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11 Overall Findings and Recommendations CURRENT EMPHASIS AND JUSTIFICATION NASA currently is focusing on more frequent use of smaller, more technically advanced, and less expensive scientific spacecraft to replace large, expensive, one-of-a- kind spacecraft. This approach is intended to promote not simply a specific category of technologies and missions with a lower cost, faster development ant} launch time, and higher tolerance for risk but also a space program that enhances productivity and economic competitiveness. Small spacecraft already have server! a long-stanciing role in space physics, astrophysics, and planetary missions, notably at GSFC and at JPL, which predates the recent enthusiasm for small spacecraft. With decreasing NASA budgets projected for at least the next five years and with over 50 percent of NASA's overall budget allocated for the Space Station, the Space Shuttle, and Mission to Planet Earth, the Pane! on Small Spacecraft Technology believes the increaser} emphasis on small spacecraft is well placed if NASA is to have a meaningful science program in the future (Goldin, 19931. Although small, less-expensive spacecraft cannot satisfy all potential mission requirements, such as manned exploration ant! more demanding science missions, the pane! believes they can contribute to the revitalization of the space program. Further, more-frequent ant! less- expensive missions can help to promote structural and cultural changes that are vital to the future of the space program considering the current budgetary and political environment. These changes include increased opportunities for infusion of new technology in ongoing programs, along with an increased tolerance for technological risk; overall improvements in program responsiveness, versatility, and cost-effectiveness; and economic competitiveness in both aerospace and nonaerospace industries. SMALL SPACECRAFT CAPABILITIES While the pane! believes that for many missions small spacecraft have the potential to achieve the mission requirements with capability approaching that of tociay's large spacecraft, it must acknowledge that even with the application of currently available technology, today's small NASA spacecraft have limitations. Furthermore, not all small 83
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84 Technology for Small Spacecraft spacecraft missions are simultaneously faster and less expensive, since technology research and development for miniaturization can be expensive. However, the pane! believes that with a vigorous technology-development and miniaturization program that focuses on areas that provide the highest payoff, small spacecraft, either singular or in constellations, can be used to achieve increasingly significant mission requirements. RESPONSE TO TASK STATEMENT The task statement for this study asked the pane! 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, and 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. Review of NASA's Small Spacecraft Technology Program While NASA's technology program has not, until recently, been focused on small spacecraft, NASA has had several development programs for small scientific spacecraft in the past, which used advanced technology that was developed, to a significant degree, by DoD and industry. The current NASA development programs for small scientific spacecraft include the ongoing Small Explorer program at GSFC and NASA activities in support of small DoD spacecraft, such as Clementine and MSTI. In addition to the existing activities, OACT recently established the Small Spacecraft Technology Initiative and the Office of Space Science initiated the Discovery program to develop a series of smaller scientific spacecraft. The first two Discovery missions, which are both scheduled for launch in 1996 are JPE's Mars Pathfinder and the Applied Physics Laboratory's Near Earth Asteroid Rendezvous. Appendix D gives a more complete summary of NASA small spacecraft programs. The goals of the OACT Small Spacecraft Technology Initiative are to develop and infuse technology into planned missions and to demonstrate a new approach to small spacecraft technology integration through development and flight of several small spacecraft. Because of the recent establishment of OACT's Small Spacecraft Technology
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Overall Fir~ings and Recommendations Initiative, small spacecraft technology-development activities may receive greater emphasis in the future. It is the intent of OACT to infuse technology into proposed internal NASA development programs for small spacecraft. A new ethos of technology infusion should be actively promoted by NASA, and project managers should be encouraged to incorporate new technology into all future small spacecraft missions. The pane} believes that every space mission could contribute substantially to the achievement of NASA's larger mission if every mission were also, to one degree or another, a flight test of new technology. The project management philosophies utilized for the GSFC and JPE small spacecraft development programs and the one proposed for the OACT Small Spacecraft Technology Initiative ant! the Of lice of Space Science's Discovery program are markedly different. In the case of GSFC and JPL programs, spacecraft design and integration and, in many cases' the manufacturing effort, are largely kept within NASA centers, while inclustry's role is limited to that of support contractors and subsystem suppliers. Project managers of the Discovery missions and the OACT Small Spacecraft Technology Initiative propose to place responsibility for spacecraft concept, design, and integration with a prime