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Biomimetics – A new approach for space system design menon 2/22/06 10:05 AM Page 21

Biomimetics

Carlo Menon, Mark Ayre Advanced Concepts Team, ESA Directorate of European Union and Industrial Programmes, ESTEC, Noordwijk, The Netherlands

Alex Ellery Surrey Space Centre, University of Surrey, United Kingdom

iological systems represent millions of years of trial-and-error learning through according to the most stringent of metrics: survival. ‘Biomimetics’ may be defined as the practice of ‘’ ideas and concepts from nature and implementing them in a field Bof technology. This reverse engineering has recently attracted significant research due to an increasing realisation that many of the problems faced by engineers are similar to those already solved by nature.

ESA’s Advanced Concepts Team views biomimetics as a means of finding new and realistic technologies for application in future space missions. The research is not concerned with mere imitation of biological systems, but rather focuses on understanding the fundamental processes and mechanisms used in nature, in order to discover promising concepts valuable to space engineering. Benefits are expected in areas as diverse as , actuators, smart materials, locomotion, and autonomous operations.

Biomimetics Technology Tree Biomimetics The success of biological organisms in Novel Structures solving problems encountered in their Structures Dynamic/adaptive Structures environments is attributed to the process of Structures and Deployment, Folding and Packing natural selection, whose primary metric is Materials survival – failure implies extinction! Such Composites biological solutions offer insights into Materials Bio-Incorporated Composites alternative strategies for designing Smart Materials engineering systems. Biological systems Muscles and Actuators represent millions of years (billions of years Mechanisms in the case of microbes) of trial-and-error Locomotion learning through natural selection. Nature Mechanisms and has implemented 550 million years of Processes Novel Processes multi-cellular , generating some Processes Thermal Management 5-10 million species, of which only some Fabrication Power Generation and Storage 1.7 million have so far been catalogued. This represents a huge database of Classical Artificial Intelligence biologically-inspired solutions to problems. Behavioural Artificial Intelligence There is thus much that engineers can learn Behaviour Behaviour and Learning Mechanisms from and emulate in their design of Control Swarm Intelligence (DAI) engineering systems – this discipline is called ‘biomimetics’. Reflexive Control Control Biomimetics involves ‘reverse engin- Rhythmic Control eering’ the principles of evolutionary design of biological organisms in order to Vision implement biological solutions to general Sensors Hearing engineering problems. The problems Sensors and Touch encountered by biological systems are Communication Taste and Smell similar in many respects to those encountered in engineered systems. It Communication Passive Group Communication seems appropriate therefore to examine biological solutions in order to analyse Ecological Mechanisms Genetic Mechanisms engineering issues. Research efforts in this Generational Generational direction have recently become significant Biomimicry Cultural Mechanisms Geneering/ Alteration in interdisciplinary-engineering topics.

