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3—
Key Technologies

The committee was asked to determine which high-risk, high payoff technologies have the greatest potential for improving the capabilities and reducing the costs of NASA, other government, and commercial space programs in the 2000 to 2020 time period and to determine which of these new technologies could benefit most from NASA-supported, low-level, long lead-time R&T. In this chapter, a diverse portfolio of six technologies is recommended. Determining the exact amount of funding is beyond the scope of this report, but the committee's working assumption was that funding for each technology of about $3 million to $5 million a year for three to five years would be sufficient to create a high probability of significant advances. The committee is aware that NASA is already supporting work on some of these technologies and endorses those investments.

This list of key technologies is not static. Nor does it represent all of the high-risk, high-payoff technologies NASA should pursue. Rather, it is a snapshot of six key technology areas that at this moment appear to hold great promise of yielding large future benefits for small investments today. Regular surveys of technology needs for future space activities, as well as of promising new space technologies, will be necessary to update this list.

The procedures the committee used to select the key technologies are described in Chapter 2. Narrowing the list of technologies was a difficult task, and many valuable technologies that met some, but not all, of the committee's criteria had to be left off. For example, improved thermal control systems will be valuable for a wide range of spacecraft, but large amounts of commercial funding are being invested to develop technology in this area as heat dissipation becomes more of a problem for high-power communications satellites. Another example,



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Page 12 3— Key Technologies The committee was asked to determine which high-risk, high payoff technologies have the greatest potential for improving the capabilities and reducing the costs of NASA, other government, and commercial space programs in the 2000 to 2020 time period and to determine which of these new technologies could benefit most from NASA-supported, low-level, long lead-time R&T. In this chapter, a diverse portfolio of six technologies is recommended. Determining the exact amount of funding is beyond the scope of this report, but the committee's working assumption was that funding for each technology of about $3 million to $5 million a year for three to five years would be sufficient to create a high probability of significant advances. The committee is aware that NASA is already supporting work on some of these technologies and endorses those investments. This list of key technologies is not static. Nor does it represent all of the high-risk, high-payoff technologies NASA should pursue. Rather, it is a snapshot of six key technology areas that at this moment appear to hold great promise of yielding large future benefits for small investments today. Regular surveys of technology needs for future space activities, as well as of promising new space technologies, will be necessary to update this list. The procedures the committee used to select the key technologies are described in Chapter 2. Narrowing the list of technologies was a difficult task, and many valuable technologies that met some, but not all, of the committee's criteria had to be left off. For example, improved thermal control systems will be valuable for a wide range of spacecraft, but large amounts of commercial funding are being invested to develop technology in this area as heat dissipation becomes more of a problem for high-power communications satellites. Another example,

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Page 13 task-capable telerobots, will be crucial to future space exploration, and perhaps to space station operations, but another $3 million to $5 million a year would only advance the state of the art in this field incrementally. Perhaps the most important suite of technologies that are recognized as critical but are not included in the list are technologies that would reduce the cost of access to space, including both Earth-to-orbit and intra-orbital transportation. Launch costs currently represent a large fraction of the total cost of most space activities, and reducing these costs will not only be beneficial for current activities, but will also enable new kinds of space activities. Reducing the costs of launch vehicles could also help U.S. companies regain a larger share of the growing international space launch market. Process improvements and innovative applications of existing technologies can help to reduce launch costs, but major reductions in the costs of expendable launch vehicles will require dramatic reductions in engine and structure costs. Low cost, reusable launch vehicles may require even more advanced technologies. Although the committee wholeheartedly supports technology development to reduce launch costs, it believes the low-level, long lead-time R&T recommended in this report will not have a significant timely effect on space transportation capabilities. These six key technologies are described below. Wideband, High Data-Rate Communications Over Planetary Distances Description Communications over planetary distances are now conducted over radio frequencies. Higher frequency carriers could enable the rapid transfer of much larger amounts of data. Wideband, high data-rate communications might be conducted by high frequency microwave transmissions or optical transmissions based on laser technology. Challenges to be overcome include detecting weak signals over distances of hundreds of millions of miles and maintaining extremely precise pointing accuracies. Importance Wideband, high data-rate communications over planetary distances would enable the real-time transmission of high-resolution images. For example, a robotic rover using this technology could transmit high-definition, live, hyperspectral stereo imagery to Earth as it traveled over the surface of Europa. In the event of an accident, astronauts on the way to Mars could rapidly transmit detailed video of damaged components or injuries, providing technical experts and doctors on Earth with data that could be critical to helping the crew. A Jupiter orbiter equipped with this technology could provide nearly continuous high-resolution movies of the turbulent Jovian atmosphere.

