This article discusses that a wealth of technological breakthroughs is likely to come from mimicking the interactions of biological systems and their response to the environment. The following next few decades will witness thinking, learning, evolvable aerospace systems. It will also see systems-on-a-chip, in which miniaturization allows all electronic systems of an aerospace vehicle (computer, memory, guidance, navigation, communications, power, and sensors) to fit on a tiny chip. Such aerospace systems cannot be realized with present technologies. The synergistic coupling of biotechnology, nanotechnology, and information technology with other leading edge aerospace technologies can produce breakthroughs in vehicle concepts and exploration missions, enable new science, and reshape our frame of reference for the future. The potential benefits of these technologies are pervasive and extend to several non-aerospace fields, such as high-performance computing and communications, land and sea transportation systems, health care, and advanced energy conversion and storage.
It is often where disparate fields intersect that unexpected and useful insights into nature and engineering arise. And so it might be with the impact of biology on future aerospace systems. A wealth of technological breakthroughs is likely to come from mimicking the interactions of biological systems and their response to the environment.
The next decades will witness thinking, learning, evolvable aerospace systems. It will also see systems-on- a-chip, in which miniaturization allows all electronic systems of an aerospace vehicle (computer, memory, guidance, navigation, communications, power, and sensors) to fit on a tiny chip. Such aerospace systems cannot be realized with present technologies.
The development and deployment of these systems will lead to a new era of aviation systems, space transportation, and exploration. Safer, less costly and more accessible air transportation will become available. Two orders of magnitude reduction in cost and four orders of magnitude increase in reliability will be achieved for Earth- to-orbit transportation. Rapid human and robotic transportation to the planets and nearby celestial bodies, and possibly, outside the solar system could be realized.
Sustained in-depth scientific studies will be performed in increasingly remote and harsh space environments. The goals of these latter activities include a vigilant intelligent presence in the solar system, exploration of interstellar space, and search for life in the universe. An integrated human-robotic exploration strategy, one more advanced than that associated with the space station, will be used for the solar system and beyond. This strategy focuses on enhancing safety, improving performance, expanding objectives, and minimizing life cycle costs.
Nano, Bio, Info
Realizing these ambitious goals with the current budget constraints will require new kinds of aerospace tools, systems, and missions that use novel technologies and manage risks in new ways. The three most promising technologies that have emerged in the last few years are nanotechnology, biotechnology, and information technology.
Nanotechnology aims at creation of useful materials, devices, and systems through control of matter at the nanometer (10~9 m) length scale. This is accomplished by having every atom or molecule in a designed location. The resulting materials and systems can be rationally designed to exhibit novel and significantly improved optical, chemical, mechanical, and electrical properties.
Carbon nanotubes, for example, are promising building blocks for nanosystems. They consist of honeycomb lattices rolled into cylinders with a nanometer-scale diameter and length of about a micron, and have one-sixth the weight of steel. On the basis of computer simulations and available experimental data, some specific forms of carbon nanotubes appear to possess extraordinary properties: Young’s modulus over one terapascal (five times that of steel) and tensile strength approaching 100 giga-pascals (over 100 times the strength of steel).
Nanometer-scale carbon wires have 100,000 times better current-carrying capacity than copper, and that capability makes them particularly useful for performing functions in molecular electronic circuitry now performed by semiconductor devices in electronic circuits. Electronic devices constructed from molecules will be hundreds of times smaller than their semiconductor-based counterparts.
Biotechnology can be defined as the application of biological knowledge and techniques to produce innovative materials, devices, and systems. The realization that biological processes are designed and operate at the atomic, or nanometer, scale led to the recent coupling between nanotechnology and biotechnology.
Information technology deals with the dissemination, processing, storage, retrieval, and use of information. It enables the transition from passive software, and the effective use of information to create high-value knowledge and intelligence in devices and products.
