Chronicles of Soviet Nuclear Rocket Engines
Decades before Burevestnik
Today, a nuclear engine is still perceived as something unusual and almost exotic. Based on publicly available information, only one Russian nuclear-powered product is actually in serial production—the strategic cruise missile. Rocket "Burevestnik." However, in the 1950s, such projects didn't seem out of the ordinary. Riding the wave of post-war scientific optimism and advances in atomic physics, many engineers believed that the creation of nuclear engines wasn't just a matter of fundamental possibility, but rather a matter of the near future.
The idea of using a different, much more concentrated form of atomic energy for propulsion, rather than chemical energy, arose long before the advent of actual reactors. As early as the late 1920s, Valentin Glushko conducted experiments at the Gas Dynamics Laboratory in Leningrad using the electrical explosion of a metal wire. He was interested in the possibility of generating thrust without a traditional oxidizer. Light metals, primarily lithium, were considered in his experiments.
Valentin Petrovich Glushko
By 1933, this research had led to the creation of a small electrothermal engine. The principle was simple: an electrical pulse converted the working fluid to a high-temperature state and ejected it through a nozzle. For its time, this was a truly groundbreaking idea, but it lacked a key element: a compact power source. Electric generators were too heavy, meaning the design had no practical application.
During those same decades, Konstantin Tsiolkovsky proposed the possibility of harnessing the internal energy of matter for interplanetary travel. Later, after World War II, when nuclear reactors became an engineering reality, this idea took on concrete form. If a reactor can heat the working fluid to extreme temperatures, then theoretically it could replace a chemical combustion chamber and provide a much higher specific impulse.
The fundamental advantage was obvious: a chemical rocket requires both fuel and oxidizer, while a nuclear rocket requires only the working fluid, most often hydrogen. This dramatically improved the energy balance. For comparison, the best oxygen-hydrogen chemical engines achieved a specific impulse of approximately 430–450 seconds, while solid-phase nuclear engines promised 800–900 seconds, and gas-phase engines, up to 1500–2000 seconds.
The American Kiwi reactor, built as part of Project Rover, 1960
The United States was the first to launch large-scale practical research. In 1955, the Rover program was launched, focused primarily on nuclear rocket engines for space missions, while Project Pluto focused on a ramjet nuclear engine for the SLAM ultra-long-range cruise missile. Preparations for hot-fire tests of Kiwi reactors began at the Jackass Flats test site in Nevada. Later, the Americans developed the NERVA series of engines, and in 1969, they achieved a thrust of approximately 25 tons on a test rig with a burn time of over ten minutes—one of the most impressive results in the world. stories nuclear rocket technology.
In the USSR, the signal for similar research was given as early as 1953, when Mstislav Keldysh was tasked with exploring the possibility of using nuclear energy in direct-flow systems. A group led by Vitaly Ievlev was formed at NII-1. It soon became clear that this was not a private project, but a whole new field of science and technology.
Vitaly Mikhailovich Ievlev
On November 22, 1956, the Council of Ministers of the USSR and the Central Committee of the CPSU issued secret decree No. 1529-769 "On the development of ballistic missiles with a nuclear engine." Sergei Korolev was appointed chief designer of the missile, Valentin Glushko and OKB-456 were responsible for the engine, and Alexander Leypunsky and the Obninsk Institute of Physics and Power Engineering were responsible for the reactor section. The Kurchatov Institute of Atomic Energy, TsIAM, TsAGI, VIAM, NII-9, and dozens of manufacturing enterprises also participated in the work.
Three schemes, three levels of difficulty
By the end of the 1950s, three main concepts had emerged.
Type A is a solid-phase engine. A reactor heats hydrogen, which expands and is expelled through a nozzle. This design was considered the most realistic, and it was the one later used by both Soviet and American designers.
Type "B" was a hybrid design in which, after reactor heating, the working fluid was further accelerated or burned in a combustion chamber. Theoretically, this provided a thrust gain, but added complexity to the system.
Type "B" was a gas-phase reactor, in which the nuclear fuel itself was in a gaseous or plasma state. This design promised record-breaking performance, but was extremely complex: it required containing the hot, fissile environment while preventing structural failure and fuel release.
A more radical option was also being studied in parallel: a ramjet nuclear engine. In it, atmospheric air passed through the reactor core and was heated without conventional combustion. But this design almost immediately ran into a fundamental problem: the air passing through the core itself became radioactive. Practical use of such an engine in the atmosphere seemed extremely dangerous.
On June 30, 1958, Resolution No. 711-339 redefined the program. Now, the focus was not only on military applications but also on heavy space launch vehicles with nuclear stages. Korolev envisioned such systems as a means for long-range expeditions to the Moon, Venus, and Mars. OKB-1 created a special division, led by Mikhail Melnikov, to develop nuclear and electric propulsion systems.
By the end of 1959, a preliminary design for a rocket was ready, in which the central reactor block was to be ignited after the system had entered the upper atmosphere. This was an important detail: even then, it was understood that launching a full-fledged nuclear engine near the Earth's surface was extremely risky. A number of designs assumed that chemical stages would place the vehicle on a safe trajectory, and only then would the nuclear power plant be activated.
