’s feet. Each toe of the gecko presents a highly adaptive microstructure with hundreds of hairs called setae as depicted in Figure 6A), each exertig a van der Walls force onto components, allowing the gecko to carry its own body weight up vertical surfaces or hang upside down (Kim et al., 2008). This mechanism has been replicated by multiple companies in form of a reusable adhesive tape with different microstructures as shown in Figure 6B), and tested extensively for various applications and consumer needs (Brodoceanu et al., 2016; Alizadehyazdi et al., 2020; Busche et al., 2020; Cauligi et al., 2020; Sameoto et al., 2022). One of these tapes was even sent to the ISS in 2019 to test its adhesive capabilities under micro-gravity conditions (Parness, 2017). Hence, gecko-inspired tape presents a great alternative that can achieve lasting and reusable attachment to objects in space. While some parameters such as the lasting adhesive capability or the effects of space dust on its performance still need to be explored further, gecko tape presents a great example for a substitute product within the space environment. Figure 6 FIGURE 6. From gecko feet to adhesive tape, (A) Gecko foot and magnified view of the microstructures responsible for the adhesion thanks to van der Waals forces. Reproduced from Sameoto et al. (2022), with permission from Elsevier, (B) Magnified view of microstructures of different adhesive tape inspired by gecko feet, Reproduced from Aksak et al. (2007) Copyright 2007 American Chemical Society. Republished with permission; Reproduced from Murphy et al. (2007), with permission from Taylor and Francis. Current robotic arms used for extravehicular operations on the ISS (Roa et al., 2017) and debris capturing concepts (Estable et al., 2020) suffer from shearing areas, reserve movement capabilities or chaser movement among other things (Behrens et al., 2012; Estable et al., 2020). Several of these limitations can be improved by taking advantages of nature’s diverse range of available biological examples. Octopi, for example, make use of eight identical and flexible arms for locomotion, grasping and reaching, as well as capturing food. These arms consist of mostly muscle tissue, which is able to selectively contract and therefore control their movements very efficiently (Cianchetti et al., 2015). Robotic systems inspired by octopi arms range from multi-actuator systems (Zhao et al., 2020) to soft robotics (Mazzolai et al., 2019) and have already been proposed for space debris removal (Le Letty et al., 2014; Shan et al., 2016; Jia et al., 2017). Their great mobility, maneuverability and adaptability makes them very suitable to wrap around complex target shapes. Likewise, other interesting biological models for similar tasks are presented by elephant’s trunks or seahorse tails. The trunks of elephants are highly flexible organs with multiple degrees of freedom and therefore presents higher obstacle avoidance capabilities and an increased workspace flexibility (Yang and Zhang, 2014; Zhao et al., 2018). A similar segmented approach is demonstrated by seahorses, which use their tail mainly for grasping activities involving different diameter objects such as plant stems. Seahorses present a continuously decreasing square cross-section in their tail made from four individual plates connected through special joints. This arrangements provide the seahorse with great bending and torsion abilities for grasping, especially of a diverse range of shapes and sizes. In addition, thanks to its specialized construction, their tails shows great fracture resistances under crushing and impact forces (Porter et al., 2015). The concept has been transferred into a multitude of prototypes for robotic arms (Porter and Ravikumar, 2017; Li L. et al., 2019; Zhang et al., 2022a), one of which is displayed in Figure 7. Figure 7 FIGURE 7. Seahorse tail inspired robotic arm. (A) nano-CT image of a seahorse tail skeleton, (B) CAD model of the square cross-sectioned prototype during twisting and bending movements, (C) photograph of a square cross-sectioned 3D printed prototype, Reproduced from Porter et al. (2015) , with permission from The American Association for the Advancement of Science. 3.2 The BIOINSPACED project Within the scope of the ESA-funded BIOINSPACED project (acronym for bio-inspired solutions for space debris removal) conducted from June 2020 to February 2022, several bio-inspired space debris removal scenarios were established, incorporating a diverse range of biomimetic concepts. The project aimed to support ESA’s initiative to mitigate space debris and reduce its negative impact on current and future missions. After analyzing the technical requirements for space debris removal missions, nature’s pool of organisms was investigated to find suitable concepts and mechanisms with distinct benefits for space applications. Collected ideas were assessed to identify the most promising ones, that were then integrated into holistic mission scenarios. As the last step, one of these scenarios was selected for a low-tech implementation in the form of a simple demonstrator depicted in Figure 8, underlining the benefits and variety of applications for bio-inspired technical solutions for space debris removal (Banken et al., 2021, 2022). Figure 8 FIGURE 8. Photographs of the simple demonstrator developed within the BIOINSPACED project and the project logo. Besides the final demonstrator, the project also generated a comprehensive overview over biomimetic concepts and scenarios with further potential for aerospace engineering. One mission scenario conceptualized the use of the swarming behavior of ants to enable autonomous communication among several small and lightweight spacecrafts as shown in Figure 9A). These were theorized to organize themselves in specific patterns without requiring manual input commands, and therefore converge and arrange around a target object autonomously (Gro et al., 2006; Garnier et al., 2007; Divband Soorati et al., 2019). Processes like this can deliver a greater amount of details on target behavior, especially tumbling and rotational motion, which are important factors for contact maneuvers (Stacy and D’Amico, 2018). In addition to target inspection, they can be used for target capture in the form of attachment to the debris and removal, using their own propulsion in unison to deorbit the object. Figure 9 FIGURE 9. Sketches of the scenarios developed within the scope of the BIOINSPACED project. (A) Chaser vehicle carries several sub-units capable of observing, attaching, and deorbiting a target object in unison based on swarm algorithms (e.g., ant behaviour after Katiyar et al. (2015), (B) Chaser vehicle with tactile sensing appendages passively wrapping around slow-moving target upon contact modelled after the trunk of elephants (ⓒ 12138562, pixabay.com). Another interesting feature identified during the project was tactile sensing within the space environment displayed in Figure 9B). Currently, most existing spacecrafts rely on optical sensors to determine a target’s speed, rotation, and overall orbital mechanics. Yet, systems like these are known to suffer from e.g., dynamic illumination conditions or solar glare (Yilmaz et al., 2017). Nature provides a board range of organisms, which make use of tactile sensing as primary sensory input like mammals with vibrissae and insect antenna’s. Some have already been explored in the field of robotics (Pearson et al., 2011; Lee et al., 2022). Paired with haptic sensors mimicking human skin and touch receptors capable of recognizing stimuli such as force, vibration and temperatures, as well as detecting hardness, force, slip, shapes, and textures (Yi et al., 2018), they offer great opportunities for on-orbit operations involving close contact with (un-)cooperative targets (Haschke, 2015; Pacchierotti et al., 2015; Xin et al., 2016; Yi et al., 2018), where high levels of flexibility and sensitivity are of great importance. Further biomimetic concept extracted during the BIOINSPACED project with great benefits for aerospace systems are potential vibration sensors on the example of elephant feet (Lane et al., 2020), and touch recognition modelled after thigmotropism of plants (Vidoni et al., 2013, 2015). Activities such as the BIOINSPACED project support the identification of new and innovative approaches for technical problems, while delivering an overview over existing concepts. Within the scope of the project, many promising concepts and scenarios were identified where mimicking a biological model could improve conventional aerospace systems or overcome current challenges. While none of the presented concepts comes without their challenges, they offer great alternatives and innovative ideas to approach conventional engineering limitations and disrupt existing constraints.