Some of these rockets can lift about 18,500 kg to low Earth orbit (LEO), and several are crewrated. A space shuttle can put about 29,500 kg into a due east LEO. Raw lift performance is not the issue. The issues are cost, reusability, reliability/availability, responsiveness, and turnaround time to put assets into space.
The U.S. space launch capability has evolved over nearly 50 years in response to the requirements of military, intelligence, civil space, and commercial users. The U.S. military and intelligence communities have required relatively low launch rates of uncrewed spacecraft to a variety of operational orbits, ranging from low Earth to geosynchronous. Civil space users have also required only low launch rates. So far, commercial users have implemented only uncrewed spacecraft at low launch rates into Earth orbits.
The proliferation of terrestrial fiber optics and increasingly capable and longer life satellites (both commercial and military) have tended to reduce launch rates, thereby inhibiting large new investments in launch vehicles and associated infrastructure. In recent years, fewer commercial launches and foreign (often subsidized) competition have made domestic uncrewed launch suppliers much less economically viable than had earlier been predicted (Antonio, 2003).
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Evaluation of the National Aerospace Initiative 3 Access to Space CURRENT OPERATIONAL CAPABILITIES Access to space is an international capability, with many of the world’s countries possessing very capable vehicles. A partial list of countries and their vehicles follows: United States Atlas, Delta, Pegasus, the space shuttles of the Space Transportation System, Taurus, and Titan France Ariane Russia Proton and Soyuz Ukraine Zenit China Long March Japan H-2 Some of these rockets can lift about 18,500 kg to low Earth orbit (LEO), and several are crewrated. A space shuttle can put about 29,500 kg into a due east LEO. Raw lift performance is not the issue. The issues are cost, reusability, reliability/availability, responsiveness, and turnaround time to put assets into space. The U.S. space launch capability has evolved over nearly 50 years in response to the requirements of military, intelligence, civil space, and commercial users. The U.S. military and intelligence communities have required relatively low launch rates of uncrewed spacecraft to a variety of operational orbits, ranging from low Earth to geosynchronous. Civil space users have also required only low launch rates. So far, commercial users have implemented only uncrewed spacecraft at low launch rates into Earth orbits. The proliferation of terrestrial fiber optics and increasingly capable and longer life satellites (both commercial and military) have tended to reduce launch rates, thereby inhibiting large new investments in launch vehicles and associated infrastructure. In recent years, fewer commercial launches and foreign (often subsidized) competition have made domestic uncrewed launch suppliers much less economically viable than had earlier been predicted (Antonio, 2003).
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Evaluation of the National Aerospace Initiative However, partly owing to the planned evolution of expendable launch systems by the Air Force, the U.S. government currently has available three families of expendable rockets: the soon-to-be-retired Titan IV and the about-to-be-flown Delta IV Heavy for heavy lift, and the old and new families of Delta and Atlas vehicles for medium lift. In addition, two small launchers (Taurus and Pegasus) provide on-orbit delivery of lighter spacecraft. These systems are completely expendable, will support only low launch rates, and are not crew-rated. The medium- and heavy-lift launchers also operate exclusively from two highly vulnerable Florida and California coastal locations, and one of the boosters (the Atlas V) incorporates a Russian-designed and -manufactured liquid main engine. Our nation has relied for more than 20 years on the only crew-rated reusable launch vehicle (RLV) in the world, the Space Transportation System (the shuttles). Now, two catastrophic failures in 113 flights have reduced the shuttle fleet to three, which are grounded until corrective actions can be implemented, and have severely limited the shuttle manifest. Currently, crew access to the International Space Station (ISS) depends on the Russian space program to provide limited capability with expendable launch vehicles and crew modules. If the ISS is to be completed and to have the full crew complement, the space shuttle will have to be brought back into service or there will have to be an extended delay until a replacement vehicle is available. This chapter contains at various points 34 findings and 26 recommendations. PLANNED CAPABILITY Both the Air Force and NASA are beginning to pursue new capabilities to satisfy their respective mission needs. While potential new systems may differ considerably and are not yet fully defined, many of the underlying technologies are expected to be similar. As stated earlier, raw lift performance is not the issue. The issues are cost, reusability, reliability/availability, responsiveness, and turnaround time to put assets into space. NAI has targeted these issues in its access-to-space (ATS) pillar with a three-phase program of increasingly demanding requirements. Vehicle and supporting system characteristics and, by implication, NAI technology timelines are illustrated in Figure 3-1. The ATS pillar has identified the common technical efforts and provides a mechanism for cooperation, sharing, and advocacy of these technologies. Included are reusable rocket propulsion, tanks, and airframes; thermal protection systems (TPS); integrated vehicle health management (IVHM); quick turnaround operations; hypersonic air-breathing propulsion; and many others. NASA and Air Force planning are discussed next. NASA Planning Future NASA missions are planned to include human spaceflight and logistical support for the ISS, Earth and space science, astrophysics, and exploration of the solar system. In addition, NASA may seek to develop a new launch capability for very heavy lift to facilitate both crewed and uncrewed exploration of the solar system. Until recently NASA had been funding the development of an orbital space plane (OSP), which was to become operational before the end of this decade. Initial capabilities were intended to satisfy ISS crew rescue requirements. Crew transfer capability (Earth to LEO) was planned as a follow-on spiral development. The OSP was to be launched on an existing expendable vehicle modified to become crew-rated. It should be noted that since the OSP was a current vehicle development program and not a technology development program, it was not considered part of NAI. It is only mentioned here for the sake of completeness regarding future planned capability and for its potential to compete for limited NASA resources. However, the vision articulated by President George W. Bush on January 14,
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Evaluation of the National Aerospace Initiative FIGURE 3-1 NAI phased approach to space access. Potential system payoffs and requirements. SOURCE: Sega, 2003.