contractor ant! utilize NASA in a support and oversight role. The pane! believes that each approach has merit. The internal NASA "prime contractor" role provides NASA a means for conducting special missions where a NASA lead is considered necessary and also provides an excellent training ground for future NASA project managers. However, it tends to impede the transfer of technology to industry, where it can be used in support of future NASA programs, and, perhaps more importantly, to commercial initiatives and to programs of other agencies. Having an industry prime contractor lead with support from other industry partners, universities, anti NASA, places the technology in the hands of industry where it is more likely to be applied commercially. The pane] believes that NASA should continue an active internal technology development program for small spacecraft, as discussed in the following section, independent of the project management approach. Assessment of the NASA Technology Priorities for Relevance to Small Spacecraft, Launch Vehicles, and Ground Operations The establishment of the Small Spacecraft Technology Initiative appears to have heightened emphasis, in NASA technology planning circles, on team operations involving industry, university, and NASA interaction on specific space missions, with accentuated industry leadership. "Customer needs," "user needs," anti technology transfer capability have received considerable emphasis from NASA management as the primary strivers of NASA's research and development efforts. While this emphasis is certainly healthy in establishing relevant foci for NASA's technological activities and providing a vital framework for intensive efforts, the pane! is concerned that overemphasis on this approach may lead NASA to overlook its responsibility to the long-term development of generic space technology. A mix of direct mission support, especially for NASA's own 85
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86 Technologyfor Small Spacecraft space-science projects, and generic research on a variety of advanced technology special topics should be pursued. Adequate funding for technology development is required for NASA to successfully implement this approach. Especially since the defense budgets are decreasing, NASA must be able to support its own requirements for technology research and development. The specific technology recommendations of this report are generally of a relatively short-term nature and do not address the need for a more generic research and development program that will support future generations of small spacecraft systems. It is the opinion of the panel that the recommendations of this report, coupled with such a generic technology-development activity would, over both the short and long term, enable the execution of meaningful space-science programs and economically attractive commercial space ventures using small spacecraft. In recent years, several high-level study groups have been very critical of the level of funding committed to NASA's technology development program. The groups have recommended funding levels that range from a level of 7 to 10 percent of NASA's total budget (NRC, 1987) to a factor of three increase of the 1990 technology budget (NASA, 19901. This panel recognizes that the level of expenditure for technology development should be related to NASA's long-range plans for future programs. As of this writing, several elements of NASA's overall plan are apparent to the panel: . . an international space station that uses existing systems for placement in orbit; Mission to Planet Earth, which uses existing systems for orbit placement; use of small spacecraft for future Earth and planetary science programs; technology to support the commercial industry; and technology development to support a later decision for manned exploration of space. As can be seen from this list, several different types of programs must compete for technology development funds within NASA. The panel notes that although the NASA Administrator strongly supports using small spacecraft for scientific missions, the same support was not reflected in Congress' fiscal year 1994 budget, where the Small Spacecraft Technology Initiative received only $12.5 million of the $30 million requested. Since the fiscal year 1995 budget only recently was submitted to Congress, it was not clear at the time of this report whether Congress would support NASA's $47.9 million request for the Small Spacecraft Technology Initiative. While small spacecraft based on currently available technology have significant capability, their ability to conduct more-meaningful science programs at affordable cost could be greatly enhanced through technology development. Recognizing the great potential to be clerivec! from research and development of advanced technology for small spacecraft, the panel recommends that an adequate level of funding be provicled to ensure the achievement of that potential.
