A Russian Response to the American Golden Dome

In August, the Norwegian press observed frenzied activity around the Russian Arctic base of Rogachevo on Yuzhny Island in the Novaya Zemlya archipelago, at a latitude of over 71 degrees north, with movements of ships and aircraft, including a reconnaissance and air control aircraft and planes from Rosatom, the Russian nuclear energy agency. Work and helicopter movements were also observed at the Pan'kovo site (170 km further north), equipped with a launch platform for testing the 9M730 Burevestnik (petrel) nuclear-powered cruise missile, known to NATO as SSC-X-9 Skyfall.

These activities, along with restrictions imposed on civilian flight and navigation in the north-eastern Barents Sea, suggest, according to international and Norwegian experts, that a new test of the Burevestnik is being prepared, following 13 failures.

We recall that the incident on 8 August 2019, which caused the death of 2 Russian military personnel and 5 nuclear experts following an explosion on a platform in the White Sea off the Russian naval base of Nyonoksa, was interpreted by Western experts as being related to the recovery of the wreckage of a Burevestnik that had ended up in the sea following a failed test (http://ilbolive.unipd.it/it/news/morte-65deg-parallelo-lincidente-russo).

The Burevestnik is one of the technological marvels presented by Russian President Vladimir Putin to the Federal Assembly on 1 March 2018 in his state of the union address, along with the Poseidon nuclear-powered autonomous underwater vehicle, the hypersonic missiles Tsirkon, Kinzhal and Avangard, and the super-heavy ICBM Sarmat. The development of these nuclear weapon systems, in many respects absolutely extraordinary, was motivated by Russia's concern that American progress in the anti-missile field would nullify Russia's ability to respond to a nuclear attack. An attitude that Donald Trump's new Golden Dome project can only reinforce.

An Extreme Technology

The Burevestnik is a subsonic cruise missile for nuclear missions powered by a nuclear reactor. Cruise missiles, unlike ballistic missiles, have autonomous propulsion and follow arbitrary paths, guided by an on-board computer and/or navigation satellites; flying at low altitude (a few tens of metres) they escape radar and with their high mobility can avoid anti-missile interceptors. This makes them highly penetrative weapons against enemy defences; however, cruise missiles with conventional engines have limited flight time and range (some up to a maximum of 3000 km), determined by the fuel capacity on board.

The Burevestnik is supposed to be a ramjet with a compact nuclear reactor instead of a combustion chamber. Nuclear fission makes much more energy available compared to conventional fuels, and a nuclear-powered cruise missile could reach intercontinental distances, follow unpredictable routes and remain in flight for an extremely long, practically unlimited period.

In a ramjet, external air enters a dynamic intake and is slowed to subsonic speed (usually up to Mach 0.3) by the particular geometry of suitably shaped ducts, leading to an increase in the pressure of the cold air flow. The compressed flow used as a coolant for the nuclear reactor reaches very high temperatures (up to 1400-1600° C), expands and is expelled at high speed from a suitably shaped nozzle to create the necessary thrust. Although they are more efficient above Mach 2, ramjets can also operate at subsonic speeds, as in this case.

To reach the initial transonic speed necessary for engine ignition, the missile must also have, for the initial phase, a combustion propellant, with liquid or solid fuel.

The realisation of a nuclear ramjet is a real technological challenge, which many experts believe is still far from being overcome. Between the 1950s and 1960s, the USA developed the Pluto project for such an engine to be used in a massive cruise missile (the Supersonic Low-Altitude Missile), fortunately cancelled before any testing. The Tory-IIC nuclear ramjet prototype was, however, positively tested on rails in 1964 for several minutes, but the Pluto project was definitively closed due to the enormous technical problems still open and the risks of radioactive contamination of the environment. Between 1959 and 1972, twenty reactors of the NERVA programme for space propulsion were built and tested in the USA, using hydrogen as the working fluid instead of atmospheric air, but they have not had practical use.

