The Tsar Projectile for Nuclear Artillery

National atomic projects became a forced counter-move aimed at averting the new menace to peace which suddenly sprang at the end of the World War II. Soviet scientists and engineers, like their American colleagues, worked for the victory over the deadly peril. The triumph of the first developers of nuclear weapon though was tarnished by the barbaric and unwarranted nuclear fire against the Japanese cities. The pride many people in Russia feel for their researchers and other specialists who eliminated the threat of a new, this time atomic, world war has become even stronger in the last decades.

In August 1949, the first Soviet nuclear bomb test was successfully held, and since that time the USA lost its monopoly on nuclear weapon development. In 1953, after the world’s first hydrogen aircraft bomb was tested in the USSR, the policy of a total nuclear dictate was no longer possible. Both these projects were developed by the best national scientists and specialists located in the closed town of KB-11 (or Arzamas-16, now Sarov).

Nevertheless, by the mid-fifties the American atomic arsenal remained far superior: the USA had several hundred nuclear bombs whereas the USSR had only a few. Technologically, uranium isotope separation was still a bottleneck. The possibilities of a Soviet second-strike in case of a nuclear attack were very limited.

In 1951, the USA held successful tests of artillery fired atomic projectiles. Two years later, similar research began in KB-11. In spring 1953, Academician Mikhail A. Lavrentiev was appointed head of theoretical and experimental work on developing a nuclear charge for the artillery fired projectiles. Having accumulated an impressive stockpile of achievements in mathematics and mechanics, organizational and engineering advances in experimental explosion physics and a rich experience in research administration, he appeared to be an excellent supervisor for the intricately related team of researchers, engineers, and designers. He was not only able to remember all the details and specific features of various scientific and technical auxiliary projects, but helped enthusiastically to deal with any problems arising in each of them.

The physics of a nuclear bomb developed in the late 1940s was a sphere about 100 cm in diameter with a spherical nuclear charge. The nuclear charge was made out of the active material ²³⁵U or ²³⁹Pu and shaped as a thin-walled metal spherical shell, subcritical in the initial state. At the heart of the hollow core space was the neutron primer. On the outside, the active material was contiguous with a layer of the ²³⁸U tamper; then went a layer of a solid explosive. This was surrounded with a lens system recording the shock wave from the detonators, which were located almost at the surface of the explosive’s outer layer.
The bomb explosion was triggered by simultaneous initiation of the detonators. The lens system formed a virtually regular-shaped spherical shock wave converging inwards and compressing the spherical active material shell (this type of a nuclear charge blast is called implosion). The moment the shell collapsed into a sphere, a special primer was activated to inject neutrons into the structure, which triggered a chain reaction resulting in a blast.
Initiating nuclear interaction right at the moment of the shell collapse essentially reduced the probability of the so-called low-order detonation resulting from a premature start of the chain reaction that could be triggered, for instance, by a space radiation particle. Shock wave compression (spherical cogging and squeezing) of the active material made the critical mass much lower, which provided a noticeable economy of nuclear fuel

Trouble with the “melon” design

The nuclear charge developed at KB-11 had to adhere to exceptionally rigid specifications not only in terms of size but also in terms of integrity of all its components, which was to be many times superior to that of the previously developed nuclear weapons in order to be able to cope with the huge overload.

Non-spherical symmetry required a more sophisticated design of the detonator system. Their asynchronous ignition circuit had to provide synchronous convergence of the non-symmetric shock wave towards the center of the construction. The same problem with an extra variable had to be resolved for hydrodynamic cogging and squeezing of the nuclear charge as well as for all the nuclear chain reaction calculations. Implosion resulted in the transformation of the originally hollow thin-walled shell of the active material together with the adjoining neutron-reflecting heavy ²³⁸U shell into a supercritical two-layer slightly elongated quasi-spherical body, into which neurons from the primer were injected. This design, basic for a nuclear explosion, is axisymmetrical and not spherically symmetrical. The additional variable arising in this situation essentially complicated the estimates, done at the time virtually without computers. As a result, the theoreticians had not only to find simplified physically adequate models (equations) but also to transform them to the form that lent itself easily to arithmometer calculations. The requirements imposed on the numerical methods used in the estimates were high as well: they had to be simple, economical, stable and sufficiently accurate. An important role was played by the mathematician V. S. Vladimirov, a future Academician and Hero of Socialist Labor.

MY BACKGROUND

I was completing my graduate studies at the Physics Department of Moscow University. In late 1948 I decided to prepare my graduate thesis under the supervision of Prof. N. N. Bogoliubov, a Corresponding Member of the USSR Academy of Sciences, who was very well-known at the University. A year before, he was awarded the Stalin Prize for his papers on theoretical physics, including the monograph Dynamic Equations of Statistical Physics.
I was given the task to simplify the kinetic transfer equation, i. e. the equation of neutron diffusion and moderation. This was a monstrous integral differential equation for the distribution function with three independent variables even for the case of spherical symmetry. In the general case, it could only be solved using cumbersome numerical calculations, and the approximations known (one-velocity, diffusion and age) were too rough for the practical applications in view. It is noteworthy that my boss just set the task without outlining any approaches to the solution.
The problem was exciting both technically and in substance: any serious advance could make numerical calculations much more economical, which would amount to a time gain. And this was a major factor in our activity: the first Soviet nuclear bomb was tested only in the August of the following year (1949).
In a few months, I made good progress in solving this problem. As the basis of a new approximation, I took simplification of the integral operator kernel, or the so-called dispersion index (I remember that the main idea hit me during the Moscow University Young Communists’ meeting as I was sitting in the gallery – the place chosen specifically to be as far as possible from the other delegates – and got absorbed in thought as the spokesman rambled monotonously).
After the theoretical part of my studies was declassified in the mid-1950s, the method of the so-called synthetic nucleus in the diffusion theory and neutron moderation was published in the Atomnaya energiya journal. It became clear with time that the American colleagues had failed to think of anything equivalent. Powerful computer facilities seem to indulge the philosophy “If you have a computer, you don’t need brain.”

...By the time M. A. Lavrentiev made his appearance at KB-11, I was only 25 but I had gone a four-year-long way with N. N. Bogoliubov, from a graduate student to a participant in the hydrogen bomb project. I had managed to invent and tune up a simple and accurate method for reporting neutron slowdown and diffusion in the media containing light hydrogen and deuterium nuclei. I had presented this work as my candidate’s thesis to a commission including I. V. Kurchatov himself and received my first award – the Order of the Red Banner of Labor – for participation in the project.
I believe it was owing to these results, N.N. Bogoliubov’s reference, and approval of high authorities that I was entrusted with calculating the chain reaction development from the moment of the implosion wave convergence towards the center and possibility of a low-order detonation. This was how I became a member of M.A. Lavrentiev’s team, where I worked for the following three years on the development of nuclear filling for an artillery fired projectile.

...Nuclear charge tests at the Semipalatinsk test site held in March 1956 were postponed by several days because of improper weather conditions (the wind was blowing towards the town). Waiting for the appropriate weather at the bank of the Irtysh River, Lev V. Ovsiannikov and I invented the “chess gamble” (a game of chance in which one should throw the dice before every move, which was designed to counterpoise his excellence and my adventurism) and discussed non-classified science. Lev got interested in the functional equations of the renormalization group in the quantum field theory I was then involved in, and in a few days found a solution. A paper with his results was presented by N. N. Bogoliubov to the Doklady Academii Nauk (Proceedings of the Academy of Sciences) only three weeks after our nuclear charge was successfully tested under Semipalatinsk

Physical research into the new product and its design were assigned to distinguished physicists-experimentalists, experienced designers and engineers who had taken part in the development of the atomic and hydrogen bombs. At the same time, M. A. Lavrentiev entrusted fundamental theoretical research to a young team, whose oldest member L. V. Ovsiannikov (in charge of hydrodynamic calculations) was 34 years old. Last spring, in Novosibirsk’s Academgorodok, we congratulated the Advisor of the Russian Academy of Sciences, Academician L. V. Ovsiannikov on his 90th anniversary.

Projectile test successful

By late 1955, all the mathematics, theoretical grounding, and hydrodynamic studies of the nuclear charge had been completed. Also, a bulk of experimental work had been carried out including testing the construction for integrity. Since at that time KB-11 had no equipment appropriate for conducting such tests, new appliances had to be developed. At the head of these developments M. A. Lavrentiev put experimentalist B. V. Voitsehovskiy, the future Academician and author of over a hundred inventions, whose ingenuity impressed the most experienced KB-11 designers: he was able to find easy solutions to the problems that many specialists considered unsolvable.

The main test of the new nuclear charge was held at the Semipalatinsk test site in March 1956. Present at the test were the specialists charged with the development of the construction, including theoreticians. This tradition was attributed to the need for getting prompt and comprehensive advice in case of an emergency. However, this time it was not necessary. The nuclear charge detonation demonstrated the peak of its estimated capacity. This was a total and well-deserved success.

Completion of the development of tactical atomic artillery, however, took some more time. The production of self-propelled guns, capable of firing atomic projectiles took longer than expected; experimental shooting with billets was conducted only in late 1956, at the Rzhev test site. Those were dynamic reaction pieces of ordnance (Design Bureau of V. G. Grabin, who had developed the legendary Katiusha) and conventional recoil weapons (I. I. Ivanov Design Bureau).

After the cumbersome self-propelled systems were finalized, they were displayed to the world at the military parade on the occasion of the 40th anniversary of the October revolution: two huge artillery vehicles designed to fire atomic projectiles crawled across the Red Square. The foreign defense attaches present at the parade were astounded. That was that, however. Artillery fired nuclear weapons were never produced on a full scale – the era of missiles began!

Two years later, our achievement was crowned with high governmental awards. The main participants of the project from M. A. Lavrentiev’s team received the Lenin Prize, resumed in 1957.

The list of the Lenin Prize laureates for the year 1958 included Mikhail A. Lavrientiev (head of the project), Anatoly I. Abramov (designer of the construction), Victor M. Nekrutkin (development of hydrodynamic cogging and squeezing), Lev V. Ovsiannikov (hydrodynamic cogging and squeezing calculations), and Dmitry V. Shirkov (nuclear reaction calculations).

By right, Lev V. Altshuler (measurement techniques and execution of simulated hydrodynamic cogging and squeezing) should have been on the list – put forward for the award, he was crossed out later for making a stand for genetics.

References

Andriushin I. A., Chernyshov А. K., Yudin Yu. А. Taming of the Nucleus: Pages of the History of Nuclear Weapons and the USSR Nuclear Infrastructure. Sarov, 2003. 

Lavrentiev Age. Novosibirsk: SB RAS Publishers, 2000. 456 p 

Vlasova Ye. Academician at the Installation // Nauka v Sibiri. 2000. No. 44—45. Nov. 17. 

Zhogin V. P. Atomic Projectile // Atom. 2002. No. 18.

The editors thank the Nuclear Weapons Museum (Sarov) and its Director V. I. Lukianov for the materials presented