During the height of the cold war hysteria in the 1950’s, SAC or the Strategic Air Command, America’s nuclear strike force was looking at the next generation of nuclear delivery systems. Bombers were the backbone of SAC but were slow and vulnerable to the Soviet air defences, ICBM’s were still in their early stages and not yet reliable enough but from research into nuclear-powered jet engines came an idea for one of the most insidious weapons systems ever devised.
As the cold war developed and deepened both the US and Soviets scrambled to create ever more effective ways to deliver and defend themselves from nuclear attack. In the US a system was proposed that the nuclear planners would call the Big Stick.
In a little over ten years since the first atom bombs had been dropped on Japan, the technology had moved on rapidly. SAC had a fleet of long-range nuclear bombers using the B-52, keeping a number of these in the air 24 hours a day 365 days a year, flying around the artic on constant alert.
One of the problems with jet bombers of the time is that they were limited by their fuel capacity to fly around whilst on alert. To combat this the US set out to develop a nuclear-powered bomber if this could be done their flight time and range would only be limited by how long they could keep the crew up there.
However, they soon found out that the shielding required to protect the crew from the nuclear-powered engines weighed so much that it made them slow and used up most of the payload capacity, not to mention the handling problems of such a dangerous propulsion system for the ground crew.
But from this research came a ceramic reactor core small enough to be used in an unmanned plane or cruise missile that wouldn’t need the heavy shielding.
In 1955 the US Atomic Energy Commission asked Lawrence Radiation Laboratory to do a feasibility study on using a new ceramic reactor to power a RAM jet engine and in 1956 the USAF issued system requirement No 149 for a nuclear powered winged missile.
The project was called Pluto after the code for the Ceramic reactor developed at the Lawrence Radiation Laboratory and the name given to the cruise missile was SLAM or Supersonic Low Altitude Missile but was also unofficially called the “Big Stick”.
Although Ramjets were quite well known at the time no one had proposed using a nuclear reactor as the heat source instead of the usual solid rocket fuel or liquid fuel.
A Ramjet works by using the forward speed of the of the vehicle to compress the air instead of using a turbofan compressor in the engine like a normal jet does. This compressed air is then mixed with a fuel which when burned expands and creates its thrust.
Although a Ramjet can achieve speeds of up to Mach 6, they don’t start working efficiently until its speed is over Mach 2 and as such, they are normally launched by a rocket to bring it up to speed before the Ramjet takes over.
In a nuclear powered RAMjet, the compressed air is channelled through the core of a reactor which would heat up the air in the same way as if you burned fuel, this expanded hot air is then what produces the thrust required. Even a small reactor core will create an immense amount of heat for weeks or months, effectively providing an almost unlimited fuel supply as far as the mission duration is concerned.
Nuclear reactors of the time were usually large structures surrounded by concrete and lead, so to make one that would be small enough to fly would have to rely upon some radical advances in material technology and this is where the ceramic core comes in.
The nuclear RAM jet engine would have to operate at temperatures higher than any conventional jet or rocket engines whilst also being exposed to intense radiation which would affect its electronic control systems and it would have to be able to fly for extended periods of time in any weather.
With no pilots or active remote control like we see with military drones today, it would also have to find its own way around. A new groundbreaking guidance system called TERCOM used a downward looking radar and compared that to a terrain map which it carried on board. The flight path to the targets where then plotted on to this terrain map and enabled it to fly unaided deep in the enemy territory.
SLAM would also use an electronic inertial guidance system, control and telemetry but these had to be made to withstand the intense radiation as standard electronic components would be fried a matter of minutes.
With a fuel supply that could last for weeks or months, this gave it the possibility of being launched in a time of emergency and fly around the oceans in a holding pattern close to the target until given the order carry out its mission.
SLAM was designed to carry not one but multiple nuclear warheads, the idea being that it would fly to its designated targets, releasing a nuclear weapon before moving on the next one and so on and so forth until all its targets had been hit and doing so whilst travelling at Mach 3 just a few hundred meters above ground.
This is all pretty advanced stuff even today but this was in the mid-1950’s. To test the prototypes a section of desert locally known as Jackass Flats which was about 310 sq km (120 sq miles) was set aside at the Nevada National Security site where the US tested its nuclear weapons and ultimately where all the nuclear engines including the NERVA nuclear rockets would be developed.
In order to test the system, they had to simulate the volume and temperature of the air that would be expected during its Mach 3 flight at sea level. This was well beyond anything a wind tunnel could provide so they built a pressurised air supply using miles of 10” oil pipes bolted together to create a total capacity of 545,000kg of air at a pressure of 3600 psi.
This was then passed thru a massive heat exchange to raise the temperature to 500 degrees Celsius at a flow rate of 325 kg per second to simulate the conditions that the Ramjets inlet diffuser would be expected to handle. So much air was required to do a 90-second test that it took 2 days to pressurise the system using huge compressors borrowed from the US Navies submarine base in Connecticut.
To create enough energy to propel the SLAM and carry the payload, it was calculated to require a 500MW reactor but to test its viability they made smaller prototype called the Tory-IIA which would be 1/10th of the power at 50MW.
Because the reactor core would be cooled by the incoming air, the pressures involved at Mach 3 inside the reactor core from not only the compression of the air but also the rapid heating would be up to thousands of pounds per square inch in certain areas.
To do this the Tory-IIA’s air cooled core was made up of over 100,000 pencil sized hexagonal ceramic fuel elements made from beryllium oxide and enriched Uranium dioxide. These were stacked end to end in the thousands of airflow channels in the core and because they were unattached to each other this minimised the thermal stress.
The reactor was then attached to the ramjet and the whole thing was mounted on a railcar that was shunted from its disassembly building to the test area by a remote-controlled locomotive.
In 1961 the Tory-IIA was test fired for 45 seconds and although the results were considered a success it wasn’t a complete flight-ready system, its power was too low and it had external water cooled control rods in the reactor.
The final test would need a full-sized version that was completely air cooled and with the inlet and exhaust ducts fitted to prove that they had flight ready Ramjet engine.
It took three more years before the full sized 500MW version called the Tory-IIC was ready for testing. This was the size of a locomotive and weighed about 6,300kg.
Because everything in this reactor was air cooled the pneumatic actuators that operated the control rods which increased or decreased the power output had to operate at 650C, if these failed or jammed it would not be possible to shut down the reactor once at full power.
On the 20th May 1964 the Tory-IIC was rolled out to the test area and connected to an expanded air supply system. The test ran for 5 minutes at full power and after they had brought the reactor back and stripped it down for inspection they found it had worked perfectly and there was no damage to the inside of the core or to the pneumatic actuators or electronics.
The next stage would be to flight test it with missile airframe but the problem was where, they couldn’t fly over land as a crash would spread highly radioactive material. So the plan was to launch it in the Pacific ocean then fly it around and then crash it in to one of the nuclear test sites where atomic bombs had been detonated.
But SLAM would never reach its flight testing stage and on the 1st July 1964 the program was cancelled. The world was changing fast, the shock of the Cuban missile crisis had led the US and the Soviets to banning above-ground nuclear tests and as such, this would also affect SLAM.
By 1964 ICBM’s had advanced to the point where they were seen as superior system that was easier to build and maintain reducing the need for the supercruise missile.
There was also another reason, during the development it was found that if they changed the fuel rod design, the exhaust of the ramjet could be made highly radioactive. This would make it a vengeance weapon that not only could fly around dropping its nuclear bombs on it’s targets but afterwards it could continue to fly at Mach 3 just a 100 meters above the ground, not only causing damage with the shock wave but also spewing out radiation and poisoning everything in its path until its reactor core failed which could take for weeks or months.
The government decided that it was just too provocative and dangerous and that if they deployed this effectively unstoppable weapon then the Soviets would be forced to develop their own version.
Although SLAM was never made, much of its technology, especially the guidance system is now used in modern cruise missiles. So what do think of America’s big stick, let me know in the comments and don’t forget to check out some of our other videos, so thanks for watching and please subscribe, thumbs up and share.