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Overall Findings and Recommendations The pane! has not made specific cost estimates for each of its recommendations. This was considered to be beyond the panel's capability in the time it was able to dedicate to the study. It is the paneT's belief that each of the recommendations that has survived its critical review and appears in this report should be funded and carried to the point where it is completed and the technology is ready for use or to the point where it is apparent that there is a better course to follow. The pane! leaves it to NASA to determine the cost of the recommended technology program for small spacecraft, and to make evaluations of the potential contributions of the recommendations to the health and vigor of the future NASA ant! commercial space programs. In the event that it is determined that a substantial increase in the NASA research and development budget is indicated in order to conduct the program in a timely manner, NASA should rearrange its budget priorities to accommodate the required level of funding for research and development and make the case with the Administration ant! the Congress for the substantial increase. Small Spacecraft Technologies of Other Government Agencies and Technology Efforts in Industry that are Relevant to Small Spacecraft, Launch Vehicles, and Ground Operations The pane! was briefed by numerous government agencies and companies regarding the activities of these groups in small spacecraft, launch-vehicle, and ground- operations technology programs. While the survey of technology was not all inclusive, due primarily to time constraints, the pane! believes that it developed a comprehensive understanding of the small spacecraft technology development activities. A summary of ~. ~ - ~ .. .. ~ .. . . .. . . . . . . . . ~ .. the panel's Endings and recommendations is provided below. In brief, it was apparent that the DoD agencies, in particular the Naval Research Laboratory, BMDO, and ARPA, ~ ~ ~ ~ i' . i. · '' a,, ~ ~ ~ ~ have llad, in the past, very active programs in small spacecraft technology development. These programs were supported by industry, both in contractual efforts for the DoD agencies and with company-funded research and development projects. Table ~ i-1 is a summary of the technologies that were identified by the pane! as being currently available, that is, those technologies that could be used by small spacecraft designers today with minimal risk, but with the unclerstancling that some degree of further development and flight qualification may be required. The availability was based on the experienced judgment of the pane! members. Table ~ I-! includes, in addition to DoD and industry technologies, those technologies developed in the NASA technology program, primarily at GSFC, JPL, and LeRC. Many of these technologies currently are being used in ongoing programs such as in the Clementine spacecraft, in the Small Explorer program, and in the Lockheed commercial spacecraft being developed for the TRlDIUMT24/SM program. 87
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88 Technology for Small Spacecraft TABLE Il-l Currently Available Technologies for Small Spacecraft within NASA, Other Government Agencies, and industry TECHNOLOGY AREA TECHNOLOGY LOCATION* SYSTEMS ENGrNEERING AND OPERATIONS PROPULSION POWER MATERIALS AND STRUCTURES COMMUNICATIONS Phase-change memory materials to replace explosive devices on the spacecraft Autonomous, on-board health monitoring of launch vehicle and spacecraft Autonomous determination of orbit parameters and autonomous station keeping Bipropellant thruster (756 newtons) with high response valving and low weight (64 grams) Monopropellant thruster (223 500 newtons) with high pulse rate, low weight (184 326 grams) Carbon composites and fiber overwraps on aluminum propulsion tanks for reduced weight Arc jets for station keeping (less than 1- kilowatt power levels) SPT-70 electromagnetic Hall thruster Silicon, Gallium Arsenide, and Gallium Arsenide/Germanium solar arrays U.S. Air Force Phillips Laboratory, Industry, Naval Research Laboratory U.S. Air Force, NASA, Industry, U.S. Army BMDO, JPL BMDO, U.S. Air Force Phillips Laboratory, Industry BMDO, U.S. Air Force Phillips Laboratory, Industry BMDO, U.S. Air Force Phillips Laboratory, Industry NASA, U.S. Air Force Phillips Laboratory BMDO, JPL, U.S. Air Force Phillips Laboratory, Industry NASA, BMDO, DoD, Industry Radioisotope thermoelectric generators DOE, NASA Individual and common pressure vessel nickel hydrogen batteries Smart structures for jitter suppression Aluminum-lithium alloys for primary structures Naval Research Laboratory U.S. Air Force Phillips Laboratory NASA, Industry Polymer matrix composites for primary Industry structures High speed switching from the Advanced Communications Technology Satellite (Ka band) Radio frequency satellite link components Radio frequency phased array antennas Solid-state amplifiers NASA, Industry NASA, Industry NASA, Industry NASA, Industry .
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Overall Findings and Recommendations 89 TABLE 11-l Currently Available Technologies for Small Spacecraft within NASA, Other Government Agencies, and Industry (Continued) TECHNOLOGY AREA TECHNOLOGY LOCATION* GUIDANCE AND CONTROL SENSORS LAUNCH VEHICLES Ring laser gyroscopes Focal-plane-array star trackers Small, lightweight reaction wheels using Industry conventional bearings GPS receivers for position determination Solid-state recorders, radiation hardened 32-bit computers, radiation hardened Standard electro-optical bus (e.g., Military Standard 1773) BMDO-developed instruments using passive and/or active sensors: star trackers, near infrared camera, long-wavelength infrared camera, ultraviolet/visible infrared camera, laser imaging and detection ranger Industry BMDO, Industry Industry, Naval Research Laboratory Industry Industry U.S. Air Force Phillips Laboratory, Industry, NASA BMDO NASA-developed instruments for the NASA Mission to Planet Earth program Aluminum-lithium alloys for propellant tanks and other structures Graphite epoxy for propellant tanks and Industry other structures NASA, Industry * The location indicated is intended to be representative and may not include all sources. in addition, since the pane] was tasked to survey small spacecraft technology in NASA, industry, and other government agencies, work at universities was not thoroughly assessed by the panel.
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go Technology for Small Spacecraft TABLE 1 1-2 Technologies Under Development within NASA, Other Government Agencies, and Industry TECHNOLOGY AREA TECHNOLOGY LOCATION* SYSTEMS Capability to use factory-to-launch sequencing BMDO, JPL ENGINEERING AND OPERATIONS Processors that enable significant on-board NASA, JPL data processing to relieve ground data processing requirements Automated preparation of flight software Industry, BMDO, JPL PROPULSION XLR-132, advanced bipropellant orbit transfer U.S. Air Force Phillips Laboratory, engine Industry Iridium-rhenium thrusters, 445 newtons Piston-pump propellant supply systems Weight reduction and miniaturization of propulsion system components Carbon composites for thrust-chamber structure and high-pressure propellant tangs Xenon ion thrusters, 1-5 kilowatts Solar thermal propulsion POWER LeRC, Industry Lawrence Livermore Laboratory, Industry U.S. Air Force Phillips Laboratory, NASA, Industry BMDO, U.S. Air Force Phillips Laboratory, Industry NASA, JPL, Industry Amorphous silicon, copper indium diselenide, cadmium telluride, indium phosphide on germanium, and multibandgap cells Thin-film cells Ultra-light flexible panels and flexible arrays Nickel metal hydride batteries Lithium batteries Advanced energy conversion systems (Stirling, thermophotovoltaic, and alkali metal thermoelectric converters) U.S. Air Force Phillips Laboratory, Industry LeRC, U.S. Air Force, Industry BMDO, U.S. Air Force, JPL, Industry LeRC LeRC, JPL JPL, LeRC, DOE, BMDO, U.S. Air Force NASA, DOE, Industry MATERIALS AND Inflatable structures Lawrence Livermore National STRUCTURES Laboratory, Industry, U.S. Air Force Phillips Laboratory Smart structures for vibration and jitter control Embedded sensors U.S. Air Force Phillips Laboratory U.S. Air Force Phillips Laboratory
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Overall Findings and Recommendations TABLE Il-2 Technologies Under Development within NASA, Other Government Agencies, and Industry (Continued) 91 TECHNOLOGY AREA TECHNOLOGY LOCATION* MATERIALS AND STRUCTURES (continued) COMMUNICATIONS GUIDANCE AND CONE ROL SENSORS Advanced composite materials and manufacturing methods Metal-matrix composites for structures Electro-emissive panels Transponders Superconducting communications components Optical communications Radio frequency space-to-space links and associated components and antenna systems New multiple-access schemes Interferometric fiber-optic gyroscopes Advanced, miniaturized small reaction wheel GPS for three-axis control of spacecraft Radiation-hardened, fault-tolerant electronics Advanced electronics packaging techniques GPS receivers for attitude determination Advanced inertial measurement unit based on emerging technologies Technologies being developed for Mission to NASA Planet Earth (see Appendix F) Technology being developed for BMDO programs Indium antimonide detectors for midwave infrared sensors Arsenic-doped silicon for long-wave infrared sensors Multispectral imager Superconducting materials Solar-blind ultraviolet detectors Analog processor Industry Industry, NASA, U.S. Air Force Industry Industry, NASA Industry NASA/GSEC, JPL, U.S. Air Force, BMDO, U.S. Navy, Industry U.S. Air Force Phillips Laboratory Industry JPL, DOE, Industry Industry NASA, Naval Research Laboratory Industry, NASA Industry, Naval Research Laboratory Industry, NASA, Universities Industry, Universities BMDO, Industry, Lawrence Livermore National Laboratory BMDO, Industry BMDO, Industry ARPA ARPA, Industry Applied Physics Laboratory, Naval Research Laboratory Applied Physics Laboratory
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92 Technology for Small Spacecraft TABLE ~ I-2 Technologies Under Development within NASA, Other Government Agencies, and Industry (Continued) TECHNOLOGY AREA TECHNOLOGY LOCATION* SENSORS Laser radar Industry, BMDO (continued) ROBOTICS Remotely programmed microrovers JPL Tools for autonomous operation of NASA, ARPA, Industry mlcrorovers Spaceborne geophysical sampling device LAUNCH VEHICLES Advanced composite materials for fabrication Industry of intertank structure, skirts, and payload shrouds Lower-cost solid- and liquid-rocket motor components through use of advanced manufacturing methods Hybrid propellant motors and stages Reusable cryogenic and tripropellant propulsion components (injectors, thrust chambers, pumps) for application to single stage-to-orbit Clean propellants using higher-performance ingredients such as ammonium dinitramide Clean solid propellants exploiting ammonium nitrate, solution propellant, and scavenged approaches NASA, Applied Physics Laboratory U.S. Air Force Phillips Laboratory, Industry Industry, NASA, U.S. Air Force U.S. Air Force Phillips Laboratory, NASA, Industry U.S. Air Force Phillips Laboratory, Industry, U.S. Navy Industry, U.S. Air Force Phillips Laboratory * The location indicated is intended to be representative and may not include all sources. In addition, since the pane! was tasked to survey small spacecraft technology in NASA, industry, ant! other government agencies, work at universities was not thoroughly assessed by the panel. it should be noted that some technologies listed as being currently available in Table ~ I-! may also appear in Table ~ I-2 as technology under development. The available technologies in Table ~ I-} currently possess a specific level of capability that can be useful for small spacecraft, but the technology may also be uncler development to expand! its mission capability or to complete the flight qualification. Recommendations for future work on many of the technology areas noted in Table Il-! ant} Table il-2 are presented in the last section of this chapter. Based on its review, the Pane! on Small Spacecraft Technology believes that the technologies noted in Table 11-] can be used, with an acceptable risk level, in current NASA development programs for small spacecraft.
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Overall Firulings and Recommendations · . . ~ Technologies currently under development in government and in industry are shown in Table .:~-2. Table Il-2 was intended to serve two purposes: (~) to identify ongoing technology programs that, if continued, are likely to result in available technology that could be applied to future small spacecraft programs, and (2) to identify ongoing developments in industry and government agencies to assist NASA in avoiding duplication in their small spacecraft technology development program. The Pane! on Small Spacecraft Technology recommends that NASA monitor the progress being made in the technology programs listed in Table 11-2 arm that the programs be evaluated to avoid possible duplication. It is further recommended that, in the event that the sponsoring agency is other than NASA, aM decides to discontinue the development activity, NASA should consider completing the technology development. - · Again, tne panel does not intend the technology lists in Tables ~ i-! ant! ~ :~-2 to be all inclusive. The tables do, however, reflect the results of the panel's fairly extensive review. Technology Gaps and Overlaps The panel's review ctici not identify any overlaps of NASA's research and development with that of DoD and industry that were considered to be serious. On the contrary, the panel believes that the level of technology development underway in the United States is deficient, considering the NASA objective of widely expancled use of small spacecraft. Although gaps in technology are difficult to (lefine, the panel believes that there is a significant gap between the technology that is now available and that which is being used in the NASA small spacecraft programs. This may be a result of the conservatism of the NASA project managers, which is understandable because of the dire consequences of failure engendered by the current, very costly large space programs. In acictition, the pane! believes that there are gaps relating to the technology needed to achieve the maximum return from small spacecraft in the future. These gaps are addressed in the recommendations for technology development in the following section. Prioritized Areas in Which Greater Investments are Likely to Have High Payoff Considering Current and Projected Budgets, the NASA Mission Statement, and the Needs of Industries That Utilize Space As stated in Chapter i, the principal deterrent to an expanded space program, both in NASA and commercially, is high cost. This is true for NASA because of today's budgetary and political climate and for industry because of the high cost in providing a 93
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94 Technology for Small Spacecraft potential service to a buyer, along with increasing international competition. If technology can be developed that will enable small spacecraft to achieve increasingly capable missions while maintaining the ability to produce the spacecraft at reasonable cost, the utilization of space by both NASA and industry could expand. The pane! believes that there are numerous opportunities in the development of technology related to small spacecraft systems. The difficulty is in how to prioritize and invest in technologies to achieve the greatest reduction in cost. In this section, the pane! has assigned priority levels to the technology recommendations contained in the body of the report. Three priority levels were chosen: high, higher, and highest. The pane! applied criteria (not in priority order) that included the following: 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 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 applied research programs rather than generic research activities. As discussed earlier, generic research also is an essential part of a total technology program. Such programs not only continue to extend the state of the art but also provide an opportunity for NASA to attract talented} college graduates to work in NASA's laboratories and 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 includle the continual monitoring by NASA of research arm development activities of other government agencies, foreign governments and organizations. and! industry. ~- , The pane! believes that each recommendation is worthy of implementation. However, recognizing the uncertainty of NASA funding for technology development, the pane! has identified those areas as highest priority, which in its judgement, offer the 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 recommended areas will be pursued at some point, with those in the highest priority level being funded first. The fact that the development of a
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Overall Findings and Recommendations particular technology may not come to fruition for several years should not bias a decision regarding early funding. The pane} believes that advanced technology has the potential to greatly enhance the ability of small spacecraft to perform meaningful missions at Tow cost. It is the opinion of the pane! that the totality of the recommendations, if executed, would enable an important part of the United States' space-science program to be accomplished very economically with small spacecraft. It would also provide a very strong technolo~v base for the emerging small spacecraft commercial industry. , ~i, The technology recommendations were assigned priority levels as discussed above and are listed at the end of this chapter. Discussions of the specific technologies can be found in the appropriate sections of the body of the report. Some technologies that have a particularly high potential to make a large impact on the cost and capability of small spacecraft are . technologies to reduce cost ant! improve efficiency of up-front systems engineering, launch, and mission operations; 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. Many launch and mission operations functions that now are 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 devices 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 accurately, probably at significantly reduced weight and cost. GPS also provides the 9s
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96 Technology for Small Spacecraft 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. Small, lightweight spacecraft are particularly suited to this technology because of the relatively higher thrust-to-weight ratios achievable with these very-low-thrust electric propulsion systems. In order to gain maximum potential from these high-specific-impuIse 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, clevelopment activity is needled 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-propuIsion systems during manufacturing and shipping because of their inherent inertness and over both solid and liquid systems during launch operations. The reduction in special safety requirements should translate into reduced cost. Hybrid propulsion systems have the added advantage of an environmentally acceptable exhaust product, which conic] 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 ant! 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. Table ~ I-2 lists those technology development programs currently underway that were identified by the pane! during its review activity. Before NASA initiates programs responsive to the recommendations in Table ~ 1-3, it shouIc3 review development currently underway in other agencies and industry.
