Rocket engines on liquid fuel gave man the opportunity to go into space - into near-Earth orbits. However, such rockets burn 99% of their fuel in the first few minutes of flight. The remaining fuel may not be enough to travel to other planets, and the speed will be so low that the voyage will take tens or hundreds of years. Nuclear engines can solve the problem. How? We'll figure it out together.
The operating principle of a jet engine is very simple: it converts fuel into the kinetic energy of a jet (the law of conservation of energy), and due to the direction of this jet, the rocket moves in space (the law of conservation of momentum). It is important to understand that we cannot accelerate a rocket or an airplane to a speed greater than the speed of the outflow of fuel - hot gas thrown back.
New Horizons spacecraft
What distinguishes an effective engine from an unsuccessful or outdated analogue? First of all, how much fuel the engine will need to accelerate the rocket to the desired speed. This the most important parameter rocket engine is called specific impulse, which is defined as the ratio of total impulse to fuel consumption: the higher this indicator, the more efficient the rocket engine. If the rocket consists almost entirely of fuel (meaning there is no room for a payload, an extreme case), the specific impulse can be considered equal to the speed of the fuel (working fluid) flowing out of the rocket nozzle. Launching a rocket is an extremely expensive undertaking; every gram of not only the payload, but also the fuel, which also weighs and takes up space, is taken into account. Therefore, engineers are selecting more and more active fuel, a unit of which would give maximum efficiency, increasing the specific impulse.
The vast majority of rockets in history and modern times have been equipped with engines that use a chemical combustion reaction (oxidation) of fuel.
They made it possible to reach the Moon, Venus, Mars and even the distant planets - Jupiter, Saturn and Neptune. True, space expeditions took months and years (automatic stations Pioneer, Voyager, New Horizons, etc.). It should be noted that all such rockets consume a significant part of the fuel to lift off from the Earth, and then continue to fly by inertia with rare moments of turning on the engine.
Pioneer spacecraft
Such engines are suitable for launching rockets into near-Earth orbit, but to accelerate it to at least a quarter of the speed of light, an incredible amount of fuel will be needed (calculations show that 103,200 grams of fuel are needed, despite the fact that the mass of our Galaxy is no more than 1056 grams). It is obvious that in order to reach the nearest planets, and even more so the stars, we need sufficiently high speeds, which liquid-fuel rockets are not able to provide.
Gas-phase nuclear engine
Deep space is a completely different matter. Take Mars, for example, “habitated” by science fiction writers far and wide: it is well studied and scientifically promising, and most importantly, it is closer than anyone else. The point is a “space bus” that can deliver the crew there in a reasonable time, that is, as quickly as possible. But there are problems with interplanetary transport. It is difficult to accelerate it to the required speed while maintaining acceptable dimensions and spending a reasonable amount of fuel.
RS-25 (Rocket System 25) is a liquid-propellant rocket engine produced by Rocketdyne, USA. It was used on the glider of the Space Shuttle space transportation system, each of which had three such engines installed. Better known as the SSME engine (English Space Shuttle Main Engine - the main engine of the space shuttle). The main components of the fuel are liquid oxygen (oxidizer) and hydrogen (fuel). RS-25 uses a closed cycle scheme (with afterburning of the generator gas).
The solution may be a “peaceful atom” pushing spaceships. Engineers started thinking about creating a lightweight and compact device capable of launching at least itself into orbit back in the late 50s of the last century. The main difference between nuclear engines and rockets with engines internal combustion The point is that kinetic energy is obtained not due to the combustion of fuel, but due to the thermal energy of the decay of radioactive elements. Let's compare these approaches.
From liquid engines a hot “cocktail” of exhaust gases emerges (the law of conservation of momentum), formed during the reaction of fuel and oxidizer (the law of conservation of energy). In most cases, it is a combination of oxygen and hydrogen (the result of burning hydrogen is ordinary water). H2O has a much larger molar mass than hydrogen or helium, so it is more difficult to accelerate; the specific impulse for such an engine is 4,500 m/s.
NASA ground tests new system space rocket launch, 2016 (Utah, USA). These engines will be installed on the Orion spacecraft, which is planned for a mission to Mars.
IN nuclear engines It is proposed to use only hydrogen and accelerate (heat) it using the energy of nuclear decay. This results in savings on the oxidizer (oxygen), which is already great, but not everything. Since hydrogen has a relatively low specific gravity, it is easier for us to accelerate it to higher speeds. Of course, you can use other heat-sensitive gases (helium, argon, ammonia and methane), but all of them are at least two times inferior to hydrogen in the most important thing - achievable specific impulse (more than 8 km/s).
