2
Overall SERT Program Evaluation

2-1 EVALUATION OF TOTAL PROGRAM PLAN AND INVESTMENT STRATEGY

The Space Solar Power (SSP) Exploratory Research and Technology (SERT) program was evaluated in the context of the “plan’s likely effectiveness to meet the program’s technical and economic objectives,” as stated in the committee’s statement of task (see Appendix A). This top-level assessment leads to identification of the most important technology investment options, opportunities for increased synergy with other efforts, assessment of adequacy of available resources, and possible recommendations for changes in the investment strategy to achieve desired objectives. Discussion and recommendations are grouped into three basic areas: (1) improving technical management processes, (2) sharpening the technology development focus, and (3) capitalizing on other work.

Improving Technical Management Processes

Program Organization

The SERT program was charged to develop technologies needed to provide cost-competitive ground baseload electrical power from space-based solar energy converters. In addition, during its 2-year tenure, the SERT program was also expected to provide a roadmap of research and technology investment to enhance other space, military, and commercial applications such as satellites operating with improved power supplies, free-flying technology platforms, space propulsion technology, and techniques for planetary surface exploration.

With such a broad scope it is not surprising that the National Aeronautics and Space Administration (NASA) centers, the Jet Propulsion Laboratory, and industry participants have defined a myriad of technologies that could be developed for the future applications. It should also not be surprising that if NASA’s year-to-year expenditure remains at around $10 million or less, the program will be inadequate to meet the identified needs. Funding has been in yearly incremental add-ons by the U.S. Congress and has not been part of the formal NASA operating plan. It is impossible to make efficient progress in technology development when funding and management support are uncertain. However, the current SERT managers have defined a potentially valuable program despite these obstacles.

Central to the SERT program is a series of experimental demonstrations called model system categories (MSCs) that serve as focal points for the technology definition. Table 2-1 outlines these MSCs (Mankins and Howell, 2000a). Top-level schedule and resources for accomplishing the technology development work as defined by NASA are shown in Figure 2-1 (Mankins and Howell, 2000b). The committee endorses this approach to defining flight test demonstration milestones



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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy 2 Overall SERT Program Evaluation 2-1 EVALUATION OF TOTAL PROGRAM PLAN AND INVESTMENT STRATEGY The Space Solar Power (SSP) Exploratory Research and Technology (SERT) program was evaluated in the context of the “plan’s likely effectiveness to meet the program’s technical and economic objectives,” as stated in the committee’s statement of task (see Appendix A). This top-level assessment leads to identification of the most important technology investment options, opportunities for increased synergy with other efforts, assessment of adequacy of available resources, and possible recommendations for changes in the investment strategy to achieve desired objectives. Discussion and recommendations are grouped into three basic areas: (1) improving technical management processes, (2) sharpening the technology development focus, and (3) capitalizing on other work. Improving Technical Management Processes Program Organization The SERT program was charged to develop technologies needed to provide cost-competitive ground baseload electrical power from space-based solar energy converters. In addition, during its 2-year tenure, the SERT program was also expected to provide a roadmap of research and technology investment to enhance other space, military, and commercial applications such as satellites operating with improved power supplies, free-flying technology platforms, space propulsion technology, and techniques for planetary surface exploration. With such a broad scope it is not surprising that the National Aeronautics and Space Administration (NASA) centers, the Jet Propulsion Laboratory, and industry participants have defined a myriad of technologies that could be developed for the future applications. It should also not be surprising that if NASA’s year-to-year expenditure remains at around $10 million or less, the program will be inadequate to meet the identified needs. Funding has been in yearly incremental add-ons by the U.S. Congress and has not been part of the formal NASA operating plan. It is impossible to make efficient progress in technology development when funding and management support are uncertain. However, the current SERT managers have defined a potentially valuable program despite these obstacles. Central to the SERT program is a series of experimental demonstrations called model system categories (MSCs) that serve as focal points for the technology definition. Table 2-1 outlines these MSCs (Mankins and Howell, 2000a). Top-level schedule and resources for accomplishing the technology development work as defined by NASA are shown in Figure 2-1 (Mankins and Howell, 2000b). The committee endorses this approach to defining flight test demonstration milestones

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy TABLE 2-1 NASA’s SERT Program—Model System Category Definitions NASA Model System Category Power Capability Flight Test Demonstration Options (to be chosen competitively) Projected Time Frame MSC 1 ~100 kW Free flyer LEO-to-Earth power beaming research platform Solar power plug in space Cryogenic propellant depot “Mega-commsat” demonstrator 2006–2007 MSC 1.5 ~1 MW GEO-to-Earth solar power satellite (SPS) demonstrator Lunar exploration SPS platform Earth neighborhood transportation system 2011–2012 MSC 3 ~10 MW Free flyer GEO-based SPS demonstration platforms for wireless power transmission, solar power generation, power management and distribution, and solar electric propulsion Interplanetary transportation system 2016–2017 MSC 4 ~1 GW Commercial space full-scale solar power satellite 2021+   SOURCE: Adapted in part from Mankins and Howell, 2000a. to validate technology advancement. However, the committee also realizes, as does NASA, that the schedule of milestones and roadmap should be reconfigured as research and development for components of the program are realized (or not realized) and new results are obtained. NASA demonstrated during the course of the study that the roadmaps were revamped several times during the first 2 years of the program in response to both internal agency assessments and external peer review. Continued annual and biannual assessment of the roadmaps, schedules, and goals are an inherent part of the program. The committee recommends that future roadmaps, however, contain more transparent information tying together cost, performance, and schedule. The roadmaps should also more visibly demonstrate their reliance on advances in space transportation and robotics that are entirely or largely funded by other programs. NASA’s SERT program presented a concept for reviewing its time-phased plans, which include the incorporation of NASA’s strategic plans and goals, information gleaned from independent program and technology assessments, new innovative technology applications, government and commercial application opportunities, and research efforts in other organizations. This iterative process review would be cycled at least annually because strategic research and technology investments must be selected each fiscal year as part of the NASA budget development process (assuming the work becomes part of the overall NASA program). The committee has also seen evidence that the current SERT program’s roadmaps do not adequately incorporate the planned advances of low-cost space transportation development, both Earth-to-low-Earth-orbit (LEO) and in-space options. Because any advancements in space transportation are key to the SSP program’s ultimate success, the timing and achievement of technology advances and cost and mass goals by the separate space transportation programs within NASA should be included directly in the SSP roadmaps. A periodic revamping of the roadmaps should be made based on the achievements of NASA in space transportation. SSP program technology investments, flight test demonstrations, and full-scale deployment should be rescheduled accordingly. Adequate contingency plans also need to be developed to be able to react positively to the failure of any flight or ground test demonstration planned by the program.