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Evaluation of the National Aerospace Initiative FIGURE 3-2 Integrated space transportation plan influenced by Presidential Vision announcement of January 14, 2004. SOURCE: Rogacki, 2003. 2004, called for the cancellation of the OSP in favor of a crew exploration vehicle (CEV) to be developed and tested by 2008.1 Like its predecessor, the CEV is initially planned to satisfy the ISS crew transport and eventually the ISS crew rescue missions. By any measure, the CEV development schedule is very aggressive. Compounding the obvious issues of funding and schedule is the apparent requirement (articulated in the Presidential Vision) to use this same vehicle to provide a crewed capability to destinations beyond low Earth orbit. It is assumed that the CEV will not fall under the NAI umbrella, but, like the OSP, it could compete for NAI resources within a tightly constrained NASA budget. This problem could be exacerbated if NASA finds that much of the CEV technology development is NASA-unique—an example would be technologies to support the beyond-Earth-orbit capabilities that would not be needed by the Air Force—and would therefore have to be funded at the expense of other common technologies sponsored by NAI. The President’s Vision calls for retiring the space shuttles in 2010. After that, cargo up-mass and down-mass capability to the ISS will have to come from adapting evolved, expendable launch vehicles (EELVs) to the cargo mission, utilizing future European and Japanese cargo vehicles, or developing a new U.S. cargo capability (Williams, 2000). In parallel, NASA is developing next-generation launch technology (NGLT) to enable a decision on a rocket-based reusable launch system by 2008. Air-breathing hypersonic technology is not baselined for any near-term space access application but is under consideration for a long-term, crewed launch vehicle (Rogacki, 2003). Detailed plans and roadmaps for these new development programs (other than NGLT) were not available to the committee at the time of this writing. The top-level timelines for these activities are shown in Figure 3-2. 1 See http://www.nasa.gov/pdf/54868main_bush_trans.pdf.
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Evaluation of the National Aerospace Initiative FIGURE 3-3 Military space plane system architecture. SOURCE: Koozin, 2003. Air Force Planning The Air Force’s increasing emphasis on missions such as Prompt Global Strike (PGS), Operationally Responsive Spacelift (ORS), and Space Control (SC) may require both rapid-launch, expendable systems and reusable launch systems capable of turnaround times measured in hours rather than weeks or months. A concept for satisfying many of these requirements is shown in Figure 3-3. A potential access-to-space element of the architecture includes a two-stage-to-orbit (TSTO), reusable space operations vehicle (SOV) (booster) mated with either an expendable or a reusable upper stage. The associated development schedule for these vehicles is shown in Figure 3-4. The Air Force may find a low-cost, time-responsive, expendable vehicle to be a cost-effective solution to meeting certain mission requirements. Upgrades to the current fleet of expendable vehicles may also prove beneficial. However, as demand for a responsive launch capability and the corresponding launch rates increase, reusable launch systems become more attractive, both operationally and economically. The propulsion system for both expendable and reusable systems will remain rocket-based in the near- to mid-term (2004-2018) owing to the immaturity of air-breathing engine technology. It is hoped that near-term demonstration vehicles (e.g., RASCAL and FALCON) will help to advance air-breathing engine technology and should provide data to help determine the feasibility of scaling these engines for medium to heavy lift vehicles. Because air-breathing hypersonics technology is not baselined for any near-term space access concept but is being considered for longer-term designs (Rogacki, 2003), the committee’s assessments in this chapter focus on rocket-based launch vehicles. The assessment of air-breathing-based launch vehicles is restricted to comments on the feasibility of the basic technology and on the data needed for deciding if air-breathing engines can be applied to launch vehicles for medium and heavy loads.
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Evaluation of the National Aerospace Initiative FIGURE 3-4 Military space plane roadmap. SOURCE: Sponable, 2003. Finding 3-1. The United States will continue to rely on rocket-based systems for access to space for at least two more decades. The current expendable rocket families provide adequate lift capability for scheduled uncrewed launches to Earth orbit but will not support emerging military needs for rapid-rate, time-responsive launches. The two latest versions in the expendable rocket families utilize a new U.S. engine (RS-68) of undemonstrated reliability and an engine available only from a foreign supplier (RD-180.) The only reusable launch capability, NASA’s Space Transportation System, is scheduled to be retired by the end of the decade. Owing to the loss of the shuttle Columbia and the resulting Presidential Vision announcement, the plans for crewed flights are undergoing extensive revision. That said, it is anticipated that human flight will be accommodated by the development of a CEV fitted atop a (yet-to-be-defined) booster. Compounding the obvious funding issues are the CEV multimission requirements, the aggressive schedule, and the likely desire to make the CEV compatible with both the Delta and Atlas families of expendables. Although not a part of NAI, the NASA-unique nature of the CEV and resulting demand on the NASA budget may affect NASA’s ability to participate in NAI-sponsored technology development programs. The CEV booster might be further augmented and/or replaced in the next decade by a rocket-based, reusable launch system. Robust, reusable access to space will require a phased flight-test program to demonstrate reliability, affordability, and responsiveness relative to expendable systems. Airbreathing hypersonics technology is being considered for crewed and/or uncrewed launch systems in about two decades. Recommendation 3-1. The Air Force and NASA need to strike a balance between vehicle development programs and the NAI-sponsored technology development programs. Both organizations should continue to invest in basic and applied research, technology development, demonstration,