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Page 14 The same technologies that would to enable wideband, high data-rate communications over planetary distances could also be used for Earth-orbiting spacecraft, allowing them to use lower-power lasers or smaller receivers for inter-satellite links. These communications technologies could also prove to be superior to current technologies from a cost and weight perspective and would certainly not encounter the problems of congestion associated with many radio frequencies in the near-Earth region. Rationale for NASA Involvement NASA is the only organization in the United States that has both an interest in planetary exploration and the capability and will to fund technology development to support planetary exploration. Although the European Space Agency, the National Space Development Agency of Japan, the DOD, and U.S. companies are all working on optical communications, they have focused on Earth-to-orbit applications. Planetary distances are four to five orders of magnitude greater than Earth-to-orbit distances. Consequently wideband communications over planetary distances will require technologies unlikely to be developed for Earth-orbit applications. If wideband, high data-rate communications over planetary distances are to be realized, NASA will have to take the lead. Industry support in this area will be limited to responses to NASA procurements for the foreseeable future. Key Areas for NASA-Funded Research The basic technologies for wideband high data-rate communications in space have already been developed. However, there are still barriers to high data-rate communications over extremely long distances. The broad key technology areas for NASA investment are listed below: • high-precision spatial acquisition and tracking systems (maintaining the extreme pointing precision required for long-distance communication may require highly stable structures and high-precision mirrors) • high-efficiency, high-brightness lasers for lightweight, low-power, long-range optical communications • technologies to reduce the mass and power requirements of communication systems, including nonmechanical, beam-steering technology, such as optical phased-arrays, and low drive voltage modulators • the development of architectures to reduce the cost of facilities that receive signals on (or near) Earth, including innovative Earth and space-based receivers

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Page 15 Precisely Controlled Space Structures Description Structures in a weightless environment, especially structures that are unique to space—including gossamer structures and distributed structures—pose difficult control challenges. The field of precisely controlled space structures involves high-accuracy measurement and control of the geometrical configurations, attitudes, and positions of single and multiple space structures. Actuators with a large dynamic range and mechanisms that can control geometrical configurations ranging in size from meters to nanometers will be required, as will technologies for high performance vibration damping and thermal isolation. Importance Continued scientific exploration of our galaxy and the universe for the purpose of expanding knowledge through optical, infrared, and x-ray astronomy requires increasingly precise measurements and stable control of large space-based mirrors, antennas, and interferometric baselines. Astrometry, for example, requires measurements of the positions of structures over tens of meters to accuracies of tens of picometers, deployment accuracies of millimeters, and maintaining vibrations to nanometer amplitudes for frequencies above 10 Hz. Nulling for exoplanet detection requires precision deployment and control of up to 150-meter structures to accuracies of several centimeters, with final operating temperatures of approximately 30 Kelvin. Multiple thin-mirror infrared telescopes with diameters of a meter or more operating at approximately 30 Kelvin need to be stable to tens of nanometers for long periods of time. Applications like these will require advanced precision control capabilities. New technologies to meet these requirements may include highly damped structural members, passive and active vibration control, precise thermal control and low thermal expansion materials, ''smart" (active) structural elements, and distributed vehicles that can perform precision free-flying. Once developed, these technologies might also be useful for controlling large antennas on communication satellites, pointing Earth-sensing satellites with precision, and controlling large gossamer solar arrays, radiators, and tethers. Rationale for NASA Involvement Although the DOD and companies that build satellites are interested in somewhat larger space antennas and mirrors than are currently available, they are not investing in the development of technologies for much larger, precisely controlled space structures. NASA-funded research will be needed in areas where NASA requirements will be more exacting than DOD requirements.

