Nuclear rocket engine is a rocket engine whose operating principle is based on nuclear reaction or radioactive decay, in this case, energy is released that heats the working fluid, which can be reaction products or some other substance, such as hydrogen.
Let's look at the options and principles from action...
There are several types of rocket engines that use the principle of operation described above: nuclear, radioisotope, thermonuclear. Using nuclear rocket engines, it is possible to obtain specific impulse values significantly higher than those that can be achieved by chemical rocket engines. High value specific impulse is explained by the high speed of outflow of the working fluid - about 8-50 km/s. The thrust force of a nuclear engine is comparable to that of chemical engines, which will make it possible in the future to replace all chemical engines with nuclear ones.
The main obstacle to complete replacement is the radioactive pollution caused by nuclear rocket engines.
They are divided into two types - solid and gas phase. In the first type of engines, fissile material is placed in rod assemblies with a developed surface. This makes it possible to effectively heat a gaseous working fluid, usually hydrogen acts as a working fluid. The exhaust speed is limited by the maximum temperature of the working fluid, which, in turn, directly depends on the maximum permissible temperature of the structural elements, and it does not exceed 3000 K. In gas-phase nuclear rocket engines, the fissile substance is in a gaseous state. Its retention in work area carried out through influence electromagnetic field. For this type of nuclear rocket engines, the structural elements are not a limiting factor, so the exhaust speed of the working fluid can exceed 30 km/s. They can be used as first stage engines, despite the leakage of fissile material.
In the 70s XX century In the USA and the Soviet Union, nuclear rocket engines with fissile matter in the solid phase were actively tested. In the United States, a program was being developed to create an experimental nuclear rocket engine as part of the NERVA program.
The Americans developed a graphite reactor cooled by liquid hydrogen, which was heated, evaporated and ejected through a rocket nozzle. The choice of graphite was due to its temperature resistance. According to this project, the specific impulse of the resulting engine should have been twice as high as the corresponding figure characteristic of chemical engines, with a thrust of 1100 kN. The Nerva reactor was supposed to work as part of the third stage of the Saturn V launch vehicle, but due to the closure of the lunar program and the lack of other tasks for rocket engines of this class, the reactor was never tested in practice.
A gas-phase nuclear rocket engine is currently in the theoretical development stage. A gas-phase nuclear engine involves using plutonium, whose slow-moving gas stream is surrounded by a faster flow of cooling hydrogen. Experiments were conducted at the MIR and ISS orbital space stations that could give impetus to the further development of gas-phase engines.
Today we can say that Russia has slightly “frozen” its research in the field of nuclear propulsion systems. The work of Russian scientists is more focused on the development and improvement of basic components and assemblies of nuclear power plants, as well as their unification. The priority direction for further research in this area is the creation of nuclear power propulsion systems capable of operating in two modes. The first is the nuclear rocket engine mode, and the second is the installation mode of generating electricity to power the equipment installed on board the spacecraft.
Russian military space drive
A lot of noise in the media and social networks was caused by Vladimir Putin’s statements that Russia was testing a new generation cruise missile with almost unlimited range and is therefore virtually invulnerable to all existing and planned missile defense systems.
“At the end of 2017 at the central training ground Russian Federation The latest Russian cruise missile was successfully launched from nuclear energy installation. During the flight, the power plant reached the specified power and provided the required level of thrust,” Putin said during his traditional address to the Federal Assembly.
The missile was discussed in the context of other advanced Russian developments in the field of weapons, along with the new Sarmat intercontinental ballistic missile, the Kinzhal hypersonic missile, etc. Therefore, it is not at all surprising that Putin’s statements are analyzed primarily in a military-political vein. However, in fact, the question is much broader: it seems that Russia is on the verge of developing real technology future, capable of bringing revolutionary changes to rocket and space technology and beyond. But first things first…
Jet technologies: a “chemical” dead end
Almost now a hundred years When talking about a jet engine, we most often mean a chemical one jet engine. And jet planes and space rockets are driven by the energy obtained from the combustion of the fuel on board.
