Although secondary pressurization propulsion technology is not as good as high-speed ion propulsion technology, it has incomparable advantages over traditional chemical fuel propulsion technology. From a basic principle point of view, it is actually very simple. First of all, it also uses traditional chemical fuels as propellants, such as liquid hydrogen, liquid oxygen, methane and liquid oxygen. After these chemical fuels burn in the combustion chamber, the temperature and pressure will rise sharply. This is the so-called first pressurization. The traditional propulsion method is to directly eject high-temperature and high-pressure gas after it is generated, thereby obtaining reverse thrust. But the secondary pressurization propulsion technology is that after the first combustion and pressurization, these gases are not ejected out, but introduced into another chamber. The nuclear fission reactor is located next to this chamber. The nuclear fission process releases unimaginably high temperatures, and temperature is related to pressure: the higher the temperature, the higher the pressure. Therefore, the energy from the nuclear fission reactor is used to pressurize the gas in this chamber, which already has extremely high pressure, again after the first pressurization. This is the secondary pressurization.
After the second pressurization, the internal energy of the gas will expand to a level far beyond that of ordinary chemical combustion. The speed at which the gas is ejected from the injection pipe will also far exceed the limit of ordinary chemical combustion. The magnitude of the reverse thrust is positively correlated with the injection velocity of the working fluid. In normal chemical combustion, the jet speed of the gas working fluid would not exceed 5 kilometers per second. After secondary pressurization, their jet speed could be increased to more than 30 kilometers per second, which is six times the original speed! As a result, the utilization rate of these working fluids has increased to six times the original level. The journey that originally required carrying 60 tons of fuel can now be completed with only 10 tons! How much more cargo and people can be carried by the 50 tons of mass saved? Even if there is no more cargo, and 60 tons of fuel are loaded, how much can the speed of the spacecraft be increased after adopting the secondary pressurization technology? How much can the maneuverability be improved? This is the advantage of secondary pressurization propulsion technology. It can be said that without this technology, relying solely on chemical fuel propulsion, it would be impossible for Li Qingsong to complete the long journey of more than 10 billion kilometers from Luoshen to the inner solar system. Now, the task of miniaturizing nuclear fission reactors has been preliminarily completed. Although it is still not small enough to fit into a warship or a small spacecraft, at least it can fit into a large cargo ship. In this case, it is time to start research on secondary pressurization propulsion technology. Li Qingsong treated himself as if facing a formidable enemy and went all out, once again mobilizing all the forces under his command to launch this most important scientific research task at the current stage. Although the basic principle of this technology is simple, it is even more difficult to apply it in reality than to miniaturize a nuclear fission reactor. The reason is simple. The secondary pressurization propulsion technology has very high requirements on material performance. The combustion of chemical fuels releases extremely high temperatures, which requires extremely advanced heat-resistant materials to contain. After the second pressurization, their temperature will rise sharply again, even to tens of thousands of degrees Celsius. What material can withstand this temperature? Li Qingsong's knowledge of physics and chemistry told him that no material could withstand it. This means that Li Qingsong cannot use any traditional restraint methods, such as building a sturdy container, to restrain the gases after the second pressurization.
New forms of restraint must be introduced. Fortunately, Li Qingsong has another method to use. After undergoing the secondary pressurization process and being heated to tens of thousands of degrees Celsius by a nuclear fission reactor, the carbon dioxide and water generated by the combustion of methane and oxygen can no longer remain in a gaseous state at this temperature. The molecules that make them up will be directly decomposed, and electrons will be stripped from the atoms to form plasma. Since it is plasma, it will be affected by the magnetic field, so Li Qingsong has an appropriate way to restrain it. Magnetic field confinement. Powered by a nuclear fission reactor, a powerful magnetic field confinement system is constructed with the help of electrical energy. Without the use of any physical container, these high-temperature and high-pressure plasmas can be bound together to prevent them from exploding inside the thruster. Then, guided by the magnetic field, the plasma is ejected from the tail of the spacecraft at a very high speed, thus completing a secondary pressurization process and greatly improving the utilization efficiency of the working fluid. But even if magnetic field confinement devices are used, the containers in which these devices are installed will still be affected by intense radiation and extremely high temperatures, and still require extremely high material properties to withstand them. At the same time, various equipment also need to work under extremely harsh working conditions and maintain sufficient stability and reliability, which places higher requirements on material performance. This is also a project that has no shortcuts and requires one to study it diligently and conscientiously. While pushing forward his work, Li Qingsong sighed silently in his heart: "Sure enough, the development of science and technology is interconnected, like a chain. Preceding technologies are the foundation for subsequent more advanced technologies. Without preceding technologies, subsequent technologies cannot be born for no reason. Just like the core technology of the secondary pressurization propulsion technology that I am working on now, magnetic confinement is very likely to be the key to future controlled nuclear fusion technology. At the same time, electromagnetic conversion technology is also very likely to be the key to future high-speed ion propulsion technology. Mastering the secondary pressurization propulsion technology will lay the foundation for overcoming these two crucial technical challenges in the future.” With Li Qingsong's full efforts, the first propulsion experiment soon began in a newly built propulsion laboratory in a basin somewhere on Luoshen Star. The modular nuclear fission reactor and the traditional chemical combustion engine are placed on the left and right respectively, and the two are connected by thick pipes. There is also a huge nozzle behind the nuclear fission reactor. With an ignition command, a large amount of liquid oxygen and methane were transported to the chemical combustion chamber. During the intense combustion, they turned into gaseous carbon dioxide and water, and then were transported to the nuclear fission reactor module. The nuclear fission reactor modules simultaneously started the fission reaction. Through the fission of uranium 235, the surging energy hidden deep in the material was released. A part of it heated the gaseous carbon dioxide and water, causing them to directly rise to a high temperature of tens of thousands of degrees Celsius, and then turned into plasma. The other part of the energy was converted into electricity, creating a strong magnetic field to bind these plasmas. Then the next moment, there was a bang and it exploded. The earth shook and the mountains trembled, and everything within a radius of dozens of meters was razed to the ground.