And Hypersonic Flight

erate equally well on transcontinental routes or at the fringesof space. It could achieve far more economical delivery ofpayloads to space than the existing Space Shuttle.Technology IntegrationThe TAV cannot be viewed as a simple amalgam of unrelatedcomponents. Performance requirements are so highthat every aspect of the design must be integrated withevery other. The very shape of the aircraft must meet theneeds of the propulsion system. Dr. Lee Beach, who headsup the hypersonic flight work at NASA-Langley, put it thisway: "In our terminology, the undersurface of the vehicle,all of it, is the engine. The forebody precompresses theflow coming into the propulsion system. The aft surface ofthe vehicle is the nozzle, designed to divert exhaustsmoothly. In hypersonic vehicles, an integrated airframedesign is not just a performance increment. It's absolutelyessential."The need for cryogenically cooled liquid fuels can alsobe seen from this perspective. Before being burned forpower, the liquid fuel, which has been cooled to cryogenictemperatures near absolute zero, is used as a coolant. Sustainedhypersonic flight means that the wings must operateat high temperatures. Cryogenic cooling systems will beused throughout the TAV to reduce heat at the most criticalpoints.The most important element in the integrated design ofa TAV is the science of hypersonic flow—engineering shockwaves. At high Mach numbers, the Shockwaves created bythe aircraft cannot be treated with conventional fluid mechanicalconcepts. The hypersonic shock produces plasma—ionizationof the air—and the plasma dynamics ofthese hypersonic shock waves play a crucial role in theoperating characteristics of the TAV.It is not coincidental, therefore, that hypersonic pioneerslike Adolf Busemann and Antonio Ferri initiated and pioneeredresearch in the 1950s into the hydrodynamics ofenergy-dense plasma configurations. Today this line of investigationhas led to the development of many advancednuclear fusion concepts, including the spheromak, reversedfield pinch, and compact tori. Afterthe shutdown ofmost NASA projects in the late 1960s and the almost completedisappearance of significant hypersonic aircraft development,however, this highly productive cross disciplinecollaboration between aeronautic and plasma-fusionscientists was disrupted. Hopefully, the reinitiation of seriousTAV development will lead to the rapid resurrection.The Nuclear TAVOne of the original concepts for fueling advanced TAVtransports was the use of nuclear fission reactors. Detaileddesigns were actually developed decades ago for safe, cleannuclear powered aircraft. The TAV has sufficient size toutilize nuclear power, and significant advances in nuclearreactor technology make its potential incorporation intoadvanced TAVs feasible and desirable. The introduction ofnuclear-powered TAVs would make transport into nearspaceorbit sufficiently economical to support large-scalecolonization of space, the Moon, and nearby planets.Theother area that theTAVwill revolutionize is materials.The TAV will operate in a highly stressed environment andmust be durable with a minimum of maintenance problems.The structure for the aircraft must be lightweight aswell as relatively simple to permit inspection with standardnondestructive techniques. TAV materials under considerationrange from advanced metai alloys, such as the quasicrystalmetallic glasses being researched at the NationalBureau of Standards, to advanced composites and ceramics.Two recent developments in resin matrix compositematerials include the new classes of carbon fibers capableof being used in mass production and the new toughresins like elastomer modified epoxies and polyethertherketone,a thermplastic. This particular material, called PEEK,makes a good laminating resin and when so used will givecomposite materials an interlaminar fracture toughness thatis an order of magnitude higher than that of existing epoxyresin-matrix composites.Other materials concepts are being harnessed for moreadvanced propulsion systems. For example, it has beensuggested that metastable helium can be produced in asolid-fuel form by aligning the helium atoms and bondingthem together to produce an excited but stable state. Astrong bonding of the atoms will then provide a solid witha high melting temperature and have a useful life of up toeight years. Its energy content is projected as being 100times greater than conventional chemical fuels.SDI MissionsThe TAV would make essential contributions to the SDIprogram. It could provide a cheaper means for deployingand repairing satellites in space and could provide certainrapid deployment capabilities not possible with alternativesystems. According to the Air Force, "The TAV allows us toconsider new missions for which no capability existed before,while providing an alternative way to perform existingmissions."Keyworth's Office of Science and Technology Policy haspresented a plan to implement many features of the TAVproposal prepared by NASA. The plan would combine federalR&D work on advanced aeronautics to take into accountcivilian hypersonic transport, increase basic researchat universities, increase federal support for advanced aeronauticsresearch, and begin to work out now how TAV willfunction in future air traffic control systems.It is clear that the science and engineering to perfecthypersonic aircraft are possible in the immediate future. Sowith the proper funding, we may soon be able to board thehypersonic Orient Express and in less than three hoursarrive in Tokyo.Charles B. Stevens is director of fusion engineering forthe Fusion Energy Foundation.Notes1. A ramjet has a specially shaped duct open at both ends in which the air forcombustion is compressed by the forward motion of the engine, mixes withthe fuel, and burns: the exhaust gases issue in a jef from the rear. A scramjetis a supersonic combustion ramjet.2. Ramjets utilize high flight velocities to produce the necessary air flow throughtheir engines: turbojets use turbines to generate this air flow.FUSION January-February 1986 57