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Overall Findings and Recommendations TABLE ~ i-3 Pnontized Technology Recommendations 97 HIGHEST Systems Engineering and Operations - Capabilities and design tools should be developed that facilitate improved up-front concept development for low-cost small spacecraft missions. These capabilities and tools should facilitate in-depth trades that result in improving the ability to estimate and in lowering overall life-cycle costs. Key trades include: Tools that would be useful are operational mission concepts; many small spacecraft versus larger, fully integrated systems; the degree of autonomy on the spacecraft and on the ground; the effect of launch strategy and vehicle selection; the degree of acceptable risk and approach to reliability; and dedicated versus shared mission operations facilities. data bases and cost estimating software that address life-cycle cost of small missions; and · nationally available data bases for existing parts, components, and new technologies. Technologies and techniques should be developed that would reduce the required number of mission operations personnel. These techniques include: autonomous orbit determination and correction; · on-board data screening to reduce the amount of data to be transmitted to the ground; and · communication systems for distribution of mission data directly from the spacecraft to the data users. . Technologies and practices required to enable a factory-to-launch sequence with minimum checkout at the launch site should be developed and demonstrated. These should utilize expert systems when appropriate, including, as a minimum, the following: on-board health monitoring and checkout and, where economical, fault correction, for both the launch vehicle and the spacecraft; techniques for remote system checkout; automated preparation of flight software for guidance and control of both the launch vehicle and spacecraft; a set of standard hardware interfaces for small launch vehicles and spacecraft; on-board launch trajectory determination for range safety tracking; spacecraft accessibility late in the countdown; and reduction of launch pad safety requirements through use of technologies such as hybrid propulsion and nonexplosive separation devices. Propulsion - An aggressive program should be established to demonstrate, in ground tests, the life of xenon ion propulsion systems that operate at power levels in the range from about 0.5 kilowatt to about 2.5 kilowatts for lifetimes of up to 8,000 hours. Arc jet thrusters for small spacecraft applications also should be evaluated. The systems demonstrated should be capable of being integrated into solar electric propulsion systems with total power levels in the range of 1 to 5 kilowatts. Both the ion thruster and the arc jet should then be demonstrated in space flight tests in the near term. The propulsion system requirements should be determined for precision station keeping of clusters of small spacecraft, and the capability of currently available systems should be evaluated. If it is necessary, systems should be developed to meet specific mission requirements.
