The problem of reliability is being given considerable attention in designing and testing space station components which will be capable of operating for a year or more on manned missions and for about 10 years in the case of unmanned spacecraft propulsion units. To avoid future propulsion system operational problems, space ignition, venting, and similar problems associated with high energy propellants and new propulsion system designs were being thoroughly investigated.

The new component technology program included intensive effort to devise a thrust chamber for very long duration firings with OF2-diborane propellants. Carbon chamber liners effective with other fluorine-oxidized systems were chemically attacked by the boron compounds. It now appears possible to regeneratively cool a metal-walled chamber using vaporized diborane, and if this is possible, the usefulness of this high energy space storable system may be extended to entirely new applications.

Research on combustion stability and heat transfer continued to make steady progress. Design capabilities for acoustic liners to control stability were improved, and a better understanding of the parameters affecting transpiration cooling was obtained.

Work on the very high energy tripropellant system, Lithium

Fluorine-Hydrogen, was reduced following a very successful feasibility test. A specific thrust of 508 seconds was recorded in an altitude facility-the highest chemical rocket performance yet achieved. However, vehicle analyses show only modest payload improvements over an equally advanced fluorine-hydrogen system, the weight of the three propellant feed systems nearly canceling out the performance increase over a bipropellent system. Work on this project will resume when funding is available and suitable missions are identified.

In the experimental liquid engine systems area, a new approach was made to fabricating the segments of an aerospike thrust chamber. The new method, which involved castings in a copper alloy with an electrodeposited nickel closure of coolant passages, apparently will make it possible to achieve significant cost reductions. The liquid hydrogen and liquid oxygen high pressure engine concept became ready to enter the development stage. It will be the foundation for the main propulsion for the Space Shuttle. At the JPL Edwards Test Site, a test stand was converted to operation with the space-storable propellant combination oxygen difluoride/diborane, and testing of experimental thrust chambers was begun (fig. 4-28). At the Lewis Research Center, another space storable propellant combination, a mixture of fluorine and oxygen (FLOX) with liquid methane, was being studied; it demonstrated high combustion efficiency and good cooling capability. In addition, detailed analyses of engine cycles and component layouts suggested an optimum engine configuration (fig. 4-29).

BASIC RESEARCH

Fluid Physics

A significant advance in gas dynamic laser research was achieved with the demonstration of an all-chemical laser. Developed under NASA sponsorship, the new laser is the first to be activated for continuous operation by mixing commercially available bottled gases. (Fig. 4-30.) This chemical CO2 laser, which requires no external energy sources to excite the reactants, is compact, simple, and efficient. Such lasers are potentially useful for applications in space communications and power transmission to satellites.

The research program on sonic boom prediction and reduction also made good progress. The program provided techniques for predicting the pressure waves from aircraft maneuvering through a nonuniform atmosphere and extended current theories to include

the effects of unsteady winds and atmospheric turbulence. In addition, several theoretical investigations of aircraft configurations indicated that significant boom reductions are potentially feasible; the theoretical concepts to achieve the reductions were being evaluated in the NASA wind tunnels.

Wind tunnel studies were made of the interaction and dispersion of atmospheric pollutants from airborne and ground sources in urban areas. Models of typical buildings and street layouts were tested in a low-speed wind tunnel. The tests indicated that perpendicular to the wind direction, there appears to be low ventilation, or a high concentration of pollutants into the adjacent streets. Figure 4-31 shows this result from a single source of pollution (left) and from multiple sources. The wind, blowing at right angles to the street, creates vortices at the vertical edges of the buildings. The smoke is thus confined in the street, producing a highly polluted

area.

Applied Mathematics

The applied mathematics program is stressing research in information sciences and problems of information utilization. The new information sciences effort is designed to build bases for:

• Automatically recognizing visual patterns (cloud formations, air and water pollution characteristics, crop damage, etc.);

Improving the performance of men and machines through interactive problem solving;

• Storing and retrieving information effectively and efficiently;

Designing self-adaptive machines (or robots) that can perform tasks without the need for direct human intervention;

• Utilizing new mathematical research and discoveries in such areas as linguistics, graph theory, automata theory, logic, and mathematical programing.

• Verifying the correctness of computer programs, leading toward automatic programing.

Although the research is intended primarily to support NASA space and aeronautical objectives, its results should contribute to other technological approaches in pollution, health, transportation, and education.

In pattern recognition research, where recognizing speech automatically has been one of the prime objectives, worthwhile progress was made with the building of a system capable of evaluating competing speech recognition methods quantitatively. (Primary speech recognition methods are statistical analysis of the acoustic wave; linguistic analysis of the distinctive features; and "analy sis-by-synthesis" or modeling the vocal tract and correlating the received signal with a signal that could be produced by a vocal