Supersonic transport

Equation 25 represents the reaction responsible for the removal of uv-B radiation (280—330 nm) that would otherwise reach the earth s surface. There is concern that any process that depletes stratospheric o2one will consequently increase uv-B (in the 293—320 nm region) reaching the surface. Increased uv-B is expected to lead to increased incidence of skin cancer and it could have deleterious effects on certain ecosystems. The first concern over depletion was from NO emissions from a fleet of supersonic transport aircraft that would fly through the stratosphere and cause reactions according to equations 3 and 26 (59) ... 

Control of nitrogen oxides ia aircraft exhaust is of increa sing concern because nitrogen oxides react with ozone ia the protective layer of atmosphere which exists ia the altitude region where supersonic aircraft operate. Research is under way to produce a new type of combustor which minimizes NO formation. It is an essential component of the advanced propulsion unit needed for a successflil supersonic transport fleet. 

The first commercial supersonic transport, the Concorde, operates on Jet A1 kerosene but produces unacceptable noise and exhaust emissions. Moreover, it is limited in capacity to 100 passengers and to about 3000 miles in range. At supersonic speed of Mach 2, the surfaces of the aircraft are heated by ram air. These surfaces can raise the temperature of fuel held in the tanks to 80 °C. Since fuel is the coolant for airframe and engine subsystems, fuel to the engine can reach 150°C (26). An HSCT operated at Mach 3 would place much greater thermal stress on fuel. To minimize the formation of thermal oxidation deposits, it is likely that fuel deflvered to the HSCT would have to be deoxygenated. 

The following figures were obtained from a brochure produced by the Boeing Company. From these figures determine whether it would have been a good deal for the American taxpayer to support the building of the Supersonic Transport (SST) in the winter of 1971. What other factors should be considered ... 

This report deals primarily with the origins and effects of ozone and other photochemical oxidants. It is limited, more or less, to the problem of urban pollution and to such closely related topics as natural background in the earth s boundary layer. No consideration is given to the stratospheric ozone layer and the effects produced by supersonic transport (sst) emission or halocarbons. 

The main purpose of this chapter is to survi atmospheric concentrations of photochemical oxidants, with emphasis on surface concentrations and the distribution patterns associated with them. The reason for that em> phasis is that the photochemical oxidants that affect public health and welfare are largely concentrated in this region. The whole subject of stratospheric ozone (and its filtering of ultraviolet light and interactions with supersonic-transport exhaust products), nuclear weapon reaction products, and halogenated hydrocarbon decomposition pr ucts is not treated here. 

Johnston, H. S Reduction of Stratospheric Ozone by Nitrogen Oxide Catalysts from Supersonic Transport Exhaust, Science, 173, 517-522 (1971). 

In 1971, Johnston suggested that anthropogenic emissions of NOx from a proposed fleet of supersonic transports (SSTs) could cause a reduction in ozone due to the set of chain reactions (10) and (11). At the time, a fleet of 500 SSTs flying seven hours a day in the stratosphere by 1985 was projected, and based on that, Johnston (1971) showed that the emissions would be expected to lead to significant ozone depletion. This was never realized because of the much smaller use of SSTs than projected. However, a subsequent proposal for the development of a high-speed civil transport (HSCT) raised some of the same issues, as discussed in the following section. 

Perhaps the biggest thrust for the development of high performance polymers over the next 10 years will be in the aerospace industry where materials will be required for a fleet of high speed civil transports (supersonic transports). At a speed of Mach 2.4, an aircraft surface temperature of about 150 to 180°C will be generated. The life requirement of materials at these temperatures will be about 60000 hours. Many different types of materials such as adhesives, composite matrices, fuel tank sealants, finishes and windows will be needed. These materials must exhibit a favorable combination of processability, performance and price. The potential market for these materials total several billions of US dollars. 

Photochemical air pollution in the troposphere results from a complex interplay between sunlight and primary air pollutants emitted in ambient air that leads to the formation of ozone and other oxidizing and cye-irritaling agents. On the other hand, pollutants injected into the stratosphere by such human activities as supersonic transports (SST s) and release ofchlorofiuoro-methancs in air by their use as aerosol propellants and refrigerants may eventually reduce the protective layer of ozone from harsh solar ultraviolet radiation. Although the full impact of injected air pollutants in the stratosphere is not apparent at present, various model calculations show conclusively that the continuous future release of chlorofluoromethanes and NO (NO and N02) would result in substantial reduction of ozone in the stratosphere. 

Two cases have been considered as a possible threat to human healtli > a result of the partial destruction of ozone in the stratosphere (1) injection of NO into the stratosphere by SSTs (supersonic transports) and of H< i by the space shuttle and (2) release of chlorofluoromethanes into the in. posphere. 

Johnston, H. (1971) Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport exhaust, J. Geophys. Res., 173,517. 

PROBLEM 13.23 Nitric oxide emitted from the engines of supersonic transport planes can contribute to the destruction of stratospheric ozone ... 

Atmospheric pollution has become a worldwide concern. With the prospect of supersonic transports fiying in the stratosphere came initial questions as to how the water vapor ejected by the power plants of these planes would affect the stratosphere. This concern led to the consideration of the effects of injecting large amounts of any species on the ozone balance in the atmosphere. It then became evident that the major species that would affect the ozone balance were the oxides... 

Wallace (1975) calculated absorbed doses to passengers for a round trip, for both subsonic and supersonic transport between various city pairs. Some of these estimates are shown in Table 3.8. Doses for a round trip in supersonic aircraft are approximately 70% of those for subsonic speeds, because of the shorter flying time. However, the dose rates in supersonic aircraft are about twice as high as in subsonic aircraft. For a round trip across the Atlantic, the tissue-absorbed doses in passengers may be estimated to be about 2 10" Gy for an SST and 3 10 Gy for a subsonic aircraft, under average solar conditions. 

International Commission on Radiological Protection. A report of the ICRP Task Group on the Biological Effects of High-energy Radiations. Radiobiological aspects of the supersonic transport. Radiobiological aspects of the supersonic transport. Health Phys. 12 (1966) 209-226. 

Use In pumps handling corrosive liquids, protective coating for titanium skins on supersonic transports, disk brakes, etc. 

If hydrogen makes subsonic planes look good, its use in a future supersonic transport (SST) glows with economic promise and environmental health, although studies are still needed to determine whether and how increased water vapor (in itself harmless) might change weather dynamics in the high stratosphere. 

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