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98 Technology for Small Spacecraft TABLE il-3 Pnontized Technology Recommendations (Continued) HIGJ~EST (Continued) Power An advanced solar array program should be initiated at a funding level that will allow reaching a goal of 200 watts per kilogram with 5 to 10 kilowatts of total power within the next five years. The development, characterization, and testing of NiMH batteries for low-power small spacecraft should be completed. Building on the work already completed for the Clementine mission, the characterization and testing of CPV NiH2 batteries for mid- to high-power small spacecraft should be completed. Communications Development of the following technologies should be supported: an electronically steered Ka-band phased array antenna; a Ka-band solid-state amplifier; and a Ka-band power module. Guidance and Control A high-priority program to realize the potential of GPS on small spacecraft should be established. The unique combination of capability and small size made possible by integrating GPS receivers/processors with other existing and emerging guidance components should be assessed. The design, documentation, and appropriate qualification of the following components and subsystems should be completed: fiber-optic interferometric gyroscope; miniature focal plane array star tracker; space-hardened GPS receiver/processor with attitude capability; advanced, miniaturized small reaction wheel; hardened 32-bit processor; and hardened solid-state recorder. Sensors The feasibility of achieving the required simultaneity of measurements of different instruments using a cluster of small spacecraft should be evaluated, and, if feasible, technology should be developed. The employment of GPS and very low- thrust and high-response attitude control thrusters might enable this technique. Robotics and Automation Technology work related to autonomous operations in unstructured environments should be supported and expanded. Launch Vehicle Technology Hybrid rocket motors that simulate operational requirements, thrust level, and burn duration for small launch vehicles
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Overall Findings and Recommendations TABLE 1 1-3 Prioritized Technology Recommendations (Continued) 99 RIGGER Systems Engineering and Operations Data storage and transmission techniques should be developed that meet the needs unique to small spacecraft. These techniques should utilize: low-cost, miniaturized, high-capacity, reliable data storage devices; efficient, high-data-rate transmission techniques; better forward error-correction codes; and efficient protocols for high-speed-data interactive transactions. Standardized communications interfaces for mission control functions should be developed. Areas for standardization include: tracking and orbit data formats; telecommunications characteristics; standard-format data units; time-code formats; packetized telecommands; packetized telemetry; and telemetry channel coding. Propulsion A technology program should be established to demonstrate the Light Exo-Atmospheric Projectile propulsion technologies at mission duty cycles and lifetimes consistent with small spacecraft mission life and operational requirements. The 445-newton rhenium-iridium thruster should be evaluated for application to an apogee kick stage for small spacecraft. This includes demonstration over a duty cycle typical of the missions envisioned for small spacecraft. The suitability of the XLR-132 engine as an upper-stage propulsion system for launching small spacecraft with deep- space propulsion needs should be evaluated. Power The development of lithium alloy (LiTiS2) batteries, particularly for low-energy-demand planetary missions, should be continued. The application of lithium ion batteries developed by the DOE should be evaluated for possible use in low-Earth-orbit spacecraft. If found promising, the technology should be adapted for small spacecraft. For mid- to far-tenn applications, the development of lithium polymer batteries should be accelerated. In the long-term, work on other advanced solar cell and solar array technology, including thin-film cell development, inflatable arrays, and flexible blanket wing APSA arrays, should continue at an increased funding level, with the goal of achieving a specific power of 300 watts per kilogram. Structures and Materials Research on simple, low-cost deployable booms and surfaces should be emphasized. The objectives should include high deployment reliability, compact stowage, and adequate precision. Ground-test proof of successful deployment in space is essential.
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100 TABLE 1 1-3 Pnontized Technology Recommendations (Continued) Technology for Small Spacecraft HIGHER (Continued) Structures and Materials (continued) A joint NASA-industry program should be initiated to demonstrate developments of advanced small-spacecraft designs that are based on polymer-composite components, exploiting available as well as novel technology as appropriate to meet the paramount demands of low cost, low weight, reliability, and adaptability. The NASA Small Spacecraft Technology Initiative may fulfill this objective. In coordination with ongoing research at universities and other government agencies, research efforts should be intensified in the area of smart structures and control-structures interaction. Research should be generic in character as well as focused on specific needs for small spacecraft. Communications Optical frequency (laser) communications systems and components (e.g., electronically controlled antennas and signal processing) should be developed for space-to-space links. Radio frequency space-to-space links, the associated components, and spacecraft antenna systems for complex spacecraft constellations in both low Earth orbit or other orbits should be developed. New, multiple access schemes and the associated critical components should be developed, as well as optimization of bandwidth utilization in the mobile satellite frequencies for low-Earth-orbit systems. Guidance and Control Design and ground-testing techniques should be developed that ensure acceptable performance in the space radiation environment. Additional support should be provided for the work in this field. The payoff in reduced flight-test time and funding will more than compensate for the investment in this effort. Further, the added assurance will encourage project managers to use more current technology. These techniques could be applicable to a broad range of electronic components and systems. Sensors . A research and development program should be directed toward the development of miniaturized, power-efficient, high performance instruments in the following areas: multifrequency radar altimeter and scatterometer systems; advanced coherent lidar systems; multispectral Earth observation systems operating in the ultraviolet, visible, and infrared wavelengths, employing lightweight optics and advanced detector array technology; advanced, passive, larger-aperture, high-sensitivity, low-weight, microwave radiometry employing lightweight deployable antennas, room-temperature superconducting sensors, and advanced on-board processors; and lightweight, deployable-mirror optical systems with deformable mirrors correctable to the diffraction limit, for ultraviolet, infrared, and visible long baseline interferometry using several small spacecraft, ultimately resulting in an extremely large-aperture phased array for astronomical observations. _ Robotics and Automation Autonomous systems and artificial intelligence should be developed for application to microrovers. .
