Air University Review, November-December 1969

Colonel Burl R. Williams

Nuclear fission, the jet and rocket engines, radar, and many other scientific and technical advances have a common thread which relates them: they were heavily dependent upon the achievements of foreign scientists. Accordingly, the U.S. Air Force and Americans generally recognize the importance of scientific contributions that have emanated from all parts of the world. The Air Force in particular is vitally interested in having its military technology broadly based on the latest and most advanced scientific and technical programs, regardless of source.

It has long been recognized and accepted that the United States should be involved in some manner in the scientific activities being conducted in foreign countries. As reported by the International Committee of the Federal Council for Science and Technology in September 1964:

This involvement is a fundamental necessity, because our scientific community cannot remain aloof from the world of science without paying a penalty in terms of wasted and ineffective effort and without missing new advances useful to our society. . . There exist outside our borders unique opportunities in the form of natural conditions, unusual materials, unusually qualified people and special facilities.

At present, the Air Force has about 300 contracts and grants with foreign scientists, sponsored by Air Force laboratories through the European Office of Aerospace Research in Brussels, Belgium. Because of cost-sharing arrangements, the preponderance of the foreign research cost is borne by the foreign countries through their universities, national research councils, and other support agencies. Results of sponsored research are fed directly into Air Force research programs and are widely disseminated throughout the U.S. scientific community through the Defense Documentation Center and the published literature.

Air Force-supported foreign scientists are world leaders in their fields, as evidenced by the international awards and recognition they have received from their scientist colleagues. These foreign scientists contribute to the Air Force in all the basic disciplines: the physical, environmental, engineering, and life sciences.

It is often difficult, particularly for the layman, to ascertain exactly the actual or potential applications of the research that these scientists are conducting. The reason for this was pointed out in a 1966 Project Hindsight report by the Department of Defense, which stated that "delays of 5 to 10 years, or more, frequently occur between a scientific discovery or an invention and the time of its actual utilization." Nevertheless, it can be stated that the foreign research being supported by the Air Force does hold considerable technological promise.

A sample of contractors and grantees and their programs will illustrate the capability of the foreign scientists being supported by the Air Force. This particular selection was made simply to illustrate work being supported in different disciplines. It would not have been possible to make a selection on the basis of merit alone, since all the foreign scientists being supported by the Air Force are eminent in their respective fields.

Professor Porter:
rapid chemical reactions

Professor George Porter has long been recognized as an outstanding scholar, educator, and research scientist. He graduated from Emmanuel College, Cambridge University, in 1949, having studied under Professor Ronald Norrish, with whom he shared the joint Nobel Prize for Chemistry in 1967. After graduation he remained at Cambridge as Assistant Director of Research in Physical Chemistry. Later he accepted an appointment as Professor of Physical Chemistry at the University of Sheffield, where his outstanding abilities led to his appointment in 1963 as head of its Chemistry Department. Since 1966 he has been Director of the Davy Faraday Research Laboratory of the Royal Institute of Great Britain.

Of the many honors that have been accorded Professor Porter, it suffices to say that the Nobel award represented the ultimate in world recognition for his scientific work on "studies of extremely fast chemical reactions effected by disturbing the equilibrium by means of very short pulses of energy."

As Professor Porter has pointed out, one of the principal activities of scientists has been the extension of the very limited senses with which man is endowed, enabling him to observe phenomena beyond his normal experience. Thus microscopes and microbalances allow observation of things of smaller dimension or mass than can normally be seen or felt. In the dimension of time, man is naturally limited to a minimum perception time of about one-twentieth of a second, the response time of the eye. Since most fundamental chemical reactions occur in the range of milliseconds or less, it is important that observations be made in microtime. It is in the field of developing techniques to make these microtime observations and interpreting the resulting data that Professor Porter is such an eminent authority.

The technique that has allowed Professor Porter and others to investigate the rapid reactions which are so fundamental to nature was conceived by him about twenty years ago. This technique, called flash photolysis, has been much improved by Professor Porter over the years. The principle is relatively simple, as is true of so many great scientific innovations. The short-lived intermediate chemical species of interest are produced by a flash of visible or ultraviolet light. The flash must be of sufficient energy to produce the desired measurable overall change and of short duration (approximately 10^-3second) compared with the lifetime of the intermediates. This latter requirement is necessary in order that the resulting transient species may be identified by means of their absorption spectra. The spectrum is obtained by means of a second flash, operating after a short time delay. The spectrum thus recorded can then be interpreted to yield information concerning the mechanism and kinetics of the photochemical reactions that occurred.

The limiting factor of this technique is the flash duration. In December 1968 Professor Porter reported a much improved apparatus utilizing a Q-switched pulsed laser as the energy source. With this innovation it is now possible to observe and study species that have lifetimes in the nanosecond (10^-9 second) range. Although subnanosecond flash photolysis has not yet been attained, picosecond (10^-12 second) laser pulses have been used in other studies, and there is every reason to believe the picosecond laser pulse is capable of being adapted to the flash photolysis technique for rapid-reaction studies.

The contractual relationship between the U.S. Air Force and Professor Porter began in 1957, when he proposed to conduct research on low-level excitation and energy transfer of gases. This field of study was of interest to the Air Force Cambridge Research Laboratories because of their in-house research in the fields of photosynthesis, organic semiconductors, and photogalvanics. His association with AFCRL continued, with the exception of one year, until 1967, when the Aerospace Research Laboratories (ARL) at Wright-Patterson AFB asked him to investigate the primary processes in organic materials. This work is continuing today, partially supported by the Air Force Office of Scientific Research (OSR) in order to complement their long-time research interest in photochemistry.

The research conducted by Professor Porter is a vital part of the OSR program in chemical energetics, which is concerned with various aspects of energy storage and transfer on the molecular level. This information is of interest because it helps define the electronic structure of the system and thus explain its properties. Further, it describes the energy prelude to chemical events such as isomerization or cleavage. These chemical processes involve various beneficial and deleterious interactions of light with matter, and studying these processes will lead to better understanding and thus to improved control of them.  This control is related to such Air Force needs as solar energy conversion devices, photographic imaging, flash blindness protection, and radiation damage control in biological systems. Professor Porter’s unique experience and unrivaled capacity have afforded and will continue to afford further advancement in this vital field of research.

Professor Chauvin:
supersonic compressors

Professor Jacques Chauvin, one of the world’s foremost authorities on supersonic compressors, is head of the Turbomachinery Laboratory at the Von Kármán Institute for Fluid Dynamics, an aerodynamics research facility in Rhode St. Genese, Belgium. The Institute was founded in 1956 by the renowned Dr. Theodore von Kármán and is under the auspices of the North Atlantic Treaty Organization. Professor Chauvin is a Belgian representative to NATO’s Propulsion and Energetics Panel, has been a Visiting Professor at the University of Liége and the University of Brussels, and has frequently acted as a scientific adviser to research institutions and companies in the United States, France, England, Germany, and Belgium.

Professor Chauvin’s research for the Air Force is aimed at developing a supersonic compressor in which the flow exceeds the speed of sound relative to one or more blade rows. This is independent of the vehicle velocity, which may be anything from zero to supersonic, depending on the specific application.  Air Force interest in supersonic compressors relates to their potential performance, which is much greater than that of more conventional, lower-speed compressors. Supersonic compressors offer two special advantages: high pressure ratio per stage and the ability to accept higher subsonic inlet mach numbers than present compressors. The higher pressure ratio means that fewer compressor stages are needed, and therefore a turbojet engine can be smaller, lighter, less complex, and less expensive. The ability to accept higher inlet mach numbers simplifies the problem of designing inlets for advanced aircraft.

It has been known for many years that the key to obtaining these advantages was to turn the compressor at a higher speed. Of course, this is an understatement, and if that were all of the problem, it would have been solved long ago. In fact, an apparently straightforward approach was tried when jet engines were in their infancy but was soon abandoned when tests indicated that compressor efficiency and off-design performance were poor. The central problem is that, as the compressor blades are spun to higher rotational speeds, they are soon moving at the speed of sound with respect to the air through which they are passing. Thus the flow problems here are entirely different from conventional subsonic flow problems. The resultant shock patterns create starting problems, choking of the flow, and severe losses in efficiency.

In the early 1950s Dr. Hans von Ohain and Mr. Elmer Johnson of the Aerospace Research Laboratories conceived a blade approach which promised to overcome the problems experienced with more conventional blades and which potentially would yield high performance over a wide range of mach numbers. This concept was based on diffusion of the flow by a multiple shock system, similar to the diffusion experienced in flow through a straight duct. This flow pattern is extremely complex, but certain characteristics of the flow have been well determined by experiments. One of the most important characteristics is that this flow pattern will always occur under broad and easily determined conditions. Also, diffusion of the shock in a constant-area duct permits operation without the extensive boundary layer separation and associated losses that occur in the conventional blading shock pattern.

A primary feature of this new blading concept is that the cross-sectional area of the flow passage is nearly constant from passage entrance to passage exit. This is accomplished by a continuous increase of blade thickness from the sharp leading edge to the trailing edge, giving the trailing edge a blunt appearance; hence the concept is called the "blunt trailing-edge supersonic compressor."

After this idea was conceived, the Aerospace Research Laboratories let a contract to Professor Chauvin to investigate the problem further. He was selected to participate in the project because of his important achievements in turbomachinery research. Also, the Air Force Systems Command’s Arnold Engineering Development Center was called upon to test certain of the ARL designs. Thus a closely working three-member team has been active in the Air Force’s development of supersonic compressors.

Professor Chauvin has contributed very important innovations. He allowed the channel between the blades to diverge slightly to allow for boundary layer buildup, and he rounded the trailing edges to minimize dump diffusion losses. Also his tests have created a better understanding of the influence of back pressure and distance between rotor and stator. As a result, he has developed a laboratory compressor with an adiabatic efficiency of 87 percent and with very good oft-design performance, which is extremely important.

Professor Chauvin has made it a point to brief U.S. industry frequently on his developments; arid new research designs by American manufacturers often reflect his work, Professor Chauvin is now further developing his ideas for the Air Force, in an attempt to achieve high mass flow rates. He and his American partners are laying the groundwork for substantially improved power plants for military jet aircraft of the future.

Professor Prigogine:
statistical mechanics

Professor Ylia Prigogine is on the Faculty of Science of the University of Brussels. He has been engaged for many years in research in nonequilibrium statistical mechanics. The Brussels group established under his leadership is an international center for nonequilibrium statistical mechanics. Because of the many significant contributions made by him and his group in this field of research, Professor Prigogine has been accorded much international recognition. Among other honors, he has received the Prix Francqui and Prix E. J. Solvay, awarded in Belgium, and the 1969 Arrhenius Medal from the Swedish Royal Academy of Sciences. Professor Prigogine has served as visiting professor at leading universities, such as Harvard, Columbia, California, and Manchester, and has lectured at such international symposia as the Nobel Symposium. He has been accorded membership in leading scientific societies and academies in Belgium, France, Sweden, and the United States. Professor Prigogine has written or coauthored four books that have been standard texts in nonequilibrium statistical mechanics. In addition, he is Director of the Institute of Statistical Mechanics and Thermodynamics, University of Texas.

The Prigogine group is performing very basic pioneering research in nonequilibrium statistical mechanics. The general subject of statistical mechanics involves the study of the particular laws which govern the behavior and properties of macroscopic bodies, i.e., bodies made up of a large number of separate particles (atoms and molecules).

In principle, all the equations of motion of a mechanical system could be written down and then integrated to obtain the motion of the mechanical system. There would be as many equations as there are degrees of freedom. Imagine the number of degrees of freedom in a single system such as a snow flake, which is composed of billions of atoms. The problem with solving such a system of equations is that the initial conditions are unknown. Even if all the initial conditions were known, the largest computer would be severely taxed to solve even the simplest imaginable problem, considering the time and paper required to print out the answer.

Fortunately, there is another approach to the problem, in which a mathematical transformation permits representation of the motion of a mechanical system in phase space. This is not a space in the usual three-dimensional way of considering ordinary space. With this new way of thinking, every system has a phase space with twice as many coordinates as there are degrees of freedom. At first it may appear that the problem has been infinitely complicated, until it is noted that a single point in phase space completely describes the state of a crystal. That is, the single point in phase space uniquely specifies the position and velocity of every atom of the crystal. Hence a significant shorthand has been achieved.

However, the initial conditions are still not known, so only a subsystem of the whole closed system is considered at first. Then the subsystem is permitted to interact with the entire system. After a period of time the subsystem will pass sufficiently through all its possible states. Based on this fact, it becomes possible to construct probability functions and thus determine the probability that a system will have a particular behavior. In this way many interesting functions, such as transport coefficients, hydrodynamic functions, and thermodynamic functions, can be calculated.

The Prigogine group has attacked the broader and more difficult problem of non-equilibrium statistical mechanics by considering the interaction of the subsystems. During the course of this research the group has developed new mathematical and analysis techniques. The results of this work are applicable to a wide range of physical situations of interest to the Air Force in thermodynamics, aerodynamics, hydrodynamics, ionized media, combustion, electric field effect, astrophysics, turbulence, and high-energy physics.

In 1966 the National Academy of Sciences—National Research Council of Washington, D.C., recognized the significance of Professor Prigogines contributions as follows:

The more complex problems of the fundamentals of irreversible statistical mechanics have been attacked only recently by Prigogine and colleagues at the University of Brussels. The understanding of the nature of the approach of equilibrium developed by the Prigogine school represents a contribution to the statistical theory of matter comparable in importance, perhaps, to the work of Gibbs.

(Josiah Willard Gibbs [1839-1903], America’s foremost physical chemist, established the basic theory for physical chemistry during his approximately 50-year career at Yale.)

Professor Vassy:
ionospheric studies

Professor Etienne Vassy is the Director of the Atmospheric Physics Laboratory at the University of Paris, France. He has held such prominent positions as Vice-President of the French Association of Engineers and Doctors, President of the French Committee on Scientific Radioelectricity, President of the Geomagnetism and Aeronomy Section of the French Committee of Geodesy and Geophysics, Chairman of the Joint Commission of the Upper Atmosphere for the International Union of Geodesy and Geophysics, and Chairman of the Commission on Research of the Ionosphere for the Advisory Group for Aeronautical Research. He has been elected an Honorary Life Member of the Academy of Sciences, an organization that has honored him with three "Laureate" awards.

Professor Vassy is a key member of the Joint Satellite Studies Group. This group was formed upon the initiative of the Ionospheric Physics Laboratory at the Air Force Cambridge Research Laboratories shortly after the first artificial earth satellites were launched in 1957. The original role of this group involved the collection and correlation of data for more accurate prediction of satellite trajectories. The members of the group included working parties at observatories in the United States, Japan, Germany, England, Italy, Norway, Sweden, and France, and its original work was significantly important to Project Spacetrack.

During the course of the work for Spacetrack the group found that records of transmissions from satellites showed irregularities caused by heterogeneities of the ionosphere. Signals from the satellites suffered amplitude fading and phase changes in traversing the ionosphere. In effect, the ionospheric irregularities reduced the reliability of transmitted information. These findings were noteworthy, since satellites for communication and navigation were envisioned by the Air Force and other agencies.

To understand more fully the role of the ionosphere and its effects on electromagnetic wave propagation from satellites, the Air Force Cambridge Research Laboratories encouraged the Joint Satellite Studies Group to make a collective effort to derive a synoptic picture of the ionosphere from simultaneous observations of satellite beacons recorded at widely separated locations. Since the disturbing effects of the ionosphere result from different causes and each cause is associated with definite latitude regions, the original group was expanded to include at least one observatory on each continent. With the support of NATO, working parties were formed at observatories in Spain, Denmark, Greenland, Turkey, and Greece. In Africa and the Middle East working parties were organized in Ghana, Kenya, and Israel. Coordination of all activities was vested in the Air Force Cambridge Research Laboratories, and they called upon such prominent scientists as Professor Vassy to guide the efforts of the group. The various working groups are now cooperating to determine the characteristics of the ionosphere from the auroral regions through the middle latitudes to the equatorial regions.

The work performed by Professor Vassy and other members of the Joint Satellite Studies Group is very similar. Teams maintain recording watches to collect data transmitted from selected active beacon satellites. Principal satellites are the S-66 series orbiting vehicles and the synchronous satellites, ATS-1 and ATS-3. In the past, recordings were also made of transmissions from such satellites as Communications Satellite Corporation’s Early Bird and Canary Bird, the U.S. Navy’s Transit 4A, and AFCRL’S ORBIS vehicles. Records of data are forwarded to the Air Force Cambridge Research Laboratories for special analysis. Much of the data is also distributed to various member scientists for analysis of particular ionospheric parameters such as total electron content and scintillation. In processing and analyzing the data, the group generates useful statistics for prediction of ionospheric conditions and the probability of low signal level occurrences as a function of magnetic latitude. These statistics are most essential and necessary in the design of satellite-borne systems.

Professor Vassy has personally made many contributions to systems designers through his Joint Satellites Studies Group activities. He has made a considerable number of measurements of the total electron content of the ionosphere and has given these data particular meaning by evaluating quantitatively the maximum possible error in the calculation of total electron content. He has developed a program to correlate total electron content with the period of the year, the solar time, the latitude, the elevation of the satellite, the elevation of the sun, and the geomagnetic index. He has determined the trajectories of radio waves through the ionosphere, with and without the presence of the geomagnetic field, and has compared trajectory lengths with satellite-to-receiver distances. He has also performed these same studies using a specially developed "ray tracing" computer program. Another vital contribution by Professor Vassy resulted from his study of refraction using measurements of Doppler differential effects. The Doppler differential chain developed by him increased the precision of measurements by a factor of ten over previously used methods.

The Air Force uses the results of the work by Professor Vassy and other members of the Joint Satellite Studies Group for the design and evaluation of communication systems. DOD, FAA, COMSAT, and other agencies use scintillation data for evaluation of aircraft to synchronous satellite-to-ground communication and data links. NATO has an interest in ionospheric phenomena affecting a satellite communication system in development under NATO auspices. Observations of auroral data have been provided to the Lincoln Laboratory of Massachusetts Institute of Technology for evaluation of modulation systems for military communications The U.S Environmental Science Services Administration is utilizing scintillation information to evaluate a system for broadcasting frequency and time signals from a synchronous satellite.

The work of Professor Vassy and the Joint Satellite Studies Group continues. As new requirements are generated, new aspects of ionospheric phenomena will require research and evaluation.

Professor Wessel-Berg:
bulk semiconductor technology

Professor Tore Wessel-Berg is the head of the Division of Physical Electronics at the Norwegian Institute of Technology, Trondheim, Norway. Before assuming this position he was Head of the Microwave Electronics Group at the Norwegian Defense Research Establishment and a Research Associate in Microwave Electronics at Stanford University. While at Stanford he also served as a consultant to a number of U.S. industrial companies in the field of high-power extended interaction klystrons, transverse wave electron tubes, and relativistic electron beam theory.

During his early microwave tube research work at Stanford University, Professor Wessel-Berg formed a close working relationship with electronics research groups at the Air Force’s Rome Air Development Center, New York. In support of an Air Force program, he served as an invaluable consultant in the development of a one-megawatt continuous-wave (CW) X-band extended interaction klystron for application in high-power radar systems. In conjunction with this work, he published a unified and comprehensive study of advanced theories concerning the wave phenomena of electron beams. Entitled "The Electron Beam as an Electromagnetic Medium," it is recognized as an invaluable treatise which will serve as a basis for research in years to come. By his early contributions Professor Wessel-Berg established himself as a leading authority in wave interactions and electron beam technology.

Following discovery of the "Gunn effect," which manifests itself as a microwave generation mechanism in the bulk of gallium arsenide samples when these samples are subjected to a critical d-c electric field, Professor Wessel-Berg reoriented his research to investigation of traveling-wave interactions in solid medium, particularly bulk semiconductors. These semiconductors possess high-power handling capability and other unique properties which depend on a solid volume of semiconducting material rather than a film or coating. In reorienting his research interests, Professor Wessel-Berg was motivated by the intriguing possibilities of utilizing drifting carriers in semiconducting materials as the primary energy source for traveling-wave amplification of microwave signals. He thus envisioned the development of miniaturized solid-state microwave devices and circuits for applications in advanced electronic systems, particularly phased-array radar systems.

Shortly after beginning this new work, Professor Wessel-Berg investigated the possibilities for active or cumulative mode interactions resulting in growing or amplifying waves in bulk semiconductors. While performing this work, he advanced unique approaches to the description of wave propagation and electronic phenomena in these semiconductors. In developing these approaches, he applied the coupled mode theory, a subject on which he is an expert, to the solution of transport processes in semiconductors by considering the semiconductor as an electromagnetic medium analogous to but differing from an electron beam.

As a consequence of this work, Professor Wessel-Berg developed sound theoretical bases for advancing solid-state technology. Notably, he paved the way for improvements of output power and efficiency in "Gunn effect" oscillators. His work also provided a basis for the fabrication of a low-loss, nondispersive, real-time delay device for application in phased-array radar systems. Yet a solid-state equivalent for the traveling-wave tube has not been realized. Some progress has been made in electroacoustic devices; however, Professor Wessel-Berg is convinced that the most promising aspect for traveling-wave amplification is in direct-carrier electromagnetic interaction without the intermediary of acoustic waves. To realize fully the potentials of this type of interaction, he recognized that it was essential to understand the fundamental differences between the charge-modulation processes in electron beams and the collision-dominated carriers in solids. This is the work toward which Professor Wessel-Berg has now directed his attention.

In recent work sponsored by the Rome Air Development Center, Professor Wessel-Berg showed that carrier waves cannot be modulated at frequencies in the microwave region in the bulk of semiconductors with uniform properties; namely, materials like germanium, with constant values of mobility, drift velocity, and doping density. Doping density (that is, the amount of impurities diffused into the substrate materials, like germanium, to control the electrical properties) is an important factor governing bulk semi-conductor characteristics. Professor Wessel-Berg found that carrier waves and electromagnetic waves do not couple in the bulk of uniformly doped samples, so amplification or cumulative gain cannot be achieved. As a consequence of this finding, Professor Wessel-Berg proposed a traveling-wave scheme involving periodic semiconductor configurations.

In preliminary investigations these configurations, which permit variations of doping density, show promise as a means to achieve a coupling of drifting carriers to electromagnetic waves, so that cumulative gain can be obtained. Professor Wessel-Berg plans to continue this work and the search for solid-state traveling-wave components.

The work which Professor Wessel-Berg is performing is an integral part of an Air Force program dealing with the application of solid-state phenomena to perform conventional microwave device functions. Program emphasis is directed toward the use of solid-state devices to generate, amplify, and electronically control the delay of microwave energy for radar applications. The contributions of Professor Wessel-Berg will lead to the development of miniaturized, highly reliable devices to replace conventional microwave components, not only in radar systems but also in Air Force communications, countermeasures, and other electronic systems.

The Air Force is the beneficiary of high-quality research being conducted for it by gifted foreign scientists possessing unique capabilities. It is important that the relationship of the Air Force with the foreign scientist be maintained, since there will continue to be great scientific progress outside, as well as inside, the United States. Our technological and scientific self-interest, plus our desire to establish closer ties with our foreign friends, demands that we remain actively involved with these productive people wherever they may be.

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