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segunda-feira, 25 de dezembro de 2023

How did the USSR miss stealth technology? Part 1 P.Yu. Ufimtsev and the edge wave method-Como a URSS perdeu a tecnologia furtiva? Parte 1 P.Yu. Ufimtsev e o método da onda de borda

The discovery that actually enabled the development of the Lockheed F-117, the first truly stealthy aircraft, was achieved by the Russian physicist Pyotr Ufimtsev, who in 1962 published a paper on a new method (not the first) for estimating edge diffraction, which became known as the Physical Theory of Diffraction. Ufimtsev postulated that Maxwell's equations would make it possible to calculate the behavior of radar waves relayed from a reflective object. The radar return would depend in part on the shape of the object.

Probably one of the main achievements of the Soviet era is the enormous development of technical and basic sciences. It is worth saying that during the period 1950–1970, 7 people became Nobel Prize laureates in physics, 1 in chemistry (from 1980 to 2019, only 3, and that’s a stretch). The number of scientific workers in the USSR in 1975 was a quarter (a quarter, Karl) of the scientific workers of the whole world.

The era of 1950-1970 was marked by brilliant achievements in astronautics, nuclear energy and the aviation industry. It’s the last one I’d like to talk about. Ufimtsev and the edge wave method All this enormous scientific potential often transformed from quantity to quality. So, in 1962, a young scientist,

P.Ya. Ufimtsev published a monograph “The method of edge waves in the physical theory of diffraction.”

Being familiar with it from a course in electrodynamics, I can say that the reading is quite difficult, but entertaining, and non-specialists in the field of antennas and microwave devices will understand little in it. This book consists of solving diffraction problems on simple bodies and mainly consists of deriving formulas. Here are some, for example:

Example of output of one of the formulas

With the help of such calculations, solutions to a number of diffraction problems for a wedge and disk were obtained, and non-uniform parts of the current were found for these bodies. The theory of physical optics existing at that time did not take into account the uneven part of the current, which was concentrated near the kink. To put it more roughly, it turned out to be possible to more accurately describe the further behavior of electromagnetic waves when falling on surfaces with kinks and sharp edges. More accurately predict the structure of scattered waves. It would seem, what does aviation have to do with it?

Stealth aircraft concept Since the mid-20th century, almost all countries have used radar stations to monitor air or water space.

Let's focus only on air. The detection range of an object: an airplane, a helicopter, a seagull or a crow is largely determined by the characteristics of the radar, but there is one characteristic that is inherent to the object - the effective scattering area (ESR). EPR is a quantitative measure of the scattering of an electromagnetic wave. The higher the EPR value, the further away the object can be detected. The EPR is determined by the physical and geometric properties of the object.

The problems solved by Ufimtsev allowed us to formulate the concept of inconspicuous objects. Using such an ideology in the construction of aircraft and knowing the characteristics of enemy radars, it was possible to significantly reduce the detection range. This technology, which will later become evident in Yugoslavia (this will be discussed in Part 2), can provide a huge advantage. Let me remind you that the time of writing the monograph was 1962, the time of the Cuban Missile Crisis and the Cold War. The world was on the brink of war and destruction. The arms race continued and the use of stealth technology could make it possible to take the lead in this race.

However, the Soviet Union did not take the idea seriously. And there are many reasons for this. At that time, the Soviet Union focused on the speed and maneuverability of aircraft (MiG-15, MiG-17). The new concept implied a complete abandonment of these parameters. To build an airplane using stealth technology, it was necessary to reinvent the airplane, just as Steve Jobs later reinvented the telephone. Unfortunately, the USSR is not a country in which any discussion on this matter was possible. The exact reason why the Soviet Union abandoned the development of a low-observability aircraft is unknown. The monograph sold a large circulation of 6,500 copies and it is doubtful that none of the management thought about using this theory.

Development in the USA

Let's move to the USA. At that time, American aircraft could not boast of their power. The first development of a stealth aircraft in the United States began in 1958. However, the attempts were unsuccessful. The planes were much inferior to the Soviet ones, as demonstrated by the Vietnam War. Their basic science lagged behind. They had not heard about the edge wave method until they accidentally (or maybe not) translated Ufimtsev’s monograph in 1971. Having got their hands on the theory, the missing link, they began development. The project received funding of several billion dollars. Lockheed and Northrop, using Ufimtsev’s theory and computer modeling (this was already possible in the USA in 1975), were able to develop in 1983 the first aircraft completely made using Stealth technology (Stealth - cunning) - the F-117 Night Hawk. one of the F-117 developers stated

“Ufimtsev’s contribution to the construction of this aircraft is about 30-40%, that is, a controlling stake.”

Many journalists began to write about the "invisible plane." But this is absolutely incorrect. Firstly, it is visible in the optical range, and secondly, it is inconspicuous in a certain sector of angles for certain radars.

I will share my calculation, carried out while still at the institute. If you look at the scattering diagram of the F-117, you can see how much lower its frontal RCS is. Thanks to this shape, the aircraft re-radiates most of the energy of electromagnetic waves into the upper hemisphere. In the direction of the radar, the radiation is extremely small. The ESR of the F-117 aircraft when irradiated from frontal and tail angles is reduced to 0.1-0.01 m2, which is approximately 100-200 times less than that of a conventional aircraft of similar sizes.

Pyotr Yakovlevich Ufimtsev, who at that time was working at a research institute in Moscow, did not know anything about the fact that an airplane had been developed in the USA based on his monograph. Imagine his surprise when, in 1990, he went to a conference in the USA by invitation, after finishing his report, the audience gave him a standing ovation, but he could not understand how he had gained such fame. In the USSR he was known to few people. But his monograph became a reference book for Lokcheed Martin engineers. After so many years, he got what he deserved. True, not in my home country. In the 90s, no one in Russia needed scientific personnel, the economic crisis and meager salaries. Ufimtsev goes to work at the University of California at Los Angeles as a visiting professor and participates in the creation of the B2 strategic bomber. Now Ufimtsev is 88 years old and lives in America.

P.Ya. Ufimtsev published a monograph “The method of edge waves in the physical theory of diffraction.” «Метод краевых волн в физической теории дифракции».