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy FIGURE 2-1 NASA’s SERT program: research and technology schedule of milestones roadmap. NOTE: Figure reprinted in original form. SOURCE: Mankins and Howell, 2000b.

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Performance Goals NASA has made a determined effort in the SERT program to focus the effort by beginning the definition of a “strawman” or baseline SSP system to provide 10– 100 GW to the ground electrical power grid with a series of 1.2-GW satellites in geosynchronous Earth orbit (GEO). Since no one knows the time scale to build, launch, and assemble on orbit such a system, the committee did not comment on this particular scenario’s potential for commercial appeal (or any of the potential scenarios for MSC 4). Chosen scenarios will be a direct result of the program’s investment strategy, the progress of technology development, and a competitive selection process. The committee did not feel it was appropriate to evaluate each individual scenario for a full-scale system. As a result, various scenarios are not presented in the report. Time to market and size of investment necessary for such a system will be issues that need to be addressed as the program progresses; however, the SERT program previously funded an independent economic analysis to evaluate such issues. Assessment of this analysis was outside the scope of this study. Top-level cost targets in cents per kilowatt-hour were developed for each of the major SSP systems that NASA managers believed were necessary to finally deliver baseload power at less than a selected target of 5 cents/kW-hr.1 Major system and subsystem functions were each allocated a “contributory” cost goal by program managers. The sum of the contributory goals should, in theory, be equal to the overall cost target of 5 cents/kW-hr. These targets are shown for various design options in Figure 2-2 (Mankins and Howell, 2000b). For brevity, the specific design concepts and options (Mankins and Howell, 2000a; Carrington and Feingold, 2000) listed in Figure 2-2 are not presented in the report. The NASA program plans to continue monitoring this target as markets for electricity change and to adjust this target and its distribution among technologies accordingly. As such, the manner in which current cost goals are set is justified. A corresponding set of mass, cost, and performance targets was then used to help define where technology funds should be applied, and detailed roadmaps have been developed to accomplish these technology goals. The result of this work is a set of time-phased plans with associated cost estimates, which provide the basis for an investment strategy. The committee notes that there is a lack of traceability (of cost and mass goals) to the next lower level. The committee expects that in future program documents there will be traceability of cost and mass targets down to the subsystem level and to the component level. Without consistent cost and mass goals with clear traceability from the top level to the component technology level, individual technology teams may not make the most appropriate technology investments. The major SERT system cost and performance targets, as shown in Figure 2-2, are extremely aggressive.2 Additionally, they include reliance that NASA’s separate Space Launch Initiative (SLI) program will be successful in reducing Earth-to-LEO transportation costs to $400/kg. NASA’s second-generation SLI goal is $2,200/kg, and the third-generation goal is approximately $220/kg (NASA, 1999; Davis, 2000). In a SERT Program Status report (Mankins, 2000b), NASA reported that current SERT concepts (December 13, 2000) result in predicted costs for power in the range of 10–20 cents/kW-hr, versus NASA’s full-scale system goal of 5 cents/kW-hr. NASA has adopted an allowable cost of 5 cents/ kW-hr as its target goal for competitive terrestrial power production. The committee suggests that this value be revisited as the program proceeds; however, it is viewed by the committee as a reasonable starting point for the investment strategy. This choice sets the revenue stream level for a 1.2-GW facility. Once the revenue stream is known, the net present value of this revenue stream can be computed. A simplified calculation was made by the committee for the required return on investment, assuming zero operating costs and a 40-year operating period. The calculation demonstrates the importance of strengthening the cost analysis for the operational system. For instance, using a 10 percent rate of return, $5 billion is available for the entire system. 1   This 5 cents/kW-hr goal was based on cost estimates gleaned by NASA from an independent economic analysis (Macauley et al., 2000). 2   Subsystem cost, mass, and performance targets were also supplied to the committee for each technical area in the program’s work breakdown structure. For brevity, only the top-level program goals are presented in this publication. More specific information can be obtained from the listed reference.

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy FIGURE 2-2 NASA’s SERT program: strategic research and technology goals. NOTE: Figure reprinted in original form. SOURCE: Mankins and Howell, 2000b.

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Using the NASA target goal of allocating 2.5 cents of the 5 cent/kW-hr revenue stream to launch costs, in-space transportation, and ground assembly personnel allows $2.5 billion to be spent on construction and installation of the system. At an assumed launch cost of $800/kg to GEO, it would cost $14 billion to launch a 1.2-GW system unless the currently assumed weight of the 1.2-GW facility is substantially reduced. The calculations should be developed further consistent with stationary power plant funding procedures and perhaps using the models for fission nuclear power introduction. In any event, more stringent cost and mass goals must be achieved in order to meet current NASA cost goals for competitive terrestrial electric power. The NASA team must be more rigorous in their cost and mass allocations to the subsystems and components, as well as launch costs. Current space transportation and technology subsystem goals, for example, are already driving near-term choices within the SERT program, creating the possibility that technology investment choices may be based on goals that are not stringent enough in this area. Consequently, the committee believes that NASA not only should reevaluate its cost goals in various technology areas but also should complete a rigorous analysis of its cost goals in the space transportation area. Many of the goals for launch costs and system mass and cost must be significantly lower than currently being used by the NASA team if the system is to produce competitive terrestrial power. Allocations should also be made in absolute terms, dollars and kilograms, as well as familiar ratios such as dollars per watt and watts per kilogram. These absolute terms can be used directly by SSP technical staff in answering the question, How much can this specific technology subsystem cost to attain an overall 5 cents/kW-hr cost? The committee notes that the 5 cents/kW-hr target may be unnecessarily low for nonterrestrial applications of space solar power, such as space-to-space power beaming for interplanetary spacecraft or space-to-planetary surface beaming for rovers, for example. Resource Allocation NASA’s Space Solar Power Strategic Research and Technology Roadmap proposes resource allocations as given in Table 2-2. The figures are broken down into systems integration, analysis, and modeling, total technology development, and flight test demonstrations (referred to by NASA as technology flight demonstra TABLE 2-2 Proposed Space Solar Power Program Resources Allocation, FY 2002 to FY 2006 (millions of dollars) Investment Area FY 2002 FY 2003 FY 2004 FY 2005 FY 2006 Systems integration, analysis, and modeling 5 7 8 8 8 Total technology development 73 92 128 149 154 Technology flight demonstrations 10 25 75 125 150 Total investment 88 124 211 282 312   SOURCE: Adapted in part from “Strategic Research and Technology Road Map.” Briefing by John Mankins and Joe Howell, National Aeronautics and Space Administration, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Research Council, Washington, D.C., December 14, 2000. tions). Breakouts were also provided for each of the main technology development categories providing a description of the proposed work, schedule, and cost goals (see Appendixes C and D for more detailed information). The committee restricted its attention to the first 5 years of the program (FY 2002 to FY 2006) due to the large uncertainty in the out years. The committee’s reactions to NASA’s proposed resource allocations are as follows: This is a reasonable first projection of resource requirements through FY 2006. The committee supports NASA’s approach of dividing the program into three major elements: (1) systems integration, analysis, and modeling, (2) technology development, and (3) technology flight demonstration. In the future, if some ground demonstrations are added as key milestones, it would be appropriate to group them with the technology flight demonstrations and rename the category “technology demonstration.” Although it was not given a cost breakdown for the eight subelements within systems integration, analysis and modeling, the committee would expect the systems and infrastructure modeling to decrease markedly after the first few years and be replaced by technology validation and studies of mission architecture. Technology development is broken down by main resource applications. NASA’s chosen distribution shows emphasis in the areas of greatest impact: solar power generation (SPG); wireless power trans-

