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Executive Summary In 1992, the National Research Council's Aeronautics and Space Engineering Board established the Pane! on Small Spacecraft Technology to review the National Aeronautics and Space Administration's (NASA) plans for a new small spacecraft technology development program; review NASA's current technology program and priorities for relevance to small spacecraft, launch vehicles for small spacecraft, and small spacecraft ground operations; examine small spacecraft technology programs of other government agencies; assess technology efforts in industry that are relevant to small spacecraft, launch vehicles, and ground operations; and identify technology gaps and overlaps and prioritize areas in which greater investments are likely to have high payoff, considering the current and projected budgets, the NASA mission statement (see Appendix A), and the needs of industries that utilize space. Although many missions have been carried out with large, expensive, and very capable spacecraft, smaller systems have key advantages that make them attractive. Small spacecraft are incrementally less expensive and more tolerant of funding, schedule, and technical risk than large, expensive spacecraft. in addition, small spacecraft are not dependent on the costly Space Shuttle or Titan IV launch vehicles required for large spacecraft. The pane! believes that using smaller, less-expensive spacecraft will encourage use of more advanced technology, because the consequences of failure are reduced. The pane} concluded that with advanced technology, significant scientific, communications, and remote sensing missions can be performed using a single small spacecraft or constellations of small spacecraft. A vigorous NASA technology development program could provide technology that facilitates the use of small spacecraft for a higher percentage of NASA's future space missions. Potential technologies are identified and prioritized in this report. The 22-member Pane! on Small Spacecraft Technology was composed of recognized experts in key space mission technologies. The panel, established in late

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Executive Summary greatest potential for enhancing the mission capability and reducing the cost of small spacecraft. The remaining areas were identified as either high or higher priority. The assumption is that all of the remaining areas will be pursued at some point, with those in the highest priority level being funded first. The fact that the development of a particular technology may not come to fruition for several years should not bias a decision regarding early funding. In prioritizing all of the recommendations as high, higher, or highest, the pane! applied the following criteria (not in priority order): the potential to reduce mission cost; the cost to develop the technology; the potential to reduce weight (permitting a higher payload mass fraction or use of a smaller launch vehicle); the likelihood of a successful development; and the potential to enable key mission goals. Since hard data regarding these criteria are not available, the qualitative judgment of the pane! members, based upon their experience and background, was the determining factor. In order to balance out differences in judgments, the priority selections were made independently by two separate groups of pane! members, and then a consensus was reached by the entire panel. The recommendations, in general, address technology development programs rather than generic research activities. However, the pane! believes generic research is also an essential part of a total technology program. Such programs are necessary not only to continue to extend the state of the art but also to provide an opportunity for NASA to attract talented college graduates to work in NASA's laboratories and for it to engage universities, graduate students, and industry in stimulating research and development activity under contract to NASA. In addition, since many of the technologies that can be used on small spacecraft have been developed by DoD and industry, the pane! believes that a normal part of NASA's research and development activity should include the continual monitoring by NASA of research and development activities of other government agencies, foreign governments and organizations, and industry. Some technologies that the pane! believes have the highest potential to make a large impact on the cost and capability of small spacecraft are technologies to reduce cost and improve efficiency of up-front systems engineering and launch and mission operations; the Global Positioning System (GPS) for precision guidance and control; high-efficiency solar electric power generation and electric propulsion; hybrid propulsion for launch vehicles; and miniaturization of electronic devices. It has been demonstrated that a fundamental design philosophy for minimization of costs is to design, build, and operate the system with minimal personnel and only the 3

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4 Technology for Small Spacecraft absolutely necessary documentation. Broad application of these techniques in combination with new technology development programs can have a major impact on the cost and utility of future NASA and commercial space systems. Many launch and mission operations functions that are now performed by ground personnel can be automated with lightweight, low-cost, on-board systems. For example, on-board vehicle monitoring and, in some cases, defect correction can be automated, enabling factory-to-launch operations without the requirement for extensive intermediate ground testing. On-board launch trajectory monitoring for range safety purposes is achievable using GPS on board the spacecraft, eliminating the need for ground-based radar tracking during launch. Automated, on-board orbit determination and station keeping is also possible using GPS, which simplifies the mission operations task. High- density computers and memory devices combined with advanced software techniques enable extensive on-board data processing and screening, reducing the amount of data to be stored and transmitted to Earth. The compact memory crevices reduce the requirement for numerous data-reception locations on the ground. Communication systems can be developed that will permit direct delivery of data, partially processed on board, to researchers in their own laboratories, where they have powerful computing capability at their desks. Chapter 2 provides more detail on these and other technologies that could be applied to make substantial reductions in the personnel required to launch and operate a space mission using a small spacecraft. Two potential applications of GPS to small spacecraft, as noted above, are launch trajectory monitoring and automated on-board orbit determination. The pane! believes that GPS also has great potential in other applications. Use of GPS in various combinations with other guidance components can determine position and attitude very accurately, probably at significantly reduced weight and cost. GPS also provides the capability to precisely fly clusters of small spacecraft in close proximity to one another, simulating a much larger spacecraft. Electric propulsion is a very promising technology that can enable more ambitious missions in high-altitude orbits and at interplanetary distances. Such missions, however, must be able to tolerate orbit transfer times of several days or even months, en c} to allow for increased radiation exposure due to the longer transfer times. Small, lightweight spacecraft are particularly suited to this technology because of the relatively high thrust- to-weight ratios achievable with these very low-thrust electric propulsion systems. In order to gain maximum potential from these high specific impulse systems, a high electric power level is required. Advanced technology in solar-generated power could supply the required power levels with array sizes and weights compatible with small spacecraft. Extensive development work on both the solar power and electric propulsion technologies has been conducted in the past, but a concentrated, well-funded development activity is needed to bring these technologies to fruition. Hybrid propulsion is a technology that has great potential! for application to small spacecraft launch vehicles and has been under development for some time. Hybrid propulsion systems offer unique advantages over conventional solid propulsion systems because of their inherent inertness during manufacturing and shipping and over both solid and liquid systems during launch operations. The reduction in special safety requirements

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Executive Summary should translate into reduced cost. Hybrid propulsion systems have the added advantage of an environmentally acceptable exhaust product, which could be an important factor if environmental restrictions increase. Advances in miniaturization of electronic devices have the potential to increase the payload mass fraction, lower the spacecraft weight, reduce the power requirements, and reduce overall cost. These devices can be combined to form highly capable systems for remote sensing, guidance and control, communications, and on-board operations. Continued investment in advanced design and ground testing techniques for adapting commercial products for the space environment can assure the availability of up-to-date technology for space application. The pane! believes that advanced technology has the potential to greatly enhance the ability of small spacecraft to perform meaningful missions at low cost. It is the opinion of the pane! that the totality of the recommendations within this report, if implemented, would enable an important part of the U.S. space science program to be accomplished economically with small spacecraft. it would also provide a strong technology base for the emerging small spacecraft commercial industry. s