Gradually, another idea matured at OKB-1: using the reactor not to directly heat the working fluid, but as a source of electricity. In this case, it would power ion or plasma engines. This approach yielded less thrust, but a much higher specific impulse and was better suited for long-duration space flights. Essentially, it was here that the foundations of Soviet nuclear space energy were laid. On June 23, 1960, new decree No. 715-296 established the course for the creation of powerful launch vehicles and spacecraft with nuclear stages. The program included 74 organizations, and their number later exceeded one hundred. It was a project of national significance.
The RD-0410 became the only domestic nuclear rocket engine made of metal.
The main challenges were not only in the reactor physics but also in the materials. The core and fuel supply channels had to withstand temperatures of 2500–3000°C, sudden thermal loads, vibrations, and neutron irradiation. To achieve this, molybdenum, niobium, graphite, beryllium, uranium and zirconium carbides, as well as high-temperature ceramics, were studied. A separate problem was the cracking of fuel elements during repeated startups.
Biological shielding was no less challenging. Early calculations estimated the reactor's mass, including shielding, could reach 20 tons or more. This was especially critical for manned missions: the crew needed to be shielded from neutron and gamma radiation without making the spacecraft unwieldy. This led to design solutions featuring long trusses, with the reactor positioned as far away from the living quarters as possible.
To test this concept, a special complex, "Baikal," was created at the Semipalatinsk test site. It was intended to conduct bench tests of reactor components and associated power systems. However, even preparing the test facilities proved enormously challenging. There was a shortage of electromagnetic pumps for liquid-metal circuits, the technology for pure refractory metals had not been established, and the industry was already overburdened with urgent defense programs.
Soviet projects and real results
In the late 1950s and early 1960s, OKB-456 developed a number of experimental engines: the RD-401, RD-402, RD-404, and RD-405. They differed in the moderator type, propellant, and core layout. Simultaneously, calculations were underway for more complex systems, including the gas-phase RD-600, fueled by hydrogen with added lithium. This project was nearing the ultimate in complexity, with magnetic confinement, nuclear fuel circulation, and extremely intense thermal conditions.
But by 1962, it became clear that the program was disintegrating. Numerous organizations were duplicating each other's work, some projects were lagging, and some areas were too far from achieving practical results. Vasily Mishin reviewed the entire cooperation and proposed cutting redundant staff and concentrating resources on key tasks.
The Cuban Missile Crisis was an additional blow. The military and political situation demanded rapid and comprehensive solutions. Chemical intercontinental missiles could be developed and deployed immediately, while nuclear engines remained a matter of an uncertain future. It was at this point that the program effectively lost its former priority.
However, it didn't disappear without a trace. On the contrary, it gave rise to many real advances in electric propulsion technology. In the 1960s, the USSR actively developed ion and plasma thrusters, which were later used to create attitude control and correction systems for spacecraft. Later, the Soviet school became one of the world's leading experts in the field of stationary plasma thrusters, known today from the SPT series, which are widely used on satellites.
The RD-0410 was the primary practical outcome of the entire Soviet nuclear rocket engine program. It was the project that truly brought the idea of nuclear propulsion to fruition in engineering form. It was a solid-core rocket engine: its core contained a compact reactor that heated liquid hydrogen to extremely high temperatures, after which the superheated gas was expelled through a nozzle, generating thrust.
The designers created a compact reactor capable of stable operation under extremely high heat fluxes, selected materials that could withstand high temperatures, vibrations, and neutron irradiation, and ensured a reliable supply of hydrogen through the core without damaging its structure. Safety was no less challenging: testing such an engine required specialized infrastructure and exceptional care. But the RD-0410 remained a mere episode in Soviet technical history.
Why the nuclear missile didn't take off
The reasons were systemic.
First, complexity. The nuclear engine turned out to be more than just a new product, a component that required a revolution in reactor design, materials science, cooling systems, radiation protection, and ground infrastructure.
Secondly, there was the danger. Any accident at launch or during rig testing threatened radioactive contamination. Even if the engine was ignited in space, the actual launch of the reactor into orbit remained a sensitive task.
Third, economics. Chemical engines were inferior in theoretical efficiency, but superior in price, mass production, and technological readiness. For the military, this was the decisive argument.
Fourth, a shift in priorities. After the moon race and the shift in interest from ultra-expensive interplanetary programs to more practical applications, political support for nuclear space propulsion has weakened.
Although the nuclear rocket engine never became a mass-produced reality, the program left a significant legacy. It accelerated the development of electric propulsion, gave impetus to new materials and technologies for welding refractory metals, and strengthened cooperation between the nuclear industry and rocket and space design bureaus.
Moreover, it laid the intellectual groundwork for later Soviet and Russian space power systems. As early as the 1970s and 1980s, the USSR launched the Buk and Topaz series of reactor power systems into space, used on radar reconnaissance satellites. These weren't nuclear rocket engines in the strict sense, but they demonstrated that compact space nuclear power had moved from the realm of theory to practice.
Today, as humanity once again considers manned missions to Mars and beyond, the idea of a nuclear rocket engine is experiencing a renaissance. Remarkably, modern projects—both Russian and foreign—are largely based on the very groundwork laid in secret design bureaus and research institutes six decades ago. What nearly became a dead end in technological progress has become one of the cornerstones of future space exploration. And this is perhaps the best reward for those who once—in the era of great hopes and the harsh realities of the Cold War—believed that the atom was capable not only of destruction but also of carrying humanity to the stars.
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