The Case For Orion by Wayne Smith
What do you think? Should we have nuked our way to to Saturn in 1970?
The Niven and Pournelle novel Footfall used this concept to launch a spaceship to destroy the mothership of the alien elephants invading Earth.
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The nuclear pulse method of propulsion was seriously considered for long distance space travel, but only for deployment once the ship in question was already a suitably safe distance from Earth. Using nuclear weapons for a launch system was a crazy idea even by 1950s standards.
But, if you want a truly crazy application of nuclear technology for propulsion, allow me to start with a preamble, on why nuclear reactors work in submarines and ships, followed by why they were tried (and abandoned) for manned aircraft, before introducing you to the most nightmare system ever to have R&D money spent upon it …
Nuclear Power at Sea
The US Navy, famously built a nuclear powered submarine, the USS Nautilus, which as we now know, turned out to be a tremendous success, and formed the basis for pretty much every nuclear powered submarine built since.
There’s a reason it worked so well.
A World War II era submarine was already an entity composed of a substantial mass of metal. A Type IXD/42 German U-Boat, for example, had a submerged displacement of 1,808 tons. This was a vessel that was 287 feet long, and had a pressure hull around 224 feet long. As part of that mass, there would be a pair of marine diesel engines (each around 50 tons), 442 tons of diesel fuel fully laden, a pair of electric motors for submerged operation (around 25 tons each), and batteries for those motors (lead-acid batteries were not light - this would have added another 100 tons or so to the hardware inventory).
Replace that propulsion system with a nuclear reactor (call it 50 tons), a pair of steam turbines (50 tons each), and remove the need for both the diesel engines and their fuel, and the electric motors, and hey presto, you’ve reduced the mass of the submarine by about 500 tons. That mass saving allows more crew, more weapons and other equipment to be included.
The nuclear reactor has other benefits too. It produces far more power than marine diesels could hope to match in a submarine setting. As a consequence, there’s a huge amount of excess power to operate other equipment. A third steam turbine to operate an electric generator opens up a wealth of possibilities, because now, the submarine has the same electrical power as a small city.
With that much on tap, you can operate two other pieces of equipment that make the submarine far more tactically and strategically useful. Because there’s no combustion taking place eating into the oxygen inside the hull, the submerged endurance is already increased.
But that vast surplus of electrical power allows for energy hungry systems to be installed, one of which is the so-called “electrolytic gill”, which extracts fresh oxygen from seawater, so that the crew have, in effect, an unlimited supply of breathable air underwater. With that in place, the underwater endurance of the submarine rises dramatically.
You can also install a desalination plant in the submarine, to keep the crew supplied with fresh drinking water. Again, extending the submerged endurance of the submarine, which now, instead of being restricted to a few hours beneath the surface, can in theory operate indefinitely underwater. Once beneath the waves, that submarine then presents enemies with the headache of detecting it in the vast expanse of an ocean.
In practice, the limitation on submerged endurance consists of how much food you can store at the start of each voyage. Typically, that allows for a 90 day turnaround, though in some cases, such as modern ballistic missile subs, that could be extended further, because ballistic missile subs are big. They have to be, simply to have space for modern SLBMs.
So, installing a nuclear reactor in a submarine is a win-win move. Massive amounts of power, no worries about weight saving because a submarine is already a large lump of metal, the ability to fit endurance enhancing technology inside the hull and power it with the massive surplus power the reactor provides, and keep the crew alive with fresh air and fresh water available in effectively unlimited supply.
A similar win-win application is aircraft carriers. You remove the need for diesel fuel for the ship, and can carry more aircraft and more aircraft fuel. You also have the ability to operate the carrier at sea non-stop for decades if you wish, though again, human factors typically limit operational endurance to about 120 days per voyage.
So, you have massive amounts of power, no need to refuel the reactor for up to 25 years, and the ability to install equipment that isn’t possible on a ship or submarine using non-nuclear propulsion. No wonder modern blue water navies choose nuclear power for their top end vessels.