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Page 16 Precision control of space structures is an inherently space-oriented, cross-cutting technology that will incorporate a variety of basic disciplines (damping/ elasticity, dynamics, materials, cryogenics, microelectromechanical systems [MEMS], computational structural mechanics, piezoelectricity) and a wide range of physical applications (mirrors, antennas, deployable structures, precise actuators). This technology supports the kinds of generic engineering space research for which NASA is responsible. NASA is capable of undertaking this R&T by virtue of its experience with various aspects of control-structures interaction (CSI). Key Areas for NASA-Funded Research The broad key technology areas for NASA investment in R&T on precisely controlled space structures are listed below. Close coordination with the DOD should be maintained to ensure that work is not being duplicated. • extending nanometer-precision metrology to long baselines (which will enable the operation of very large interferometers) • figure control of deformable reflectors by mechanical, thermal, and piezoelectric techniques (which could lead to dramatic decreases in the weight of primary mirrors) • vibration isolation and structural damping technologies for dimensional stability and to simplify the acquisition of metrology data • thermal control of structures, including sunshades and insulation (particularly at cryogenic temperatures) • long-term maintenance of precise antenna-pointing attitudes to simplify system operations • long-term measurement and control of the relative positions and attitudes of spacecraft flying in formation (which would enable very long-baseline interferometry, potentially with baselines of thousands of kilometers) • system optimization studies of launch, deployment, and control of large elastic structures Microelectromechanical Systems For Space Description MEMS involve the synthesis, integration, and application of materials, processes, and devices in the submicron to millimeter size range. MEMS development-based materials and fabrication methods are already being used to produce miniature gears, inertial sensors (gyroscopes and accelerometers), pressure and acoustic sensors, digital distributed surface controls, pumps, valves, and switches (for microwave, optical and radio frequency communications). MEMS and

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Page 17 nanoelectronic technologies can be combined into application-specific, integrated microinstruments (ASIMs) and can be further integrated to create subsystems. Importance MEMS technologies could enable the development of small, relatively low-cost spacecraft devices and subsystems—including sensors and communications, navigation, power, thermal, and propulsion subsystems—with very low mass, volume, and power consumption. On conventional spacecraft, MEMS technologies could increase mission survivability by enabling the use of more redundant systems with a relatively small increase in weight and power requirements. If spacecraft mass can be reduced, missions to the outer planets could be launched from smaller launch vehicles at higher velocities. MEMS could also provide distributed control and sensing capabilities to enhance and enable large, lightweight, or deployable space structures. MEMS technologies could also be integrated to create entire miniature spacecraft, which could be deployed in large numbers to function as a sparse-array, synthetic-aperture radar or to take distributed measurements of Martian surface temperatures or the atmosphere of Titan. The combination of redundancy, flexibility, and potential low cost to launch distributed systems (because no connecting structures are required) could enable a broad range of new space activities. Miniature spacecraft could also be launched singly as secondary payloads to conduct simple missions—such as measuring a single atmospheric variable for a limited period of time. Alternative launch options, such as cannons or other gun launchers (e.g., rail guns, coil guns, light gas guns, ram accelerators) may be feasible for miniature spacecraft. Rationale for NASA Involvement MEMS R&T programs supported by multiple government agencies and industry are developing concepts and processes for a broad range of applications. The MEMS field is growing rapidly and is currently largely driven by ground-based commercial and defense expectations. Except for work at NASA's Jet Propulsion Laboratory, little of this R&T is aimed at space applications (although the Aerospace Corporation has explored applications of ASIMs for space systems). The space environment poses unique challenges and opportunities for small systems (often based on fundamental characteristics, such as surface-to-volume ratios and radiation damage) that can be very different from the challenges faced by terrestrial systems. The limited efforts at space applications by the government and industry appear to be concentrated on "payload" or micro-electronic devices. Little work is being done on spacecraft bus technologies (such as power, thermal, structure, and propulsion). By focusing on these technologies and lever-aging existing MEMS technology and infrastructure, NASA could provide a service for all space efforts, as well as enable a wide range of future space activities.

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Page 18 Key Areas for NASA-Funded Research The broad key technology areas for NASA investment in MEMS R&T are listed below: • sufficient investments in bus technologies that are not being developed by other organizations to take full advantage of miniaturizing space systems • "payloads" that are NASA space-mission-unique and (unlike such items as miniature accelerometers) are not likely to be available from commercial ventures • solutions to problems specific to space missions, including surviving in unique environments (particularly the radiation and vacuum environments), comparatively low production rates, and controlling distributed formations of small satellites Space Nuclear Power Systems Description Almost all space activities require a supply of conditioned electrical energy. Near-Earth spacecraft generally use arrays of photovoltaic solar cells linked with chemical storage batteries to provide power. However, solar power systems may not be feasible for many deep space missions, lunar and planetary bases, extended human exploration missions, or for powering high-thrust, high-efficiency propulsion systems. Advanced space nuclear power systems—including various types of reactors and radioisotope thermoelectric generators (RTGs)—will probably be required. Developing these systems will require major funding, but low-level research into improving conversion efficiency and developing demonstrably safer nuclear power sources through the use of new materials and designs could greatly improve the technical efficiency and lower the cost of the nuclear power sources that are eventually developed. Importance Nuclear power sources are typically compact, produce power reliably for many years, are relatively unaffected by the external environment (e.g., radiation belts, Martian dust storms), and do not require exposure to sunlight. Solar power systems, on the other hand, are generally not compact, are affected by the external environment, and require exposure to sunlight. Moreover, their efficiency drops rapidly as the distance from the sun increases. Batteries or other energy storage devices, although they are compact and insensitive to the external environment, cannot produce power for long durations. Nuclear power will be a critical technology for many future space activities (probably including lunar bases and outer-planet missions) for which solar power will not be feasible (AIAA, 1995).

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Page 19 The NRC has stated in a previous report that "nuclear power eventually will be essential for lunar and Mars bases" (NRC, 1990). Advanced radioisotope power sources with conversion efficiencies well above today's 5 to 10 percent efficiencies would enable smaller, more capable outer planet probes. High-power advanced reactors could power either high specific-impulse electric propulsion systems for deep-space missions or high-thrust thermal propulsion systems to enable shorter crewed missions to Mars or the asteroids. Lower-power reactors, which present an extremely low radiation hazard during launch, could power sensors and communications systems onboard deep space probes. Rationale for NASA Involvement Unlike solar arrays and battery technologies, for which commercial interests will continue to drive R&T, space nuclear power has no commercial R&T program to enable ambitious future space activities. Some research on thermionic conversion is being conducted by the DOD, but it is not aimed at supporting NASA missions. Unless NASA supports R&T on advanced nuclear power for space, the required technologies will probably not be available for future space missions (see Box 3-1). It is important to note that low level R&T alone will not be sufficient to enable space nuclear power systems—major investments will eventually be needed to develop advanced space nuclear power sources. The R&T investments should, however, make the advanced space nuclear power systems that are eventually developed more efficient, less expensive, and safer. Low-level investments

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Page 20 in this area may also help to ensure that expertise in space nuclear power is available when major investments are eventually made. Key Areas for NASA-Funded Research The broad key technology areas for low-level long lead-time NASA investment in nuclear power sources for space are listed below: • innovative conversion to electricity, including advanced static conversion (e.g., thermoelectric, alkali metal thermal to electric [AMTEC], thermophotovoltaic) and dynamic conversion of heat to electricity (e.g., Brayton, Rankine, Stirling conversion) • innovative packaging and integration, including the development of small, safe, modular, nuclear power packages that can be added incrementally to increase power levels • innovative materials, including components that can operate in high temperatures and high radiation environments • innovative power management, including the use of supplementary devices (such as ultracapacitors) that can store energy and release it quickly for high power, and power management schemes that can reduce output power requirements Low-Cost, Radiation-Resistant Memories And Electronics Description The Earth's atmosphere and magnetic field protect electronics on the Earth's surface from the harsh radiation environment in space. Various types of radiation in the space environment, including trapped radiation, solar particle events, and galactic cosmic rays, can damage sensitive electronics, disrupt signals, cause single-event phenomena, and degrade microelectronic devices. This problem is especially severe in regions, such as the Earth's Van Allen belts and Jupiter's magnetosphere, where the radiation environment is particularly harsh. Low-cost, high-capacity, low-mass, radiation-resistant memories and electronics are not currently available. Importance Many future space activities, including high-resolution imaging and deep-space missions with onboard mission planners and autonomous operations, will require the storage of large volumes of data. These memories, as well as electronic devices and subsystems, will be subjected to long-duration exposure to the space radiation environment. Radiation-resistant electronics would reduce the

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Page 21 need for redundancy in some systems, as well as allow spacecraft operations in the Van Allen belts and other high-radiation areas. Rationale for NASA Involvement Industry has developed some radiation-resistant processors, and several small companies have been developing shielding concepts. The U.S. Department of Energy, the DOD, and other organizations have also invested in R&T on radiation-resistant electronics. However, most of this work is focused on the immediate future rather than long-term benefits. Very little exploratory research has been funded in this area since the late 1970s. NASA's key niche should be supporting the investigation of truly fresh ideas that may not result in immediate payoffs but would enable low-cost, high-capacity, low-mass, radiation-resistant memories and electronics in the longer term. Key Areas for NASA-Funded Research The broad key technology areas for NASA investment in low-cost radiation-resistant memories and electronics R&T are listed below. Emphasis should be on exploratory research that could have large payoffs in the post-2005 time frame: • improving logic and storage elements to improve recovery from single-event upsets • logic and storage elements with higher linear energy transfer (LET) thresholds that are less susceptible to single-event upsets. • innovative low-mass shielding that is more effective and lighter than current shielding (which would enable spacecraft to use advanced, off-the-shelf microprocessors, which would be a huge improvement over currently available systems) • use of radiation-resistant materials, including silicon-on-insulator and silicon-on-sapphire circuitry or other radiation-resistant materials, for electronic circuitry Extraction And Utilization Of Extraterrestrial Resources Description The capability to extract and utilize space resources, particularly from the Moon, Mars, and near-Earth asteroids, would provide an alternative to transporting certain products from Earth into space. This technology area includes exploring for resources; mining and refining raw materials; processing, manufacturing, and storing materials derived from raw resources; transporting materials to their point of use; and identifying potential uses or customers. Technology development