So is it worth losing it? The gain is so great that engineers are not stopped either by the complexity of the design and control of the reactor, or by its heavy weight, not even radiation hazards. Moreover, no one is going to launch from the surface of the Earth - the assembly of such ships will be carried out in orbit.
"Flying" reactor
How does a nuclear engine work? The reactor in a space engine is much smaller and more compact than its terrestrial counterparts, but all the main components and control mechanisms are fundamentally the same. The reactor acts as a heater into which liquid hydrogen is supplied. Temperatures in the core reach (and can exceed) 3000 degrees. The heated gas is then released through the nozzle.
However, such reactors emit harmful radiation. To protect the crew and numerous electronic equipment from radiation, thorough measures are required. Therefore, projects of interplanetary spacecraft with a nuclear engine often resemble an umbrella: the engine is located in a shielded separate block connected to the main module long truss or pipe.
"Combustion chamber" The nuclear engine is the reactor core, in which hydrogen supplied under high pressure is heated to 3000 degrees or more. This limit is determined only by the heat resistance of the reactor materials and the properties of the fuel, although increasing the temperature increases the specific impulse.
Fuel elements- these are heat-resistant ribbed (to increase the heat transfer area) cylinders-“glasses” filled with uranium pellets. They are “washed” by a gas flow, which plays the role of both the working fluid and the reactor coolant. The entire structure is insulated with beryllium reflective screens that do not release dangerous radiation to the outside. To control the heat release, special rotary drums are located next to the screens
There are a number of promising designs of nuclear rocket engines, the implementation of which is waiting in the wings. After all, they will mainly be used in interplanetary travel, which, apparently, is just around the corner.
Nuclear propulsion projects
These projects were frozen for various reasons - lack of money, complexity of the design, or even the need for assembly and installation in outer space.
"ORION" (USA, 1950–1960)
A project of a manned nuclear pulse spacecraft (“explosion plane”) for the exploration of interplanetary and interstellar space.
Principle of operation. From the ship's engine, in the direction opposite to the flight, a small equivalent nuclear charge is ejected and detonated at a relatively short distance from the ship (up to 100 m). The impact force is reflected from the massive reflective plate at the tail of the ship, “pushing” it forward.
"PROMETHEUS" (USA, 2002–2005)
NASA space agency project to develop a nuclear engine for spacecraft.
Principle of operation. The spacecraft's engine was to consist of ionized particles that create thrust and a compact nuclear reactor that provides energy to the installation. The ion engine creates a thrust of about 60 grams, but can operate continuously. Ultimately, the ship will gradually be able to gain enormous speed - 50 km/sec, spending a minimum amount of energy.
"PLUTO" (USA, 1957–1964)
Project to develop a nuclear ramjet engine.
Principle of operation. The air enters the nuclear reactor through the front of the vehicle, where it is heated. Hot air expands, acquires greater speed and is released through the nozzle, providing the necessary draft.
NERVA (USA, 1952–1972)
(eng. Nuclear Engine for Rocket Vehicle Application) is a joint program of the Commission on atomic energy USA and NASA to create a nuclear rocket engine.
Principle of operation. The liquid hydrogel is fed into a special compartment in which it is heated by a nuclear reactor. The hot gas expands and is released into the nozzle, creating thrust.
© Oksana Viktorova/Collage/Ridus
The statement made by Vladimir Putin during his address to the Federal Assembly about the presence in Russia of a cruise missile driven by a nuclear engine caused a storm of excitement in society and the media. At the same time, until recently, quite little was known to both the general public and specialists about what such an engine is and the possibilities of its use.
"Reedus" tried to figure out what technical device the president could speak and what made him unique.
Considering that the presentation in the Manege was not made for an audience technical specialists, and for the “general” public, its authors could have allowed a certain substitution of concepts, Georgiy Tikhomirov, Deputy Director of the Institute of Nuclear Physics and Technology of National Research Nuclear University MEPhI, does not rule out.
“What the president said and showed, experts call compact power plants, experiments with which were carried out initially in aviation, and then in deep space exploration. These were attempts to solve the insoluble problem of a sufficient supply of fuel when flying over unlimited distances. In this sense, the presentation is completely correct: the presence of such an engine ensures power supply to the systems of a rocket or any other device for an indefinitely long time,” he told Reedus.
Work with such an engine in the USSR began exactly 60 years ago under the leadership of academicians M. Keldysh, I. Kurchatov and S. Korolev. In the same years similar works were conducted in the USA, but were discontinued in 1965. In the USSR, work continued for about another decade before it was also considered irrelevant. Perhaps that’s why Washington didn’t react too much, saying that they were not surprised by the presentation of the Russian missile.
In Russia, the idea of a nuclear engine has never died - in particular, since 2009, the practical development of such a plant has been underway. Judging by the timing, the tests announced by the president fit perfectly into this joint project of Roscosmos and Rosatom - since the developers planned to conduct field tests of the engine in 2018. Possibly due to political reasons They pushed themselves a little harder and moved the deadlines “to the left.”
“Technologically, it is designed in such a way that the nuclear power unit heats the gas coolant. And this heated gas either rotates the turbine or creates jet thrust directly. A certain cunning in the presentation of the rocket that we heard is that its flight range is not infinite: it is limited by the volume of the working fluid - liquid gas, which can physically be pumped into the rocket tanks,” says the specialist.
At the same time, space rocket and a cruise missile in principle different schemes flight control, since they have different tasks. The first flies in airless space, it does not need to maneuver - it is enough to give it an initial impulse, and then it moves along the calculated ballistic trajectory.
A cruise missile, on the other hand, must continuously change its trajectory, for which it must have a sufficient supply of fuel to create impulses. Whether this fuel will be ignited by a nuclear power plant or a traditional one is not important in this case. The only thing that matters is the supply of this fuel, Tikhomirov emphasizes.
“The meaning of a nuclear installation when flying in deep space- this is the presence on board of an energy source to power the systems of the device for an unlimited time. In this case, there may be not only a nuclear reactor, but also radioisotope thermoelectric generators. But the meaning of such an installation on a rocket, the flight of which will not last more than a few tens of minutes, is not yet entirely clear to me,” the physicist admits.
The Manege report was only a couple of weeks late compared to NASA's announcement on February 15 that the Americans were resuming research work on a nuclear rocket engine, abandoned by them half a century ago.
By the way, in November 2017, the China Aerospace Science and Technology Corporation (CASC) announced that a nuclear-powered spacecraft would be created in China by 2045. Therefore, today we can safely say that the global nuclear propulsion race has begun.
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 providing energy to 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
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 required volumes. 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 into different sides. 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. CEO enterprise A. Koroteev has already pleased the public that preliminary design spacecraft for the new nuclear 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.
Already at the end of this decade, a nuclear-powered spacecraft for interplanetary travel may be created in Russia. And this will dramatically change the situation both in near-Earth space and on the Earth itself.
The nuclear power plant (NPP) will be ready for flight in 2018. This was announced by the director of the Keldysh Center, academician Anatoly Koroteev. “We must prepare the first sample (of a nuclear power plant megawatt class. – Approx. "Expert Online") for flight tests in 2018. Whether she will fly or not is another matter, there may be a queue, but she must be ready to fly,” RIA Novosti reported his words. The above means that one of the most ambitious Soviet-Russian projects in the field of space exploration is entering the phase of immediate practical implementation.
The essence of this project, the roots of which go back to the middle of the last century, is this. Now flights into near-Earth space are carried out on rockets that move due to the combustion of liquid or liquid in their engines. solid fuel. Essentially, this is the same engine as in a car. Only in a car does gasoline, when burned, push the pistons in the cylinders, transferring its energy through them to the wheels. And in a rocket engine, burning kerosene or heptyl directly pushes the rocket forward.
Over the past half century, this rocket technology has been perfected all over the world to the smallest detail. But the rocket scientists themselves admit that . Improvement - yes, it is necessary. Trying to increase the payload of rockets from the current 23 tons to 100 and even 150 tons based on “improved” combustion engines - yes, you need to try. But this is a dead end from an evolutionary point of view. " No matter how much rocket engine specialists around the world work, the maximum effect we get will be calculated in fractions of a percent. Roughly speaking, everything has been squeezed out of existing rocket engines, be they liquid or solid fuel, and attempts to increase thrust and specific impulse are simply futile. Nuclear power propulsion systems provide a multifold increase. Using the example of a flight to Mars, now it takes one and a half to two years to fly there and back, but it will be possible to fly in two to four months “- the former head of the Russian Federal Space Agency assessed the situation at one time Anatoly Perminov.
Therefore, back in 2010, the then President of Russia, and now Prime Minister Dmitry Medvedev By the end of this decade, an order was given to create in our country a space transport and energy module based on a megawatt-class nuclear power plant. It is planned to allocate 17 billion rubles from the federal budget, Roscosmos and Rosatom for the development of this project until 2018. 7.2 billion of this amount was allocated to the Rosatom state corporation for the creation of a reactor plant (this is being done by the Dollezhal Research and Design Institute of Energy Engineering), 4 billion - to the Keldysh Center for the creation of a nuclear power propulsion plant. 5.8 billion rubles are allocated by RSC Energia to create a transport and energy module, that is, in other words, a rocket ship.
Naturally, all this work is not done in a vacuum. From 1970 to 1988, the USSR alone launched more than three dozen spy satellites equipped with nuclear power plants into space. low power type "Buk" and "Topaz". They were used to create an all-weather system for monitoring surface targets throughout the World Ocean and issuing target designation with transmission to weapon carriers or command posts - the Legend naval space reconnaissance and target designation system (1978).
NASA and American companies that produce spacecraft and their delivery vehicles have not been able to create a nuclear reactor that would operate stably in space during this time, although they tried three times. Therefore, in 1988, a ban was passed through the UN on the use of spacecraft with nuclear power propulsion systems, and the production of satellites of the US-A type with nuclear propulsion on board in the Soviet Union was discontinued.
In parallel, in the 60-70s of the last century, the Keldysh Center carried out active work on the creation of an ion engine (electroplasma engine), which is most suitable for creating a high-power propulsion system operating on nuclear fuel. The reactor produces heat, which is converted into electricity by a generator. Using electricity inert gas xenon in such an engine is first ionized, and then positively charged particles ( positive ions xenon) are accelerated in an electrostatic field to a given speed and create thrust when leaving the engine. This is the operating principle of the ion engine, a prototype of which has already been created at the Keldysh Center.
« In the 90s of the 20th century, we at the Keldysh Center resumed work on ion engines. Now a new cooperation must be created for such a powerful project. There is already a prototype of an ion engine on which basic technological and Constructive decisions. But standard products still need to be created. We have a set deadline - by 2018 the product should be ready for flight tests, and by 2015 the main engine testing should be completed. Next - life tests and tests of the entire unit as a whole.“, noted last year the head of the electrophysics department of the Research Center named after M.V. Keldysh, Professor, Faculty of Aerophysics and Space Research, MIPT Oleg Gorshkov.
What is the practical benefit for Russia from these developments? This benefit far exceeds the 17 billion rubles that the state intends to spend by 2018 on creating a launch vehicle with a nuclear power plant on board with a capacity of 1 MW. Firstly, this is a dramatic expansion of the capabilities of our country and humanity in general. A nuclear-powered spacecraft provides real opportunities for people to accomplish things on other planets. Now many countries have such ships. They also resumed in the United States in 2003, after two samples reached the Americans. Russian satellites with nuclear power plants.
However, despite this, a member of the NASA special commission on manned flights Edward Crowley for example, he believes that a ship for an international flight to Mars should have Russian nuclear engines. " In demand Russian experience in the field of nuclear engine development. I think Russia has a lot of experience both in the development of rocket engines and in nuclear technology. She also has extensive experience in human adaptation to space conditions, since Russian cosmonauts made very long flights “,” Crowley told reporters last spring after a lecture at Moscow State University on American plans for manned space exploration.
Secondly, such ships make it possible to sharply intensify activity in near-Earth space and provide real opportunity the beginning of the colonization of the Moon (there are already construction projects on the Earth’s satellite nuclear power plants). « The use of nuclear propulsion systems is being considered for large manned systems, rather than for small spacecraft, which can fly on other types of installations using ion engines or solar wind energy. Nuclear propulsion systems with ion engines can be used on an interorbital reusable tug. For example, transport cargo between low and high orbits, and fly to asteroids. You can create a reusable lunar tug or send an expedition to Mars“, says Professor Oleg Gorshkov. Ships like these are dramatically changing the economics of space exploration. According to calculations by RSC Energia specialists, a nuclear-powered launch vehicle reduces the cost of launching a payload into lunar orbit by more than half compared to liquid rocket engines.
Third, these are new materials and technologies that will be created during the implementation of this project and then introduced into other industries - metallurgy, mechanical engineering, etc. That is, this is one of those breakthrough projects that can really push both the Russian and global economies forward.