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Industrial Programmes

Biomimetics Applied to Space Engineering of onboard autonomy. Although autonomy Implementing Concepts from Nature in A spacecraft is designed to cope with a is typically associated with exploration Technological Fields hostile and highly variable physical spacecraft, the issue of autonomy is Reverse engineering of ideas and concepts environment. Although it may not seem also relevant to Earth-orbiting platforms, from nature and implementing them in a totally appropriate to examine biological as ground-station-based control is the particular technological field is not a organisms that have evolved in the dominant factor in operational costs. straightforward process. There are a terrestrial environment in order to seek Biological organisms evolve, adapt number of major differences between novel solutions to problems encountered in and learn in highly variable environ- engineered products and biological space engineering, we seek not to replicate ments whilst maintaining their systems when designing a bio-inspired biological organisms in toto, but rather to functionality. They exhibit autonomy par system:* abstract the biological principles by which excellence, and could therefore inspire organisms function and survive. The new solutions for highly autonomous 1. Most organisms are characterised by appropriate level of abstraction of such engineered systems. cylindrical shapes and curved bio-inspiration is not a trivial issue. A surfaces, while engineered structures successful example of already developed Miniaturisation generally have straight edges and bio-inspired engineered solutions is Volume, mass and power are important and sharp corners. represented by artificial neural networks often critical parameters for spacecraft and 2. Engineered products are generally used for control systems, which are highly their payloads. Their reduction implies constructed from homogeneous simplified and re-structured abstractions several benefits, including significant cost materials, while biological materials of biological neural architectures. savings. are composites to a variety of degrees. Biomimetics applied to space 3. Engineered structures are designed for Satisfying solutions engineering promises the prospect of stiffness (and so tend to be brittle), Engineers often seek optimal solutions in greater miniaturisation, integration and while organisms favour strength over spacecraft and payload design. The process, packaging efficiency, which biological stiffness for toughness. which is generally very costly/time systems exhibit. This has natural synergies 4. Biological features often have multi- consuming, could benefit if ‘satisfying with micro-systems technology, which functional roles. solutions’ are already known. Satisfying integrates electronics, mechanics and solutions represent the approach in biology on a highly reduced scale to achieve When reverse-engineering concepts whereby the historical constraints of high and high complexity from nature and adopting biomimetic available genetic resources lead to the within a very small volume (e.g. a few solutions, the following general caveats are evolution of organisms compliant with the mm3). An important consideration for such proposed in order to obtain applicable prevailing environment. miniaturised systems is that their surface- engineering solutions:** area/volume ratio increases, and this has (i) Biomimetics may be a good starting Robustness and adaptability two important consequences: their power point. Robustness and adaptability are dissipation increases, requiring greater (ii) Pure biomimetic approaches can particularly critical issues in space, as the power volume density, and their structural yield non-optimal performance environments to be explored are typically strength increases, allowing greater solutions. unknown and vary with unpredictable loadings. (iii) Sometimes optimal solutions result dynamics. The most sophisticated from traditional technology. engineered systems are often lacking in System design (iv) Biology relies heavily on good robustness and adaptability, while simple A characteristic of natural systems is their integration through the use of natural organisms excel in terms of holistic design. A more systematic multifunctional structures. adaptability to their environment, adoption of biomimetics in space systems actuation flexibility and sensory design could involve a new approach that A wide number of engineering disciplines robustness. Ideas inspired by nature could treats a functional unit in a concurrent and could be analysed taking into account therefore represent valuable solutions with multidisciplinary way. The payload of the existing solutions adopted by nature, some regard to these issues. spacecraft is thereby not treated separately, of which are shown in the ‘Biomimetics but as an integrated, indeed primary output Technology Tree’ on the facing page. Autonomy of the space mission – its behaviour. The Although this tree could be greatly Another critical issue for space systems is environment also acts as a feedback that of autonomy – the distances involved, mechanism to the spacecraft. This provides particularly once spacecraft venture the basis for the modular and hierarchical * From P. Husbands et al. (1998), Connection Science, pp. 185-210. beyond Earth orbit, preclude real-time division of the spacecraft. ** From R. Michelson & M. Navqi (2003), Von Karman Institute for Fluid control, thus necessitating high degrees Dynamics Lecture Series.

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Biomimetics

expanded and extended, it can be used as a starting point for future studies and analyses.

Research on Biomimetics Considering the advantages of reverse- engineering concepts from nature and taking into account the major differences between engineered products and biological systems, ESA’s Advanced Concepts Team has already analysed some bio-inspired systems for space applications.

Biologically inspired solutions for mobility Mobility is one of the most interesting fields for bio-inspired space solutions. In nature, there exist several types of systems Overlap in terms of similar performances for wind-propulsion and ballast-drive mechanisms used for mobility in the air, on the ground, and in liquids. Dandelion seeds, maple Helsinki University of Technology in mechanisms were compared and seeds (see lead photo) and hoppers are just collaboration with ESA’s Advanced interesting results were obtained, as shown a few examples that have been considered Concepts Team. While rolling in the wind, in the accompanying figure. for bio-inspired space system design. this thistle disperses its seeds (typically Considering the Mars surface One design concept based on the 250 000 per plant) over a wide area. Both environment as one potential application, Russian thistle was produced by the passive wind propulsion and ballast-drive particular attention was paid to ways in which natural energy sources could be harnessed (solar, wind, thermal, gravitational potential energy, etc.). In the bio-inspired thistle-based design concept shown here, the system, which has turbine blades and an external skeleton, may have an open (top figure) or a pressurised closed section (bottom figure). An optimal wind- turbine configuration would increase the efficiency of the system and perhaps include a ballast-drive mechanism for steering, overcoming obstacles, and actively moving the system to locations of Maple seeds scientific interest.

Digging mechanisms Natural digging mechanisms used by have also been investigated to identify techniques that space engineers could replicate to produce better surface diggers. Among the wide variety of such mechanisms in nature, two specific ‘biological drills’ have been studied in more detail. The first are the ovipositor ‘valves’ of the female locust (analysed together with D’Appolonia, Italy, and the University of Russian thistle caught on a barbed-wire fence. Image courtesy of DesertUSA.Com A bio-inspired thistle-based design concept Bath, UK). Snodgrass presented his