Nuclear Power in the Air
Now we come to the fun section.
The US Air Force saw the spectacular success that the US Navy enjoyed, and, naturally, thought “we’d like a piece of this action too”. And so, in the 1950s, plans were drawn up to find out if it was possible to power an aircraft using a nuclear reactor.
Immediately, one big problem emerged. Mass isn’t a problem on a submarine or a ship that already involves thousands of tons of steel in its construction. Not so on an aircraft, where paring away mass as much as possible, without compromising structural integrity, is essential.
Building a reactor compact enough to mount in an aircraft was itself a challenge. Then there was the matter of finding a test bed.
Luckily for the US Air Force, they had a test bed. The B-36 Peacemaker.
But … the only reason that was a viable test bed, was because it had already been built to be a colossal aircraft. It made a B-29 look tiny. This was an aircraft that had a wingspan of two hundred and thirty feet, and in later incarnations was propelled by no less than ten engines. Look this one up and see what a giant it was.
So, the US Air Force set about tests, in the hope of building a nuclear powered bomber that could stay airborne for days or even weeks at a time, drastically reducing reliance on runways. Being able to keep a bomber fleet almost permanently airborne would, back in the 1950s, have been a huge strategic advantage.
But, that dream never materialised.
In order to keep the crew shielded from radiation, the reactor would always be too heavy. There was, at the time, no means of transferring the reactor’s output directly to usable aircraft engines. 1950s technology simply wouldn’t cut it, and it’s doubtful that 2020s technology could deliver a working nuclear powered aircraft for that matter, certainly not a manned aircraft.
Project Pluto.
This is when the planners had another idea. Namely, if it wasn’t possible to build a manned nuclear bomber, what about an unmanned nuclear bomber? Which would have the advantage of needing far less heavy reactor shielding?
Thus was born Project Pluto. Project Pluto, in some respects, I find amusing, in others, utterly terrifying, and ultimately, wonder what recreational pharmaceuticals the people responsible had been taking when they dreamed up this plan, which involves possibly the most bizarre aircraft-related project ever to have serious research and development money spent upon it.
This was, in effect, an early version of the Tomahawk cruise missile, but with some important differences. First, the size of the Pluto missile was considerably larger - this would have been a missile the size of a Union Pacific “Big Boy” steam locomotive, which means that the missile would have been around 200 tons in fully operational trim. Second, the missile was intended to operate at speeds well into the supersonic or even hypersonic realm, unlike the subsonic Tomahawk. Third, the missile was intended to be more of an unmanned bomber aircraft than a true missile, and the design involved equipping the missile with a warhead compartment bearing considerable similarities to the missile launch compartment of a nuclear ballistic missile submarine. This compartment would contain neat rows of nuclear warheads, that would be ejected into the air as the missile flew over the target, whereupon the missile would escape from the target area at extremely high speed, whilst the warhead delivered multi-megaton death to the unfortunates over whom it had just been deployed. Some idea of the eventual operational system, had it ever been deployed, can be obtained from this conceptual rendering:
So, what we have, in the above, is a low-altitude penetrating unmanned bomber, that would fly at treetop height, at speeds of Mach 4 or thereabouts, and which would dispense, say, 12 thermonuclear warheads of around 10 to 15 megatons yield.
It doesn’t take much imagining to realise what a horrendous weapons system this would have been, if it had ever become operational. Because the plan involved taking advantage of the nuclear reactor, to give the aircraft/missile effectively unlimited range once airborne, and thus make the system invulnerable to countermeasures. Large numbers of Pluto missiles would be kept airborne permanently, flying along ‘racetrack’ orbits at 50,000 feet above the Pacific Ocean, awaiting the radio signal that would tell their onboard guidance systems to head for the Soviet Union and begin pre-programmed bombing runs over various targets. The combination of speed and altitude would make them invulnerable to interceptor attack, and make them extremely difficult even for advanced surface to air missiles to intercept and destroy during the ‘racetrack’ orbit phase. However, once the command was given, the missiles would switch from high-altitude holding flights in their racetrack orbits, and fly at treetop height, skimming first the ocean, then the enemy’s land mass, still at speeds of around Mach 3 or even Mach 4. Each of the Pluto missiles would then dispense the warhead cargo over various pre-assigned targets, and saturate the Soviet Union with mutli-megaton warheads, effectively turning around 100 million Russians into radioactive lava.
What made the concept particularly horrendous, however, was the fact that even during the peacetime ‘racetrack’ phase of the operation, each Pluto missile would be carrying around with it an almost unshielded nuclear reactor. Therefore, it would be irradiating anything that approached within a mile of it, with lethal doses of gamma rays and spare neutrons. To make matters worse, the reactor would be shedding fission fragments into the exhaust air stream, constituting a nuclear pollution hazard of truly frightening proportions. The superheated air from the nuclear ramjet, laden with lethally radioactive particles, would be blasted out with such force that any living organisms unfortunate enough to find themselves in the wake of the missile would be killed by the shock wave before some of them had time to notice that they had been irradiated. Indeed, once operating at treetop altitude, the shock wave from the missile passing overhead would be sufficient to flatten quite a few buildings before any actual ordnance was delivered.
One member of the project development team suggested using these features as a secondary weapon, so that once the missile had dispensed its warheads, it could be programmed to keep flying over the Soviet Union, dispensing lethal hot gases, radioactive debris and a destructive shock wave upon everything it flew over. Finally, the missile, having unleashed this level of havoc over the target, could be programmed to crash into any remaining population centres, releasing the reactor core materials, and exterminating anything left living after the missile’s previous activities. The project developers were nothing if not thorough about their work.
However, turning this nightmare into reality proved to be littered with enormous technical hurdles. The first, and really important one from the standpoint of the developers, being producing a working nuclear engine. The idea that they hit upon was fiendishly simple: a nuclear ramjet.
Pluto’s engine would work by ramming air into the reactor chamber at supersonic or hypersonic speed, heating it to high temperatures using the reactor core, then ejecting it through the exhaust to provide thrust. Nice and simple, but for one little problem … building a reactor that would work as planned. Because, in order for the ramjet to work, the reactor had to be capable of heating the air to very high temperatures. Nuclear reactors were certainly capable of producing enough heat, but usually, this was the result of a meltdown. Producing this much heat in a controlled fashion, however, and maintaining the structural integrity of the reactor, was going to test the engineers’ skills to the limit. The reactor would have to be controllable, which meant that systems for inserting control rods would have to be developed, that would work within an intensely radioactive environment, which would withstand the extreme vibrational and thermal tolerances required, whilst still providing precise reactor control, and therefore precise engine thrust control.
Remember, normal nuclear reactors are surrounded by several hundred tons of concrete and lead shielding, whereas this reactor would be bereft of such shielding, in order to save as much weight as possible to enable the engine to loft a missile into the air. Thus, the engine compartment would have to be walled off from the rest of the aircraft with some suitable shielding to protect the payload and the electronics, whilst the outer integument of the engine compartment would be thin, allowing the lethal radiation from the reactor to irradiate the surroundings once the reactor was operational. The reactor would thus create one of the most hostile environments possible for its own control systems, and indeed, finding materials that would remain solid and maintain the necessary structural integrity under those conditions was a severe challenge - most metal alloys softened or even melted at the temperatures that the reactor was capable of delivering. So, when engineers at Lawrence Livermore set about building a test bed nuclear ramjet engine to make sure everything would work, one of the more unusual solutions they chose was to use ceramics for the reactor core - provided by, wait for its, a porcelain manufacturer called Coors, which would later abandon the porcelain business altogether in favour of brewing beer.
The metal parts of the reactor still had to withstand corrosion - remember, the missile was to fly in ‘racetrack’ orbits over oceans, and salt deposition would still be a problem over the long term, even at 50,000 feet, because these missiles would be flying over the oceans for years, possibly decades, awaiting their launch orders. Once airborne, the missiles would stay airborne, and be an air traffic controller’s nightmare for anything up to 25 years. The alloys that were eventually alighted on involved some very close tolerances - some of the metal parts had an auto-ignition temperature that was only 150 degrees above the peak output temperature of the reactor …
Remarkably, the Lawrence Livermore engineers not only built a working reactor, but, when they fired it up in a static test rig and operated it as a ramjet, it delivered 35,000 pounds of thrust, which is a pretty respectable figure even for a modern jet engine, let alone a unit designed in the mid-1950s and fired up as a prototype in 1964. But, the project was canned.
It’s not hard to work out why. First of all, the missiles, had they ever been launched, would have spent 25 years irradiating strategic allies of the USA all around the Pacific, long before they delivered any ordnance to the enemy. When the order to head for the USSR came, the missiles would have unleashed almost as much havoc upon America’s friends en route as upon the enemy. Missiles flying in paths over the Atlantic would have had an even worse effect, irradiating and shock-blasting strategic allies in Europe en route to the target - the very countries that the USA was purportedly pledged to protect if World War III ever got underway.
Second, Pluto was rendered obsolete by the development of cheaper, much more efficient, and much less troublesome ICBMs. Even the US Navy, which had expressed an interest in a submarine launched version of Pluto, abandoned the idea when successful tests of Polaris were complete. Land-based and submarine based ICBMs not only allowed the delivery of nuclear warheads to the target at lower cost, much higher speed, and greater accuracy, but did so without frying America’s friends during the transit flight.
Third, there was the little question of how a prototype would be tested. If the only powerplant that could propel Pluto was a nuclear powerplant, then testing an entire weapons system that would be experimental in its entirety with a live nuclear powerplant opened up some less than delightful possibilities. Such as a test missile “going rogue” and deciding that it was going to dispense its lethal shockwave and fission fragments all over Los Angeles, San Francisco, New York or Washington DC. Once the politicians woke up to how that sort of accident would cause their ratings to plummet below those of Jeffrey Dahmer, they started shitting themselves big time at the thought that they’d committed themselves to building and launching something that could, if it decided to go AWOL, become what one magazine article writer covering this project labelled “a flying Chernobyl”.
So, there you have it. The weird amalgam of nuclear powered cruise missile and unmanned bomber, with ordnance dispenser resembling that of a ballistic missile submarine, that was Pluto, and which the USA blew a cool $260 million upon in the days when that sort of money bought you two aircraft carriers. Today, that project would easily eat into $20 billion if it was restarted, even using the advances that have been made in 55 years to ease some of the technical problems, always assuming that some politician was stark, raving mad enough to resurrect this radioactive zombie.
Aren’t you so glad it never got off the ground? 
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Human perversity never ceases to amaze me.
While I understand that there are treaties in place that forbid the use of poison gas in warfare, it has always seemed to me that substances like sarin, VX, soman, and the newer novachok nerve agents offer greater possibilities for depopulating cities at a miniscule fraction of the cost when compared to things like this Pluto obscenity.
Besides, the buildings and infrastructure would be largely intact, and cleaning up the residue left after a chemical warfare attack would be a simpler and cheaper process than cleaning up radioactive contamination.
100 pounds of VX can kill almost 10 million people if we accept 0.5 mg as a lethal dose, and there are agents that are much more powerful than VX.
Small drones, suicide squads, and sleeper cells would be enough to cause uncounted millions of deaths in an enemy country at a tiny fraction of the expense of a single Pluto device.
When we consider these points, I never understood why there would even be interest in things like this stupid Pluto weapon.
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Big Geopolitics has always involved big dick swinging.
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