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Evaluation of the National Aerospace Initiative and implementation leading to new rocket-based capabilities. These investments should address both expendable vehicles and technology appropriate for deploying and operating reusable, rocket-based launch systems. Of near-term importance is the need to ensure the reliability and availability of the propulsion units used by the latest Delta and Atlas expendable boosters. Technologies developed under NAI sponsorship should be infused into the RS-68 under a component improvement program aimed at accelerating the near-term maturation of that engine. The question of assured availability of the Russian-built RD-180 used by the Atlas should be revisited in light of the potential increased demand following the loss of Columbia and the ensuing Presidential Vision announcement. TECHNICAL FEASIBILITY IN NAI TIME FRAME This section follows the taxonomy in the draft NAI plan for access-to-space S&T (DDR&E, 2002). It summarizes, in table form, the technical feasibility of each major technology area and its constituent technologies. The committee was hindered in its evaluation by the uncertainty surrounding budget projections. Consequently, the following subsections evaluate the various constituent technologies on the basis of their current maturity and their potential contribution to the overall NAI objectives of cost reduction, launch availability, and increased mission reliability and safety. An individual table is devoted to each NAI-designated vehicle system: Airframe Propulsion Flight subsystems Launch operations Mission operations Software Each table further divides the vehicle system into major technology areas, which are in turn broken down into the constituent technologies defined (for the most part) by NAI. The tables provide the committee’s assessment of (1) the current maturity of the constituent technologies, (2) the impact of the constituent technology on the major technology area, (3) the likelihood of achieving the desired results, and (4) the overall criticality of the major technology areas. Both the impact and criticality evaluations are based on the committee’s estimate of their contribution to the overall NAI goals—economics, safety, reliability, responsiveness, performance, or benefit to the industrial base. Impact was described as negligible, little, moderate, significant, or extreme. Maturity levels, from 1 to 5, are not to be confused with TRLs; rather, they correspond roughly to the DoD S&T categories: Basic research, Applied research, Advanced development, Demonstration/validation, and Engineering and manufacturing development. According to the committee, constituent technologies with low maturity levels, high impact, and low likelihood of achievement should be afforded special attention if they lie within a major technology area with high criticality. Conversely, technologies with high maturity levels, low impact, and high likelihood of achievement should retain the current level of attention or less, depending on the criticality of the major technology area. The assessments in these tables should
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Evaluation of the National Aerospace Initiative help to determine if appropriate attention is being paid to the development of technologies supporting NAI goals. Finding 3-2. The committee assessed the technical feasibility of NAI technical objectives by examining the main technical challenges and evaluating the NAI response to those challenges. The committee’s assessments are summarized in a set of tables corresponding to the NAI taxonomy. Finding 3-3. The committee was hindered in its evaluation of financial feasibility by the uncertainty surrounding budget projections. Recommendation 3-2. NAI should compare its current and projected resource allocations with the information contained in this report to assure appropriate attention is devoted to technologies with the best payoff in terms of costs, benefits, and risk. Airframe Depending on their configuration, the airframes of launch vehicles can serve several purposes, including thermal protection; enabling favorable lift-to-drag and thrust-to-drag ratios; housing and protection of onboard electrical equipment, pumps, feed systems, and engine systems; and fuel storage. The airframe is expected to be fully active in aerodynamic control of the vehicle. The external uncooled sections of the airframe may easily experience recovery temperatures in excess of 4000°F at Mach numbers of 8 and above (NRC, 1998). Compounding the mechanical and thermal loads on the airframe are the formation and movement of strong shock waves on the surface of the airframe; hot gas-solid (catalytic) chemical reactions on the surface; and unsteady boundary layers with flow separation. Several challenges must be overcome to operate the airframe effectively and efficiently in a complex aerothermodynamic environment. These challenges include extreme thermal, vibrational, and dynamic loading, and reliability, maintainability, and survivability, along with their impact on maintenance operations. Component and subsystem development leading to space launch capability faces challenges of accurate and efficient simulation and integration (for design), experimental testing (ground and flight), and, most critical, scalability. Table 3-1 captures the primary technology issues for airframes supporting space launch. First, the committee found that none of the identified technology areas was fully matured. Second, it rated relative criticality as “high” in three of the four major technology areas and as “medium” in the fourth. Third, the thermal protection technologies and design and analysis tools were rated “low” or “medium” with respect to the likelihood of achieving their goals. Further development of the technologies may be costly and risky and will require a multidisciplinary research and development (R&D) framework to ensure system-level optimization. Ongoing and planned R&D activities in each of the three technology areas rated with “high” criticality are summarized below. Thermal Protection Three research areas with high-payoff potential have been identified and are summarized in the findings below. Finding 3-4. The integrated high-payoff rocket propulsion technology (IHPRPT) program has a materials system component that addresses oxygen-compatible superalloys and metal matrix composites (MMC) for liquid oxygen turbopump housing (Brockmeyer, 2003). Finding 3-5. The IHPRPT program has a three-component ceramic matrix composite (CMC)
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Evaluation of the National Aerospace Initiative TABLE 3-1 Status of Technologies for the Airframe System NAI-Defined Technology Areas Committee Evaluations Constituent Technology Ratings Major Technology Area Constituent Technology Current Maturity Level (1-5) Relative Impact on Major Tech Area (Negligible, Little, Moderate, Significant, Extreme) Likelihood of Achieving in Time Frame (Current Funding Level) (Low, Medium, High) Relative Criticality of Major Technology Area (Low, Medium, High) Thermal protection Materials 3 Extreme Medium High Leading edges 3 Extreme Medium Control surfaces 4 Significant Medium Acreage surfaces 3 Extreme Low Seals 2.5 Significant Low Hot structure 2 Significant Low Active/passive cooled CMC 2.5 Significant Low Propellant tanks and feed systems Reusable metallic 3 Significant Medium Medium Reusable cryo composites 1 Significant Low Insulation 4 Significant High Leak detection 4 Moderate High Integrated structures Isogrids 3 Moderate Medium High Highly integrated subsystems 3 Significant Medium Design and analysis tools Integrated design environment (modeling) 2 Extreme Low High Vehicle CFD/aerothermal 2 Extreme Low Structural design 3 Moderate Medium Cost and safety analyses 2 Moderate Low materials initiative addressing thermal protection for bearings, nozzles, thrust chambers, gas generators, hot gas ducting, and turbomachinery (Brockmeyer, 2003). Finding 3-6. The NAI and the NASA NGLT programs have identified critical and enabling airframe technologies for far-term development and use (McClinton, 2003).
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Evaluation of the National Aerospace Initiative Recommendation 3-3. The potential for high payoffs exists in each of these technology research areas, and NAI should continue to support them. Integrated Structures The National Aerospace Plane (NASP) and X-33 programs resulted in several advances in integrated structures. Much, however, remains to be mastered to ensure the reliability, safety, and short turnaround time of full-scale systems. Although integrated structures are one of the largest single contributors to improving vehicle mass fraction, very little experience exists in developing approaches and validating techniques for the engineering and manufacture of full-scale integrated structures. Finding 3-7. The experience base of highly integrated structure, components, and subsystems is very shallow, and much time is required to develop new materials and integration techniques. Recommendation 3-4. Research should concentrate on the development of (1) tools for the automated optimization of configuration, (2) design processes, (3) material characterization, and (4) testing to validate techniques and processes that enable highly integrated structures. NAI should recognize the time-intensive nature of this research and ensure that the effort is integrated into the overall NAI timeline. Design and Analysis Tools Model development is a component of the R&D program managed by NASA in its NGLT program. Design and analysis tools in support of two large areas of research remain underdevel-oped. The first is the hypersonic reentry environment. These tools would be applicable for either a rocket-based or air-breathing reentry vehicle. The second area is the flow path environment for air-breathing hypersonic propulsion, both turbine and nonturbine. The need for robust and high-fidelity design tools and for ground-based testing to verify and validate these tools is well documented. Finding 3-8. Some examples of numerical tools correlated to national ground testing facilities can be found. In general, numerical tools have not been validated by test data (Candler, 2003; Holden, 2003). Recommendation 3-5. NAI should support programs to validate numerical tools using ground-based and/or airborne testing. Summary Lightweight reusable fuel tanks and highly integrated structures are significant contributors to increasing the overall system margin and the payload fraction of launch vehicles. Since the 1970s, NASA has been performing R&D on hypersonic airframe integration, with intermittent progress. The X-30 NASP exemplifies NASA’s involvement in this area. Key airframe technology shortfalls were identified and risk assessments were made following NASP (McClinton, 2003). The NGLT value stream process—which is an interactive, multidisciplinary process to guide technology development—appears to be mature. Detailed work breakdown structures and various technology shortfalls are identified (McClinton, 2003). However, funding levels were not available to the committee. Generally, these programs have a goal of safe, affordable access to space while supporting DoD’s recently elevated interest in Global Strike, Global Response, and Responsive Access to
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Evaluation of the National Aerospace Initiative Space. Some airframe technology metrics, technology readiness levels, technology gaps, and value streams have been established. A disciplined technique called goals, objectives, technical challenges, and approach (GOTChA) has been used to identify and map some technology development targets (DDR&E NAI, 2003). This technique was used to generate a state-of-the-art development plan. However, no detailed GOTChA was observed for the other 17 constituent technology areas listed in the second column of Table 3-1. Recommendation 3-6. Congruent roadmap taxonomies with consistent metrics and TRL goals should be established between the NASA NGLT program and the NAI GOTChA results. Recommendation 3-7. Project-level descriptions of airframe technology development approaches should be developed, integrated, and facilitated across government, industry, and university participants. Propulsion The state of development of rocket propulsion vis-à-vis that of air-breathing propulsion points to the exclusive use of rocket propulsion in the near and medium term (2003-2015). By 2015, air-breathing propulsion may have advanced enough to put small assets (<500 kg) into LEO as the first stage of a system with a rocket-propelled second stage. Heavy lift (2,000-20,000 kg) with air-breathing propulsion will only mature in the far term (2025 and beyond). Turbine engines must be significantly scaled up in thrust and in Mach number capability if they are to support heavy-lift horizontal takeoff. Also, airframes must be developed with adequate support systems—TPS, structures, materials, controls, and so forth—to be viable. (Development of these support systems would also benefit rocket propulsion vehicles but might go beyond what is required by rocket systems.) The development work to enable a reusable, heavy-lift, air-breathing propulsion vehicle will be extensive, costly, and require basic research in many areas. Therefore, in the near to medium term, reusable, rocket-propelled, heavy-lift vehicles that take off vertically and land horizontally appear to be the best approach to meeting the access-to-space requirement. The assessment in Table 3-2 considers rocket-propelled vehicles and follows the taxonomy specified by the NAI program (DDR&E, 2002). It should be noted that the NASA NGLT program not only targets reduced cost, faster turnaround time, and more reuse than the current shuttle capability but also specifies a lift capability of 30 to 50 metric tons. Only NASA has embraced this requirement. The cost reduction that might be realized from increased vehicle utilization will not materialize if NASA remains the only entity requiring this high-lift capability. Finding 3-9. Only NASA specifies a requirement for a reusable, heavy-lift (~40 metric tons) space launch vehicle. Recommendation 3-8. NASA should reevaluate its heavy-lift requirement. A trade study between high lift capacity and alternative approaches to meeting mission needs utilizing a common vehicle should be conducted, especially in light of the recently demonstrated ability to construct a large space structure, the ISS, in orbit. Adjusting the NASA lift requirement to match that of other users (e.g., DoD) would increase utilization and save billions of dollars for the development of a unique, low-flight-rate vehicle. A TSTO approach with a liquid oxygen (LOx)/HC first stage and a LOx/liquid hydrogen (LH2) second stage appears to be the configuration baseline on which propulsion improvements are to be made. The goals are to reduce the failure rate, increase specific impulse (Isp), reduce hardware and
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Evaluation of the National Aerospace Initiative of automation and the potential to automate. The NAI plan proposes to examine emerging system architectures for ground-handling requirements and approaches, including automated mating and assembly, component sensing and locating, and rapid ground power connections. Umbilicals containing propellant, electrical power/signals, and cooling fluid connections require a significant amount of attention to maintain in reliable states. NAI intends to develop smart umbilicals to drive down the recurring cost and support high-tempo operations. These devices will automatically align themselves to the correct mating position and then perform a built-in test function. Nonpyrotechnic release technologies will be incorporated into the umbilicals to avoid the serial processing generally required when handling hazardous materials. Research into the automated handling of hypergolic fuels will also be initiated. The criticality value assigned to system calibrations is due mainly to the need to calibrate flight safety-critical landing aids. The overall criticality of automated operations has been rated “high” due to its significant contribution to manpower reduction and safety enhancements. Integrated Range Network Architecture Current range safety tracking and communication systems at the Eastern Test Range are based on 1950s technology. These systems, located near the launch site and spread many miles down-range, are very expensive to operate and maintain. Another hindrance is their inability to handle more than one launch vehicle in any 48-hour period. A space-based range architecture would provide a flexible network of tracking and communication links, enabling global launch operations. Furthermore, the only precision landing aid available at the Eastern Range is an antiquated microwave landing system used by the shuttle. Future RLVs will most likely incorporate a differential Global Positioning System (GPS) system owing to its lower costs, increased reliability, and growing acceptance as a global standard precision landing aid. NAI is planning improvements to ground sensors and instrumentation to alleviate the inflexibility of range tracking assets, increase their accuracy, and reduce operating costs. Several projects are planned to accomplish these tasks: Passive metric tracking system, Advanced landing systems using differential GPS, Automated range resource management system, Mobile launch head range system, Integrated launch head air-sea surveillance system, and Range dispersion monitoring system improvement. Finding 3-25. Although large investments in range upgrades have been made over several decades, fundamental advancements in range functions and techniques remain elusive. NAI planning and resources appear to concentrate on improvements in existing systems. Real cost reductions will only come from a genuine paradigm shift in range operations. Recommendation 3-19. NAI should continue to rethink the fundamental requirements and services provided by the range organizations. Experience gained in many years of military remotely piloted vehicle operations should be incorporated into the range concepts of operation. Finding 3-26. The development of a secure advanced differential GPS landing aid will provide the most universal benefits applicable to all future RLVs. Recommendation 3-20. NAI should concentrate appropriate resources to develop a secure advanced differential GPS landing aid.
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Evaluation of the National Aerospace Initiative The criticality of integrated range network architecture has been rated “medium” owing to the paradigm shift required to produce significant cost savings. Intelligent Inspection Systems to detect and isolate component or system failure have been in use for many years. Integrated vehicle health management (IVHM) systems not only perform those functions but also should identify part degradation and assist in vehicle maintenance. They could also enable a system to mitigate a failure by reconfiguring itself well enough to continue the mission or safely abort. An often used example is the detection of an impending engine failure during a multiengine assent. Failing engines may be throttled back (or completely shut down) prior to failure and other engines throttled up to compensate. The IVHM system could also notify the vehicle management computer (VMC) to alter the flight trajectory into a more benign environment. Development of such systems could help increase system safety and mission reliability. It could also greatly reduce operation costs by driving down scheduled maintenance and inspection hours. This technology will show tremendous benefits if and when it progresses to the point of predicting a premature component failure by examining real-time sensor data. Reaching this level of sophistication will require a significant investment. If the technology succeeds in this task, other subtle questions may surface. For example, will the decision authority authorize the next flight if the IVHM predicts the failure of a critical component on the second flight? Questions such as this should be fully examined in the course of this research. If successful, the payoff for developing IVHM systems could be substantial. Autonomous systems with embedded knowledge enhance operability while reducing highly skilled touch labor and enhance safety of hazardous operations and greatly enhance the overall responsiveness of the system. Automated postflight inspection is another avenue toward significant cost savings. Specifically, reducing the time and manpower required for the inspection of large-acreage TPS and cryogenic assemblies could reduce the turnaround time and recurring costs of any RLV. These vehicles typically endure damage from both launch and orbital debris. TPS must be revalidated prior to each flight. Automatic detection and evaluation of impact damage via a scanning sensor would be of great benefit. The criticality of intelligent inspection has been rated “high” due to a significant potential reduction in turnaround time and postflight manpower requirements. Security Space systems require protection against unauthorized penetration of both facilities and electronic systems. Finding 3-27. Although the security of space systems is vitally important to successful operations, very little security technology is unique to the space operations arena. Recommendation 3-21. NAI should harvest and incorporate advances in security technology and techniques from sources outside the traditional aerospace community. The criticality of security has been rated “low” since the technologies generated elsewhere can be imported as needed. Summary Launch operations is a key driver for total space lift costs. However, spending in some areas should be gated until a clear understanding of the final vehicle configuration emerges. Other
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Evaluation of the National Aerospace Initiative technologies should be actively pursued to ensure they are ready when needed to realize the NAI program goals. Mission Operations The major NAI needs identified for mission operations are rapid mission planning (for the military), rapid response (for the military), on-orbit servicing and orbit transfer capability (both military and civilian), and affordable launch (both military and civilian). Affordable launch was discussed previously. Rapid mission planning for military operations is required to respond effectively to threats. The need for situational awareness and for flexible systems that can adapt in near real time to changing mission requirements is increasing (Morrish, 2003). Space technologies for command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) were identified as part of NAI but are beyond the scope of this access-to-space section. However, the ability to plan and launch missions effectively depends on global situational awareness and inputs from C4ISR. The ability to rapidly plan missions requires communications architectures matched to the situational awareness. Efficient mission planning requires automated tools to trade off mission options. These tools must be capable of rapidly making complex trades between options for responding to threats. Tools are being used now by Operationally Responsive Spacelift (ORS) for long-range planning and launch vehicle requirements and evaluation. It is not clear if these tools are adaptable to real-time response planning—for example, which assets to launch in response to a given situation. NASA has extensive mission-planning tools for its missions, but these are either not designed for rapid response, or are extremely specialized to science missions. Mission planning tools must take into account surveillance and communications before the onset of hostilities, which space assets are capable of responsive launch and on-orbit checkout, the ability to launch on schedule (prehostilities), the ability to plan for persistent on-orbit presence, quick reconstitution of on-orbit assets, and quick launch to support tactical needs. These tools will need to be developed or upgraded from their current status. Range tracking, that is the detection of the position and condition of vehicles during launch and landing, is currently a safety requirement. This function (see also “Launch Operations,” above) is currently tied to fixed range systems for launch vehicles, but there is a desire to make the tracking of launch and landing independent of fixed locations to provide flexibility in launch and landing location and to facilitate rapid response (Morrish, 2003). The NASA tracking and data relay satellite system (TDRSS) and the Global Positioning System (GPS) were identified as the basis for such systems. DARPA’s Responsive Access, Small Cargo, Affordable Launch (RASCAL) program includes an attempt to demonstrate this capability. DARPA’s RASCAL also proposes to demonstrate 24-hour mission turnaround and 1-hour scramble with aircraftlike sorties. RASCAL is to demonstrate a system that can launch microsatellites into any Earth-centered orbit without requiring fixed, ground-based ranges. A goal is to demonstrate mobile operations from any coastal airfield with a 5,000-ft runway and a system that can adapt in near real time to changing mission requirements. Advances in orbit operations are required by both the Air Force and NASA to increase capability (e.g., for the Space Control mission) and, in turn, reduce costs. Both are focused on moving and servicing space assets. DARPA currently has a program called Orbital Express (it is not part of NAI), which is targeted for demonstrating the technical feasibility of robotic on-orbit servicing, robotic fueling, and orbital replacement unit (ORU) replacement by 2006. Operationally Responsive Spacelift (ORS) requires an orbital transfer capability to reposition/boost orbital assets and perform spacecraft servicing. The AFRL Space Vehicles directorate is working on a military space plane,
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Evaluation of the National Aerospace Initiative which it defines as a space operation vehicle (booster), a space maneuver vehicle (a reusable transfer stage), a modular insertion stage (expendable for affordable space access), and a CAV (for Prompt Global Strike) (DDR&E, 2002). DARPA’s Orbital Express, plus NASA’s planned work on an orbital maneuvering vehicle and its automated rendezvous and docking experience with the Russian Soyuz and Progress vehicles and others, make many of these technologies fairly mature. No funding has been identified for the XTV orbital transfer vehicle shown as part of NASA’s Space Architecture, but the Space Transportation System and Russian technology base should make crewed XTV operations mature. Most existing DoD assets are probably not serviceable, so on-orbit servicing technology would only be applicable to certain future assets that show some economic or performance advantage to being designed for on-orbit servicing. The technology requirements for on-orbit operations are focused on autonomy and associated technologies to make autonomous systems work. Specific technology needs are identified in Table 3-6. Finding 3-28. Mission operations are hindered by the long-lead planning, antiquated range processes and requirements, and the arduous overhead that is imposed on space mission operations. These obstacles stem from a combination of factors—some are from 40 years of heritage and others from vehicle-unique constraints imposed by current vehicle designs. Recommendation 3-22. Consider mission planning, quick response, and on-orbit operations as prime requirement drivers in the next series of vehicle designs. Specifically focus on an integrated program to develop the technologies needed for faster, more affordable operations. Software All aspects of the National Aerospace Initiative rely heavily on the use of software for successful applications. These include the three NAI major pillars: hypersonics, access to space, and space technology. One cannot imagine any aspect of this initiative that could be successfully completed without the use of modern-day computers and software. In fact, the software aspects often are one of the most costly items of the system life cycle. It is imperative that NAI reduce software costs and software errors if the initiative is to be successful. The widespread, pervasive use of software throughout all programs related to the NAI is both a blessing and a burden to the program. The blessing is that there is much current work under way throughout the country, both in industry and academia, that can be used in the program. However, many of these programs must be focused specifically on NAI problems for NAI to be completely successful. This should not be difficult to make happen considering the high-level visibility of the NAI. Software evaluations are provided in Table 3-7. Open Architectures The criticality of open architectures was ranked “medium” because of the large body of work both in industry and in academia to solve these problems. Many of the presentations given to the committee listed these areas in the late 6.3 category, with TRLs of 6 or above. Modularity The probability of achieving the NAI goals of modularity is ranked “high.” This is because much work on plug-and-play interfaces has already been done and is continuing. This work is in the late stages of development by industry and was covered in many of the presentations to the
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Evaluation of the National Aerospace Initiative TABLE 3-6 Status of Technologies for Mission Operations NAI-Defined Technology Areas Committee Evaluations Constituent Technology Ratings Major Technology Area Constituent Technology Current Maturity Level (1-5) Relative Impact on Major Tech Area (Negligible, Little, Moderate, Significant, Extreme) Likelihood of Achieving in Time Frame (Current Funding Level) (Low, Medium, High) Relative Criticality of Major Technology Area (Low, Medium, High) Rapid mission planning—mission-unique constraints and analysis Integrated mission planning tools 2 Moderate Medium High Mission unique constraints and analysis 1 Significant Medium Rapid mission response Range tracking 3 Moderate High Medium Launch and landing flexibility 2 Significant Medium Command and control 3 Moderate Medium Air traffic management 4 Little High On-orbit operations Autonomous GNC 3 Extreme Medium Medium Proximity operations 4 Significant High Grapple, soft dock 2 Moderate High Fuel/consumable transfer 2 Little Medium ORU transfer 1 Little Medium Orbit-assembly-compatible structures 4 Significant High Rapid sensor initialization 3 Extreme Medium committee. This does not mean that some additional effort is not required to make these interfaces suitable for aerospace applications, but they are currently well developed generally speaking. Engineering Design Software Multiple engineering design software issues are very critical to the success of the NAI. The good news, however, is that there is a large body of work under way in all areas of engineering software. Several organizations presented their work to the committee. The areas presented covered combustion flow and analysis, simulation of aero control, stability and autopilot design, hypersonic inlet and nozzle design, thermal structural design, and propulsion system design. Most of these areas were being studied in the late 6.3 research category with moderate TRLs.
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Evaluation of the National Aerospace Initiative TABLE 3-7 Status of Technologies for Software NAI-Defined Technology Areas Committee Evaluations Constituent Technology Ratings Major Technology Area Constituent Technology Current Maturity Level (1-5) Relative Impact on Major Tech Area (Negligible, Little, Moderate, Significant, Extreme) Likelihood of Achieving in Time Frame (Current Funding Level) (Low, Medium, High) Relative Criticality of Major Technology Area (Low, Medium, High) Open architectures Secure wireless communications 3 N/A High Medium Modularity Plug-and-play interface 4 N/A High High Engineering design software issues Combustion flow analysis 3 Significant Medium Medium Simulation of aero control, stability, and autopilot design 4 Significant Medium Hypersonic inlet/ nozzle design 4 Significant Medium Thermal structural testing 4 Significant Medium Propulsion system design 2 Significant Low Quick modification 3 N/A Medium Medium Verification and validation Parallel processing 2 Little Low High Prediction of vehicle performance 2 Significant Low Autonomous flight control (transportable) Vehicle to vehicle transportability 2 Moderate Low Medium Secure, wireless communications 4 Little Medium Automatic decision-making process 2 Significant Low Autonomous software for integration and test process 2 Little Low Software engineering Reliable, error-free codes 2 N/A Low High
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Evaluation of the National Aerospace Initiative Quick Modification The committee was presented a reasonable amount of work addressing quick software modification of aerospace equipment and facilities. The work reported in this area had technology readiness levels of 5 and above and was therefore regarded as “medium” in criticality. Verification and Validation The relative criticality of software validation and verification (V&V) is ranked “high” because of the potentially catastrophic consequences of software errors and because of the extraordinary expense necessary to accomplish the task. Software verification is cumbersome and labor intensive. Research should not only concentrate on unique aerospace V&V issues but should also capitalize on the latest techniques being generated by the civilian software industries. Autonomous Flight Control Transportable, autonomous flight control has a number of critical areas to be addressed: vehicle-to-vehicle transportability, secure wireless communications, automatic decision processes, and software for autonomous integration and test processes. These areas are all in the early stages of applied research (6.2) with low TRLs. In particular, basic research should emphasize the automatic decision-making process. Software Engineering The software engineering area requires considerable work to develop reliable methods for generating and checking code. This is a very important area of research, with much work being done throughout the country, both in industry and academia. However, the state of development in this area is still judged to be low, and there are many opportunities for major breakthroughs if NAI gives it sufficient attention. TECHNOLOGY EMPHASIS IN THE NEXT 5 TO 7 YEARS Many areas of research require attention under the umbrella of the National Aerospace Initiative. This section delineates those that might be brought to bear on near-term applications (e.g., the military space plane or the next-generation launcher.) This is not to say that long-term technologies presented in the following sections should be discontinued—in fact, all technology presented in both groups must be pursued in parallel and given appropriate weighting. Technologies having the greatest probability of enhancing the near-term goals of NAI are advanced materials for use in propulsion and thermal protection systems, electrical/hydraulic power generation and management, software transportability, integrated structures, and error-free software generation and verification. Furthermore, the development of computational analysis tools and methodologies should be emphasized—especially when coupled to test analysis and ground test facilities. Propulsion research work should focus on all technologies contributing to engine reusability and reliability, such as the development of new engine materials that will support combustion of both hydrocarbon and hydrogen fuels. Additionally, advances in health management technologies would pay dividends in safety, extend engine life, and lower maintenance burdens. Additional work in the materials area should focus on the needs of high-strength, LOx-compatible materials, lightweight durable thermal protection materials, and structural materials useful in
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Evaluation of the National Aerospace Initiative new airframe designs. Durability should be the prime consideration in the development of these materials. The need for this work was emphasized in an earlier National Research Council report on hypersonics (NRC, 1998). Additional materials research must be focused on the need for reusable fuel tanks. Both the DoD and NASA will benefit by leveraging work being developed by DOE for electrical power management and control. In this general area, advances in intelligent sensors and vehicle system thermal control should be sought by the NAI. Multiple programs being supported by the DoD and other agencies might be applicable. Finally, the coupling of high-performance computing (numerical analysis) with emerging capabilities in ground test facilities (diagnostics, analysis tools, and methodologies) appears to show great promise in reducing the cost of vehicle development. Finding 3-29. Milestones depicting the start of operational vehicle full-scale development have been established. The goal of NAI is to develop the underlying technologies to a level sufficient to support the decision milestones. The committee was not given a clear policy specifying the desired technology development thresholds at the milestones. Underlying technologies must be ready for full-scale engineering development at the appropriate decision points delineated in the NAI time-tables—2008, 2015, 2018, and 2020 (Rogacki, 2003; Sponable, 2003). Significant flight test activity must also be completed prior to these decision points. Considering the short time between now and the end of Phase I in 2008, it is unlikely that the underlying technologies can be developed in time to meet the Phase I goals depicted in Figure 3-1. Finding 3-30. The United States has failed to sustain many X-vehicle programs through completion of their flight test phase. Consequently, many years of technology advances have been prematurely halted and remain unproven in flight. Recommendation 3-23. DoD and NASA should develop time-phased, reusable, rocket-based flight demonstration programs to move these and other near-term, unproven technologies through flight test; specify and disseminate the technology readiness levels and specific exit criteria necessary to support the operational decision points; ensure that research is directed toward obtaining the specified data and that the demonstrations—both flight and ground—are structured to obtain the required information and data; concentrate on technologies that contribute to reusability; and fund multiple copies of each design to mitigate potential loss of the entire program if a single vehicle is lost. Finding 3-31. Advances in lightweight, high-strength materials—especially TPS, energy storage, and engine LOx-compatible materials—can make significant contributions to mass fraction and reusability. Recommendation 3-24. DoD and NASA should strongly support basic and applied materials research programs. They should focus materials research in support of reliable, reusable, long-life, low-weight TPS, energy storage, and rocket engine systems. Finding 3-32. Rocket-based RLVs are technically feasible in the near future and may provide lowest life-cycle costs for responsive, high launch rate requirements. Finding 3-33. Achieving aircraftlike operations will require higher margin, more robust vehicles, and more efficient ground operations than current launch systems, as well as automated flight planning operations.
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Evaluation of the National Aerospace Initiative Recommendation 3-25. Adequate margin should be incorporated into all aspects of the next generation launch vehicle design. If necessary, payload capability should be sacrificed to achieve robust design goals. Finding 3-34. Software is one of the most demanding and expensive aspects of any modern aerospace vehicle. Delays in software development ripple throughout the entire development process and significantly increase the overall cost of projects. Recommendation 3-26. DoD and NASA should, through NAI, support a comprehensive research capability devoted to lowering the costs of aerospace software production. This research should concentrate on the safety-critical nature of aerospace software. BUDGET SCENARIOS The statement of task asks the committee to consider two budget scenarios for the development of NAI timelines: one that recognizes the current constrained Air Force budget, assuming no additional NAI funds are allocated, and one that meets the optimal NAI development timelines as developed by the committee. A rough order of magnitude estimate of the difference is also requested. The following paragraph addresses these requests only for the Air Force rocket-based access to space budgets. Projected specific and related funding of AFRL space access efforts averages more than $100 million per year through FY 2009 without additional NAI-designated funds. This funding encompasses both upgrades to current expendable launch vehicles and technology for reusable systems. The NAI envisions a multiphase demonstration program with increasingly capable reusable vehicles available in 2009, 2015, and 2018. The development of these vehicles is not supported by current budgets. Additionally, while the first of these vehicles would essentially rely on current technology, the advances required for subsequent vehicles would require significant technology funding. The committee estimates that the first demonstration vehicle, the X-42, will cost $1 billion to $2 billion dollars and that subsequent phases will be increasingly expensive if they lead to an operational, high-rate, responsive launch system. In addition to the funding for the X-42, the committee believes it will be necessary to augment the space access technology budget by 100 to 200 percent to develop the requisite reusable systems capability for the Phase II and III systems. LONG-TERM TECHNOLOGY AND PROGRAMS Within the U.S. defense establishment, typical development periods from concept to initial operational capability (IOC) span 18 to 25 years (as they did for the C-17, F-22, FA-18 E/F, V-22, and others). Even the AIM-120 missile (AMRAAM), a relatively small system, took 12 years. This means that, with few exceptions, the concepts now emerging are close to what we can expect to be fielded—if and when the nation commits to improved spacelift capability and the improved effectiveness it provides to the LRS, ORS, and Space Control missions. Can these systems be developed faster and (consequently) cheaper? Yes. Will they be developed faster? Probably not without the impetus of a national crisis or some other cataclysmic precipitating event. Therefore, in the absence of unforeseen revolutionary technology advances, the fundamental difference between near- and far-term capabilities can be defined in terms of incremental advances in current research efforts. The results of this incremental process should not be underestimated. Slight changes in subsystem performance can drastically affect the vehicle configuration, operating characteristics, and consequently the life-cycle costs. A discussion of likely technology advancements follows.
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Evaluation of the National Aerospace Initiative Engine performance will undergo modest improvements in the medium term. A little more Isp and thrust-to-weight ratio can be squeezed out of chemical engines by making the mixture ratios leaner and incorporating lighter weight materials. With higher sortie rates, IVHM should mature to the point of making genuine contributions to safety and lower recurring costs. Higher sortie rates will also tip the economic scales toward automating current labor-intensive mission planning cycles. Aircraftlike ground and flight operations will become reality if vehicles are consciously allocated and constructed with substantial margin. Improvements in TPS materials will most likely result in robust, precipitation-tolerant flight characteristics. Advanced TPS materials may also enable durable, sharp leading edges and the accompanying improvements in maneuverability and operational flexibility they bring. Large-scale, high-Mach turbines might advance to the point of viability for launching low or possibly intermediate size payloads. However, their utility for launching large payloads will be severely challenged considering the extraordinary development and operating costs of multistaged, multifueled, multiengined, extremely heavy, horizontal take-off vehicles. Finally, the most significant advance will likely be seen in the way software is produced. It is likely that the extensive, worldwide resources devoted to software generation can be leveraged to form a development environment capable of producing timely, error-free code. The military space plane has a good chance of becoming the next revolutionary/transformational/ disruptive weapon system. Its development will only add to our already recognized dependency on space systems. Therefore, most space assets—including the MSP—will become valued targets in the eyes of our enemies. Concentrating on defensive maneuver, offensive engagement, and recovery from launch site attack will be necessary to counter the threat and capitalize fully on these emerging capabilities. The technology to produce an MSP currently exists or is very near term. Delaying the decision to field the MSP (while allowing other potentially useful technologies to mature) may or may not result in an overall lower cost system. SUMMARY The committee studied a variety of inputs and reference sources pertaining to the access-to-space pillar of the National Aerospace Initiative. Although NAI is chartered as a technology development effort, the pillar goals are expressed in terms of future operational system characteristics. This approach allows NAI to cast its net across a broad range of possible contributing technologies but necessitates the translation from system characteristics to technology objectives—a process open to some interpretation. Furthermore, without a clear understanding of the eventual system configuration, the specific system characteristics specified in the three-phase pillar could be difficult to justify and may result in expending resources on low-payoff technologies. It is projected that the military space plane, as currently conceived, can perform the PGS, ORS, and Space Control missions in a very cost effective manner. The United States and several other countries currently possess the capability to develop the technology to produce this weapon system in the near term. However, over the last two decades, this country has lacked the conviction to demonstrate the underpinning technologies in flight. A flight demonstration is the next logical step to develop this transformational capability. It is yet to be seen if the emerging Air Force interest in these missions will produce tangible results. Summarized in this chapter is the committee’s analysis and opinion of the NAI plan and the critical technologies that are required to enable the near- and long-term goals of the NAI. In general, the committee finds the NAI space access goals to be operationally relevant, technically feasible, and underfunded to meet the proposed schedule. This chapter has been prepared so that the NAI participants can compare these findings and recommendations with established plans and programs. The recommendations here are therefore intended to serve as input for evaluation.
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Evaluation of the National Aerospace Initiative REFERENCES Published Antonio, M. 2003. Launch services: Too many rockets, too few payloads. Aviation Week and Space Technology. Available at http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?id=news/sb03_12.xml. February 24. Boeing. 2001. Rocketdyne receives $65 million from NASA for next-generation space propulsion development. News release found at http://www.boeing.com/news/release/2001/q2/news release 010522s.html. Accessed on January 6, 2004 . DoD (Department of Defense). 2000. Department of Defense Space Technology Guide, FY 2000-01. Available at http://www.defenselink.mil/nii/org/c3is/spacesys/STGMainbody.pdf. Accessed on January 6, 2004. NRC (National Research Council). 1998. Review and Evaluation of the Air Force Hypersonic Technology Program. Washington, D.C.: National Academy Press. Singer, J. 2003. New test facility to save time, money on RASCAL program. SpaceNews. November 3, p. 9. Williams, K. 2000. Small Companies to Study Potential Use of Emerging Launch Systems for Alternative Access to Space Station. Available at http://www.spaceref.com/news/viewpr.html?pid=2467. Accessed on January 7, 2004. Unpublished Brockmeyer, J.W. 2003. Integrated High Payoff Rocket Propulsion Technologies (IHPRPT). Briefing by Jerry Brockmeyer to a fact-finding subgroup of the Committee on the National Aerospace Initiative. September 29. Candler, G.V. 2003. Synthesizing Numerical Analysis Data to Design and Develop Hypersonic Engines and Airframes. Briefing by Graham Chandler, University of Minnesota, to the Committee on the National Aerospace Initiative. October 7. DDR&E. 2002. National Aerospace Initiative. Access to Space Draft S&T Plan. Rosslyn, Va.: DDR&E. September. DDR&E NAI. 2003. Space Access Taxonomy. Handout given to committee to understand GOTChA process for space access. Rosslyn, Va.: DDR&E, October 22. DeGeorge, D. 2003. Intersection of Air Force Propulsion S&T and the National Aerospace Initiative. Briefing by Drew DeGeorge, AFRL, to the Committee on the National Aerospace Initiative . September 3. Holden, M.S. 2003. Requirements and Facilities for Ground Test of Full-Scale Scramjet Engines at Duplicated Flight Conditions from Mach 8 to 15. Briefing by Michael Holden, CUBRC, to the Committee on the National Aerospace Initiative. October 7. Kastenholz, C. 2003. National Aerospace Initiative (NAI) Payloads. Briefing by Lt. Col. Chuck Kastenholz, AFRL, to the Committee on the National Aerospace Initiative. September 3. Koozin, W. 2003. ORS Operations Concept. Briefing by Walt Koozin, AFSPC, to the Committee on the National Aerospace Initiative. October 7. Lyles, G. 2003. NGLT Briefing to the Air Force Science and Technology Board. Briefing by Garry Lyles, NASA Marshall Space Flight Center, to the Committee on the National Aerospace Initiative. October 7. McClinton, C. 2003. NASA Hypersonics. Briefing by Charles McClinton, NASA Langley, to the Committee on the National Aerospace Initiative. September 4. Morrish, A. 2003. DARPA Programs for the National Aerospace Initiative Objective. Briefing by Art Morrish, DARPA, to the Committee on the National Aerospace Initiative. August 5. Rogacki, J. 2003. The National Aerospace Initiative—A Synergistic Partnership Between NASA and DoD. Briefing by John “Row” Rogacki, NASA, to the Committee on the National Aerospace Initiative. August 5. Sega, 2003. National Aerospace Initiative—NRC Briefing. Briefing by Ronald M. Sega, DDR&E, to the Committee on the National Aerospace Initiative. August 6. Sponable, J. 2003. National Aerospace Initiative Overview. Briefing by Jess Sponable, AFRL, to the Committee on the National Aerospace Initiative . September 3.
Representative terms from entire chapter: