Nuclear rocket engines. Atomic space engine

Alexander Losev

The rapid development of rocket and space technology in the 20th century was due to the military-strategic, political and, to a certain extent, ideological goals and interests of the two superpowers - the USSR and the USA, and all state space programs were a continuation of their military projects, where the main task was the need to ensure defense capability and strategic parity with a potential adversary. The cost of creating equipment and the cost of operating then did not have a fundamental significance. Enormous resources were allocated to the creation of launch vehicles and spacecraft, and the 108-minute flight of Yuri Gagarin in 1961 and the television broadcast of Neil Armstrong and Buzz Aldrin from the surface of the Moon in 1969 were not just triumphs of scientific and technical thought, they were also considered as strategic victories in battles of the Cold War.

But after the Soviet Union collapsed and dropped out of the race for world leadership, its geopolitical opponents, primarily the United States, no longer needed to implement prestigious, but extremely costly space projects in order to prove to the whole world the superiority of the Western economic system and ideological concepts.
In the 90s, the main political tasks of the past years lost their relevance, the bloc confrontation was replaced by globalization, pragmatism prevailed in the world, so most space programs were curtailed or postponed, only the ISS remained from the large-scale projects of the past. In addition, Western democracy has made all expensive state programs dependent on electoral cycles.
The voter support needed to gain or stay in power makes politicians, parliaments and governments lean towards populism and to solve immediate problems, so spending on space exploration is reduced year by year.
Most of the fundamental discoveries were made in the first half of the twentieth century, and today science and technology have reached certain limits, in addition, the popularity of scientific knowledge has decreased all over the world, and the quality of teaching mathematics, physics and other natural sciences has deteriorated. This was the reason for the stagnation, including in the space sector, of the last two decades.
But now it becomes obvious that the world is approaching the end of the next technological cycle based on the discoveries of the last century. Therefore, any power that will have fundamentally new promising technologies at the time of the change in the global technological order will automatically secure world leadership for at least the next fifty years.

Principal device of a nuclear rocket engine with hydrogen as a working fluid

This is realized in the United States, where a course has been taken to revive American greatness in all spheres of activity, and in China, challenging American hegemony, and in the European Union, which is trying with all its might to maintain its weight in the global economy.
There exists industrial policy and are seriously engaged in the development of their own scientific, technical and production potential, and the space sphere can become the best testing ground for developing new technologies and for proving or refuting scientific hypotheses that can lay the foundation for creating a fundamentally different, more advanced technology of the future.
And it is quite natural to expect that the United States will be the first country where deep space exploration projects are resumed in order to create unique innovative technologies both in the field of weapons, transport and structural materials, and in biomedicine and in the field of telecommunications
True, not even the United States is guaranteed success on the path to creating revolutionary technologies. There is a high risk of getting into a dead end, improving rocket engines half a century ago based on chemical fuel, as Elon Musk's SpaceX does, or by creating life support systems for a long flight similar to those already implemented on the ISS.
Can Russia, whose stagnation in the space industry is becoming more noticeable every year, make a breakthrough in the race for future technological leadership in order to remain in the club of superpowers, and not in the list of developing countries?
Yes, of course, Russia can, and moreover, a significant step forward has already been made in nuclear power and nuclear rocket engine technologies, despite the chronic underfunding of the space industry.
The future of astronautics is the use of nuclear energy. To understand how nuclear technology and space are related, it is necessary to consider the basic principles of jet propulsion.
So, the main types of modern space engines are created on the principles of chemical energy. These are solid-propellant boosters and liquid-propellant rocket engines, in their combustion chambers, the fuel components (fuel and oxidizer), entering into an exothermic physico-chemical combustion reaction, form a jet stream that ejects tons of matter from the engine nozzle every second. The kinetic energy of the working fluid of the jet is converted into a reactive force sufficient to propel the rocket. The specific impulse (the ratio of thrust produced to the mass of fuel used) of such chemical engines depends on the fuel components, the pressure and temperature in the combustion chamber, and the molecular weight of the gaseous mixture ejected through the engine nozzle.
And the higher the temperature of the substance and the pressure inside the combustion chamber, and the lower the molecular weight of the gas, the higher the specific impulse, and hence the efficiency of the engine. Specific impulse is the amount of motion, and it is customary to measure it in meters per second, as well as speed.
In chemical engines, fuel mixtures oxygen-hydrogen and fluorine-hydrogen (4500–4700 m/s) give the highest specific impulse, but rocket engines powered by kerosene and oxygen, such as Soyuz and missiles "Falcon" Mask, as well as engines on asymmetric dimethylhydrazine (UDMH) with an oxidizer in the form of a mixture of nitrogen tetroxide and nitric acid (Soviet and Russian "Proton", French "Arian", American "Titan"). Their efficiency is 1.5 times lower than that of hydrogen-fueled engines, but an impulse of 3000 m / s and power is quite enough to make it economically profitable to launch tons of payloads into near-Earth orbits.
But flights to other planets require much larger spacecraft than anything that has been created by mankind before, including the modular ISS. In these ships, it is necessary to provide long-term autonomous existence crews, and a certain amount of fuel and service life of main engines and engines for maneuvers and orbit correction, provide for the delivery of astronauts in a special landing module to the surface of another planet, and their return to the main transport ship, and then the return of the expedition to Earth.
The accumulated engineering and technical knowledge and the chemical energy of the engines make it possible to return to the Moon and reach Mars, so it is highly likely that in the next decade humanity will visit the Red Planet.
If we rely only on available space technologies, then the minimum mass of a habitable module for a manned flight to Mars or to the satellites of Jupiter and Saturn will be approximately 90 tons, which is 3 times more than the lunar ships of the early 1970s, which means that launch vehicles for their insertion into reference orbits for further flight to Mars will be far superior to the Saturn-5 (launch weight 2965 tons) of the Apollo lunar project or the Soviet carrier Energia (launch weight 2400 tons). It will be necessary to create an interplanetary complex weighing up to 500 tons in orbit. A flight on an interplanetary ship with chemical rocket engines will require from 8 months to 1 year of time only in one direction, because you will have to do gravitational maneuvers, using the force of gravity of the planets for additional acceleration of the ship, and a huge supply of fuel.
But using the chemical energy of rocket engines, humanity will not fly beyond the orbit of Mars or Venus. We need other speeds of flight of spaceships and other more powerful energy of movement.

Modern nuclear rocket engine project Princeton Satellite Systems

To explore deep space, it is necessary to significantly increase the thrust-to-weight ratio and efficiency of a rocket engine, which means increasing its specific impulse and service life. And for this it is necessary to heat the gas or substance of the working fluid with a low temperature inside the engine chamber. atomic mass to temperatures several times higher than the temperature of chemical combustion of traditional fuel mixtures, and this can be done using a nuclear reaction.
If, instead of a conventional combustion chamber, a nuclear reactor is placed inside a rocket engine, into the active zone of which a substance in liquid or gaseous form is supplied, then it, heating up under high pressure up to several thousand degrees, will begin to be ejected through the nozzle channel, creating jet thrust. The specific impulse of such a nuclear jet engine will be several times greater than that of a conventional one based on chemical components, which means that the efficiency of both the engine itself and the launch vehicle as a whole will increase many times over. In this case, an oxidizer for fuel combustion is not required, and light hydrogen gas can be used as a substance that creates jet thrust, but we know that the lower the molecular weight of the gas, the higher the momentum, and this will significantly reduce the mass of the rocket with better performance engine power.
A nuclear engine would be better than a conventional one, because in the reactor zone, light gas can be heated to temperatures in excess of 9 thousand degrees Kelvin, and a jet of such superheated gas will provide a much higher specific impulse than ordinary chemical engines can give. But that's in theory.
The danger is not even that during the launch of a launch vehicle with such a nuclear installation, radioactive contamination of the atmosphere and space around the launch pad can occur, the main problem is that at high temperatures the engine itself can melt along with the spacecraft. Designers and engineers understand this and have been trying to find suitable solutions for several decades.
Nuclear rocket engines (NRE) already have their own history of creation and operation in space. The first development of nuclear engines began in the mid-1950s, that is, even before manned space flight, and almost simultaneously in the USSR and the USA, and the very idea of ​​using nuclear reactors to heat the working substance in a rocket engine was born together with the first reactors in mid-40s, that is, more than 70 years ago.
In our country, the thermal physicist Vitaly Mikhailovich Ievlev became the initiator of the creation of the NRE. In 1947, he presented a project that was supported by S. P. Korolev, I. V. Kurchatov and M. V. Keldysh. Initially, it was planned to use such engines for cruise missiles, and then put them on ballistic missiles. The leading defense design bureaus of the Soviet Union, as well as the research institutes NIITP, CIAM, IAE, VNIINM, took up the development.
The Soviet nuclear engine RD-0410 was assembled in the mid-60s by the Voronezh "Design Bureau of Chemical Automation", where most of the liquid-propellant rocket engines for space technology were created.
Hydrogen was used as a working fluid in RD-0410, which in liquid form passed through the "cooling jacket", removing excess heat from the walls of the nozzle and preventing it from melting, and then entered the reactor core, where it was heated to 3000K and ejected through the channel nozzles, thus converting thermal energy into kinetic energy and creating a specific impulse of 9100 m/s.
In the USA, the NRE project was launched in 1952, and the first operating engine was created in 1966 and was named NERVA (Nuclear Engine for Rocket Vehicle Application). In the 60s - 70s, the Soviet Union and the United States tried not to yield to each other.
True, both our RD-0410 and the American NERVA were solid-phase NREs (nuclear fuel based on uranium carbides was in a solid state in the reactor), and their operating temperature was in the range of 2300–3100K.
In order to increase the temperature of the core without the risk of an explosion or melting of the reactor walls, it is necessary to create conditions for a nuclear reaction under which the fuel (uranium) passes into a gaseous state or turns into a plasma and is kept inside the reactor due to a strong magnetic field, without touching the walls. And then the hydrogen entering the reactor core “flows around” the uranium in the gas phase, and turning into plasma, is ejected through the nozzle channel at a very high speed.
This type of engine is called the gas-phase YRD. The temperatures of gaseous uranium fuel in such nuclear engines can range from 10,000 to 20,000 degrees Kelvin, and the specific impulse can reach 50,000 m/s, which is 11 times higher than the most efficient chemical rocket engines.
Creation and use in space technology of gas-phase NREs of open and closed types is the most promising direction development of space rocket engines and exactly what humanity needs to explore the planets solar system and their companions.
The first studies on the gas-phase NRE project began in the USSR in 1957 at the Research Institute of Thermal Processes (NRC named after M. V. Keldysh), and the very decision to develop nuclear space power plants based on gas-phase nuclear reactors was made in 1963 by Academician V. P. Glushko (NPO Energomash), and then approved by a resolution of the Central Committee of the CPSU and the Council of Ministers of the USSR.
The development of a gas-phase NRE was carried out in the Soviet Union for two decades, but, unfortunately, was never completed due to insufficient funding and the need for additional fundamental research in the field of thermodynamics of nuclear fuel and hydrogen plasma, neutron physics and magnetohydrodynamics.
Soviet nuclear scientists and design engineers faced a number of problems, such as achieving criticality and ensuring the stability of the operation of a gas-phase nuclear reactor, reducing the loss of molten uranium during the release of hydrogen heated to several thousand degrees, thermal protection of the nozzle and magnetic field generator, accumulation of uranium fission products , the choice of chemically resistant structural materials, etc.
And when for Soviet program"Mars-94" of the first manned flight to Mars, the Energia launch vehicle began to be created, the nuclear engine project was postponed indefinitely. The Soviet Union did not have enough time, and most importantly political will and economic efficiency, to land our cosmonauts on the planet Mars in 1994. This would be an indisputable achievement and proof of our leadership in high technologies over the next few decades. But space, like many other things, was betrayed by the last leadership of the USSR. History cannot be changed, departed scientists and engineers cannot be returned, and lost knowledge cannot be restored. A lot of things will have to be re-created.
But space nuclear power is not limited to the sphere of solid- and gas-phase NREs. To create a heated flow of matter in a jet engine, you can use electrical energy. This idea was first expressed by Konstantin Eduardovich Tsiolkovsky back in 1903 in his work "The Study of the World Spaces with Reactive Instruments".
And the first electrothermal rocket engine in the USSR was created in the 1930s by Valentin Petrovich Glushko, a future academician of the USSR Academy of Sciences and head of NPO Energia.
The principles of operation of electric rocket engines can be different. They are usually divided into four types:

• electrothermal (heating or electric arc). In them, the gas is heated to temperatures of 1000–5000K and is ejected from the nozzle in the same way as in the NRE.
• electrostatic engines (colloidal and ionic), in which the working substance is ionized first, and then positive ions (atoms devoid of electrons) are accelerated in an electrostatic field and are also ejected through the nozzle channel, creating jet thrust. Stationary plasma engines also belong to electrostatic engines.
• magnetoplasma and magnetodynamic rocket engines. There, the gaseous plasma is accelerated by the Ampère force in perpendicularly intersecting magnetic and electric fields.
• impulse rocket engines, which use the energy of gases arising from the evaporation of the working fluid in an electric discharge.

The advantage of these electric rocket engines is the low consumption of the working fluid, the efficiency of up to 60% and the high particle flow rate, which can significantly reduce the mass of the spacecraft, but there is also a minus - low thrust density, and, accordingly, low power, as well as the high cost of the working fluid (inert gases or alkali metal vapors) to create a plasma.
All of the listed types of electric motors have been implemented in practice and have been repeatedly used in space on both Soviet and American vehicles since the mid-1960s, but due to their low power, they were mainly used as orbit correction engines.
From 1968 to 1988, the USSR launched a whole series of Kosmos satellites with nuclear installations on board. The types of reactors were named: "Buk", "Topaz" and "Yenisei".
The reactor of the Yenisei project had a thermal power of up to 135 kW and an electrical power of about 5 kW. The heat carrier was a sodium-potassium melt. This project was closed in 1996.
For a real sustainer rocket motor, a very powerful source of energy is required. And the best source of energy for such space engines is a nuclear reactor.
Nuclear energy is one of the high-tech industries where our country maintains its leading position. And a fundamentally new rocket engine is already being created in Russia, and this project is close to successful completion in 2018. Flight tests are scheduled for 2020.
And if the gas-phase NRE is a topic of the future decades to which we will have to return after fundamental research, then its current alternative is a megawatt-class nuclear power plant (NPP), and it has already been created by the enterprises of Rosatom and Roscosmos since 2009.
NPO Krasnaya Zvezda, which is currently the only developer and manufacturer of space nuclear power plants in the world, and Research Center them. M. V. Keldysh, NIKIET them. N. A. Dollezhala, Research Institute NPO Luch, Kurchatov Institute, IRM, IPPE, NIIAR and NPO Mashinostroeniya.
The nuclear power plant includes a high-temperature gas-cooled fast-neutron nuclear reactor with a system of turbomachine conversion of thermal energy into electrical energy, a system of refrigerator-emitters for removing excess heat into space, an instrument-assembly compartment, a block of marching plasma or ion electric motors and a container for placing a payload .
In a power propulsion system, a nuclear reactor serves as a source of electricity for the operation of electric plasma engines, while the gas coolant of the reactor passing through the core enters the turbine of the electric generator and compressor and returns back to the reactor in a closed loop, and is not thrown into space as in the NRE, which makes the design more reliable and safe, and therefore suitable for manned astronautics.
It is planned that a nuclear power plant will be used for a reusable space tug to ensure the delivery of cargo during the exploration of the Moon or the creation of multi-purpose orbital complexes. The advantage will be not only the reusable use of elements of the transport system (which Elon Musk is trying to achieve in his SpaceX space projects), but also the possibility of delivering three times more mass of cargo than on rockets with chemical jet engines of comparable power by reducing the launch mass of the transport system . The special design of the installation makes it safe for people and the environment on Earth.
In 2014, the first standard design fuel element (fuel element) for this nuclear electric propulsion plant was assembled at OJSC Mashinostroitelny Zavod in Elektrostal, and in 2016 a reactor core basket simulator was tested.
Now (in 2017), work is underway to manufacture structural elements of the installation and test components and assemblies on mock-ups, as well as autonomous testing of turbomachine energy conversion systems and power unit prototypes. Completion of works is scheduled for the end of the next 2018, however, since 2015, the backlog from the schedule began to accumulate.
So, as soon as this installation is created, Russia will become the first country in the world to possess nuclear space technologies, which will form the basis of not only future projects for the development of the solar system, but also terrestrial and extraterrestrial energy. Space nuclear power plants can be used to create systems for remote transmission of electricity to the Earth or to space modules using electromagnetic radiation. And this will also become the advanced technology of the future, where our country will have a leading position.
On the basis of the developed plasma motors, powerful propulsion systems will be created for long-distance human spaceflight and, first of all, for the exploration of Mars, the orbit of which can be reached in just 1.5 months, and not more than a year, as when using conventional chemical jet engines .
And the future always starts with a revolution in energy. And nothing else. Energy is primary and it is the magnitude of energy consumption that affects technical progress, defense capability and the quality of life of people.

NASA experimental plasma rocket engine

Soviet astrophysicist Nikolai Kardashev proposed a scale for the development of civilizations back in 1964. According to this scale, the level of technological development of civilizations depends on the amount of energy that the population of the planet uses for their needs. So type I civilization uses everything available resources available on the planet; type II civilization - receives the energy of its star, in the system of which it is located; and a type III civilization uses the available energy of its galaxy. Humanity has not yet grown to a type I civilization on this scale. We use only 0.16% of the total potential energy supply of the planet Earth. This means that Russia and the whole world have room to grow, and these nuclear technologies will open the way for our country not only into space, but also future economic prosperity.
And, perhaps, the only option for Russia in the scientific and technical sphere is now to make a revolutionary breakthrough in nuclear space technologies in order to overcome the many years behind the leaders in one “jump” and immediately be at the origins of a new technological revolution in the next cycle of development of human civilization. Such a unique chance falls to this or that country only once in several centuries.
Unfortunately, Russia, which has not paid due attention to fundamental sciences and the quality of higher and secondary education over the past 25 years, risks losing this chance forever if the program is curtailed and the current scientists and engineers are not replaced by a new generation of researchers. The geopolitical and technological challenges that Russia will face in 10-12 years will be very serious, comparable to the threats of the mid-twentieth century. In order to preserve the sovereignty and integrity of Russia in the future, it is urgently necessary to start training specialists capable of responding to these challenges and creating something fundamentally new right now.
There is only about 10 years to turn Russia into a world intellectual and technological center, and this cannot be done without a serious change in the quality of education. For a scientific and technological breakthrough, it is necessary to return to the education system (both school and university) a systematic view of the picture of the world, scientific fundamentality and ideological integrity.
As for the current stagnation in the space industry, this is not terrible. Physical principles, on which modern space technologies are based, will be in demand by the conventional satellite services sector for a long time to come. Recall that mankind has been using the sail for 5.5 thousand years, and the era of steam lasted almost 200 years, and only in the twentieth century the world began to change rapidly, because there was another scientific and technological revolution that launched a wave of innovations and a change in technological patterns, which ultimately changed the world economy and politics. The main thing is to be at the origins of these changes.

The idea of ​​throwing atomic bombs astern turned out to be too brutal, but the amount of energy that a nuclear fission reaction gives, not to mention fusion, is extremely attractive for astronautics. Therefore, many non-impulse systems were created, free from the problems of storing hundreds of nuclear bombs on board and cyclopean shock absorbers. We will talk about them today.

Nuclear physics at your fingertips

NERVA

Project history

Design

Hydrogen from the tank entered the reactor, heated there, and was thrown out, creating jet thrust. Hydrogen was chosen as the working fluid because it has light atoms, and it is easier to disperse them to high speed. The greater the speed of the jet exhaust, the more efficient the rocket engine.
The neutron reflector was used to ensure that the neutrons returned back to the reactor to maintain the nuclear chain reaction.
Control rods were used to control the reactor. Each such rod consisted of two halves - a reflector and a neutron absorber. When the rod was turned by a neutron reflector, their flux in the reactor increased and the reactor increased heat transfer. When the rod was turned by the neutron absorber, their flux in the reactor decreased, and the reactor lowered the heat transfer.
Hydrogen was also used to cool the nozzle, and warm hydrogen from the nozzle cooling system rotated the turbopump to supply more hydrogen.

The engine is at work. Hydrogen was ignited specially at the outlet of the nozzle in order to avoid the threat of an explosion; there would be no burning in space.

The NERVA engine produced 34 tons of thrust, about one and a half times smaller than the J-2 engine that powered the second and third stages of the Saturn-V rocket. The specific impulse was 800-900 seconds, which was twice as much as the best oxygen-hydrogen engines, but less than the ERE or the Orion engine.

A little about security

RD-0410

The Soviet RD-0410 engine has a similar history. The idea of ​​the engine was born in the late 40s among the pioneers of rocket and nuclear technology. As with the Rover project, the initial idea was an atomic air-jet engine for the first stage of a ballistic missile, then the development moved to the space industry. RD-0410 was developed more slowly, domestic developers were carried away by the idea of ​​a gas-phase NRE (this will be discussed below). The project was started in 1966 and continued until the mid-1980s. The target for the engine was the mission "Mars-94" - a manned flight to Mars in 1994.
The RD-0410 scheme is similar to NERVA - hydrogen passes through the nozzle and reflectors, cooling them, is fed into the reactor core, heated there and thrown out.
According to its characteristics, the RD-0410 was better than NERVA - the temperature of the reactor core was 3000 K instead of 2000 K for NERVA, and the specific impulse exceeded 900 s. RD-0410 was lighter and more compact than NERVA and developed ten times less thrust.

Engine testing. The side torch on the bottom left ignites the hydrogen to avoid an explosion.

Development of solid-phase NREs

Nuclear fuel salt engine

The idea was proposed in 1991 by Robert Zubrin and, according to various estimates, promises a specific impulse of 1300 to 6700 s with tons of thrust. Unfortunately, this scheme also has disadvantages:

• Difficulty in storing fuel - a chain reaction in the tank must be avoided by placing the fuel, for example, in thin tubes from a neutron absorber, so the tanks will be complex, heavy and expensive.


• Large consumption of nuclear fuel - the fact is that the reaction efficiency (number of decayed / number of spent atoms) will be very low. Even in an atomic bomb, the fissile material does not "burn out" completely; immediately, most of the valuable nuclear fuel will be thrown away.


• Ground tests are practically impossible - the exhaust of such an engine will be very dirty, even dirtier than the Orion.


• There are some questions about the control of a nuclear reaction - it is not a fact that a scheme that is simple in verbal description will be easy in technical implementation.

Gas-phase YRD

The gas-phase YARD promises a specific impulse of up to 3000-5000 seconds. In the USSR, a project of a gas-phase YARD (RD-600) was launched, but it did not even reach the mock-up stage.
"Open cycle" means that the nuclear fuel will be thrown out, which, of course, reduces the efficiency. Therefore, the following idea was invented, which dialectically returned to solid-phase NREs - let's surround the nuclear reaction area with a sufficiently heat-resistant substance that will pass the radiated heat. Quartz was proposed as such a substance, because at tens of thousands of degrees heat is transferred by radiation and the material of the container must be transparent. The result was a gas-phase YARD of a closed cycle, or a "nuclear light bulb":

In this case, the limitation for the core temperature will be the thermal strength of the "bulb" shell. The melting temperature of quartz is 1700 degrees Celsius, with active cooling the temperature can be increased, but, in any case, the specific impulse will be lower than the open circuit (1300-1500 s), but nuclear fuel will be spent more economically, and the exhaust will be cleaner.

Alternative projects

Fissile Fragment Engine

Even more interesting idea consists in creating a dusty plasma (remember on the ISS) from fissile materials, in which the decay products of nuclear fuel nanoparticles are ionized by an electric field and thrown out, creating thrust:

They promise a fantastic specific impulse of 1,000,000 seconds. Enthusiasm is cooled by the fact that the development is at the level of theoretical research.

Nuclear fusion engines

Nuclear photon rocket

radioisotope rocket

Conclusion

Sources of information

At the end of the 1940s, in the wake of euphoria from the prospects for the use of nuclear energy, both in the USA and in the USSR, work was underway to install nuclear engines on everything that could move. The idea of ​​creating such a “perpetual motion machine” was especially attractive for the military. Nuclear power plants (NPPs) primarily found application in the navy, since ship power plants were not subject to such strict weight and size requirements as, for example, in aviation. Nevertheless, the Air Force could not "pass by" the possibility of an unlimited increase in the radius of action of strategic aviation. In May 1946 The US Air Force Command has approved the Nuclear Energy for the Propulsion of Aircraft (abbreviated NEPA) project for the creation of nuclear engines for equipping strategic bombers. Work on its implementation began at the Oak Ridge National Laboratory. In 1951 it was replaced by the joint program of the Air Force and the Atomic Energy Commission (AEC) "Aircraft Nuclear Propulsion" (ANP, "Aircraft Nuclear Propulsion"). The General Electric company created a turbojet (TRD) that differed from the “ordinary” one only in that instead of a conventional combustion chamber there was a nuclear reactor that heated the air compressed by the compressor. At the same time, the air became radioactive - an open circuit. In those years, this was treated more simply, but still, in order not to pollute their airfield, it was supposed to equip the aircraft for takeoff and landing with conventional kerosene engines. The first US nuclear aircraft project was based on the B-58 supersonic strategic bomber. From the developer (Convair), he received the designation X-6. Four nuclear turbojet engines were placed under the delta wing, in addition, 2 more “ordinary” turbojet engines were supposed to work on takeoff and landing. By the mid-1950s, a prototype of a small air-cooled nuclear reactor with a capacity of 1 MW was manufactured. A B-36H bomber was allocated for its flight and crew protection tests. The crew of the flying laboratory was in a protective capsule, but the reactor itself, located in the bomb bay, had no biological protection. The flying laboratory was named NB-36H. From July 1955 to March 1957 she made 47 flights over the desert regions of Texas and New Mexico during which the reactor was turned on and off. At the next stage, a new nuclear reactor HTRE was created (its last model had a power of 35 MW, sufficient to operate two engines) and an experimental X-39 engine that successfully passed joint ground bench tests. However, by this time, the Americans realized that an open circuit was not suitable, and began designing a power plant with air heating in a heat exchanger. The new Convair NX-2 machine had a “duck” scheme (horizontal tail was located in front of the wing). The nuclear reactor was supposed to be located in the center section, the engines - in the stern, the air intakes - under the wing. The aircraft was supposed to use from 2 to 6 auxiliary turbojets. But in March 1961 the ANP program was closed. In 1954-1955. a group of scientists at the Los Alamos Laboratory prepared a report on the possibility of creating a nuclear rocket engine (NRE). The US AEC has decided to start work on its creation. The program was named "Rover". Work was carried out in parallel at the Los Alamos Scientific Laboratory and at the Radiation Laboratory at Livermore at the University of California. Since 1956, all the efforts of the Radiation Laboratory were directed to the creation of a nuclear ramjet engine (YAPJE) under the PLUTO project (in Los Alamos, they started creating the NRE).

The YaPVRD was planned to be installed on the developed supersonic low-altitude missile (Supersonic Low-Altitude Missile - SLAM). The missile (now it would be called a cruise missile) was essentially an unmanned bomber with a vertical launch (with the help of four solid-fuel boosters). The ramjet was switched on when a certain speed was reached already at a sufficient distance from its own territory. The air entering through the air intake was heated in nuclear reactor and, flowing through the nozzle, created thrust. The flight to the target and the release of warheads for the purpose of secrecy had to be carried out at an ultra-low altitude at a speed of three times the speed of sound. The nuclear reactor had a thermal power of 500 MW, the operating temperature of the core was more than 1600 degrees C. A special test site was built to test the engine.

Skeptics argue that the creation of a nuclear engine is not a significant progress in the field of science and technology, but only a “modernization of a steam boiler”, where uranium acts as a fuel instead of coal and firewood, and hydrogen acts as a working fluid. Is the NRE (nuclear jet engine) so unpromising? Let's try to figure it out.

First rockets

All the merits of mankind in the development of near-Earth space can be safely attributed to chemical jet engines. The operation of such power units is based on energy conversion chemical reaction burning fuel in the oxidizer into the kinetic energy of the jet stream, and hence the rocket. The fuel used is kerosene, liquid hydrogen, heptane (for liquid-fuel rocket engines (LTE)) and a polymerized mixture of ammonium perchlorate, aluminum and iron oxide (for solid propellant (RDTT)).

It is well known that the first rockets used for fireworks appeared in China as early as the second century BC. They rose into the sky thanks to the energy of powder gases. The theoretical research of the German gunsmith Konrad Haas (1556), the Polish general Kazimir Semenovich (1650), the Russian lieutenant general Alexander Zasyadko made a significant contribution to the development of rocket technology.

A patent for the invention of the first liquid-propellant rocket engine was received by an American scientist Robert Goddard. His apparatus, with a weight of 5 kg and a length of about 3 m, running on gasoline and liquid oxygen, in 1926 for 2.5 s. flew 56 meters.

In pursuit of speed

Serious experimental work on the creation of serial chemical jet engines started in the 30s of the last century. In the Soviet Union, V. P. Glushko and F. A. Zander are considered to be the pioneers of rocket engine building. With their participation, the power units RD-107 and RD-108 were developed, which provided the USSR with the championship in space exploration and laid the foundation for Russia's future leadership in the field of manned space exploration.

With the modernization of the liquid-propellant engine, it became clear that the theoretical maximum speed of the jet stream could not exceed 5 km/s. This may be enough to study the near-Earth space, but flights to other planets, and even more stars, will remain an unrealizable dream for mankind. As a result, already in the middle of the last century, projects of alternative (non-chemical) rocket engines began to appear. The most popular and promising were installations that use the energy of nuclear reactions. The first experimental samples of nuclear space engines (NRE) in the Soviet Union and the USA were tested in 1970. However, after the Chernobyl disaster, under pressure from the public, work in this area was suspended (in the USSR in 1988, in the USA - since 1994).

The functioning of nuclear power plants is based on the same principles as those of thermochemical ones. The only difference is that the heating of the working fluid is carried out by the energy of decay or fusion of nuclear fuel. The energy efficiency of such engines is much higher than chemical ones. For example, the energy that can be released by 1 kg of the best fuel (a mixture of beryllium with oxygen) is 3 × 107 J, while for Po210 polonium isotopes this value is 5 × 1011 J.

The released energy in a nuclear engine can be used in a variety of ways:

heating the working fluid emitted through the nozzles, as in a traditional rocket engine, after being converted into an electric one, ionizing and accelerating the particles of the working fluid, creating an impulse directly by fission or fusion products. Even ordinary water can act as a working fluid, but the use of alcohol will be much more effective, ammonia or liquid hydrogen. Depending on the state of aggregation of the fuel for the reactor, nuclear rocket engines are divided into solid-, liquid- and gas-phase. The most developed NRE with a solid-phase fission reactor, which uses fuel rods (fuel elements) used in nuclear power plants as fuel. The first such engine in the framework of the American project Nerva passed ground test tests in 1966, having worked for about two hours.

Design features

At the heart of any nuclear space engine is a reactor consisting of an active zone and a beryllium reflector placed in a power building. It is in the active zone that the fission of the atoms of the combustible substance occurs, as a rule, uranium U238, enriched with U235 isotopes. To give the process of nuclear decay certain properties, moderators are also located here - refractory tungsten or molybdenum. If the moderator is included in the composition of fuel elements, the reactor is called homogeneous, and if placed separately - heterogeneous. The nuclear engine also includes a working fluid supply unit, controls, shadow radiation protection, and a nozzle. Structural elements and components of the reactor, experiencing high thermal loads, are cooled by the working fluid, which is then injected into the fuel assemblies by a turbopump unit. Here it is heated to almost 3000˚С. Expiring through the nozzle, the working fluid creates jet thrust.

Typical reactor controls are control rods and rotary drums made of a substance that absorbs neutrons (boron or cadmium). The rods are placed directly in the core or in special niches of the reflector, and the rotary drums are placed on the periphery of the reactor. By moving the rods or turning the drums, the number of fissile nuclei per unit of time is changed, adjusting the level of energy release of the reactor, and, consequently, its thermal power.

To reduce the intensity of neutron and gamma radiation, which is dangerous for all living things, elements of the primary reactor protection are placed in the power building.

Improving Efficiency

A liquid-phase nuclear engine is similar in principle and device to solid-phase ones, but the liquid state of the fuel makes it possible to increase the temperature of the reaction, and, consequently, the thrust of the power unit. So if for chemical units (LTE and solid propellant rocket engines) the maximum specific impulse (jet blast velocity) is 5,420 m/s, for solid-phase nuclear and 10,000 m/s it is far from the limit, then the average value of this indicator for gas-phase NRE lies in the range 30,000 - 50,000 m/s.

There are two types of gas-phase nuclear engine projects:

An open cycle, in which a nuclear reaction takes place inside a plasma cloud from a working fluid held by an electromagnetic field and absorbing all the generated heat. The temperature can reach several tens of thousands of degrees. In this case, the active region is surrounded by a heat-resistant substance (for example, quartz) - a nuclear lamp that freely transmits radiated energy. In installations of the second type, the reaction temperature will be limited by the melting point of the bulb material. At the same time, the energy efficiency of a nuclear space engine decreases somewhat (specific impulse up to 15,000 m/s), but efficiency and radiation safety increase.

Practical achievements

Formally, the American scientist and physicist Richard Feynman is considered to be the inventor of the atomic power plant. The start of large-scale work on the development and creation of nuclear engines for spacecraft within the framework of the Rover program was given at the Los Alamos Research Center (USA) in 1955. American inventors preferred plants with a homogeneous nuclear reactor. The first experimental sample of "Kiwi-A" was assembled at the plant at the atomic center in Albuquerque (New Mexico, USA) and tested in 1959. The reactor was placed vertically on the stand with the nozzle up. During the tests, a heated jet of spent hydrogen was emitted directly into the atmosphere. And although the rector worked at low power for only about 5 minutes, the success inspired the developers.

In the Soviet Union, a powerful impetus to such studies was given by the meeting of the "three great K" held in 1959 at the Institute of Atomic Energy - the creator of atomic bomb I. V. Kurchatov, the chief theorist of Russian cosmonautics M. V. Keldysh and the general designer of Soviet rockets S. P. Korolev. Unlike the American model, the Soviet RD-0410 engine, developed at the design bureau of the Khimavtomatika association (Voronezh), had a heterogeneous reactor. fire tests took place at a training ground near the city of Semipalatinsk in 1978.

It is worth noting that quite a lot of theoretical projects were created, but the matter never came to practical implementation. The reasons for this were the presence of a huge number of problems in materials science, the lack of human and financial resources.

For a note: an important practical achievement was the conduct of flight tests of aircraft with a nuclear engine. In the USSR, the experimental strategic bomber Tu-95LAL was the most promising, in the USA - the B-36.

Orion Project or Pulse NREs

For flights in space, a pulsed nuclear engine was first proposed to be used in 1945 by an American mathematician of Polish origin, Stanislav Ulam. In the next decade, the idea was developed and refined by T. Taylor and F. Dyson. The bottom line is that the energy of small nuclear charges, detonated at some distance from the pushing platform on the bottom of the rocket, gives it a great acceleration.

In the course of the Orion project, which started in 1958, it was planned to equip a rocket capable of delivering people to the surface of Mars or the orbit of Jupiter with just such an engine. The crew stationed in the forward compartment would be protected from the damaging effects of gigantic accelerations by a damping device. The result of detailed engineering work was march tests of a large-scale model of the ship to study the stability of the flight (conventional explosives were used instead of nuclear charges). Due to the high cost, the project was closed in 1965.

Similar ideas for creating an "explosive" were expressed by the Soviet academician A. Sakharov in July 1961. To put the ship into orbit, the scientist proposed using conventional liquid-propellant engines.

Alternative projects

Great amount projects have not gone beyond theoretical research. Among them were many original and very promising. Confirmation is the idea of ​​a nuclear power plant based on fissile fragments. The design features and arrangement of this engine make it possible to do without a working fluid at all. The jet stream, which provides the necessary propulsion characteristics, is formed from spent nuclear material. The reactor is based on rotating disks with a subcritical nuclear mass (the fission coefficient of atoms is less than one). When rotating in the sector of the disk located in the active zone, a chain reaction is started and decaying high-energy atoms are sent to the engine nozzle, forming a jet stream. The surviving whole atoms will take part in the reaction at the next revolutions of the fuel disk.

Projects of a nuclear engine for ships performing certain tasks in near-earth space based on RTGs (radioisotope thermoelectric generators) are quite workable, but such installations are not very promising for interplanetary, and even more so interstellar flights.

Nuclear fusion engines have huge potential. Already at the current stage of the development of science and technology, a pulse installation is quite feasible, in which, like the Orion project, thermonuclear charges will be detonated under the bottom of the rocket. However, many experts consider the implementation of controlled nuclear fusion to be a matter of the near future.

Advantages and disadvantages of YARD

The indisputable advantages of using nuclear engines as power units for spacecraft include their high energy efficiency, which provides a high specific impulse and good traction performance (up to a thousand tons in vacuum), an impressive energy reserve during autonomous operation. The current level of scientific and technological development makes it possible to ensure the comparative compactness of such an installation.

The main drawback of the NRE, which caused the curtailment of design and research work, is a high radiation hazard. This is especially true when conducting ground fire tests, as a result of which radioactive gases, compounds of uranium and its isotopes may enter the atmosphere together with the working fluid, and the destructive effect of penetrating radiation. For the same reasons, it is unacceptable to launch a spacecraft equipped with a nuclear engine directly from the Earth's surface.

Present and future

According to the assurances of the Academician of the Russian Academy of Sciences, General Director of the Keldysh Center Anatoly Koroteev, a fundamentally new type of nuclear engine in Russia will be created in the near future. The essence of the approach is that the energy of the space reactor will be directed not to the direct heating of the working fluid and the formation of a jet stream, but to generate electricity. The role of propulsor in the installation is assigned to the plasma engine, the specific thrust of which is 20 times higher than the thrust of currently existing chemical rocket vehicles. The head enterprise of the project is a subdivision of the state corporation "Rosatom" JSC "NIKIET" (Moscow).

Full-scale mock-up tests were successfully passed back in 2015 on the basis of NPO Mashinostroeniya (Reutov). November of this year has been named as the start date for flight design tests of the nuclear power plant. The most important elements and systems will have to be tested, including on board the ISS.

The operation of the new Russian nuclear engine occurs in a closed cycle, which completely excludes radioactive substances into the surrounding space. The mass and overall characteristics of the main elements of the power plant ensure its use with existing domestic Proton and Angara launch vehicles.

Beware of many letters.

A flight model of a spacecraft with a nuclear power plant (NPP) in Russia is planned to be created by 2025. The relevant work is included in the draft Federal Space Program for 2016–2025 (FKP-25), which was sent by Roscosmos to the ministries for approval.

Nuclear power systems are considered the main promising sources of energy in space when planning large-scale interplanetary expeditions. In the future, nuclear power plants, which are currently being developed by Rosatom enterprises, will be able to provide megawatt power in space in the future.

All work on the creation of nuclear power plants is proceeding in accordance with the planned deadlines. We can say with a great deal of confidence that the work will be completed on time, stipulated by the target program, - says Andrey Ivanov, project manager of the communications department of the state corporation Rosatom.

Recently, two important stages have been passed within the framework of the project: a unique design of the fuel element has been created, which ensures operability at high temperatures, large temperature gradients, and high-dose irradiation. Technological tests of the reactor vessel of the future space power unit have also been successfully completed. As part of these tests, the body was pressurized and 3D measurements were made in the areas of the base metal, girth weld and cone transition.

Operating principle. History of creation.

There are no fundamental difficulties with a nuclear reactor for space use. In the period from 1962 to 1993, a rich experience in the production of similar installations was accumulated in our country. Similar work was carried out in the USA. Since the beginning of the 1960s, several types of electric propulsion engines have been developed in the world: ion, stationary plasma, an anode layer engine, pulsed plasma engine, magnetoplasma, magnetoplasmodynamic.

Work on the creation of nuclear engines for spacecraft was actively carried out in the USSR and the USA in the last century: the Americans closed the project in 1994, the USSR - in 1988. The closure of work was largely facilitated by the Chernobyl disaster, which negatively set public opinion regarding the use of nuclear energy. In addition, tests of nuclear installations in space were not always carried out regularly: in 1978, the Soviet satellite Kosmos-954 entered the atmosphere and fell apart, scattering thousands of radioactive fragments over an area of ​​100 thousand square meters. km in northwestern Canada. The Soviet Union paid Canada monetary compensation in the amount of more than $10 million.

In May 1988, two organizations - the Federation of American Scientists and the Committee of Soviet Scientists for Peace Against the Nuclear Threat - made a joint proposal to ban the use of nuclear energy in space. That proposal did not receive formal consequences, but since then no country has launched spacecraft with nuclear power plants on board.

The great advantages of the project are practically important operational characteristics - a long service life (10 years of operation), a significant overhaul interval and a long operating time on one switch.

In 2010, technical proposals for the project were formulated. Design began this year.

The nuclear power plant contains three main devices: 1) a reactor plant with a working fluid and auxiliary devices (a heat exchanger-recuperator and a turbogenerator-compressor); 2) electric rocket propulsion system; 3) refrigerator-emitter.

Reactor.

From a physical point of view, this is a compact gas-cooled fast neutron reactor.
The fuel used is a compound (dioxide or carbonitride) of uranium, but because the design must be very compact, uranium has a higher enrichment in the 235 isotope than in fuel rods in conventional (civilian) nuclear power plants, perhaps over 20%. And their shell is a monocrystalline alloy of refractory metals based on molybdenum.

This fuel will have to work at very high temperatures. Therefore, it was necessary to choose materials that could restrain the negative factors associated with temperature, and at the same time allow the fuel to perform its main function - to heat the gas coolant, which will be used to produce electricity.

Fridge.

Gas cooling during the operation of a nuclear installation is absolutely necessary. How to dissipate heat open space? The only possibility is radiation cooling. The heated surface in the void is cooled, radiating electromagnetic waves over a wide range, including visible light. The uniqueness of the project is in the use of a special coolant - helium-xenon mixture. The installation provides a high efficiency.

Engine.

The principle of operation of the ion engine is as follows. A rarefied plasma is created in the gas-discharge chamber with the help of anodes and a cathode block located in a magnetic field. Ions of the working fluid (xenon or other substance) are "drawn" from it by the emission electrode and accelerated in the gap between it and the accelerating electrode.

For the implementation of the plan, 17 billion rubles were promised in the period from 2010 to 2018. Of these funds, 7.245 billion rubles were earmarked for the state corporation Rosatom to build the reactor itself. Other 3.955 billion - FSUE "Center of Keldysh" for the creation of a nuclear - power propulsion plant. Another 5.8 billion rubles will go to RSC Energia, where the working image of the entire transport and energy module will have to be formed within the same time frame.

According to plans, by the end of 2017, a nuclear power plant will be prepared to complete the transport and energy module (interplanetary flight module). By the end of 2018, the nuclear power plant will be ready for flight design tests. The project is financed from the federal budget.

It is no secret that work on the creation of nuclear rocket engines was started in the USA and in the USSR back in the 60s of the last century. How far have they come? And what challenges did you encounter along the way?

Anatoly Koroteev: Indeed, work on the use of nuclear energy in space began and was actively carried out in our country and in the United States in the 1960s and 70s.

Initially, the task was to create rocket engines that, instead of chemical energy combustion of fuel and oxidizer would use the heating of hydrogen to a temperature of about 3000 degrees. But it turned out that such a direct path is still inefficient. We get high thrust for a short time, but at the same time we throw out a jet, which, in the event of abnormal operation of the reactor, may turn out to be radioactively contaminated.

Some experience was gained, but neither we nor the Americans were able to create reliable engines then. They worked, but not enough, because heating hydrogen to 3000 degrees in a nuclear reactor is a serious task. And besides, there were environmental problems during ground tests of such engines, since radioactive jets were emitted into the atmosphere. It's no longer a secret that similar works were carried out on a specially prepared nuclear testing Semipalatinsk test site, which remained in Kazakhstan.

That is, two parameters turned out to be critical - prohibitive temperature and radiation emissions?

Anatoly Koroteev: In general, yes. For these and some other reasons, work in our country and in the United States was terminated or suspended - it can be assessed in different ways. And it seemed to us unreasonable to resume them in such a way, I would say, in a frontal way, in order to make a nuclear engine with all the shortcomings already mentioned. We have proposed a completely different approach. It differs from the old one in the same way that a hybrid car differs from a conventional one. In a conventional car, the engine turns the wheels, while in hybrid cars, electricity is generated from the engine, and this electricity turns the wheels. That is, a certain intermediate power plant is being created.

So we proposed a scheme in which the space reactor does not heat the jet ejected from it, but generates electricity. The hot gas from the reactor turns the turbine, the turbine turns the electric generator and the compressor, which circulates the working fluid in a closed circuit. The generator, on the other hand, generates electricity for a plasma engine with a specific thrust 20 times higher than that of chemical counterparts.

Smart scheme. In essence, this is a mini-nuclear power plant in space. And what are its advantages over a ramjet nuclear engine?

Anatoly Koroteev: The main thing is that the jet coming out of the new engine will not be radioactive, since a completely different working fluid passes through the reactor, which is contained in a closed circuit.

In addition, we do not need to heat hydrogen to extreme values ​​​​with this scheme: an inert working fluid circulates in the reactor, which heats up to 1500 degrees. We seriously simplify our task. And as a result, we will raise the specific thrust not twice, but 20 times compared to chemical engines.

Another thing is also important: there is no need for complex full-scale tests, which require the infrastructure of the former Semipalatinsk test site, in particular, the bench base that remained in the city of Kurchatov.

In our case, all the necessary tests can be carried out on the territory of Russia, without getting involved in long international negotiations on the use of nuclear energy outside of our state.

Are similar works being carried out in other countries?

Anatoly Koroteev: I had a meeting with the deputy head of NASA, we discussed issues related to the return to work on nuclear energy in space, and he said that the Americans are showing great interest in this.

It is quite possible that China can also respond with active actions on its part, so it is necessary to work quickly. And not just for the sake of getting ahead of someone by half a step.

We must work quickly, first of all, so that in the emerging international cooperation, and de facto it is being formed, we look worthy.

I do not rule out that in the near future an international program for a nuclear space power plant, similar to the program for controlled thermonuclear fusion being implemented now, may be initiated.