IN general outline it works like this: fuel enters the combustion chamber, where it is mixed with an oxidizer ( atmospheric air in an air-breathing engine or oxygen from on-board reserves in a rocket engine). The mixture then ignites, resulting in the rapid release of significant amount energy in the form of heat, which is transferred to gaseous combustion products. When heated, the gas rapidly expands and, as it were, squeezes itself out through the engine nozzle at considerable speed. A jet stream appears and jet thrust is created, pushing the aircraft in the direction opposite to the direction of the jet flow.
He 178 and Falcon Heavy are different products and engines, but this does not change the essence.
Jet and rocket engines in all their diversity (from the first Heinkel 178 jet to Elon Musk's Falcon Heavy) use precisely this principle - only the approaches to its application change. And all rocketry designers are forced in one way or another to put up with the fundamental drawback of this principle: the need to carry on board aircraft a significant amount of quickly consumed fuel. How great job the engine has to perform, the more fuel must be on board and the less payload the aircraft can take with it on flight.
For example, the maximum take-off weight of a Boeing 747-200 airliner is about 380 tons. Of these, 170 tons are for the aircraft itself, about 70 tons are for the payload (weight of cargo and passengers), and 140 tons, or approximately 35%, fuel weighs, which burns in flight at a rate of about 15 tons per hour. That is, for every ton of cargo there are 2.5 tons of fuel. And the Proton-M rocket, for launching 22 tons of cargo into a low reference orbit, consumes about 630 tons of fuel, i.e. almost 30 tons of fuel per ton of payload. As you can see, the “coefficient useful action"More than modest.
If we talk about really long flights, for example, to other planets solar system, then the fuel-load ratio becomes simply murderous. For example, the American Saturn 5 rocket could deliver 45 tons of cargo to the Moon, while burning over 2000 tons of fuel. And Elon Musk’s Falcon Heavy, with a launch mass of one and a half thousand tons, is capable of delivering only 15 tons of cargo into Mars orbit, that is, 0.1% of its initial mass.
That's why manned flight to the moon still remains a task at the limit of humanity's technological capabilities, and the flight to Mars goes beyond these limits. Even worse: it is no longer possible to significantly expand these capabilities while continuing to further improve chemical missiles. In their development, humanity has “hit” a ceiling determined by the laws of nature. In order to go further, a fundamentally different approach is needed.
"Atomic" thrust
The combustion of chemical fuels has long ceased to be the most efficient known method of producing energy.
From 1 kilogram coal you can get about 7 kilowatt-hours of energy, while 1 kilogram of uranium contains about 620 thousand kilowatt-hours.
And if you create an engine that will receive energy from nuclear, and not from chemical processes, then such an engine will require tens of thousands(!) times less fuel to do the same work. The key drawback of jet engines can be eliminated in this way. However, from idea to implementation there is a long path along which a lot of complex problems have to be solved. Firstly, it was necessary to create a nuclear reactor that was light and compact enough so that it could be installed on an aircraft. Secondly, it was necessary to figure out exactly how to use the energy of the decay of an atomic nucleus to heat the gas in the engine and create a jet stream.
The most obvious option was to simply pass gas through the hot reactor core. However, interacting directly with fuel assemblies, this gas would become very radioactive. Leaving the engine in the form of a jet stream, it would heavily contaminate everything around, so using such an engine in the atmosphere would be unacceptable. This means that heat from the core must be transferred somehow differently, but how exactly? And where can I get materials that can retain their structural properties for many hours at such high temperatures Oh?
It’s even easier to imagine the use of nuclear power in “unmanned deep-sea vehicles,” also mentioned by Putin in the same message. In fact, it will be something like a super torpedo that will suck in sea water, turn it into heated steam, which will form a jet stream. Such a torpedo will be able to travel thousands of kilometers underwater, moving at any depth and being capable of hitting any target at sea or on the coast. At the same time, it will be almost impossible to intercept it on the way to the target.
Samples currently ready for deployment similar devices Russia, it seems, does not have one yet. As for the nuclear-powered cruise missile that Putin spoke about, we are apparently talking about a test launch of a “mass-size model” of such a missile with an electric heater instead of a nuclear one. This is precisely what Putin’s words about “reaching a given power” and “proper thrust level” can mean – checking whether the engine of such a device can operate with such “input parameters.” Of course, unlike a nuclear-powered sample, a “model” product is not capable of flying any significant distance, but this is not required of it. Using such a sample, it is possible to work out technological solutions related to the purely “propulsion” part, while the reactor is being finalized and tested at the stand. Separate this stage from delivery finished product maybe just a little time - a year or two.
Well, if such an engine can be used in cruise missiles, then what will prevent it from being used in aviation? Imagine nuclear powered airliner, capable of traveling tens of thousands of kilometers without landing or refueling, without consuming hundreds of tons of expensive aviation fuel! In general, we are talking about a discovery that could in the future make a real revolution in the transport sector...
Is Mars ahead?
However, the main purpose of the nuclear power plant seems to be much more exciting - to become the nuclear heart of a new generation of spacecraft, which will make possible reliable transport links with other planets of the solar system. Of course, turbojet engines using outside air cannot be used in airless space. Whatever one may say, you will have to take the substance with you to create a jet stream here. The task is to use it much more economically during operation, and for this, the rate of flow of the substance from the engine nozzle must be as high as possible. In chemical rocket engines, this speed is up to 5 thousand meters per second (usually 2–3 thousand), and it is not possible to significantly increase it.
Much higher speeds can be achieved using a different principle of creating a jet stream - acceleration of charged particles (ions) electric field. The speed of the jet in an ion engine can reach 70 thousand meters per second, that is, to obtain the same amount of movement it will be necessary to spend 20–30 times less substance. True, such an engine will consume quite a lot of electricity. And to produce this energy you will need a nuclear reactor.
Model of a reactor installation for a megawatt-class nuclear power plant
Electric (ion and plasma) rocket engines already exist, e.g. back in 1971 The USSR launched into orbit the Meteor spacecraft with a stationary plasma engine SPD-60 developed by the Fakel Design Bureau. Today, similar engines are actively used to correct the orbit of artificial Earth satellites, but their power does not exceed 3–4 kilowatts (5 and a half horsepower).
However, in 2015, the Research Center named after. Keldysh announced the creation of a prototype ion engine with a power of the order of 35 kilowatts(48 hp). It doesn't sound very impressive, but several of these engines are quite enough to power a spacecraft moving in the void and away from strong gravitational fields. The acceleration that such engines will impart to the spacecraft will be small, but they will be able to maintain it for a long time (existing ion engines have a continuous operation time up to three years).
In modern spacecraft, rocket engines operate only for a short time, while for the main part of the flight the ship flies by inertia. The ion engine, receiving energy from a nuclear reactor, will operate throughout the flight - in the first half, accelerating the ship, in the second, braking it. Calculations show that such a spacecraft could reach the orbit of Mars in 30–40 days, and not in a year, like a ship with chemical engines, and also carry with it a descent module that could deliver a person to the surface of the Red Planet, and then pick him up from there.
One could begin this article with a traditional passage about how science fiction writers put forward bold ideas, and scientists then bring them to life. You can, but you don’t want to write with stamps. It is better to remember that modern rocket engines, solid fuel and liquid, have more than unsatisfactory characteristics for flights over relatively long distances. They allow you to launch cargo into Earth orbit and deliver something to the Moon, although such a flight is more expensive. But flying to Mars with such engines is no longer easy. Give them fuel and oxidizer in the required quantities. And these volumes are directly proportional to the distance that must be overcome.
An alternative to traditional chemical rocket engines are electric, plasma and nuclear engines. Of all the alternative engines, only one system has reached the stage of engine development - nuclear (Nuclear Reaction Engine). In the Soviet Union and the United States, work began on the creation of nuclear rocket engines back in the 50s of the last century. The Americans were working on both options for such a power plant: reactive and pulsed. The first concept involves heating the working fluid using a nuclear reactor and then releasing it through nozzles. The pulse nuclear propulsion engine, in turn, propels the spacecraft through successive explosions of small amounts of nuclear fuel.
Also in the USA, the Orion project was invented, combining both versions of the nuclear powered engine. This was done in the following way: small nuclear charges with a capacity of about 100 tons of TNT were ejected from the tail of the ship. Metal discs were fired after them. At a distance from the ship, the charge was detonated, the disk evaporated, and the substance scattered in different directions. Part of it fell into the reinforced tail section of the ship and moved it forward. A small increase in thrust should have been provided by the evaporation of the plate taking the blows. The unit cost of such a flight should have been only 150 then dollars per kilogram of payload.
It even got to the point of testing: experience showed that movement with the help of successive impulses is possible, as is the creation of a stern plate of sufficient strength. But the Orion project was closed in 1965 as unpromising. However, this is so far the only existing concept that can allow expeditions at least across the solar system.
It was only possible to reach the construction of a prototype with a nuclear-powered rocket engine. These were the Soviet RD-0410 and the American NERVA. They worked on the same principle: in a “conventional” nuclear reactor, the working fluid is heated, which, when ejected from the nozzles, creates thrust. The working fluid of both engines was liquid hydrogen, but the Soviet one used heptane as an auxiliary substance.
The thrust of the RD-0410 was 3.5 tons, NERVA gave almost 34, but it also had large dimensions: 43.7 meters in length and 10.5 in diameter versus 3.5 and 1.6 meters, respectively, for the Soviet engine. At the same time, the American engine was three times inferior to the Soviet one in terms of resource - the RD-0410 could work for an hour.
However, both engines, despite their promise, also remained on Earth and did not fly anywhere. main reason the closure of both projects (NERVA in the mid-70s, RD-0410 in 1985) - money. The characteristics of chemical engines are worse than those of nuclear engines, but the cost of one launch of a ship with a nuclear propulsion engine with the same payload can be 8-12 times more than the launch of the same Soyuz with a liquid propellant engine. And this does not even take into account all the costs necessary to bring nuclear engines to the point of being suitable for practical use.
Decommissioning of "cheap" Shuttles and absence of Lately Revolutionary breakthroughs in space technology require new solutions. In April of this year, the then head of Roscosmos A. Perminov announced his intention to develop and put into operation a completely new nuclear propulsion system. This is precisely what, in the opinion of Roscosmos, should radically improve the “situation” in the entire world cosmonautics. Now it has become clear who should become the next revolutionaries in astronautics: the development of nuclear propulsion engines will be carried out by the Keldysh Center Federal State Unitary Enterprise. The general director of the enterprise, A. Koroteev, has already pleased the public that the preliminary design spaceship for the new nuclear powered engine will be ready in next year. The engine design should be ready by 2019, with testing scheduled for 2025.
The complex was called TEM - transport and energy module. It will carry a gas-cooled nuclear reactor. The direct propulsion system has not yet been decided: either it will be a jet engine like the RD-0410, or an electric rocket engine (ERE). However, the latter type has not yet been widely used anywhere in the world: only three spacecraft were equipped with them. But the fact that the reactor can power not only the engine, but also many other units, or even use the entire TEM as a space power plant, speaks in favor of the electric propulsion engine.
Soviet and American scientists have been developing nuclear-fueled rocket engines since the mid-20th century. These developments have not progressed beyond prototypes and single tests, but now the only rocket propulsion system that uses nuclear energy is being created in Russia. "Reactor" studied the history of attempts to introduce nuclear rocket engines.
When humanity just began to conquer space, scientists were faced with the task of powering spacecraft. Researchers drew attention to the possibility of using nuclear energy in space, creating the concept of a nuclear rocket engine. Such an engine was supposed to use the energy of fission or fusion of nuclei to create jet thrust.
In the USSR, already in 1947, work began on creating a nuclear rocket engine. In 1953, Soviet experts noted that “the use of atomic energy will make it possible to obtain practically unlimited ranges and dramatically reduce the flight weight of missiles” (quoted from the publication “Nuclear Rocket Engines” edited by A.S. Koroteev, M, 2001). At that time, nuclear power propulsion systems were intended primarily to equip ballistic missiles, so the government's interest in the development was great. US President John Kennedy in 1961 named the national program to create a rocket with a nuclear rocket engine (Project Rover) one of the four priority areas in the conquest of space.
KIWI reactor, 1959. Photo: NASA.
In the late 1950s, American scientists created KIWI reactors. They have been tested many times, the developers have done a large number of modifications. Failures often occurred during testing, for example, once the engine core was destroyed and a large hydrogen leak was discovered.
In the early 1960s, both the USA and the USSR created the prerequisites for the implementation of plans to create nuclear rocket engines, but each country followed its own path. The USA created many designs of solid-phase reactors for such engines and tested them on open stands. The USSR was testing the fuel assembly and other engine elements, preparing the production, testing, and personnel base for a broader “offensive.”
NERVA YARD diagram. Illustration: NASA.
In the United States, already in 1962, President Kennedy stated that “a nuclear rocket will not be used in the first flights to the Moon,” so it is worth directing funds allocated for space exploration to other developments. At the turn of the 1960s and 1970s, two more reactors were tested (PEWEE in 1968 and NF-1 in 1972) as part of the NERVA program. But funding was focused on the lunar program, so the US nuclear propulsion program dwindled and was closed in 1972.
NASA film about the NERVA nuclear jet engine.
In the Soviet Union, the development of nuclear rocket engines continued until the 1970s, and they were led by the now famous triad of domestic academic scientists: Mstislav Keldysh, Igor Kurchatov and. They assessed the possibilities of creating and using nuclear-powered missiles quite optimistically. It seemed that the USSR was about to launch such a rocket. Fire tests were carried out at the Semipalatinsk test site - in 1978, the power launch of the first reactor of the 11B91 nuclear rocket engine (or RD-0410) took place, then two more series of tests - the second and third devices 11B91-IR-100. These were the first and last Soviet nuclear rocket engines.
M.V. Keldysh and S.P. Korolev visiting I.V. Kurchatova, 1959
Every few years some
the new lieutenant colonel discovers Pluto.
After that, he calls the laboratory,
to find out the future fate of the nuclear ramjet.
This is a fashionable topic these days, but it seems to me that a nuclear ramjet engine is much more interesting, because it does not need to carry a working fluid with it.
I assume that the President’s message was about him, but for some reason everyone started posting about the YARD today???
Let me collect everything here in one place. I'll tell you, interesting thoughts appear when you read into a topic. And very uncomfortable questions.
A ramjet engine (ramjet engine; the English term is ramjet, from ram - ram) is a jet engine that is the simplest in the class of air-breathing jet engines (ramjet engines) in design. It belongs to the type of direct reaction jet engines, in which thrust is created solely by the jet stream flowing from the nozzle. The increase in pressure necessary for engine operation is achieved by braking the oncoming air flow. A ramjet engine is inoperative at low flight speeds, especially at zero speed; one or another accelerator is needed to bring it to operating power.
In the second half of the 1950s, during the era cold war, projects of ramjet engines with a nuclear reactor were developed in the USA and USSR. 
