Project Pluto
Laboratory/Department of Energy artist’s conception, public domain.
On January 1, 1957, the United States Airforce and Atomic Energy Commission greenlit an experimental new weapons project. Directed by Dr. Theodore Merkle, the Lawrence Radiation Laboratory sought to marry the Supersonic Low Altitude Missile (SLAM) concept with a nuclear-powered ramjet. The endeavor was named Project Pluto.
Project Pluto was the result of contemporary themes. One was the belief that nuclear power was the future. The other was the ceaseless quest to maintain military dominance over the Soviet Union. Fortunately for the planet, Project Pluto was too expensive and horrifying to justify its own existence even in the backdrop of the Cold War. However, it was an incredible feat of engineering that has ramifications to this day.
The SLAM was envisioned as a mix between a bomber and a modern cruise missile. It would be able to loiter in airspace long before being called into action. Once activated, it would come down from its 30,000ft cruising altitude to treetop height and race across enemy territory to deliver its nuclear payload onto preprogrammed targets.
The theory had some appeal. Directed by radio commands during cruise and terrain contour matching radar on its attack runs, the autonomous system kept pilots out of harm's way and limited the expense of keeping them on alert. Its templated payload of approximately 16 nuclear warheads matched anything the bombers of the day could carry and its ability to skim treetops between Mach Three and Four rendered it invulnerable to contemporary air defense systems. But for all of these lofty goals, the missile’s design was highly generic. Keeping the design simple allowed it the robustness necessary to accomplish the mission. One designer called it “as durable as a bucket of rocks.” It was so straightforward that it earned the nickname “the Flying Crowbar.” It just needed an engine. Project Pluto was the answer
Initially, Project Pluto was the name for the engine development, but over time it has grown to encompass the entire nuclear-powered SLAM project. Theorizing a Mach Three missile capable of loitering for months at a time was one thing, creating such a system proved quite another. The ramjet principle Dr. Merkle utilized was well understood: the forward motion of a craft compresses air through a ram into an engine where the air is heated by fuel, expands, and then is blasted out a nozzle creating thrust. The only tricky part is getting the craft moving fast enough with a conventional power source so that the ram can begin compressing enough air to move under its own power. In the case of the SLAM, this was to be achieved by ordinary rockets.
Project Pluto sought to replace the fuel in the equation with a nuclear heating element. It was the first time such a task had been attempted. Nuclear power gave the SLAM virtually unlimited range. It was theorized to be able to stay aloft for months and have a range of 113,000 miles in attack profile. The price for this range was power derived from an unshielded nuclear reactor and the accompanying radioactive exhaust.
Despite this fact, work continued, and on May 14, 1961, the first nuclear-powered ramjet, named Tory-11A, roared to life at the Nevada Test Site. While the system ran for only three seconds, it was hailed as a rousing success. Three years later, Tory-IIC, a lighter and more powerful version ran for five minutes at full power. During this run, it produced a steady 500 megawatts of energy and 35,000 pounds of thrust.
Getting to that point had required considerable investments, both in time and materials. The first problem was metallurgy. No alloy could withstand the expected mix of rain, snow, salty air, and 2,500-degree temperatures. Given this problem, Merkle turned to the Coors Porcelain Company in Colorado to create an alternative solution.
The Coors Porcelain Company — an offshoot of the Coors Brewing Company — went on to create the nearly 500,000 ceramic fuel elements used in Tory’s reactor. This was one of many problems they struggled to solve. A fortuitous browse through Hot Rod Magazine’s ad section provided the exhaust manifold paint that covered the actuators on the reactor’s pneumatic motors after more exotic materials had failed. Even measuring temperatures created challenges as the 2,500-degree temperatures and radiation regularly melted the probes.
Finally, there was the facility built to test the engine. Due to the dangers of the unshielded reactor, the engine was mounted on a remote-controlled railcar that ran the two miles between the test site and construction bunker. The observers watched the test via TV from yet another bunker. And in order to force air into the ramjet, 25 miles of oil well casings were linked together to supply the million pounds of compressed air necessary for the test.
However, for all the creative powers of the engineers, they could not solve the inherent problems with the weapon. Saner heads began asking whether they should, not just if they could. It was already apparent that Project Pluto was far more destructive than a bomber. It more closely resembled a device of terror from a science fiction novel. Skimming the treetops at Mach Three, the shockwave from the building-sized missile would likely kill anyone below it. And if the shockwave did not, the heat from the exhaust might. Anyone close would have ruptured eardrums and a house without windows. Then there was the radiation itself.
Dr. Merkle swore that the radiation from the reactor and exhaust would not harm anyone on the ground as it was dissipated by the pure speed of the missile. However, that did not stop some team members from speculating that once the SLAM had expended its ordinance it could continue to wreak havoc by zig-zagging over the top of the target country distributing radiation until it ran out of fuel and crashed into a radioactive wreck.
In the end, Project Pluto could not overcome its flaws. No allied nation would tolerate it in their airspace and it risked another arms-race with the Soviets. Plus, none of the designers could determine a way to safely test-fly it. Finally, by the time the project was canceled on July 1, 1964, ICBM technology had progressed to the point where they could do a better job at a fraction of the cost without leaving a trail of radiation. While many of the lessons learned during Project Pluto’s development were applied to future projects, the SLAM itself has rightfully been consigned to the dustbin of history.
In the mid-morning of August 8, 2019, an infrasound station located near Troms, Norway, picked up a seismic event coming from Russia. Further investigation indicated that a nuclear incident had occurred off the coast of a small town named Nyonoksa in northwestern Russia. Five weapons scientists were killed and a few more were injured. Without any confirmation on the details of the event, some western analysts came to believe that the explosion was the result of a failed 9M730 Burevestnik cruise missile test. The Burevestnik, code-named Skyfall, is an experimental and mysterious Russian nuclear-powered and tipped cruise missile. One thing is known about Skyfall though: Vladimir Putin and the Russian Ministry of Defense have touted its nearly unlimited range.
Project Pluto’s terrible legacy may yet endure.