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy mission (WPT); space power management and distribution (SPMAD); and space assembly, maintenance, and servicing. However, the relative size of the resources should vary much more between the vital technologies and those that serve to make advances on all fronts. Additionally, it appears that this first estimate does not leverage the work of other agencies in such critical areas like SPG and SPMAD or, if it does, that leverage is very small. Technology flight demonstration resources may be at an appropriate level for the first flight test demonstration (MSC 1). However, a requirements-driven conceptual study, including cost development, is needed before strong endorsement can be offered. Specifically, the requirements to be validated must be clearly defined, and alternative concepts for meeting them should be developed, including associated costs and schedules. Potential resource support from other agencies and international sources should be defined, resulting in a full conceptual plan that can be critically evaluated. The time schedule for each technology flight demonstration should be tied to demonstrating desired technology levels, rather than an arbitrary date. Sharpening the Technology Development Focus System and Cost Modeling A commendable start has been made on systems and cost modeling for various SSP concepts and technology choices (Carrington and Feingold, 2000; Feingold, 2000; Mullins, 2000). However, the committee believes there may still be a great disparity between the resources that can reasonably be expected and the desired rate of technology development progress. This will require careful evaluation of technology payoffs and tough program management decisions. The SERT program’s general approach of defining a baseline concept and coupling it with detailed system and subsystem performance plus cost modeling to guide technology investment will be an excellent tool for making some of these crucial decisions provided the modeling is strengthened, as described in Section 3–1 of this report. Additionally, the technology goals and roadmaps concept should provide a credible goal for individual technology areas. However, for this methodology to be realistic, goals must flow from the technology and cost requirements in both a top-down and bottom-up manner, involving input and decision making from both technology management and technologists. Conceptually, the use of an architecture cost goal estimate based on power costs in the future electricity market is appropriate and commended. Specification of this goal as a probability distribution representing a range of uncertainty would better represent the uncertainty inherent in any projections of future market potential. Over time, as SSP development progresses, the architecture cost goal should be adjusted to reflect changes in expectations about future power markets, environmental costs, and other social costs that may arise. The SSP cost and system analysis models should incorporate one detailed concept definition, making it possible to evaluate the payoff of specific technology efforts within the broad functional systems areas of solar power generation and wireless power transmission, among others. This concept definition should also include assembly, checkout, and maintenance techniques. The model needs to clearly show where SSP technology investments branch off to the benefit of other missions, including both in-space and terrestrial applications. Input should be gathered from hardware builders, industry, academia, and other government agencies to improve the modeling effort. The input should include information on technical performance, current state-of-the-art technology, forecasts for technology advancement, and system cost modeling. The expansion of the modeling should also include other applications (in addition to terrestrial power supply) that will benefit from the SSP technology investments. Future comparisons in the models should include transportation costs and delivered performance on orbit, which will enhance decision making between alternative technologies. This seems to have been intended in some of the past SERT program trade studies; however, the committee believes that the principle is not sufficiently ingrained in the modeling effort. Recommendation 2–1–1: The SSP team should broaden the scope and detail of the system and subsystem modeling (including cost modeling) to provide a more useful estimate of technology payoff. The models should incorporate detailed concept definitions and include increased input from indus-