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Industrial Programmes

studies of the morphology of ovipositor valves in 1935. The upper sketch in the accompanying figure represents the digging mechanism of a typical , while the lower image is a photograph of an ovipositor. The ovipositor valves open and close cyclically while the system moves up and down using different sets of muscles. The upper valve is used for excavation, whereas the lower one pulls the locust’s abdomen down the hole. When the two valves are in their Sirex ovipositor digging mechanism (From J.F.V. Vincent & M.J. closed position, they are inclined by about King (1995), Biomimetics, pp. 187-201; reproduced with the 20 degrees with respect to the direction of kind permission of Springer Science and Business Media) the apodeme. This natural mechanism has been used as the basis for a digging drill, this system requires no external mechanism design that was dynamically reaction force during drilling as the linear simulated as a concept for a miniaturised reaction forces required are generated space drill. within the pair of valves. A conceptual The second digging mechanism was design for such a bio-inspired digger has inspired by Sirex Noctilio, a type of wood been constructed to evaluate its feasibility (analysed together with the for space applications. In particular an Schematic of an asteroid micro-penetrator Universities of Surrey and Bath, and asteroid subsurface-sampling mission EADS Astrium Ltd., UK), which uses a profile was considered, but the solution reciprocating motion to drill holes in trees inspired by the Sirex Noctilio can Joint research work has been carried out into which it deposits its eggs. With this potentially be employed in a wide variety by ESA’s Advanced Concepts Team and mechanism, it is able to drill at a rate of of mission scenarios. Based on the asteroid other European research centres about 1-1.5 mm/min. The two valves, micro-penetrator shown in the (Inter-departmental Research Centre which slide longitudinally against each accompanying figure, the study confirmed ‘E. Piaggio’, University of Rome, Kayser other, have backward-pointing teeth that the feasibility of applying the wasp- Italia, and University of Reading, UK) to allow the driller to move forward into the inspired concept to design a digging assess the potential of EAPs for space hole. In contrast to a conventional rotating mechanism. systems. A thorough investigation of the While both of these systems show physical and chemical properties of the promise in terms of being novel digging different classes of EAP showed that designs, their potential benefits are still to /actuators based on dielectric effects be fully assessed through further are of particular interest for space investigations. applications. Dielectric EAPs can exert large forces and produce considerable Artificial muscles displacements, making it possible to The development of electrically deforming design high-performance actuators. A materials, in particular Electro-Active prototype linear electromechanical (EAPs), has led to improvements actuator made of a dielectric EAP in the performance of actuators designed developed by the ‘E. Piaggio’ Centre is to serve as ‘artificial muscles’. Compared shown in the accompanying figure. with conventional systems, these bio- Development of EAPs in fibre form is inspired actuators are of interest for use in currently at an early stage, but is of space systems because of their inherent particular interest because of the extra compactness, lightness and ability to flexibility that they could bring to actuator perform large displacements when an design. Promising work is also being electric field is applied. In addition, carried out on the use of dielectric EAPs in these materials, when combined with elastic energy-storage devices (e.g. as unconventional biomimetic designs, could elastic springs). This combination could Above: morphology of the ovipositor valves and muscles of typical (from Snodgrass (1935), Smithsonian provide compelling solutions for complex increase the maximum power delivery of Institution). Below: photograph of an ovipositor problem areas. these devices, allowing higher-velocity

