In a March 1, 2018 speech before Russia’s Federal Assembly, Russian President Vladimir Putin discussed new strategic weapons being developed to counter United States ballistic missile defenses. Two of these weapons are allegedly nuclear powered: a previously revealed intercontinental-range nuclear torpedo and a cruise missile. As Putin described them:
Russia’s advanced arms are based on the cutting-edge, unique achievements of our scientists, designers, and engineers. One of them is a small-scale, heavy-duty nuclear energy unit that can be installed in a missile like our latest X-101 air-launched missile or the American Tomahawk missile—a similar type but with a range dozens of times longer, dozens—basically an unlimited range. It is a low-flying stealth missile carrying a nuclear warhead, with almost an unlimited range, unpredictable trajectory and ability to bypass interception boundaries. It is invincible against all existing and prospective missile defense and counter-air defense systems.
Defense and nuclear disarmament experts did a double take. “I’m still kind of in shock,” Edward Geist, a Rand Corporation researcher specializing in Russia, told NPR. “My guess is they’re not bluffing, that they’ve flight-tested this thing. But that’s incredible.”
This is not the first time a government has worked on a nuclear-powered strategic weapon. Decades ago, the US developed engines first for a proposed nuclear-powered bomber and then for a hypersonic nuclear cruise missile. The US has also examined nuclear-powered rockets for space flight (that crazy Project Orion thing is a story for another time). These programs were all dropped, not because they didn’t work but because they were deemed impractical.
Oh… and there was always that small problem of radiation spewing from the engine exhaust.
So when Putin announced that Russia has tested the cruise missile engine successfully, it got us thinking about those past experiments in nuclear propulsion. Is it actually possible to create a nuclear reactor small enough and powerful enough to propel a cruise missile? We broke out our calculators, checked some engine ratings, and asked some experts in the field of nuclear physics.
Not everyone is sure that Russia is really this far along in developing a nuclear-powered cruise missile. But there’s plenty of evidence that they’re trying hard. An unnamed Defense Department source told Fox News recently that Russia had already crashed several test missiles in the Arctic. Other sources have suggested that the engines are still in testing and have thus far only been run with electric power.
Nuclear-powered flight is certainly possible, but it’s a terrible idea for all sorts of reasons. To understand how possible, yet horrible, it is, let’s consider the history of this absolutely insane but perfectly workable idea.
Blame Enrico FermiThe whole adventure into flying nuclear reactors began in 1942……………
The doomsday route
But even as nuclear-powered crewed aircraft were being abandoned, another bizarre chapter in nuclear aircraft propulsion was just getting started: Project Pluto…………….
At the same time Kennedy was scrapping the ANP program, the Livermore crew was finishing construction of a $1.2 million (in 1961 dollars) test facility at Jackass Flats, Nevada—Area 25 of the Nevada National Security Site. Jackass Flats has been home to all sorts of open-air testing of nuclear and ballistic missile systems, as well as depleted uranium weapons; it was also the proposed launch site for another bit of nuclear mad science, Project Orion—the idea of launching something into space using nuclear bombs as “pulse” propulsion.
Working with Vought, the aircraft company that built some of the US military’s earliest cruise missiles, Livermore researchers determined the requirements for the Pluto engine reactor:………..
The Soviet route
As with the US defense industry, the Soviets had competing design bureaus attempting to create nuclear aircraft. And just as with the US programs, the Soviets tried two different routes to nuclear-powered bombers. Neither design ever flew……….The only place the M-60 ever flew was on the pages of Aviation Week in 1958, where diagrams of the aircraft were run with an article claiming that a nuclear-powered supersonic bomber was being tested in the Soviet Union. It was an elaborate hoax………
Crawl out of the fallout
That wasn’t the end of nuclear-powered flight ideas, of course. NASA funded research into nuclear-powered thermal rockets in the 1960s and 1970s, and discussion of that sort of technology continues today as an option for interplanetary missions. But most people agreed that the risks of flying radiation-powered vehicles inside Earth’s atmosphere was too high even to consider testing them—that is, until the Russian Federation’s leadership decided the US was pushing the nuclear balance too far in its own favor.
It’s not clear whether the nuclear cruise missile engine Putin mentioned in his speech has been tested yet. Russian news outlet Vedomosti quoted a source in Russia’s military industry as saying that tests thus far have used “an electrical layout” to test the missile’s engine and not an actual nuclear reactor. But Russia does not appear to have been working hard on miniaturizing nuclear reactors.
Small-reactor technology has been advancing rapidly over the past decade. The US military has looked into using small modular reactors to power high-energy weapons and bases overseas. Other countries, including Russia, have continued research into molten-metal cooled reactors; it is rumored that the “Status-6” nuclear-powered “torpedo” Putin discussed in his speech is powered by a lead-bismuth reactor.
Putin said that the “innovative nuclear power unit” of Status-6 completed testing in December 2017 after a “test cycle that lasted many years.” Russia has been developing new reactors with lead-bismuth coolant for naval applications. Soviet “Alfa” class attack submarines were powered by lead-bismuth reactors, which are very tricky to maintain but deliver high power-to-weight ratios; the original test reactor for the “Alfa” class design (KM-1 in Sosnovy Bor) was decommissioned a year ago, and a new type of reactor was installed in its place.
A lead-bismuth reactor’s power-to-weight ratio may be perfect for a small drone submarine, but it may not be the ideal form for a missile’s engine. However, the thrust required to keep a cruise missile in flight is nowhere near what would be needed for a hypersonic missile or even a subsonic bomber.
The Williams F107 turbofan that powers the Tomahawk cruise missile puts out a thrust of 3.1 kiloNewtons (700 pounds). To fly the Tomahawk at its cruising speed of 550 mph (890 km/h), that means generating about 766 kilowatts of power. That’s well within the potential power range of a small modern nuclear reactor, according to Jeff Terry, professor of physics at Illinois Institute of Technology and an energy researcher. “One megawatt is certainly doable,” Terry said, since the core of the 85-megawatt High Flux Isotope Reactor at Oak Ridge National Laboratory is “the size of a beer keg.”
If the Russian designers of the engine for the as-of-yet-unnamed nuclear-powered cruise missile did not have any concerns about radiation shielding for anything other than the avionics, a small nuclear reactor could be incorporated into a cruise missile design. The missile could be launched with a booster and wait until it is at speed to take its reactor critical, as was planned with the SLAM.
From a deterrence standpoint, a nuclear-powered cruise missile is a destabilizing weapon. Its launch would not necessarily set off US early warning systems, and its flight path is unpredictable and long. It could be launched days or weeks before an intended attack, purposely avoiding areas where it could be detected and coming from directions that the US doesn’t watch for nuclear attacks. And if the missile uses a “direct” system like SLAM, it would spend that time spewing fallout wherever it flew, regardless of whether it ever executed its mission. In other words, just as US military planners in the 1960s found out, a nuclear cruise missile is a provocative weapon better suited to first strike than to deterrence.
SEAN GALLAGHERSean is Ars Technica’s IT and National Security Editor. A former Navy officer, systems administrator, and network systems integrator with 20 years of IT journalism experience, he lives and works in Baltimore, Maryland.
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