Photo by: Leicht modifiziert aus http://en.wikipedia.org/wiki/Image:Pluto1955.jpg
The energy source of these ramjet engines (unlike other ramjet engines) is not the chemical reaction of fuel combustion, but the heat generated by the nuclear reactor in the heating chamber of the working fluid. Air from input device in such a ramjet, it passes through the reactor core, cooling it, heats itself up to the operating temperature (about 3000 K), and then flows out of the nozzle at a speed comparable to the flow rates for the most advanced chemical rocket engines. Possible purposes of an aircraft with such an engine:
- intercontinental cruise launch vehicle of a nuclear charge;
- single-stage aerospace aircraft.
Both countries created compact, low-resource nuclear reactors that fit into the dimensions of a large rocket. In the USA, under the Pluto and Tory nuclear ramjet research programs, bench fire tests of the Tory-IIC nuclear ramjet engine were carried out in 1964 (mode full power 513 MW for five minutes with a thrust of 156 kN). No flight tests were conducted and the program was closed in July 1964. One of the reasons for the closure of the program was the improvement of the design of ballistic missiles with chemical rocket engines, which fully ensured the solution of combat missions without the use of schemes with relatively expensive nuclear ramjet engines.
It’s not customary to talk about the second one in Russian sources now...
The Pluto project was supposed to use low-altitude flight tactics. This tactic ensured secrecy from the radars of the USSR air defense system.
To achieve the speed at which a ramjet engine would operate, Pluto had to be launched from the ground using a package of conventional rocket boosters. The launch of the nuclear reactor began only after Pluto reached cruising altitude and was sufficiently removed from populated areas. The nuclear engine, which gave an almost unlimited range of action, allowed the rocket to fly in circles over the ocean while awaiting the order to switch to supersonic speed towards a target in the USSR.
SLAM concept design
It was decided to conduct a static test of a full-scale reactor, which was intended for a ramjet engine.
Since the Pluto reactor became extremely radioactive after launch, it was delivered to the test site via a specially built, fully automated railway line. Along this line, the reactor moved over a distance of approximately two miles, which separated the static test stand and the massive “dismantling” building. In the building, the “hot” reactor was dismantled for inspection using remotely controlled equipment. Livermore scientists monitored the testing process using a television system located in a tin hangar far from the test stand. Just in case, the hangar was equipped with an anti-radiation shelter with a two-week supply of food and water.
Just to supply the concrete needed to construct the demolition building's walls (which were six to eight feet thick), the United States government purchased an entire mine.
Millions of pounds of compressed air were stored in 25 miles of oil production pipes. The compressed air was intended to be used to simulate the conditions in which a ramjet engine finds itself during flight at cruising speed.
To ensure high air pressure in the system, the laboratory borrowed giant compressors from the submarine base in Groton, Connecticut.
The test, during which the unit ran at full power for five minutes, required forcing a ton of air through steel tanks that were filled with more than 14 million 4cm diameter steel balls. These tanks were heated to 730 degrees with heating elements in which oil was burned.
Installed on a railway platform, Tori-2S is ready for successful testing. May 1964
On May 14, 1961, engineers and scientists in the hangar from which the experiment was controlled held their breath as the world's first nuclear ramjet engine, mounted on a bright red railway platform, announced its birth with a loud roar. Tori-2A was launched for only a few seconds, during which it did not develop its rated power. However, the test was considered successful. The most important thing was that the reactor did not ignite, which some representatives of the Atomic Energy Committee were extremely afraid of. Almost immediately after the tests, Merkle began work on creating a second Tori reactor, which was supposed to have more power with less weight.
Work on Tori-2B has not progressed beyond the drawing board. Instead, the Livermores immediately built the Tory-2C, which broke the silence of the desert three years after testing the first reactor. A week later, the reactor was restarted and operated at full power (513 megawatts) for five minutes. It turned out that the radioactivity of the exhaust was significantly less than expected. These tests were also attended by Air Force generals and officials from the Atomic Energy Committee.
At this time, the customers from the Pentagon who financed the Pluto project began to be overcome by doubts. Since the missile was launched from US territory and flew over the territory of American allies at low altitude to avoid detection by Soviet air defense systems, some military strategists wondered whether the missile would pose a threat to the allies. Even before the Pluto missile drops bombs on the enemy, it will first stun, crush and even irradiate allies. (Pluto flying overhead was expected to produce about 150 decibels of noise on the ground. By comparison, the noise level of the rocket that sent the Americans to the Moon (Saturn V) was 200 decibels at full thrust.) Of course, ruptured eardrums would be the least of your problems if you found yourself with a naked reactor flying overhead, frying you like a chicken with gamma and neutron radiation.
Tori-2C
Although the rocket's creators argued that Pluto was also inherently elusive, military analysts expressed bafflement at how something so noisy, hot, large and radioactive could remain undetected for as long as it took to complete its mission. At the same time, the US Air Force had already begun to deploy Atlas and Titan ballistic missiles, which were capable of reaching targets several hours before a flying reactor, and the USSR anti-missile system, the fear of which became the main impetus for the creation of Pluto. , never became an obstacle for ballistic missiles, despite successful test interceptions. Critics of the project came up with their own decoding of the acronym SLAM - slow, low, and messy - slowly, low and dirty. After the successful testing of the Polaris missile, the Navy, which had initially expressed interest in using the missiles for launch from submarines or ships, also began to abandon the project. And finally, the cost of each rocket was 50 million dollars. Suddenly Pluto became a technology with no applications, a weapon with no viable targets.
However, the final nail in Pluto's coffin was just one question. It is so deceptively simple that the Livermoreians can be excused for deliberately not paying attention to it. “Where to conduct reactor flight tests? How do you convince people that during the flight the rocket will not lose control and fly over Los Angeles or Las Vegas at low altitude?” asked Livermore Laboratory physicist Jim Hadley, who worked on the Pluto project until the very end. He is currently working on detecting nuclear tests being carried out in other countries for Unit Z. By Hadley's own admission, there were no guarantees that the missile would not get out of control and turn into a flying Chernobyl.
Several solutions to this problem have been proposed. One would be a Pluto launch near Wake Island, where the rocket would fly figure-eights over the United States' part of the ocean. “Hot” missiles were supposed to be sunk at a depth of 7 kilometers in the ocean. However, even when the Atomic Energy Commission persuaded people to think of radiation as a limitless source of energy, the proposal to dump many radiation-contaminated rockets into the ocean was enough to stop work.
On July 1, 1964, seven years and six months after the start of work, the Pluto project was closed by the Atomic Energy Commission and the Air Force.
According to Hadley, every few years a new lieutenant colonel air force discovers Pluto. After this, he calls the laboratory to find out the further fate of the nuclear ramjet. The lieutenant colonels' enthusiasm disappears immediately after Hadley talks about problems with radiation and flight tests. No one called Hadley more than once.
If anyone wants to bring Pluto back to life, he might be able to find some recruits in Livermore. However, there won't be many of them. The idea of what could become one hell of a crazy weapon is best left in the past.
Technical characteristics of the SLAM rocket:
Diameter - 1500 mm.
Length - 20000 mm.
Weight - 20 tons.
The range is unlimited (theoretically).
Speed at sea level is Mach 3.
Armament - 16 thermonuclear bombs (each with a yield of 1 megaton).
The engine is a nuclear reactor (power 600 megawatts).
Guidance system - inertial + TERCOM.
The maximum skin temperature is 540 degrees Celsius.
The airframe material is high-temperature Rene 41 stainless steel.
Sheathing thickness - 4 - 10 mm.
Nevertheless, the nuclear ramjet engine is promising as propulsion system for single-stage aerospace aircraft and high-speed intercontinental heavy transport aircraft. This is facilitated by the possibility of creating a nuclear ramjet capable of operating at subsonic and zero flight speeds in rocket engine mode, using on-board propellant reserves. That is, for example, an aerospace aircraft with a nuclear ramjet starts (including takes off), supplying working fluid to the engines from the onboard (or outboard) tanks and, having already reached speeds from M = 1, switches to using atmospheric air.
As Russian President V.V. Putin said, at the beginning of 2018, “a successful launch of a cruise missile with a nuclear power plant took place.” Moreover, according to him, the range of such a cruise missile is “unlimited.”
I wonder in what region the tests were carried out and why the relevant nuclear test monitoring services slammed them. Or is the autumn release of ruthenium-106 in the atmosphere somehow connected with these tests? Those. Chelyabinsk residents were not only sprinkled with ruthenium, but also fried?
Can you find out where this rocket fell? Simply put, where was the nuclear reactor broken up? At what training ground? On Novaya Zemlya?
**************************************** ********************
Now let’s read a little about nuclear rocket engines, although that’s a completely different story
A nuclear rocket engine (NRE) is a type of rocket engine that uses the energy of fission or fusion of nuclei to create jet thrust. They can be liquid (heating a liquid working fluid in a heating chamber from a nuclear reactor and releasing gas through a nozzle) and pulse-explosive (low-power nuclear explosions at an equal period of time).
A traditional nuclear propulsion engine as a whole is a structure consisting of a heating chamber with a nuclear reactor as a heat source, a working fluid supply system and a nozzle. The working fluid (usually hydrogen) is supplied from the tank to the reactor core, where, passing through channels heated by the nuclear decay reaction, it is heated to high temperatures and then thrown out through the nozzle, creating jet thrust. Exist various designs NRD: solid-phase, liquid-phase and gas-phase - corresponding state of aggregation nuclear fuel in the reactor core - solid, melt or high-temperature gas (or even plasma). 
East. https://commons.wikimedia.org/w/index.php?curid=1822546
RD-0410 (GRAU Index - 11B91, also known as "Irgit" and "IR-100") - the first and only Soviet nuclear rocket engine 1947-78. It was developed at the Khimavtomatika design bureau, Voronezh.
The RD-0410 used a heterogeneous thermal neutron reactor. The design included 37 fuel assemblies, covered with thermal insulation that separated them from the moderator. ProjectIt was envisaged that the hydrogen flow first passed through the reflector and moderator, maintaining their temperature at room temperature, and then entered the core, where it was heated to 3100 K. At the stand, the reflector and moderator were cooled by a separate hydrogen flow. The reactor went through a significant series of tests, but was never tested for its full operating duration. The out-of-reactor components were completely exhausted.
********************************
And this is an American nuclear rocket engine. His diagram was in the title picture 
Author: NASA - Great Images in NASA Description, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6462378
NERVA (Nuclear Engine for Rocket Vehicle Application) is a joint program of the US Atomic Energy Commission and NASA to create a nuclear rocket engine (NRE), which lasted until 1972.
NERVA demonstrated that the nuclear propulsion system was viable and suitable for space exploration, and in late 1968 the SNPO confirmed that NERVA's newest modification, the NRX/XE, met the requirements for a manned mission to Mars. Although NERVA motors have been built and tested to the maximum possible extent and were considered ready for installation on a spacecraft, most of the American space program was canceled by the Nixon administration.
NERVA has been rated by the AEC, SNPO, and NASA as a highly successful program that has met or exceeded its goals. The main goal of the program was to “create technical base for nuclear rocket propulsion systems to be used in the design and development of propulsion systems for space missions.” Almost all space projects using nuclear propulsion engines are based on NERVA NRX or Pewee designs.
Mars missions were responsible for NERVA's demise. Members of Congress from both political parties have decided that a manned mission to Mars would be a tacit commitment for the United States to support the costly space race for decades. Each year the RIFT program was delayed and NERVA's goals became more complex. After all, although the NERVA engine had many successful tests and strong support from Congress, it never left Earth.
In November 2017, China Aerospace Science and Technology Corporation (CASC) published road map development of the PRC space program for the period 2017-2045. It provides, in particular, for the creation of a reusable ship powered by a nuclear rocket engine.