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Page 22 in this area would focus on extraction, processing, and storage, although advances in other areas, such as power, automation and robotics, and space transportation, will also be required for many applications. Importance The in situ production of propellant from extraterrestrial resources could significantly increase the performance and lower the costs of planetary exploration missions that require the return of people or hardware to Earth. The extraction of propellants from the Martian atmosphere, for example, could dramatically cut the cost of round-trip missions to Mars by reducing the amount of fuel that would have to be to be lifted from Earth. Using extraterrestrial resources could also make these missions safer. For example, in situ processing could be used to produce reservoirs of oxygen, nitrogen, and water that could support a crew in the event of the failure of life support systems. In the long term, in situ resource utilization will be essential for self-sustaining human settlements in space. Extraterrestrial resources could also be used for shielding or constructing human habitats. Surface materials, such as the lunar regolith, might be much cheaper than materials delivered from Earth, particularly for applications that require large masses of material (such as radiation shielding for lunar surface habitats). If in-space transportation for bulk material from the Moon or nearby asteroids became cost effective, it could also enable and accelerate the development of new generations of government and commercial in-space capabilities that require large masses of material, such as large space stations—or hotels or power stations—beyond low Earth orbit. Rationale for NASA Involvement No other agency or commercial company (with the exception of the limited efforts of one Japanese construction company) has shown an interest in the extraction and utilization of extraterrestrial resources. NASA should develop this technology both to support its own missions and to lower the barriers to the future commercial use of space resources. Key Areas for NASA-Funded Research The broad key technology areas for NASA investment the extraction and utilization of extraterrestrial resources are listed below: • robotic systems, teleoperation, and autonomous failure detection and repair systems for mining, moving, and preparing planetary materials for processing (current NASA-supported R&T toward extracting useful products from the Martian atmosphere has made progress, but very little work has been done on handling solid planetary materials, including ices)

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Page 23 • materials processing technologies at various levels, including chemical reactors—particularly energy-efficient, high production-efficiency reactors—and water and carbon dioxide electrolysis systems, including high temperature systems • systems design and engineering, particularly thermal control and thermal management systems, to optimize process efficiencies • manufacturing technologies with high throughput that are simple, effective, and have minimal repair and maintenance requirements or manufacturing systems that can be fabricated from in situ materials • self-erecting systems, in which small systems, probably multiple interacting systems, use simple manufactured pieces to assemble much larger structures • cryogenic storage technology for produced propellants, including light-weight tanks, efficient cryocoolers, and insulators Recommendations Recommendation 1. NASA should initiate a program to support low-level research and development (about $3 million to $5 million a year for each technology area for three to five years) in the six technology areas described in this chapter. The agency should also consider designating these technologies as topic areas in solicitations for existing programs. Recommendation 2. In three to five years, NASA—or a group sponsored by NASA—should re-examine promising technologies and technology requirements and modify the portfolio of key technologies, if necessary. References AIAA (American Institute of Aeronautics and Astronautics). 1995. Space Nuclear Power: Key to Outer Solar System Exploration. Aerospace Power Systems Technical Committee. Reston, Va.: American Institute of Aeronautics and Astronautics. NRC (National Research Council). 1990. Human Exploration of Space: A Review of NASA's 90-day Study and Alternatives. Washington, D.C.: National Academy Press. BOX 3-1 Nuclear Power? The committee is well aware that political constraints may make R&T on advanced space nuclear power systems unpopular. However, the committee could not ignore the fact that space nuclear power will be a key enabling technology for future space activities that will not be able to rely on solar power. The development of advanced nuclear power technologies for space has received little funding in the past decade. If NASA does not invest now in the long-term R&T that could lead to future high-efficiency, safer, nuclear power sources, future mission planners and spacecraft designers will be deprived of potentially valuable design options that could improve safety and performance and reduce the costs of future space activities.