The reactor developed for the Burevestnik is a black box as far as open source material is concerned, and nothing is known about its design parameters; taking into account the indiscretions about the missile's size and speed, it should have a power of a few megawatts. Broadly speaking, there are two configurations that can reasonably be considered: "open circuit", in which the incoming air flows directly through the reactor to extract heat, or "closed circuit", in which the reactor is isolated from the airflow by a heat exchanger that transfers heat from the reactor to the air, using liquid metals such as sodium or potassium as coolant.

Both configurations present difficulties. Open-circuit systems would have radioactive particles in the exhaust gases and would have to be large to accommodate the air flow ducts; this would require more fissile fuel to reach critical mass, thus increasing the weight of the system.

Closed-circuit systems would have a lower mass reactor, but a heat exchanger would have to be added. The increased complexity resulting from the introduction of a heat exchanger would make an open-cycle concept more interesting for faster implementation, also considering the political pressure for the completion of the new weapons presented by Putin back in 2018.

Complexity to Manage in Flight

Reactors are extremely sensitive machines and their geometry, the fluids they come into contact with and their temperature must be continuously and precisely controlled.

The reactor's fissile fuel must maintain its arrangement precisely to achieve optimal neutron flux in the core. For a cruise missile operating at an altitude of 50-100 m and following the terrain at high speed, many inertial forces will be at play. The reactor's structural elements (fuel, moderator, coolant) must be designed to handle any perturbation without significantly altering the neutron flux in the reactor, or provide mechanisms to naturally return the reactor to criticality after abnormal situations. If the fuel geometry changes, reactivity could increase out of control, or decrease until it no longer sustains the missile's motion.

At altitudes of tens of metres, dust, leaves, snow, rain, hail and perhaps even birds could enter the ramjet's air intake. Changes in humidity, temperature and pressure alone are enough to modify the reactor's reactivity, variables that will inevitably fluctuate during a journey of days across thousands of km of ocean and land. In conditions of higher humidity, water in the reactor ducts could increase the number of fission events, raising the temperature and requiring precise control to avoid criticality.

The high temperatures indicated for the Burevestnik's outgoing air require that most of the structural elements be ceramic, and therefore fragile and subject to rapid and unpredictable fractures. The enormous thermal gradient (and therefore stress) within the reactor, as well as the dynamic load caused by wind, manoeuvres and turbulence, produce strong material degradation, which could lead to critical situations for the missile.

In an open-circuit system, air flowing through the reactor core will collect gaseous radioactive fission products before being expelled as exhaust. The main radiological concern stems from the degradation of reactor materials due to heat, pressure and intense radiation during operation. As these radioactive materials degrade, they can chip and exit through the exhaust.

The Burevestnik might have to autonomously manage all these problems. In flight against a target, it will not send telemetry to a remote operator who can issue commands, as its critical advantage is precisely its stealth. Once located by adversary forces, its limited speed and low-altitude flight profile would make it an easy target for enemy fighters.

This means that all reactor control systems must be autonomous for part, if not all, of the flight duration - and must function perfectly even in conditions of intense radiation.

The integration of an open-cycle nuclear ramjet within a cruise missile, together with the implementation of highly reliable control systems and auxiliary subsystems suitable for ensuring operational sustainability for missions lasting several days, configures an engineering problem of extraordinary complexity. In light of these criticalities, a substantial part of the scientific community considers the full realisation of such a technological programme, at present, an objective of still remote feasibility.

The programme appears to be primarily oriented towards 'signalling' to the United States, emphasising how the central elements of the Russian posture are strategic surprise and the ability to elude early warning systems, also nullifying the vaunted impenetrability of the Golden Dome. In parallel, it seems aimed at reaffirming on the international stage Russia's image as a technological power capable of developing and deploying capabilities that cannot be replicated by other actors.

We therefore have a further confrontation between the two superpowers played out on the development of extreme technologies, none of which are capable of improving the global human security of their respective populations, but which aggravate the harshness of the confrontation and the risk of military escalation.