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Biomimetics

displacements. The performances of the The Venus flytrap’s behaviour has been sulphide has also been tested on house mice EAPs themselves may also be improved analysed in the context of new space (non-hibernating species), inducing a through the use of anisotropic dielectric mechanisms and structures (with harmless and reversible suspended- -fibre systems, allowing greater D’Appolonia, Italy and University of Bath, animation-like state. These successful strains for a given input. UK). A proposed engineering solution experimental results suggest the possibility Compared to the other classes of EAPs, involves the use of shape-memory- of medical applications. Regulation of however, dielectric electro-active polymers alloy, hybridised fibre-thermoplastic expression is another mechanism that could require high voltages, with the associated laminates to obtain bi-stable tubular potentially provide a means of inducing risk of electrical breakdown. This will have extendable systems. The structural, modal human hibernation, as evidenced by the to be carefully considered for practical and stability analyses performed ability of some seasonal animal hibernators implementations, and especially in space suggest that they could be used, for to enter torpor in the absence of any applications where spacecraft safety is of example, in jointless deployable environmental changes. primary importance. mechanisms. The induction of a hypo-metabolic state in would require the careful Energy-storage structures Hibernation and a possible human hypo- monitoring of such parameters as blood Although plants are not renowned for their metabolic state pressure, body temperature, respiratory mobility, some species are capable of rapid Human hibernation is one of the fascinating rate and tremor, as well as electro- movements, especially when such essential concepts that could enable astronauts to cardiograms, electro-encephalograms and functions as defence, nutrition and seed reach the farthest planets and moons of the electro-myograms. Special equipment dispersal are involved. The leaf of the Venus Solar System and beyond, by reducing their would also be needed to induce, maintain, flytrap plant is particularly interesting due to -support-system requirements during monitor and arouse the subject from a its ability to close up in a fraction of second. long-duration space flights. Given the hypo-metabolic state. Nevertheless, In the initial phase, whilst the leaf is still compelling nature of this concept, ESA’s the ‘technology’ remains potentially convex, its movement is quite slow. In a Advanced Concepts Team has studied the interesting for long-duration human space second phase, the leaf changes its curvature technical feasibility of, and possible flight due to the possibility of significantly to become concave and performs about 60% performance gains from this technology, reducing the overall mass of the life- of the displacement needed for closure in with the help of biomedical scientists. There support systems needed. roughly 0.1 seconds. In the final closing are many mammals, of at least six While the studies that have been carried phase, the leaf again moves slowly. mammalian orders, which exhibit torpor. out so far show that we are far from being The behaviour of the Venus flytrap during This torpor, which can be seasonal or non- able to induce hypo-metabolic states in its opening phase suggests that the system seasonal, is characterised by a drastic humans, and that even the processes undergoes a redistribution of stresses, reduction in body temperature. Also, when involved are not well-understood, the probably caused by changes in -wall an animal is entering torpor, its heart and relevant subject areas will continue to be stiffness and modifications to the turgor respiratory rates decrease, accompanied by monitored to constantly review the pressure. The leaf’s motion during a reduction in oxygen consumption. approach’s feasibility in the light of the opening phase also suggests that its Physiological functions are kept to a scientific developments. elastic instability boundary is not crossed. minimum during torpor and the body is Once the leaf opens again, it returns to the maintained at near-ambient temperature. Future work and studies initial pre-strained state, accumulating the Several mechanisms could induce such a To facilitate the transfer of biomimetic ideas necessary elastic strain energy for another hypo-metabolic state in humans. The first from nature to space technology, a special cycle. involves a lowering of body temperature that database (www.bionics2space.org) is under could be achieved by changing its ‘set-point’ construction. The aim is to link researchers or lowering it directly, for example by in the biological and space-related fields by inhibiting the shivering mechanism. Other providing a resource that makes it easier for mechanisms might effect a variation in the them to find and communicate bio-inspired human metabolism or the modulation of solutions. cell-nucleus activity. One example of the Current research is focusing on latter involves the use of DADLE, an opiate mechanical joints inspired by nature. New derivative, which inhibits the activity of biomimetic designs have been produced living cells. When injected into a rodent, the that promise performance gains due to animal is considerably less active and its space and mass savings compared with body temperature drops notably. Hydrogen conventional systems. Behaviour and control is another area Prototype of a linear Electro-Active Polymer (EAP) actuator that can benefit from biomimetic studies

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(see table). Some bio-inspired algorithms Conclusions European space systems have already been have in fact already been developed by There are numerous instances of technology performed through joint collaborations looking at natural mechanisms and and mission requirements across most between ESA’s Advanced Concepts Team processes. These studies, which are technical and service domains that could and European research centres. This currently being carried out within the benefit from the application of biomimetics. fascinating domain of interdisciplinary Advanced Concepts Team, will be further They range in the technology domain from research is already producing innovative pursued in the near future with the help of the potential application of bio-inspired ideas and conceptual solutions for the long- experts in the field. artificial intelligence to onboard data- term development of space systems and As biological micro-sensors and management systems, formation-flying subsystems. actuators (biologically sensitive mechano- control, deep-space navigation, rendezvous receptors, campaniform sensilla, cilia, etc.) and docking. Biomimetic proprioceptors, have the potential to be small, light and and technologies such as electro- Acknowledgements embedded in an ordinary structure, just as active polymers could also be considered for The authors would like to thank their they are embedded in the bodies of insects, autonomous orbital systems, in support of colleagues in the Advanced Concepts they will also be the subject of future life-sciences research. Biomimetics also has Team, and in particular Nicholas research. This research could eventually potential applications across several service Lan, Cristina de Negueruela, Leopold lead to the design of new bio-inspired domains, ranging from the use of Summerer and Andrés Gálvez, for their force sensors, strain sensors and biomimetic automation and data-fusion valuable suggestions and inputs. r distributed actuators for particle or fluid algorithms in Earth-observation systems, to motion. biomimetic-based environmental control For more information about the work of and life-support subsystems. As reported the Advanced Concepts Team, visit: here, the first short studies aimed at assessing new bio-inspired concepts for www.esa.int/act

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