What is a nuclear rocket engine?
Nuclear rocket engine (NRE) is a type of rocket
The traditional nuclear propulsion system as a whole isa design 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.
There are various designs of NRE:solid-phase, liquid-phase and gas-phase - corresponding to the aggregate state of nuclear fuel in the reactor core - solid, melt or high-temperature gas (or even plasma).
YARD NERVA
Solid state nuclear rocket engine
In solid-phase nuclear propellant rocket engines (SPNRD), the fissile substance isas in conventional nuclear reactors, it is placed in rod assemblies (fuel rods) of complex shape with a developed surface, which makes it possible to effectively heat the gaseous working fluid (usually hydrogen, less often ammonia), which is also a coolant that cools the structural elements and the assemblies themselves.
Heating temperature limited by temperaturemelting of structural elements (no more than 3000 K). The specific impulse of a solid-phase nuclear rocket engine, according to modern estimates, will be 850–900 s, which is more than twice as high as the most advanced chemical rocket engines.
Ground demonstrators of TfNRD technologies in the twentieth century were created and successfully tested at stands (the NERVA program in the USA, RD-0410 in the USSR).
TFYARD
Gas phase nuclear rocket engine
Gas-phase nuclear jet engine (GNRE) -a conceptual type of jet engine in which reactive force is created by the release of a coolant (working fluid) from a nuclear reactor, in which the fuel is in gaseous or plasma form. It is believed that in such engines the specific impulse will be 30–50 thousand m/s.
Heat transfer from the fuel to the coolant is achieved mainly due to radiation, mostly in the ultraviolet region of the spectrum (at fuel temperatures of about 25,000 ° C).
Nuclear Pulse Engine
Atomic charges with a power of approximately a kiloton perDuring takeoff, they should explode at a rate of one charge per second. The shock wave - an expanding plasma cloud - was supposed to be received by a “pusher” - a powerful metal disk with a heat-protective coating and then, reflected from it, to create jet thrust.
The impulse received by the pusher plate throughstructural elements must be transferred to the ship. Then, as the altitude and speed increase, the frequency of explosions can be reduced. During takeoff, the ship must fly strictly vertically in order to minimize the area of radioactive contamination of the atmosphere.
In the United States, space development using pulsed nuclear rocket engines was carried out from 1958 to 1965 as part of the Orion project by General Atomics by order of the US Air Force.
For the Orion project, not only calculations were carried out,but also full-scale tests. Flight tests of impulse-driven aircraft models (conventional chemical explosives were used for explosions).
Orion project spacecraft, artist's drawing
Positive results were obtained aboutthe fundamental possibility of controlled flight of a device with a pulse engine. Also, to study the strength of the traction plate, tests were carried out on Enewetak Atoll.
During nuclear tests on this atollgraphite-coated steel spheres were placed 9 m from the epicenter of the explosion. The spheres were found intact after the explosion, a thin layer of graphite evaporated (ablated) from their surfaces.
In the USSR, a similar project was developed in1950–1970s. The device contained additional chemical jet engines that propelled it 30–40 km from the Earth's surface. Then it was supposed to turn on the main nuclear pulse engine.
Durability was the main concerna pusher screen that could not withstand the enormous heat loads from nearby nuclear explosions. At the same time, several technical solutions were proposed that allow the development of a pusher plate design with a sufficient resource. The project was not completed. No real tests of pulsed NRM with detonation of nuclear devices have been carried out.
Nuclear electric propulsion system
A nuclear electric propulsion system (NEP) is used to generate electricity, which in turn is used to power an electric rocket engine.
A similar program in the USA (the NERVA project) wasclosed in 1971, but in 2020 the Americans returned to this topic, ordering the development of a nuclear thermal propulsion (Nuclear Thermal Propulsion, NTP) from Gryphon Technologies for military space raiders on nuclear engines to patrol the lunar and near-Earth space, also since 2015 work on the Kilopower project.
Since 2010, work on the project has begun in Russianuclear electric propulsion system of megawatt class for space transport systems (space tug "Nuclon"). The layout is being developed for 2021; by 2025, it is planned to create prototypes of this nuclear power plant; the planned date of flight tests of a space tractor with a nuclear power plant is announced - 2030.
Power
According to A.V. Bagrov, M.A. Smirnov and S.A.Smirnov, a nuclear rocket engine can get to Pluto in 2 months and return back in 4 months using 75 tons of fuel, to Alpha Centauri in 12 years, and to Epsilon Eridani in 24.8 years.
Is a nuclear engine dangerous?
The main disadvantage is the high radiation hazard of the propulsion system:
- fluxes of penetrating radiation (gamma radiation, neutrons) in nuclear reactions;
- carryover of highly radioactive uranium compounds and its alloys;
- the outflow of radioactive gases with a working fluid.
The use of the discovery of Russian scientists in the civilian sector is closely related to the safety of a nuclear power plant. It was necessary to ensure the safety of its exhaust.
The protection of a small nuclear engine is smaller,the larger it is, so neutrons will penetrate into the “combustion chamber”, thereby with some probability making everything around radioactive.
Nitrogen and oxygen have radioactive isotopes with a short half-life and are not dangerous. Radioactive carbon is a long-lived thing. But there is good news as well.
Radioactive carbon is generated in the upper atmosphere by cosmic rays. But most importantly, the concentration of carbon dioxide in dry air is only 0.02 ÷ 0.04%.
Considering that the percentage of carbon becomingradioactive, the value is still several orders of magnitude smaller, preliminary it can be assumed that the exhaust of nuclear engines is no more dangerous than the exhaust of a coal-fired power plant.
Are they going to use a nuclear engine for the latest space flights?
Yes, in early February it became known that NASAwill test the latest nuclear engine for flights to Mars. It is expected that with its help it will be possible to reach the Red Planet in just three months.
In recent years, scientists and engineers from NASA and other space agencies around the world have been actively discussing plans to build permanent habitable bases on the surface of the Moon and Mars.
- What are its advantages?
The main key to ensuring their autonomy andTo reduce the cost of construction, NASA experts consider three-dimensional printing technologies that make it possible to use water and local resources - soil, rocks and gases from the atmosphere - to build base buildings on site.
Similar printers as shown by onboard experiencesThe ISS and on Earth make it possible to print almost everything necessary for the life of colonists on Mars, except for one, the most important component of the base - a power source, whose power would be sufficient to ensure the operation of the 3D printer itself, as well as power and heat the entire base.
As part of NASA's preparations for landing on Mars in 2035, the American company Ultra Safe Nuclear Technologies (USNT) from Seattle proposed its solution - a nuclear thermal engine (NTP)
- What will the nuclear engine be like?
USNT offers a classic solution - nuclearengine using liquefied hydrogen as the working fluid: a nuclear reactor produces heat from uranium fuel, this energy heats the liquid hydrogen passing through the coolants, which expands into a gas and is expelled through the engine nozzle, creating thrust.
One of the main problems when creating this typeengines - find uranium fuel that can withstand sudden temperature fluctuations inside the engine. The USNT says it has solved this problem by developing a fuel that can operate at temperatures up to 2,400 degrees Celsius.
The fuel assembly contains silicon carbide:This material, used in the layer of the three-structural-isotropic coating, forms a gas-tight barrier that prevents the leakage of radioactive products from the nuclear reactor, protecting the astronauts.
- Security
In addition, to protect the crew and in caseIn unforeseen situations, the nuclear engine will not be used during launch from Earth - it will start working already in orbit to minimize possible damage in the event of an accident or abnormal operation.
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