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5 Space Transportation Technology
Pages 77-88

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From page 77...
... Thus, the committee suggests that NASA consider modifying the existing goals or adding additional goals to provide ''stretch challenges" for: reducing the overall cost of space transportation, including the launch stage and the final propulsive stage used in orbital transfer minimizing the cost of developing far-reaching space transportation technologies that enable new deep-space missions ' From January 1, 1988, to January 1, 1998, launched operational payloacis (not including rocket stages or debris) reached the following operational orbits: low-Earth orbit (less than 2,000 km)
From page 78...
... Complete or near-compete reuse of hardware will keep replacement costs low. Thus, the most viable way to achieve the NASA goals for low-cost access to space is to develop robust, highly reusable launch vehicles (REVS)
From page 79...
... In addition, the higher drag associated with atmospheric flight reduces the effective specific impulse. Nevertheless, airbreathing engines, in combination with chemical rockets, have the potential to improve payload fraction, be more robust, and would be more reusable than existing expendable launch vehicles, which would result in lower costs per pound of payload to orbit.
From page 80...
... The technical assessment should encompass the following engine concepts: rocket-based combined-cycle engines, including rocket-scramjet systems and rocket-ramjet systems interturbo-rocket engines, including the U.S. air-core enhanced turbo-ramjet engine and the innovative Japanese ATREX cryogenic fuel engine cycles, inclucling LACE-clerivecl engines and the cleeply coo~ed engines explored by the United Kingdom and Russia gas turbine engines incorporating advanced materials and better aerodynamics that could improve thrust-to-weight ratio Fincling.
From page 81...
... Pulse detonation wave engines could provide the equivalent performance of high chamber pressure conventional rocket engines while operating at one-sixth the pressure, representing an increase of ~ 0 to ~ 5 percent in potential specific impulse. Critical technologies for pulse detonation wave engines include scaling limits, process controllability, and fast acting valves for booster-sized engines.
From page 82...
... However, because of the premium on performance, advantages associated with variable expansionratio nozzles will especially benefit REVs, especially single-stage-to-orbit REVs. Although the exact thrust specific impulse benefit will depend on the engine design and flight profile of a given launch vehicle, variable expansion-ratio nozzles enable efficient altitude compensation that increases the average nozzle thrust coefficient over that of a conventional fixed area-ratio nozzle.
From page 83...
... Proposed concepts for study inc~ucle cryogenic solid hydrogen, metallic hydrogen, the carbon and carbon-boron absorptivity of hydrogen, and cryogenic solid oxygen. These propellants could provide specific impulse increases as high as 200 seconds over today's state of the art, and could be the basis for achieving launch costs of less than $100 per pound of pay~oacl to LEo.3 Improvements in performance with solid hydrogen are achieved by exploiting the recombination energy of energetic atomic ingredients, such as boron, carbon, hydrogen, and lithium.
From page 84...
... Notable improvements in chemical propellants, which could be important to the achievement of NASA's space transportation goals, are possible. Potential advances include the recombination of highly energetic atomic ingredients, hydrogen storage at high effective clensities, and the clevelopment of metallic hydrogen.
From page 85...
... Novel Launch System Concepts Achieving the NASA cost goals may require revolutionary concepts and somewhat unconventional approaches to launch systems. Many concepts in this category, such as electric and solar propulsion, solar sails, and most forms of nuclear propulsion, are most appropriate to orbital transfer vehicles or station keeping.
From page 86...
... However, novel launch vehicle configurations and automated launch operations based on systems approaches aimed at reducing costs and increasing reusability appear to have wider applicability and may approach NASA's first launch cost goal. Rove/ Launch Vehicle Configurations Compared to the accepted design configurations for expendable launch vehicles, all REVs in use or being considered are novel or unconventional.
From page 87...
... Aeronautics and Space Engineering Board, Committee on Reusable Launch Vehicle Technology and Test Program. Washington, D.C.: National Academy Press.


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