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy try and academia in the specification of model metrics. The costs of transportation, assembly, checkout, and maintenance must also be included in all cost comparisons to properly evaluate alternative technology investment options. In the economics modeling of new technologies, taking explicit account of risk and uncertainty is key to an effective understanding of the sensitivity of models to assumptions and the quality of the data used to inform the models. The SERT program is currently using conventional measures of technology readiness (the Technology Readiness Level index [Mankins, 1995]) and a rough measure of technological uncertainty (the Research and Development Degree of Difficulty [Mankins, 1998]) in its modeling effort. These measures address dimensions of the engineering stages of development of new technologies but are silent as to these technologies’ ultimate usefulness and cost-effectiveness, which are important factors in setting priorities for roadmaps. The program may be better served by integrating measures in the cost and system modeling that consider the cost-effectiveness of new technologies, the relationships among different technologies, and their effect on overall program structure. The SERT team began to take this step in results presented to this committee in December 2000 (Mankins, 2000b). Further development would provide a more effective, resilient, and defensible roadmap for SSP, that is, not only the integrated technology analysis methodology but also explicit incorporation of risk, uncertainty, cost, and benefit data. However, subsequent decision making based solely on these models is not encouraged by the committee until the models have been adequately validated and tested against baseline SSP concepts (see Section 3–1). In addition to this validation, model assumptions and their possible impacts on cost, use of certain technologies, and mass should also be evaluated before further decisions are made. It is also useful that the roadmaps clearly distinguish “risk” from “uncertainty”—words often used ambiguously. Risk is generally understood as describing a known probability of an undesirable outcome— failure—while uncertainty refers to lack of knowledge about potential outcomes (Knight, 1921). The assessment of risk thus depends critically on the definition of failure, which in turn may depend on public and institutional (e.g., government agencies, Congress) expectations. Recommendation 2–1–2: The SSP team should continue integration of technology readiness measurement and cost uncertainty modeling, both in developing a consistent framework for the approach and in parameterizing the framework with the best available information. Over time, the empirical evaluation of these dimensions should become better understood as technology demonstrations begin. Overall Program Focus in a Cost-Constrained Environment Under the current NASA funding environment (i.e., yearly congressional earmarks), the program has been provided with funds that are adequate only for technology roadmap development and preliminary planning. With these constraints, it is difficult to fund every technological area with promise for SSP. The committee suggests that if full program funding is not made available, additional focusing of the SSP effort be made. With the projected level of funding, managers should select a single principal baseline concept and one technology per subsystem. For example, a magnetron might be selected as part of the WPT baseline concept. The baseline should be altered and more advanced technologies substituted when justified by technical progress and funding. Recommendation 2–1–3: The committee recommends additional focusing of the SSP program. For example, if continued underfunding of the effort continues, it would be in the program’s best interest to choose a single baseline concept and one technology per subsystem for technology advancement. There should be periodic reviews as technologies are advanced, and alternatives may be reintroduced into the design when justified and affordable. Technology Demonstration The committee endorses the approach of defining demonstration milestones of achievement (NASA’s MSC categorization) to provide program focus, as well as a clear mechanism for measuring technology advancement progress. Progression from the 100-kW MSC 1 demonstration to more technically challenging and larger demonstration missions (MSC 1.5, 2, 3, etc.) is reasonable. The committee appreciates the fact that the MSC 1 demonstration is not dependent on simultaneous invention of a new low-cost transportation sys-

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy tem. The committee also encourages the continued balance of technology flight demonstrations that test near-term and far-term technologies. Advancements in SSP-related technologies will be beneficial to the entire space program. Flight demonstrations currently planned in the program are designed to test the interactions and feasibility of advanced technologies for possible use with SSP systems. These demonstrations will test technologies at technology readiness levels that are below the level industry will accept. Without flight test experiments, industry will be hesitant to accept many of the new technologies into their programs. Recommendation 2–1–4: The SSP program should continue the use of technology flight demonstrations to provide a clear mechanism for measuring technology advancement and to provide interim opportunities for focused program and technology goals on the path to a full-scale system. The committee also sees value in testing technologies for SSP on already available space platforms. In particular, it believes that NASA should consider ways in which the International Space Station (ISS) can help advance the technology development effort in SSP. Furthermore, industry and academia should openly compete on proposals for technology demonstration so that their expertise is brought to bear on the technical issues. In addition, international cooperation will most likely be necessary for any large-scale terrestrial SSP application, and international markets for SSP should be considered, for economic reasons. Flight demonstration of technologies and testing of systems should be completed early in the SSP program. The program’s use of flight demonstration milestones is an excellent way of achieving this. Although the committee recognizes the vast difference between conditions and operational procedures in LEO and GEO, early milestone tests may have to be performed at LEO. To save cost and to maximize the engineering data returned, these experiments would have a smaller scope than the MSC system-level demonstrations. They might, for example, involve measurement of a particular mechanical effect of zero gravity on a subscale structural component rather than on a complete, functioning solar array. Serious consideration should be given to developing the first flight demonstration (MSC 1) as an ISS technology research mission and developing other experimental programs to be validated on the ISS.3 The NASA SERT program’s 100-kW MSC 1 free flyer could be assembled from the ISS as a technology demonstration test bed. For instance, various solar array concepts could be used on MSC 1 and then subjected to test after release from the ISS. Space-to-space transmission could also be demonstrated using a co-orbiting target module, which also could serve as a platform for performing experiments at lower microgravity levels than will be achievable on the ISS. After test completion, MSC 1 could be returned to the ISS for inspection and subsequent reoutfitting with other subsystems for a second round of free-flyer tests. Experiments testing low-power-level transmission to Earth should also be included for microwave and laser wireless power transmission systems—both of which are being considered in NASA’s SSP program. Transmission efficiency would be low for these initial tests, especially for microwave systems, but the experimental performance could be corrected analytically to correspond to full-scale systems. An added advantage to ISS-based assembly of the MSC 1 is that various assembly, maintenance, and service techniques could be tested and developed for future application in GEO. Upon its completion, the MSC 1 demonstration could provide an enhancement for the ISS technology demonstration program. This enhancement could be either use of a free flyer in co-orbit with ISS or an upgrade to the ISS solar array with new technology. When the ISS program is ready to procure a replacement or expansion of the ISS solar arrays, the program should consider the SSP array technology and, if possible, procure an array that is on the roadmap for an SSP system. Additionally, the ISS might be used as an orbiting platform to validate techniques for structural assembly, subsystem life, repair, and other experiments unique to an SSP program. Opportunities for collaboration with the Department of Defense (DOD) and international technologists should be considered in the MSC 1 flight demonstration program for technology leveraging and shared funding. The Air Force Research Laboratory’s 3   One previous NRC study recommended that NASA use the International Space Station as a test bed for engineering research and technology development. Areas suggested that overlap with SSP-related technologies included electric power, robotics, structures, and thermal control (NRC, 1996).

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy PowerSail program is a 30- to 50-kW thin-film photovoltaic free-flyer demonstration intended to fly in the 2004 or 2005 time frame. This may be an opportunity for collaboration with NASA’s MSC 1 demonstration. Recommendation 2–1–5: NASA should seriously consider utilizing the International Space Station as a technology test bed for SSP during the first set of flight demonstration milestones. Such tests would leverage ISS technology and infrastructure, be independent of new advances in space transportation, and provide an opportunity to test autonomous robotic systems. The starting point for considering all of these collaborative options is the development of a detailed set of requirements to be met by MSC 1 in support of SSP and other applications. Development of the technology demonstration concept and evaluation of the advantages and disadvantages presented by using the ISS should then follow. There is a need for a comprehensive ongoing program to advance critical technologies from the laboratory to operational readiness. This program must include focused flight demonstrations for many of the individual technologies, in addition to the system-level MSC flight demonstrations. The committee recommends definition of additional ground demonstration milestones to be conducted prior to the far more expensive flight tests. In addition, the committee feels that each of the demonstration projects should be evaluated against the goals for the project and the timing, based on the technology available at the time. Recommendation 2–1–6: The SSP program should define additional ground demonstration milestones to be conducted prior to the far more expensive flight tests in order to test advanced technologies and system integration issues before planned downselects of flight-demonstration technologies occur. Technology Building Blocks Specific treatment of the SERT technology building blocks can be found in Chapter 3; however, several general observations can be made from NASA’s modeling data that influence the investment strategy: By any yardstick, current expenditures of $10 million to $40 million per year cannot come close to providing the technology development progress that is necessary for application of terrestrial SSP in the next 20 years. Due to uncertainties in future funding for SSP, various near-term choices must be made by SSP program managers. Even with a large increase in funding, NASA’s SSP program would be best served by focusing its efforts more narrowly than at present. Most of the technology investments should be devoted to technologies that have multiple applications (in addition to terrestrial power generation). In many of the key enabling SSP technologies, significant advances must be made in technology performance, mass, and cost before a commercial SSP system is viable. Most far-term investments should be in research areas that are high risk but could provide high payoff to the SSP program. The SSP program should give considerable weight to nearer-term space, military, and commercial applications of this technology, or portions of it (e.g., low-mass solar arrays or WPT). Only a few technologies unique to terrestrial power generation should be funded by NASA. Specifically, the system studies indicate that greatest benefit is obtained by investing most heavily in several key technologies, described below (Carrington and Feingold, 2000; Feingold, 2000; Mullins, 2000): Solar power generation technology is currently in the midst of an exciting period of advancement with solar array improvements of benefit to all solar-powered applications, including terrestrial power and space vehicles. NASA should collaborate with DOD, DOE, and commercial efforts to avoid duplication and improve the overall effectiveness of investments in SPG technology. Wireless power transmission has possible dual application potential for free-flying platforms in space or airborne, which could attract military or commercial participants. However, investments in this area need to be focused. Currently, the SERT program is funding efforts in several major WPT technologies. Space power management and distribution is a major contributor to SSP system mass and cost. Investments should be made to reduce the mass and cost of the components while increasing efficiency and improving operation conditions. New SPMAD techniques developed under the SSP program will have application to the ISS and many other NASA, DOD, and commercial systems. Space assembly, maintenance, and servicing

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy are challenges common to all large space systems and planetary exploration, particularly when launching a complete unit is beyond the capacity of the space transportation vehicle. SSP systems should be designed from the outset to accommodate on-orbit robotic assembly and maintenance. The degree of structural deployment versus assembly should be rigorously studied, and deployment concepts should be developed that are compatible with planned robotic capabilities. Systems studies are necessary to determine what level of robotic capability is optimal (from tele-operated to fully autonomous) and how humans are best used in the assembly, maintenance, and servicing operations (on the ground or in orbit). In-space transportation is an important driver in establishing on-orbit SSP costs. Trade studies of various concepts should be made along with satellite design and assembly concepts to establish the lowest-cost methods for placing the completed SSP design in GEO. Utilities, industry, and other government programs should make the most investment in ground power management and distribution (PMAD) technologies, ground-based energy storage, and platform system technologies. These areas are either utility specific or are funded adequately through other efforts. Furthermore, key research and development should place heavy emphasis on reduction of mass and cost and improvements in efficiency, the ultimate drivers for commercial application of any SSP system. Recommendation 2–1–7: The NASA SSP program should invest most heavily in the following key enabling technologies, mainly through high-payoff, high-risk approaches: (1) solar power generation (in collaboration with DOD/USAF and DOE to avoid duplication); (2) wireless power transmission; (3) space power management and distribution; (4) space assembly, maintenance, and servicing; and (5) in-space transportation. The SSP program should not invest research and development funds in ground PMAD technologies, ground-based energy storage, or platform system technologies. Utilities, industry, and other government programs already have significant investments in those areas. Capitalizing On Other Work It was clear from material presented to the committee that the SSP program, including SSP for terrestrial use and other technology applications, is highly synergistic with the related work of other U.S. agencies, and commercial and international interests. NASA must develop strong interfaces with other organizations to ensure that funds are spent most effectively. Specifically, the U.S. Air Force has a vigorous space photovoltaics technology program that could support NASA and potentially benefit from many of the SSP demonstration programs. There may also be near-term commercial and military applications for WPT to power long-duration airships and aircraft. Similarly, DOE, with its Office of Energy Research and the National Renewable Energy Laboratory, should be involved, for both near-term benefits and long-term program planning. DOE currently spends approximately $75 million/year on solar power technologies and also supports research in related environmental health and safety areas. Internationally, Europe and Japan are rapidly increasing funding for terrestrial photovoltaics research. The U.S. government sponsors a Space Technology Alliance to increase coordination and collaboration on space-related technology development. Member agencies include the Air Force Research Laboratory, the Ballistic Missile Defense Organization, the Defense Advanced Research Projects Agency, the National Reconnaissance Office, the Naval Research Laboratory, DOE, and NASA, among others. Current initiatives of its Space Power Subcommittee include infusion of technologies such as photovoltaics, modular low-cost PMAD, and efficient compact thermal management into all government space programs. NASA is currently involved in the alliance; however, continued and increased involvement is suggested by the committee to promote increased technology leveraging. International coordination should be fostered on environmental, safety, and spectrum allocation issues, as well as on other standard space technology development topics. The committee encourages mutually beneficial cooperation consistent with the International Traffic in Arms Regulations, perhaps with a research cooperative agreement, to maximize the effectiveness of the total investment. Recommendation 2–1–8: NASA should expand its current cooperation with other solar power generation research and technology efforts by developing closer working relationships with the U.S. Air Force photovoltaics program, the National Center for

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Photovoltaics, industry, and the U.S. government’s Space Technology Alliance. 2-2 APPLICATIONS NASA’s SSP technologies have extensive applications both in space and terrestrially. The program’s technology development can also be leveraged by other internal NASA programs and industry. Technology development crucial for an SSP system includes solar array advancements; robotic maintenance and servicing development; power management and distribution; and enhanced systems integration activity for large technical programs. These technologies have applications to many other engineering and science efforts in both government and industry. The following sections outline NASA’s current efforts in these areas and provide recommendations for future activities in relation to potential applications of SSP and areas for potential technology transfer. Applications to Enable Space Science The objective of the NASA SERT science effort is to “enable science efforts to identify, focus, and quantify the scientific benefit of new concepts created by providing a source of beamed power in space and the science missions made possible by the SSP developed technologies” (Marzwell, 2000). The basic premise of the effort is that high power and large, lightweight structures can enable in-space science. The higher power available from an SSP system can be used for increased penetrating power for imaging and sounding instruments; increased power for drilling and the volatilization of subsurface materials with beamed energy; and increased mobility and power for remote drillers, rovers, and moles in areas where current power systems cannot provide adequate resources. Many SSP technologies have already been identified by NASA to enable science (Marzwell, 2000). Advanced space-based structures, including large apertures, large photovoltaic arrays, and space-rigidized aerobrake structures, are expected to be a secondary product of SSP research and development. Laser-electric and solar-thermal propulsion and beamed energy power could be directly applicable to Earth-orbit and Mars-orbit missions as well as to future lunar activities. SSP research and development can also improve active sensing technology utilized to map hidden surfaces of planets and asteroids, discover new planetary bodies, analyze atmospheric properties, perform surface imaging, and track resources such as ice and water. Power beaming has application in space (Earth orbit, Mars orbit), as power from an orbit to a planetary surface, or in transportation (including laser sails and laser-thermal and laser-electric propulsion). SSP can also be utilized as an inexpensive, abundant power source for conventional orbital science. Several specific applications are being pursued by NASA in these areas. HEDS Applications The strategic plan of NASA’s Human Exploration and Development of Space (HEDS) effort establishes a range of visionary goals and objectives, including multiple targets for human exploration outside LEO, goals for scientific discovery through research in space, and research to enable humans to live and work permanently in space. The SERT program has identified potential space applications of SSP technologies and concepts in relation to the HEDS effort (Mankins, 2000a). Preliminary assessments of many applications have been performed by NASA. These preliminary assessments are an excellent initiation in providing motivation for the development of a much smaller SSP system in addition to the development of a future terrestrial baseload power system. Assessments were divided into categories based on the requirements of SSP technology. Nearer-term applications such as the use of evolutionary power systems for the ISS and solar power systems for GEO communications satellites are considered Generation I applications. Generation II applications include robotic planetary outpost power systems, wireless planetary power grids, and public space travel and tourism. Industrial space stations in LEO, power plugs in space, in-space propellant depots, and integrated human and robotic exploration applications are considered Generation III and IV applications. These applications would utilize SSP technologies in the mid- to far-term time frame (2005–2025). Many other potential applications such as space business parks, space utilities, interplanetary electromagnetic propulsion, and solar system resource development are very far-term applications. The committee believes that, while these far-term applications are important, the SSP program may be better served by focusing on nearer-term applications and technology under current funding conditions.

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Recommendation 2–2–1: Under current funding constraints, the SSP program should devote a large portion of its efforts to technologies that have nearer-term applications (e.g., low-mass solar arrays) while continuing to develop technology and concepts for long-term terrestrial baseload power applications. These applications for power may provide a better business case for industry development during the commercialization phase because such applications will be able to absorb power costs that are higher than future terrestrial power markets will accept. The committee believes, however, that pursuit of such large-scale applications may be possible only with increased cooperation between NASA and foreign governments and industry. The committee also recognizes that this proposed SSP program will require the development of closer working relationships with industry. NASA should lay the groundwork for commercialization. Recommendation 2–2–2: The SSP program, as well as any future effort in space solar power on the part of NASA, should involve a concerted effort to develop closer ties to industry, the U.S. government, international groups, and other internal NASA efforts for purposes of technology development, peer review, and possible shared resources. There is a need to involve more outside people in the Senior Management Oversight Committee (SMOC) or the appropriate technical interchange meetings and system working groups meetings (not just organizations external to NASA that are funded by the program, but others as well). Continued and expanded peer review should be an element of any future SSP effort. This may simply be accomplished by expanding the role of SMOC, including more industry and academic researchers in various areas germane to SSP technology development. These actions on the part of NASA may alleviate the issues raised in other sections of this report on the validity and reality of technical assumptions and forecasts (see Sections 2–1 and 3–1). Technology Transfer and Cross-Cutting Applications Individual technologies labeled as SSP-enabling technologies also have potential for terrestrial use and use in other space or aviation activities. Basic research in support of SSP is being performed in the areas of photon interaction and ablative physics, wireless power transmission, photovoltaics, robotics, and advanced materials development. Such technology advancement activities are important endeavors that should be continued. One previous NRC study recommended that NASA use the ISS as a test bed to develop new space technologies (NRC, 1996). Many SSP-enabling technologies, such as robotics, solar arrays, structures, WPT, and assembly techniques, could be tested on the ISS. Unfortunately, little support has been seen within NASA for cross-enterprise technology programs except from the personnel directly involved in such efforts (NRC, 1998). Increased leverage of current NASA programs directly related to SSP-enabling technologies should be pursued. The NASA SERT program has attempted, on a preliminary basis, to coordinate its research and technology roadmaps with other NASA programs. Specific examples follow: HEDS Technology-Commercialization Initiative; Gossamer Spacecraft program; Small Business and Innovative Research program; Spacecraft power and propulsion “core technology competency” funding , i.e., the Cross-Enterprise Technology program; Advanced Space Transportation and Space Launch Initiative programs; Intelligent Systems (IS) program; and Space science spacecraft technology demonstration programs (e.g., New Millennium). The SERT program has also attempted coordination with various efforts external to NASA, including DOE’s National Renewable Energy Laboratory photovoltaics research, the National Science Foundation’s efforts in innovative manufacturing and robotics, and DOD and the Naval Research Laboratory’s work in the area of intelligent systems. Program managers agree that the SSP effort within NASA needs to improve its track record of coordination with other research and technology programs across NASA, the U.S. government, and non-U.S.-government organizations. Furthermore, there is a need to incorporate flight test demonstrations of key technologies on space platforms such as the International Space Station or geosynchronous communications satellites. Also, as reflected in Section 2–3, the SERT program has had little detailed dis-

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy cussion with international efforts except in the area of frequency allocation. One improvement in international relations seen in the last 2 months of the study was the organization of an Open Forum on Space Solar Power, with participation by several countries. More activities such as this one are encouraged by the committee. Recommendation 2–2–3: The SSP program should assess in detail how to use research by other organizations to expedite the development of SSP-enabling technologies. During the tenure of this study, the SERT program did indeed begin what was termed a “gap analysis” in order to uncover areas within NASA in which increased technology leveraging may occur. The assessment of investments external to NASA is scheduled to be completed by the time this report is published, but as of December 2000 efforts had not yet been initiated. As the NASA SERT program management agrees, it will be imperative for the SSP program to carry this analysis a step further by actually using the knowledge from these yet-to-be-identified programs and leading efforts to adjust the focus of other related NASA technology development programs to help achieve SSP research and technology goals. Factors to be considered in such an evaluation should include information solicited from the outside research community and program balance between various issues such as technology push versus program pull, near-term versus far-term applications, and competitive technology development versus the need for system design choices. An example of such integrated technology planning and cross-enterprise technology can be found in NASA’s Office of Space Science; it is described in a National Research Council study (NRC, 1998). As part of the 2-year SERT effort, NASA contracted with the American Institute of Aeronautics and Astronautics (AIAA) to perform an assessment of certain aspects of NASA’s SSP research and technology effort (AIAA, 2000). Part II of the report discussed multiple-use technologies and applications. It is expected that these findings will be incorporated into the current SSP effort at NASA. The report identified multiple use of SSP technologies as a major area for indepth consideration. The prospects for these technologies were evaluated by AIAA in order to answer the following questions: How real are these technologies and applications? Are there other as-yet-unearthed opportunities for dual or alternative applications of SSP technology? How and to what extent should SSP technology studies be integrated with these non-SSP programs? What might be the payoffs of such an integration in achieving the various programs goals? Initial areas for consideration included geocentric space applications, lunar and planetary exploration, space science projects, national security applications in space, terrestrial applications, and a miscellaneous category (AIAA, 2000). Two areas mentioned by the AIAA report but not covered in the NASA material presented to this committee were national security missions and terrestrial applications such as airborne vehicles and offshore oil platforms. These areas, as well as the other applications, should be given greater consideration as potential applications for an SSP system. A need still exists to explore further potential applications and technology transfer opportunities, particularly in relation to the importance of the SSP effort having industrial support throughout the program’s lifetime. As previously witnessed during the Apollo and shuttle programs, technology development in computers, materials, and robotics can be transferred directly to many everyday industrial and personal applications. 2-3 INTERNATIONAL EFFORTS The committee examined several activities in progress outside the United States and noted a growing worldwide interest and involvement in space solar power. With a new global energy market emerging, led by electricity as the fastest-growing form of energy for users worldwide, NASA has excellent opportunities to contribute to and profit from international collaboration. Advantages to worldwide cooperation stem not only from the synergy that is possible from cooperation with other experts but also from the fact that SSP has space-based components and thus no technically imposed geographic limits on the countries that could participate in SSP’s benefits (AIAA, 2000). The committee was briefed on current international involvement in SSP and found an optimistic global picture. Japan, France, Canada, Russia, Ukraine, Georgia, Italy, Belgium, Germany, India, Netherlands, China, and

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Singapore are among the countries engaged in at least some facets of SSP studies, research, development, and technology demonstration. Several multinational organizations such as the United Nations and the European Space Agency (ESA) are also sponsoring work in SSP (Erb, 2000). The following sections show the diversity of international efforts in which NASA’s participation might be mutually beneficial. SPS 2000 SPS 2000 is a planned operational test bed for several important space solar power technologies. The project was originally proposed by Makoto Nagatomo of the Institute of Space and Astronautical Science, Sagamihara, Japan (Pignolet, 1999), working with a team of government and academic research scientists. The SPS 2000 proposal features a 10-MW solar power satellite in an 1,100-km equatorial orbit. The 1,100-km orbit corresponds to about a 100-min orbital period, permitting the satellite to furnish a power burst of about 200 s to a rectenna4 on the ground (Moore, 2000). As of November 30, 2000, 19 sites in 11 equatorial countries had been selected as candidate rectenna sites. Field visits by the SPS 2000 task team have permitted the team to establish local contacts, engage the population in the project, and examine local impacts (Mori, 2000). The Grand-Bassin Project The French government, with the Centre National d’Études Spatiales (CNES) as its primary agent, also favors international cooperation, believing that success will come when a critical mass of research that makes use of technical synergy is applied to SSP problems (Vassaux, 1999). To that end, CNES, the University of La Réunion, and researchers from Japan are sponsoring a large-scale wireless power demonstration project on the island of La Réunion. La Réunion is a volcanic island in the Indian Ocean southeast of Madagascar. Because the island has few indigenous conventional energy resources, it must import them at great expense. Local decision makers actively support new ways to provide energy to their population (Pignolet, 1999). The village of Grand-Bassin on La Réunion Island is located in a deep canyon 700 m distant from an entry point to the island’s power grid. The Grand-Bassin project involves transmitting about 10 kW of electricity via microwave energy at 2.45 GHz to provide power for the village. This project is notable for going beyond current experimental feasibility of WPT to an operational system that would be subject to real-world demands: exposure to tropical weather conditions, varying power demand level, continuous power production, and reasonable cost. CNES estimates that the system could be in place as early as 2003 (Pignolet, 1999). Demonstrations of Wireless Power Transmission Both Japan and Canada have been involved in demonstrations of WPT. A survey taken in Canada identified some 50 organizations in that country that have interests that relate to SSP. Canadian interests include space-based collection systems, space-to-ground demonstrations, ground point-to-point WPT demonstrations, and pilot plants. Canadian activity includes planning for a ground demonstration site, probably in Newfoundland, that will examine many of the same technical issues that are planned for Grand-Bassin, although in completely different climate and terrain (Erb, 2000). Canada also sponsored development of a prototype microwave-powered aircraft for use as a long-duration, high-altitude communications platform. First flights of a scale model began in 1986 (Erb, 2000). At Kobe University in Japan in 1995, researchers successfully flew a small airship using power transmitted from the ground by microwave energy. Researchers estimated that they were able to generate 10 kW of radiated power from the parabolic antenna on the ground and obtained about 5 kW from the rectenna onboard the airship. Researchers were able to use the power to make the airship climb as high as 45 m above the ground and to hover there for 4 min 15 s (Kaya, 1999). Other International Efforts The committee noted numerous other projects that dealt directly with SSP or with the development of technologies that will facilitate SSP. The Technical Uni- 4   A rectenna (the term was coined by the late William Brown, formerly of Raytheon), sometimes referred to as a rectifying antenna, is composed of a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power (DC current).

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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy versity of Berlin has been involved in SSP studies since 1985. German work has included computer simulations of GEO solar power satellites that include operational characteristics and life-cycle costs; modeling the acquisition and operation of SSP lunar installations; and modeling the development of SSP in conjunction with human exploration of the Moon and Mars (AIAA, 2000). In Russia, the Central Science Research Institute of Machine Building has designed an SSP satellite that would have a maximum output of 3.14 MW. This design would transmit solar power by microwave to orbiting or remote spacecraft and to lunar and Martian bases. In Ukraine, researchers are proposing experiments for the International Space Station dealing with semiconductor structures for solar cells, new forms of solar concentrators, and enhanced forms of power transmission (AIAA, 2000). The nations of the European Space Agency are also currently active in SSP studies and research. Early in 2000, ESA published a study conducted jointly by German, Italian, and French participants that sought to identify opportunities, capabilities, and technologies for exploration and utilization of space in the next 30 years. Among the SSP scenarios examined in this study were an experiment for ISS that involved microwave power transmission to a free-flying satellite, wireless power transmission from one terrestrial location to another via a power relay satellite in GEO, and solar-power-generating satellites for terrestrial power supply (Nordlund, 2001). NASA’s Role in International SSP Activities It was not the committee’s intent to produce an exhaustive list of efforts worldwide but to show that there are opportunities for international collaboration. The committee noted that NASA hosted an International Space Power Forum at NASA Headquarters in Washington, D.C., in January 2001. At that forum, representatives from Canada, the ESA, and Japan all indicated that increased interest and participation by the United States would be beneficial to work they were doing in their own countries. The committee understood that the International Traffic in Arms Regulations may impede transfer of certain technologies but also noted that a great deal can be accomplished under current law and that avenues exist for approving technologies for export. It may be beyond the means of any one country to fund the research, development, and implementation of SSP, but these tasks should be more achievable by international cooperation. International cooperation would allow NASA to profit from the work of experts worldwide, as well as to contribute its own expertise. The comments at the 2001 International SSP Forum from Canadian, European, and Japanese representatives reinforce the committee’s observation that NASA’s collaboration internationally would be welcome and appropriate. Recommendation 2–3–1: NASA should develop and implement appropriate mechanisms for cooperating internationally with the research, development, test, and demonstration of SSP technologies, components, and systems. REFERENCES AIAA (American Institute of Aeronautics and Astronautics). 2000. AIAA Assessment of NASA Studies of Space Solar Power Concepts. Prepared for National Aeronautics and Space Administration, Office of Space Flight, under NASA Grant NAG8–1619. Reston, Va.: American Institute of Aeronautics and Astronautics. Carrington, Connie, and Harvey Feingold. 2000. “SERT Systems Integration, Analysis, and Modeling.” Briefing by Connie Carrington, National Aeronautics and Space Administration, and Harvey Feingold, SAIC, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., September 13. Davis, Danny. 2000. “2nd Generation RLV Summary.” Presentation prepared by Danny Davis, Marshall Space Flight Center, for the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., October 24. Erb, R.B. 2000. “Interest and Activities in Space Solar Power Outside the USA.” Briefing by Bryan Erb, Canadian Space Agency, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., December 14. Feingold, Harvey. 2000. “SERT Systems Integration, Analysis, and Modeling.” Briefing by Harvey Feingold, SAIC, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., October 23. Kaya, Nobuyuki. 1999. “Ground Demonstrations and Space Experiments for Microwave Power Transmission.” Space Energy and Transportation 4(3, 4):117–123. Knight, Frank. 1921. Risk and Uncertainty. 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Laying the Foundation for Space Solar Power: An Assessment of NASA’s Space Solar Power Investment Strategy Mankins, John. 2000a. “Human Exploration and Development of Space— Space Solar Power Applications.” Briefing by John C.Mankins to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., September 14. Mankins, John. 2000b. “Space Solar Power Exploratory Research and Technology (SERT) Program Status.” Briefing by John Mankins, National Aeronautics and Space Administration, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Irvine, Calif., December 14. Mankins, John, and Joe Howell. 2000a. “Space Solar Power (SSP) Exploratory Research and Technology (SERT) Program Overview.” Briefing by John Mankins and Joe Howell, National Aeronautics and Space Administration, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., September 13. Mankins, John and Joe Howell. 2000b. “Strategic Research and Technology Roadmap.” Briefing by John Mankins, National Aeronautics and Space Administration, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Irvine, Calif., December 14. Marzwell, Neville. 2000. “Space Science Enabled Applications.” Briefing by Neville Marzwell, Jet Propulsion Laboratory, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., September 14. Moore, Taylor. 2000. “Renewed Interest in Space Solar Power.” EPRI Journal 25(1):6–17. Mori, Masahiro. 2000. Summary of Studies on Space Solar Power Systems of the National Space Development Agency of Japan. White Paper (November 30). Tokyo, Japan: Advanced Mission Research Center, Office of Technology Research, pp. 31, 33. Mullins, Carie. 2000. “Integrated Architecture Assessment Model and Risk Assessment Methodology.” Briefing by Carie Mullins, Futron Corporation, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., October 23. NASA (National Aeronautics and Space Administration). 1999. Space Launch Initiative Program Description. NASA White Paper. Washington, D.C.: National Aeronautics and Space Administration. Available online at <http://std.msfc.nasa.gov/sli/aboutsli.html>. Accessed August 15, 2001. Nordlund, Frederic. 2001. “ESA and Space Solar Power (SSP).” Presentation by Frederic Nordlund, European Space Agency, to the International Space Power Forum, Washington, D.C., January 12. NRC (National Research Council), Aeronautics and Space Engineering Board. 1996. Engineering Research and Technology Development on the Space Station. Washington, D.C.: National Academy Press. Available online at <http://books.nap.edu/catalog/9026.html>. Accessed August 16, 2001. NRC, Space Studies Board. 1998. Assessment of Technology Development in NASA’s Office of Space Science. Washington, D.C.: National Academy Press. Available online at <http://www.nationalacademies.org/ssb/tossmenu.htm>. Accessed August 16, 2001. Pignolet, Guy. 1999. “The SPS-2000 ‘Attaché Case’ Demonstrator.” Space Energy and Transportation 4(3, 4):125–126. Vassaux, Didier. 1999. “The French Policy on Space Solar Power and the Opportunities Offered by the CNES Related Activities.” Space Energy and Transportation 4(3, 4):133–134.