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Overall Findings and Recommendations TABLE ~ i-3 Prioritized Technology Recommenclations (Continue(l) Boa HIGHER (Continued) Launch Vehicle Technology Although the Panel on Small Spacecraft Technology believes it has identified several areas with potential for reducing small spacecraft launch vehicle costs, the panel was not able to identify a technology program that would achieve the desired cost of $5 million to $7 million per launch. The panel, therefore, recommends that NASA conduct a study of proposed, new launch vehicles targeted for the small payload market; with a goal of $5 million to $7 million per launch; to determine the cost benefits associated with the introduction of new technology, including unique concepts, new hardware designs, new materials, and manufacturing methods. This study should also include consideration of support for launch and mission operations. NASA should initiate advanced demonstration programs for promising concepts identified in the study, especially in propulsion technology. These demonstrations should be carried to the point that will allow decisions for system development to be made by either the government or commercial ventures. HIGH Propulsion Research and technology programs should be initiated to demonstrate fully the capability of solar thermal rockets, with emphasis on concentrator/mirror, absorber-thruster, and feed-system technology. Space flight tests should be conducted to explore deployment mechanisms and dynamics, validate packaging techniques, and demonstrate the performance and durability of absorber-thruster operation with a deployable concentrator mirror. Power There is a small but important subset of small spacecraft missions that cannot use solar power or batteries and that are enabled by radioisotope power systems. For those missions, development of more efficient conversion systems to reduce heat source mass and cost would be beneficial. Radioisotope power system designs using Stirling, thermophotovoltaic, and alkali metal thermal-to-electric converter conversion techniques should be jointly evaluated by NASA and DOE, and the ability of these techniques to satisfy various NASA missions should be assessed. Based on the evaluation, NASA and DOE should select one or more of these systems for experimental demonstrations of its performance against specific pre-determined criteria that are peculiar to the approach selected. NASA and DOE should then select the most promising approach for further development. A decision about flight demonstrations should be made contingent on future NASA planning of missions that would utilize the technology. Research on concentrator arrays, with a goal of reaching power densities in excess of 300 watts per kilogram at one-half the cost of existing arrays, should be increased. Structures and Materials A short-term demonstration program with industry should be undertaken to design, construct, and qualify a small spacecraft structure based primarily on current structural design configurations that exploit aluminum-lithium alloys in lieu of aluminum in order to determine the feasibility of rapid weight savings with minimal effort and cost. Sufficient expertise in polymer-matrix composite technology should be maintained within NASA to identify and pursue opportunities for research aimed at improving strength, stiffness, thermal properties, and economy of fabrication, with explicit attention to the possibilities of multiple-use components and the engineering of modular attachments and joints. Communications NASA should be the technical leader in developing the rationale for radio frequency reassignments in view of the new optical communications developments.
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102 TABLE 1 1-3 Pnontized Technology Recommendations (Continued) HIGH (Continued) Technology for Small Spacecraft Guidance and Control The advantages and disadvantages of applying standardization to specific interfaces for electronic and electro-optical components and subsystems (e.g., Military Standards 1553 and 1773) to simplify integration activities should be evaluated, and standardization should be implemented as indicated by the evaluation. Sensors A continuous research and development program should be conducted to improve the performance and reduce the weight and power required for infrared detector arrays; cryogenic detector coolers; and deployable antennas for radiometry and radar. Robotics and Automation . A research and development program focused on miniaturizing robotic devices, science instruments, and associated computing power should be developed. Robotic spacecraft systems incorporating the most advanced autonomous systems and artificial intelligence technology currently available should be developed for demonstration in space on small spacecraft and on the Space Shuttle. The technology should be applied to the development of a free-flying robotic spacecraft for inspection, maintenance, and research support on the Space Station. Launch Vehicles The ongoing Solid Propellant Integrity Program should be supported with increased consideration toward those solid propulsion units used in commercial small launch vehicles. Such action will help the commercial sector maintain or improve reliability. Development of advanced manufacturing methods directed toward producibility and cost reduction of small spacecraft launch vehicles should be continued. This should include potential application of advanced composites. Scavenged and solution propellants are possible near-term solutions to potential environmental limitations of propellants and should be scaled-up and qualified for use. A program to characterize the ammonium dinitramide-based clean propellants should be funded. If the results are positive, a program to develop a pilot plant to scale-up the manufacture of ammonium dinitramide should be funded. NASA should initiate technology efforts in support of a reusable single-stage-to-orbit vehicle for small spacecraft where appropriate, to ensure the availability of the enabling technologies on a realistic time scale.
Representative terms from entire chapter: