6
Technology Development

The Committee concluded that inadequate attention and funding are devoted to long-term technology development. Such development is a necessary precursor to a new generation of Earth-to-orbit launch systems. The portion of the National Aeronautics and Space Administration (NASA) Office of Aeronautics and Space Technology fiscal year (FY) 1992 budget dedicated to space technology is only $293 million. This amount is much smaller than other FY 1992 NASA program budgets, such as the physics and astronomy budget of approximately $1 billion and the Advanced Solid Rocket Motor Program budget of $465 million.

The availability of reasonably well-validated new technology is essential to carrying out the design and development of engines, boosters, spacecraft, reentry vehicles, their component parts, and the various features of infrastructure necessary for a healthy and robust space utilization and exploration program. As noted earlier, many launch vehicles and systems are based on very old technology. Development of a new system based primarily on currently available advanced technologies holds the promise of significant improvements to U.S. capabilities. The existing situation with respect to technology for new launch systems has come about, to a large extent, because managers are motivated to minimize the number of technical innovations in a new program because too much innovation affects their credibility, and cost and schedule difficulties can arise after program initiation. The paradox is that those who develop technology must have requirements or "targets" on which to base their program expenditures. Without technology readiness, innovations cannot be included in new programs; at the same time, little technology development is authorized without specific programmatic requirements.

After considering both near-and long-term goals in space utilization and exploration, the Committee has identified several areas in which current programs would now be benefiting if certain technology development had been supported in the past. In addition, the Committee urges that technical records and technology development be kept free of security classification to the maximum extent possible. Current, routine classification procedures unduly impede



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From Earth to Orbit: An Assessment of Transportation Options 6 Technology Development The Committee concluded that inadequate attention and funding are devoted to long-term technology development. Such development is a necessary precursor to a new generation of Earth-to-orbit launch systems. The portion of the National Aeronautics and Space Administration (NASA) Office of Aeronautics and Space Technology fiscal year (FY) 1992 budget dedicated to space technology is only $293 million. This amount is much smaller than other FY 1992 NASA program budgets, such as the physics and astronomy budget of approximately $1 billion and the Advanced Solid Rocket Motor Program budget of $465 million. The availability of reasonably well-validated new technology is essential to carrying out the design and development of engines, boosters, spacecraft, reentry vehicles, their component parts, and the various features of infrastructure necessary for a healthy and robust space utilization and exploration program. As noted earlier, many launch vehicles and systems are based on very old technology. Development of a new system based primarily on currently available advanced technologies holds the promise of significant improvements to U.S. capabilities. The existing situation with respect to technology for new launch systems has come about, to a large extent, because managers are motivated to minimize the number of technical innovations in a new program because too much innovation affects their credibility, and cost and schedule difficulties can arise after program initiation. The paradox is that those who develop technology must have requirements or "targets" on which to base their program expenditures. Without technology readiness, innovations cannot be included in new programs; at the same time, little technology development is authorized without specific programmatic requirements. After considering both near-and long-term goals in space utilization and exploration, the Committee has identified several areas in which current programs would now be benefiting if certain technology development had been supported in the past. In addition, the Committee urges that technical records and technology development be kept free of security classification to the maximum extent possible. Current, routine classification procedures unduly impede

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From Earth to Orbit: An Assessment of Transportation Options communication among engineers and scientists, and hamper progress. Reassessment of the criteria for classification is in order. The following are technology development areas that the Committee believes deserve long-term continuing support. PROPULSION TECHNOLOGIES To achieve U.S. space goals for the next century, new, low-cost launch vehicles are necessary. Advanced technology is the foundation for the next generation of space transportation systems and should focus on propulsion because this technology must be well in hand before being designed into any new vehicle system. However, propulsion system technology development should take place in step with other important aspects of launch vehicle and launch system design to reduce costs and improve operational efficiency. Some propulsion technology advances, in addition to the Space Transportation Main Engines (STME), that the Committee believes merit consideration for a new generation of launch vehicles are discussed below. Hybrids The hybrid rocket is a concept in which one of the propellants is a solid and the other a liquid (or gas) (see Figure 3, Chapter 5). Most frequently, this takes the form of a solid fuel and a liquid oxidizer. The higher-energy combinations tend to be of this general configuration. Although this concept is not new, it has generally suffered from a lack of funding in the propulsion industry, possibly because there has been a low priority placed on its technology development despite the recent efforts of the Hybrid Propulsion Industry Action Group (HPIAG)1. The Committee examined various means by which to increase system reliability, such as pad hold-down and motor shutdown prior to launch for propulsion system check and active redundancy. Pad hold-down, generally for five seconds after ignition, makes it possible to shut down a faulty engine and/or abort on the pad, while active redundancy implies the capability of throttling the propulsion system up to compensate for a lost engine. These attributes have been conceded to liquid systems historically but may be possible with hybrid rocket systems. Additionally, the fact that the solid grain is composed of only fuel and contains no oxidizer significantly facilitates system manufacturing and addresses handling safety issues. Further, an oxidizer-free fuel grain which has a greater elasticity than a grain containing a large amount of 1   The HPIAG is an association of 11 aerospace companies interested in hybrid propulsion.

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From Earth to Orbit: An Assessment of Transportation Options oxidizer, may reduce the risk of catastrophic failures associated with cracks in propellant grains or debonds at the case. The ability to control the flow of liquid oxidizer permits throttling and engine shutdown. An investment should be made in demonstrating the technology necessary to validate the engineering practicality of the hybrid rocket motor for large, high-thrust, strap-on applications. As envisioned, the fuel grain would be a hydrocarbon type and the oxidizer would be liquid oxygen. Technology efforts need to be directed to demonstrating satisfactory combustion characteristics along the length of the fuel grain and minimizing the residual fuel at the completion of burn. This includes tailoring the internal geometry of the motor to achieve the best combination of these characteristics. The combustion process needs to be free of oscillations that may introduce unacceptable stage vibrations or detrimental internal conditions. These investigations must be accomplished at a scale that is large enough to be representative of a full-scale booster motor, but sufficiently small to keep costs affordable. This development activity might include tests at a variety of thrust levels to permit the establishment and evaluation of scaling criteria. Hybrid rocket motor development should be advanced to the point that it can be quantitatively evaluated in competition with solid and liquid bipropellant systems designed to directly comparable criteria. This hybrid motor technology should be targeted initially for thrust-augmentation booster applications such as the 135,000-pound payload class vehicle, NLS-1. Modular Plug Engine The modular plug engine, as conceived by Aerojet General Corporation, consists of 12 identical modules arranged circumferentially to form a central, truncated surface, as shown in Figure 4. In addition, each of the modules contains 16 very small rectangular thrusters that burn the propellants and internally expand the exhaust gas, directing it along the central surface for additional, external expansion to the surrounding environment. One may think of the modular plug engine as having a nozzle that self-adjusts its expansion to the external pressure that exists at the vehicle's flight altitude. Thus, in spite of some loss caused by the truncation of the central surface, the modular plug engine is especially well suited for single-stage-to-orbit (SSTO) vehicles because it promises to operate relatively efficiently at low and high altitudes without mechanical nozzle extensions. Its fully modular design may greatly simplify the logistic and maintenance operations, thus reducing turnaround time. Also, a novel platelet2 construction promises practical and cheaper fabrication of small thrusters. Although the actual performance 2   Platelet construction permits accurate fabrication of small propellant passages required for cooling and injection.

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From Earth to Orbit: An Assessment of Transportation Options FIGURE 4 Modular plug engine. Courtesy of Aerojet General Corporation. data for such engines are meager, some analytical studies indicate that the plug engine could do the job of propelling the Delta Clipper (DC-Y) into orbit with a payload of the order of 20,000 pounds. When developed, this engine also could conceivably be used effectively in other launch vehicles. Therefore, the Committee recommends that research to provide the missing data and the development of components be continued. Modular Bell Engine Recently, the Strategic Defense Initiative Office (SDIO) proposed the development of a new, modular bell engine3 designed for rapid turnaround operations similar to those of an aircraft, including provisions for thorough monitoring to allow regular, scheduled maintenance. The modules of this engine consist of a combustion chamber and either a short nozzle or an extendable two-position nozzle. Since modules are not identical, some advantages of full 3   Multiple thrust chambers with a single turbopump.

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From Earth to Orbit: An Assessment of Transportation Options modularity would be lost. Nevertheless, the engine is similar in concept to the successful Russian RD-170 engine.4 Its development risks and the development time in all likelihood will, therefore, be relatively small. The Committee recommends that studies of the need and advantages of the proposed engine be made and that research be supported to investigate critical technologies. Virtual Staging Engine Concepts The ability to incorporate the advantages of both denser propellants and higher performance propellants in a single stage or vehicle is known as virtual staging. Such concepts could be enhancing for a SSTO rocket-powered concept. Denser, lower performance propellants result in a more compact propulsion system. For this reason, liquid-oxygen/hydrocarbon engines have been used for first stages and for strap-on boosters. The same reasoning makes solids or hybrids attractive as first stage boosters. Alternatively, a less-dense, liquid-oxygen/liquid-hydrogen fuel combination is used in upper stages to provide higher performance, even at the expense of much bulkier tankage. Current NASP-related research on slush hydrogen, a denser form of liquid hydrogen, may lead to a more compact, higher performance fuel for the future. Combining the attributes of both denser propellants and higher performance propellants through virtual staging could prove beneficial in future systems. Two concepts of virtual staging are discussed below: Dual-Fuel Engines: The engine is designed to operate with liquid oxygen and a hydrocarbon fuel at launch and then convert to liquid-oxygen and liquid-hydrogen operation at some point later in the flight. Studies have indicated that the hardware may be compatible for such operation, but issues remain to be fully evaluated in the hot firing environment. Variable Mixture Ratio Liquid-Oxygen/Liquid-Hydrogen Engines: The concept is to run the engine on an oxidizer-rich mixture ratio (12:1) for boost operations, then shift to a fuel-rich mixture ratio (6:1) for the high-performance, sustained operation to orbit. The problem is that to make such a shift, the engine must transition through the stoichiometric mixture ratio which yields the highest temperatures of engine operation. Engine control and the means to affect the mixture ratio transition are critical technologies. 4   The RD-170 engine cluster consists of four identical thrust chambers and nozzles and, therefore, is fully modular.

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From Earth to Orbit: An Assessment of Transportation Options Nuclear Propulsion and Power The Committee reviewed nuclear thermal and nuclear electric technology for space applications. At this time, it appears that the most likely potential applications of nuclear propulsion involve transportation beyond Earth's orbit. For example, many studies have shown that a nuclear thermal rocket, with a specific impulse roughly double that attainable with hydrogen-oxygen propellants, could cut in half the initial mass required in low-Earth orbit (LEO) for a human Mars mission. Similarly, nuclear-electric propulsion could greatly reduce the mass required in LEO for unmanned precursor missions or for cargo transport for human missions. There are at least three possible technological approaches to the nuclear-thermal rocket that hold promise for future space exploration missions: (1) reactors based on the 1970s Nuclear Engine Rocket for Vehicle Applications (NERVA) program, (2) pebble-bed and particle-bed reactors, and (3) the tungsten-cermet fueled fast reactor. All offer considerably higher specific impulse than chemical propulsion. Only the NERVA program has been carried to the stage of engineering demonstration; the feasibility of the others has yet to be demonstrated. In addition, the SP-100 nuclear electric power system has been underway for many years and could enable economical unmanned exploration as well as provide a source for high levels of power in remote locations such as the moon or Mars. In the context of this study, nuclear power and propulsion systems are of concern to the Committee primarily because of their potential impact on the Earth-to-orbit launch requirements as future payloads and are factored into the projected needs for space exploration. The Committee recognizes that carrying such nuclear payloads to Earth orbit requires a thorough understanding of safety under all conceivable emergencies. At this time, the Committee does not consider nuclear propulsion suitable for use in Earth-to-orbit launch vehicles, even in upper stages. Nevertheless, the potential benefits in other applications could be great, and continuing investment in research and development could have high future payoffs, presuming the inherent safety issues are adequately addressed. COMPONENT AND GENERAL TECHNOLOGIES Materials Technologies The next generation of launch vehicles should be guided as much as possible by a flexible philosophy of design and manufacturing that embodies the concurrent engineering of materials and their applications. Materials engineering should be considered throughout planning and development of any new launch system and should play a central, integrated role in the design

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From Earth to Orbit: An Assessment of Transportation Options process. In addition, a vigorous program of generic research in structural materials for space propulsion should be maintained independently of the development of particular vehicle systems. Composites made up of ceramic or intermetallic matrices reinforced by ceramic fibers are promising for elevated-temperature engine applications and may contribute to significant improvements in engine thrust/weight ratios. Similarly, conventional polymer-matrix composites and new aluminum alloys, as well as ceramic-fiber-reinforced metal-matrix composites, may permit substantial weight reductions in vehicle structures and tanks. Improved structural mass fractions may also result from the introduction of advanced monolithic metals and alloys. In all cases, rigorous test programs are essential to determine the extensive array of physical properties that are required for the characterization of new materials before they can be used in the design and fabrication of launch vehicle components. Research on methods of quantitative nondestructive evaluation of materials and structures, and the exploitation of such techniques, is strongly encouraged. The Committee recommends renewed emphasis on materials research and development for the engine environment and for modern airframes, as well as nondestructive evaluation techniques. Health Monitoring of Rocket Systems Pad hold-down with engine shutdown and throttleability are considered highly desirable attributes of a new family of vehicles. Hence, innovative methods are needed to monitor the propulsion system and implement any required shutdowns at appropriate locations. There was no evidence presented that this design approach is being addressed in the National Launch System (NLS) program as it currently exists. Connectors and Interfaces for Fuel and Electrical Systems The technology incorporated in current launch vehicle liquid propulsion systems is rooted in the 1960s. A reliability analysis5 indicated that 50 to 70 percent of propulsion system failures occur outside the engine itself. There needs to be an investment directed to upgrading propellant feed system technology, with an emphasis on improving system reliability and simplifying launch operations and serviceability of these components. The design process should include analyses to trade off the reliability and serviceability of fixed connections as opposed to other types. 5   Leonard, B.P. 1991. Projected Launch Vehicle Failure Probabilities With and Without Engine Segment-out Capabilities. L-Systems, Inc. El Segundo, Calif.

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From Earth to Orbit: An Assessment of Transportation Options The Committee believes that reusability of launch systems will come with time and encourages the development of technologies toward that end. The design of interfaces to facilitate quick disconnect and reconnect of propulsion system components is essential to achieving that goal. Research on such concepts must be supported to facilitate on-pad checkout of system operability. Guidance, Navigation, Control, and Autodocking In reviewing the proposed missions, vehicles, and potential schedules, the Committee identified guidance, navigation, and control (GN&C) as an area in which technology development carried out in the near future would enable superior vehicle and mission capability. Two specific items that could have definite application are (1) a modern, miniaturized GN&C system and (2) an automatic, unmanned docking capability within this GN&C system. The current progress in solid-state guidance components and fiber-optic gyroscopes suggests that flightworthy systems could be available in time for early missions of the proposed new vehicles. The advantages to be gained include lighter weight (redundancy), ruggedness, less sensitivity to the environment, and reduced manufacturing cost. There is also the attractive potential for updating systems based on the Global Positioning Satellite System. Unmanned docking capability has not previously been required by NASA. However, such a requirement seems likely for Space Station Freedom and space exploration. It appears that a suitable system could be derived from former Soviet Union (FSU) systems or could be assembled from more modern components. Even if new U.S. technology were employed, there would be some benefit from international cooperation with the FSU in this area. Launch Operation Technology Needs Launch operation concerns are wide ranging. They encompass closed aft compartments, fluid system leakage, conditioning of the cryogenic systems, bleeds and purges, and the need for external gas supplies for turbopump spin-up for start operations. Many of these issues can be resolved in the design of a modern launch system, but some will require new technology. For example, the issue of leaks dictates research on eliminating devices that may have the potential for leaks as well as on methods of detection that can survey a large area, determine that leakage is occurring, and isolate the location of the leakage to permit repair without extensive invasions into the vehicle system. The vehicle and engine health monitoring system is an essential ingredient for the automated checkout of the system(s) on the pad. Technology needs to be advanced that permits both launch system readiness and in-flight status evaluation.

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From Earth to Orbit: An Assessment of Transportation Options For example, a single-stage-to-orbit vehicle promises significant reduction in the number of interfaces that must be dealt with on the launch pad and, hence, the time required in launch preparations. The technology to enable such a vehicle will also serve to simplify launch operations. Similarly, the modular engine approach permits a significant reduction in the total number of components over a conventional propulsion system.6 This, in turn, reduces the complexity of launch servicing and checkout operations on the launch pad. Technology development is needed in the algorithms for the control system that permit selective shutdown of components and rerouting of propellant flows to ensure successful propulsion system operation. Manufacturing Technologies A number of overall manufacturing considerations must be included to take full advantage of cost reduction opportunities for any future launch vehicle. These require designing from the outset for producibility, which involves determination of those components, subassemblies, and parts that require close tolerances and those that do not, so that appropriate manufacturing processes can be selected. Technology advancement must be pursued in forming, joining, and machining to ensure that processes that reduce fabrication time, enhance the quality of the resultant parts, and minimize loss and wastage are brought to fruition to support the next generation launch vehicle program. Special attention should be devoted to those technologies that enhance inspection techniques to ensure the quality of manufactured parts and joined assemblies. This should include technology to facilitate in-place inspection of welds in low-pressure feed lines and other, critical, installed propulsion subsystems. The Committee assumes that any new undertaking will incorporate the discipline of total quality management (TQM). CONCLUSION Research and technology development in areas of high potential payoff such as those identified above are critical to the future of the U.S. launch industry. A greater long-term investment must be made to build the technology base for future systems. Critical, enabling technologies not associated with an ongoing program are chronically underfunded, and today's 6   Wong, George. April 24, 1990. Operationally Efficient Propulsion Systems (OEPSS) Data Book. RI/RD90-149-5. Rocketdyne.

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From Earth to Orbit: An Assessment of Transportation Options decisions are hampered by the absence of research and development in the past decades. Underlying research and development provides technical stamina for the future.