There are powerful overlaps among the three technologies. For example, the idea of nanotechnology resulted from applying an engineering perspective to the discoveries of molecular biology, and one path to nanotechnology lies through further advances in biotechnology. Also, hierarchical biological systems can be thought of as composed of autonomous agents (organisms), analogous to the autonomous software agents with built-in logic used in information technology. Moreover, the study of the inherent structure within biological information and biological systems led to the emergence of the bioinformatics discipline.
The synergistic coupling of biotechnology, nanotechnology, and information technology with other leading edge aerospace technologies can produce breakthroughs in vehicle concepts and exploration missions, enable new science, and reshape our frame of reference for the future. The potential benefits of these technologies are pervasive and extend to several nonaerospace fields, such as high-performance computing and communications, land and sea transportation systems, health care, and advanced energy conversion and storage.
To date, these technologies remain in an exploratory phase, at a level of development similar to that of computer technology in the 1950s. Scientists and engineers have yet to understand all the issues related to characterization, control, and manipulation of materials at the nanometer scale.
Studies by NASA and other groups estimate that an understanding of the foundations of nanoscience and technology will be achieved within five years, and that engineering products using these technologies will begin to appear in 10 to 15 years.
Lessons From Life
Biology is an abundant source of inspiration for future aerospace systems. It has evolved the most sophisticated, molecularly engineered devices, which are far more elaborate in their functions than most products made by humans. Biological systems are regenerative and adaptable to changing environments. They are the most robust and efficient systems known to humans at the present. Nothing approaches the inherent intelligence and reasoning capability, power efficiency, or packing density of a brain.
Biosensors are extraordinarily sensitive. Eyes, for example, are able to respond to almost a single photon.
Fireflies convert chemical energy to light with near-perfect efficiency, and living membranes, such as skin, will heal when injured. Plants spread their sophisticated chemical engineering operations throughout a habitat by using seeds—genetic information in a minimal package. Most of the mass and energy for making a new plant comes from local materials found where the seed germinates. No human-made system has a comparable ability to organize and reconfigure.
Using biology not just as a metaphor but as an actual implementation technology has the potential to revolutionize how we design, build, and use future aerospace systems. It will enable a few people to do what many do today. It can dramatically change computing devices, sensors, instruments, control systems, materials, and structures, and can support new platform concepts and system architectures that will bring them all together.
The application of biological concepts and principles to the development of technologies for engineering systems has sparked the interest of many researchers and led to the emergence of biomimetics, the science of developing synthetic products based on insight from biological systems.
An understanding of biology at the system level can pay big dividends for aerospace systems. This requires understanding in detail how biological systems store and retrieve information, control development, fabricate structural components, build molecular machines, sense the external environment, reproduce and disperse themselves throughout the environment, engage in error detection, evolve, and carry out self-repair. This type of knowledge will enable the development of more self-reliant aerospace systems that can operate and adapt in harsh environments and in remote locations farther and farther from Earth.
Biologically Based Engineering
Six major characteristics of biological systems are desirable to have in aerospace systems: selectivity and sensitivity at a scale of a few atoms; the ability of single units to massively reproduce with near-zero error; capability to self-assemble into highly complex systems; the ability to adapt form and function to changing conditions; the ability to detect and heal damage; and the ability to communicate among themselves. Biologically inspired aerospace activities aim at developing fundamental technologies to build systems that have these six basic characteristics.
Two primary categories of products can be identified: biologically inspired systems and hybrid systems obtained by embedding biological elements. In the future, a third category of bio-aerospace products and fully biological aerospace systems, based on artificial DNA, may emerge. These could include highly intelligent structures that design themselves, and aerospace systems that grow new parts from raw material or generate the parts that are needed from the ones that are not needed.
Biologically inspired products include neural networks that mimic the function of the brain, robust circuits, biorobots, and biomaterial systems.
Robust bio-inspired circuits are VLSI circuits with healing and cloning capabilities. Their design is based on the multicellular organization, cellular division, and cellular differentiation of biological systems.
Biorobots are robotic systems envisioned as models of biological systems and have some of the characteristics of these systems. Prototypes exist of insect-like robots and of behavior-based and evolutionary robots. Research is under way on clusters of robots working toward a common goal, robots with an object-tracking system in the form of a neuromimetic silicon chip having neural architecture, and visual processing algorithms inspired by the insect brain.
Hybrid systems link biologically engineered components to nonbiological systems. Examples include hybrid organ- ic/inorganic nanomechanical systems with biomolecular motors, biological cells and computer biochips used in combination to detect radiation, root-like systems that can creep into cracks and pores and grow as depositors of sealant, and surface penetration instruments (for example, tentacle-like micro- or nanoscale probes).
Consider a multifunctional material system consisting of several layers, each used for a different purpose. The outer layer, selected to be tough and durable to withstand the harsh space environment, has an embedded network of sensors, electrical carriers, and actuators to measure temperature, pressure, and radiation, and to trigger a response when needed. The network is intelligent. It automatically reconfigures itself to bypass damaged components and compensate for any loss of capability.
The next layer is an electrostrictive or piezoelectric membrane that works like muscle tissue with a network of nerves to stimulate the appropriate strands and power them. The base layer is made of biomolecular material that senses penetrations and tears, and flows into any gaps. It would trigger a reaction in the damaged layers and initiate a healing process.
There are rudimentary forms of biosensors that have bioactive layers (consisting of membrane bound enzymes, antibodies, or receptors), which lie in direct contact with transducers whose responses to change generate electronic signals for interpretation. Biosensors can be used to detect and quantify the presence of a wide range of substances, such as pollutants and radiation in the environment.
Work in Progress
A broad spectrum of worldwide activities related to nanoscale tools and biologically inspired systems is currently being pursued by NASA, various other government agencies, and universities. Their activities to develop and use nanoscale tools can be grouped into three categories: characterization of materials and imaging with atomic resolution; multiscale modeling and simulation for treating phenomena occurring at disparate spatial and time scales; and nano manipulation and fabrication. The biologically inspired systems include ultrasmall sensors, power sources, evolvable hardware, embryological electronics and immunotronics, and communications, navigation, and propulsion systems.
NASA has been working with other government agencies, including the National Institutes of Health and the National Science Foundation, on linking the fundamental sciences with information technologies to create an extraordinary capacity for researching and developing the tools that will expand and project human capabilities over time and distance. NASA ’s technology has been applied to medical problems, among others, whenever the opportunity presents itself. Examples include an artificial heart inspired by the Space Shuttle main engines, diagnostic equipment for measuring bone density quickly and noninvasively, breast cancer detection using telescope technology, and instruments for detecting microscopic signs of cataract development using laboratory equipment for fluid physics.
NASA and the National Cancer Institute have signed a memorandum of understanding to work jointly on the development of biomolecular systems and technologies. The basis for this collaboration is a common technology vision that is important to NASA’s goals of detecting extraterrestrial life and maintaining astronaut health and safety during long-term duration in space, and NCI’s goals for early detection and treatment of cancer. Both NASA and NCI can greatly benefit from advances in molecular-scale micro and nanosystems, and similar technology.
An interstellar probe, an automated, unmanned space vehicle with new generations of sensors, energy sources, and communications technology, could take space exploration outside the solar system.
The ultimate objective of the program is the development of systems that not only have sensing capability but can serve as the platform for direct intervention. The two agencies have identified several possible pilot projects, including nanoscale sensors, information processing systems capable of detecting and interpreting nanoscale signals, and autonomous devices capable of delivering treatment tailored to the identified disease. Ultimately, these biologically inspired health monitors and treatment technologies will revolutionize medical care for space explorers and permit the earliest detection, at the cellular level, of disease on earth.
Biological materials such as tendon and bone exhibit properties often surpassing those of synthetically produced materials. These materials are produced at room temperature and atmospheric pressure. The unique performance of biological materials arises from the precision of the hierarchical organization over a large range of length scales with durable interfaces linking the elements of disparate scale. Structure and generative processes at all levels of the biological structural hierarchy affect the properties of the materials. For instance, biomaterials have great potential for use in spacecraft and habitats to protect the astronauts from the effects of radiation.
As miniaturization of electronic devices through photolithographic methods becomes uneconomical, new strategies are being explored for the assembly of small molecular building blocks into larger sizes via self-organization.
Deoxyribonucleic acid, the polymeric molecule in the chromosomes that contains the genetic information for life, is particularly suitable for chip construction to realize circuit sizes below 100 nm. The key chemical feature of DNA is its ability to associate with and recognize other DNA molecules by means of specific base pairing relationships. DNA-based memory is potentially a trillion times denser than transistor-based memory and uses a billionth of the power.
Evolvable hardware allows dynamic adaptation of structure to various problems. The field draws on ideas from the evolutionary computation domain and on hardware innovations. An example of evolvable hardware is an adaptive configurable electronic circuit, such as a field programmable gate array. The circuit, or FPGA, consists of an array of logic blocks (analogous to cells) placed in an infrastructure of interconnections, which are programmed at three distinct levels: the function of the logic cells, the interconnections between cells, and the inputs and outputs to the system. FPGAs exhibit online adaptation by configuring their architecture dynamically and autonomously.
Embryological electronics aims at development of a new family of robust processor arrays with reproduction, adaptation, and evolution, inspired by the developmental processes of multicellular organisms. Immunotronics aims at fault-tolerant electronic system design that mimics the human immune system.
Examples of biologically inspired robotic systems are biomorphic explorers. These are small, dedicated robots that capture some of the key features of animals, including reconfigurable units with versatile mobility (such as aerial, surface, and subsurface explorers). They might also feature control by adaptive, fault-tolerant, bio-inspired algorithms to match changing ambient and terrain conditions.
These features enable comprehensive exploration, at lower cost and with broader coverage, through a cooperative organization of landers, rovers, and a variety of inexpensive low-mass biomorphic explorers such as gliders, balloons, and powerful aircraft. Specific science objectives targeted for biomorphic explorer missions include atmospheric information gathering by distributed multiple site measurements, close-up imaging for geological site selection, deployment of surface payloads, surface experiments, and sample return reconnaissance.
To achieve maximum capability for space exploration and communication, mission planners at NASA are considering the concept of robotic outposts that cooperate as a remote, highly distributed scientific research station. It is similar to insect or human society, because it operates autonomously using multiple cooperating robotic platforms. The highest level of autonomy would entail the use of intelligent robots that are given only the top-level goals. They would, in turn, determine their own immediate objectives in pursuit of those goals, using only occasional consultation with remote human managers. The humans perform the overall management and control.
The notion of such outposts arose from extensive work done on multiagent systems and cooperative robots. These areas, which are a branch of distributed artificial intelligence, include distributed diagnosis, resource management and execution, and coordination of heterogeneous reasoning methods.
A key challenge in the development of robotic outposts is the creation of systems that exhibit fault tolerance, reliability, and adaptivity. A fault- tolerant system should be able to detect and compensate gracefully for partial system failures, thereby minimizing its vulnerability to individual robot outages. A reliable cooperative system should guarantee that its mission would be accomplished within certain operating constraints each time it is used. An adaptable robotic team should be able to modify its actions dynamically as the environment or the individual robot characteristics change over time.
Robotic outposts would extend human senses into the solar system. With occasional resupply, they would be permanent and self-sustaining.
They could be deployed as expandable intelligent stations in space, or near-Earth objects, such as asteroids and comets, on the moon, Mars, or elsewhere.
They could conduct in situ planetary studies or remote astrophysical observations. They could also set the stage for long-duration outposts in the solar system—synergistic human-robot systems. The robots could serve as precursors to the human occupants and build the infrastructure required for human habitation. They also could enhance astronauts’ capabilities to do large-scale mapping, detailed exploration of regions of interest, and automated sampling of rocks and soil.
Moreover, by adding facilities for both reactive processing (such as sensory perception) and reflective processing (such as planning), the robotic system can have rudimentary forms of human emotions, curiosity, anxiety, or self-preservation. Systems that exhibit these characteristics could play the vital role of scientific partner to the astronauts and enhance their safety by alerting them to mistakes before they are made, and letting the astronauts know when they are showing signs of fatigue, even if they are not aware of it. In such human-robot systems, a hierarchical control capability is provided to the robots with the ultimate decision-making and control given to the humans.
For The Explorers’ Well-Being
Technology drivers for long-duration human space missions are safety, affordability, and productivity of the explorers in acquiring knowledge. Applications of biological concepts and principles promise to be important for enhancing the well-being and function of the explorers.
Biosensors, with sensitivities and detection capabilities at the molecular level, for example, could detect pollutants, pathogens, and radiation levels in spacecraft and habitats. There are three primary sources of radiation in space affecting human operations: galactic cosmic rays, solar energetic particles, and particles trapped within the confines of the geomagnetic field. An early example of such a biosensor, the electronic nose, or Enose, has been successfully tested on the Space Shuttle.
Artificial vision systems can enhance human vision, which has a number of limitations, including poor three-dimensional measurement capabilities. Artificial systems might also provide new modalities such as over-the-horizon sight. Visual computational sensors or artificial retinas (which consist of a sensor and a processor on a single chip) can be used to provide spatio-temporal processing at the place of sensing, and enable task-oriented, rapidly adaptable processing of visual information.
An autonomous nanoclinical care system and regenerative advanced life support system can be used for preventing, diagnosing, and treating some of the main health problems facing astronauts, such as microgravity-induced muscle atrophy and immune system suppression. The ability to place in the body of the astronauts nanoscale probes and devices that communicate with each other, and with more powerful diagnostic tools outside the body, enables the detection of disease signatures at subcellular level and the delivery of tailored treatment (for example, by entering and repairing living cells).
Devices can be produced as a blend of biological, chemical, and electronic systems all integrated on a chip, likely a mere speck. The advanced life support system could provide for a safe, habitable environment with high reliability over long periods of time, minimizing mass, volume, power, thermal control, and crew time requirements. It is a closed loop system that can function without major maintenance and repair.
Biofabrication And Morphogenesis
The ability to understand and model cellular function can lead to molecular engineering of particular biological mechanisms that significantly enhance the performance of engineering systems. Construction of wood, teeth, bones, hard shells, spider webs, and many other structures proceeds biologically by a process of evolutionary optimized growth, starting with molecular building materials.
The same is true, on a grander scale, for the construction of nervous systems and brains. Morphogenesis-the generation of multicellular form by signaling between cells that can grow, divide, and specialize—couples with molecular assembly at the cellular and subcellular scale to perform fabrication of organic, mineral, and computational structures in an efficient, adaptive, and optimizable way from elementary building units. Upon injury, aspects of the developmental self-fabrication process can be restarted to effect repair, resulting in a robust system.
These fabrication and repair capabilities are potentially valuable for establishing a self-sustaining industrial presence in space, which makes use of mineral and material resources on low-gravity inner solar system bodies such as asteroids and moons.
Biologically Inspired Robust Software
SOFTWARE CONTINUES TO PERVADE every aspect of aerospace missions. Concern over its quality, cost, and reliability continues to grow. Software reliability is “the probability that a given program will perform its intended functions correctly in a specified environment for a specified duration."
As the number of lines of code increases, software verification and validation become more difficult to perform, and its high reliability becomes more difficult to maintain. An increase in the number of lines of code has been the trend in spacecraft missions so far. For example, the number of lines of code for Voyager software was 3,000. They increased to 8,000 for Galileo, 32,000 for Cassini, and 160,000 for the Mars Pathfinder. Space systems currently under consideration are expected to have millions of lines of code.
The fact that conventional methods for software testing and validation are not adequate is demonstrated by the error in the software that resulted in the failure of the Mars Climate Orbiter and the Ariane 5. The Mars orbiter failed to reset a sensor in the lander’s legs when the legs deployed well above the surface. The engine shut off and the spacecraft crashed. Ariane 5 used Ariane 4 guidance software, but achieved a higher velocity than that of Ariane 4, which caused a register to overflow, and the primary and secondary reference units to shut down, driving the vehicle into a destructive angle of attack.
Because of the complexity of future aerospace missions, both the hardware and software must not only be reliable, but also robust, in the sense of having a high degree of fault tolerance-the ability to detect and recover from a fault. The software should reconfigure itself to enhance capabilities, recover from anomalies, or avoid crashing. It also should allow the devices it is controlling to continuously test themselves and to have a graceful degradation in abnormal situations outside their design envelope. These characteristics are the aims of automated reasoning, adaptation, learning, and techniques based on biological metaphors.
Advanced programming languages like Java, and the meta-language, object-oriented, and component-based paradigms, and automated verification techniques, have helped reduce the number of lines of code and have enhanced their reliability. However, these facilities cannot by themselves meet the future needs of robust software.
NASA is working on a new generation of biologically inspired, robust, ultra-fault-tolerant software for future aerospace missions. It uses, among other elements, adaptive multiagent systems and the amorphous computing paradigm. Each agent in the multiagent system can evolve through a combination of genetic algorithms and genetic programming. One of the layers of the system can perform preprogrammed self-healing actions. An amorphous computing paradigm aims at obtaining coherent behavior from the cooperation of a myriad of unreliable information processing units (sensors, actuators, and communication devices) interconnected in unknown, irregular, and time-varying ways.
Outlook For The Future
Future aerospace vehicles could use artificial DNA, biomimetic systems, and other biologically inspired technologies as a blueprint to adapt and grow into more complex and thinking systems. Aerospace systems could be built conceptually, analytically, and physically from the atomic scale to the macroscale, atom by atom. They could have the sensory capability to be aware of the dynamic environment; have the intelligence to determine how to respond to it; and have the adaptability to change in form and function.
The synergistic coupling of biotechnology, nanotechnology, and information technology with other leading edge technologies is likely to change the way almost everything is designed and made, and enable the development of new objects and systems not yet imagined. The realization of the full potential of all these technologies could result in an interstellar probe being launched from Earth as a small, affordable “seeding” spacecraft containing a continual stream of design information. It then could use biofabrication concepts, planetary resources, and photosynthesis to transform itself into successive evolvable states. This may mean using iron, carbon, and other materials to build structure, nervous system, and communications. This reconfigurable hybrid system could possibly adapt form and function to deal with changes and unanticipated problems.
The anticipated payoff for such technological boldness will be the ability to redefine the forms of aerospace vehicles and missions at the absolute frontier. However, as with anything radically new, there are ethical and social implications that are being addressed by NASA to ensure that individuals and society can be protected from any possible harm resulting from misuse of these technologies.
Realizing this vision requires linking diverse interdisciplinary teams from universities, government labs, and industry through learning and research networks. The learning networks will provide new types of education and training that promote intermingling among physical and biological nanosciences and engineering disciplines. They will create a new generation of skilled scientists and engineers who can work across traditional disciplines and think outside the box.
The research networks will link diverse, geographically dispersed teams in different scientific disciplines and have advanced tools, instruments, and facilities for modeling, characterization, and fabrication of nanoscale bioinspired materials, devices, and systems. NASA will work with other government agencies on the establishment of these networks.