Thermonuclear rocket concept vision illustration.
External and internal structures of isotope thermal batteries.
TOPAZ space nuclear reactor.
Apollo 14 isotope thermal cell placed on the moon's surface.
According to news from the Xinhua News Agency, Russiaâ€™s National Aerospace Corporation has been challenged to develop a â€œorbital nuclear power stationâ€ that uses lasers to charge orbiting satellites. In fact, nuclear energy has been widely used in space and is expected to become the core power source for space exploration in the future.
Chemical energy, solar energy have limitations
Whether it is a manned spacecraft carrying astronauts flying in space, or unmanned aerial vehicles such as various satellites and detectors, it is equipped with a lot of electronic equipment. Stable and sufficient power supply is the basic condition for the normal operation of spacecraft.
Most of the early spacecraft used chemical batteries as a source of electrical energy. The basic principles of these chemical batteries are basically the same as the dry batteries and mobile phone batteries used in our daily lives, and it is not long enough to provide continuous power supply. When the battery's power is depleted, the spacecraft will have to stop working because of no charge. Chinaâ€™s â€œDongfanghong Iâ€ satellite has only been working in space for 28 days, which is limited by the battery power.
Todayâ€™s spacecraft, when working on the track, will most often extend a wing-like device. For example, we are familiar with the Shenzhou spacecraft, in the rear of the propulsion cabin there is a pair of such "wings." This â€œwingâ€ of the spacecraft is a solar panel windsurfing. Its role is not to fly, but to convert solar energy into electrical energy. With the continuous advancement of solar energy technology, the power supply efficiency of solar-powered windsurfing is becoming higher and higher, and it has become the main power source for spacecraft working in the vicinity of the earth. Although solar energy is inexhaustible and inexhaustible, solar energy will not be sufficient to support spacecraft if it is to fly like a "new horizon" flying from Pluto and a "outdoor" exit from the solar system. Now. As the distance from the sun increases, the sun will become weaker and weaker, and solar panels will produce less and less power.
In fact, the energy required for the sun to emit light and heat comes from the nuclear reaction inside the sun. At present, mankind has mastered the technology of using nuclear power to generate electricity, and has established a number of nuclear power plants to convert nuclear energy into the electrical energy needed in our daily lives. In space, nuclear energy has also been widely used and is expected to become the core power source for space exploration in the future.
Isotope thermal battery deep-space detection mainstream power
In addition to providing stable power supply, the spacecraftâ€™s requirements for power supply also require small size and light weight, and it can work reliably for a long time without failure. In order to meet this demand, the United States and the Soviet Union chose two different technical routes: At the time, the Soviets miniaturized the nuclear reactors used on the ground-based nuclear power plants, installed satellites, and had powerful capabilities. Americans, on the other hand, prefer a safe and reliable isotope thermal battery with a simple structure.
The principle of isotope thermal batteries is not complicated, and its basic structure is similar to that of a coal stove. Isotope thermal batteries are generally cylindrical, with nuclear fuel in the middle of the column, which can generate heat through spontaneous decay reactions, such as burning coal briquettes. The reason why the isotope thermal battery can convert the heat released from the nuclear fuel into electric energy is because the outer wall of the battery enveloping the nuclear fuel is not normal. This kind of outer wall device called "thermocouple" is made of some special semiconductor materials. When the temperature on both sides of the thermocouple is not the same, it can generate electricity outwards, converting thermal energy into electrical energy. This phenomenon of generating a voltage from a temperature difference is called the "Seebeck effect" and was named after the German physicist Thomas Johann Seebeck who discovered it. As the decay of the nuclear fuel continues, the temperature difference between the inside and the outside of the isotope heat battery can continue to exist, so that stable power can be generated through the thermocouple.
In nature, there are many isotopes that can produce spontaneous decay. There is also some emphasis on which one to use as a nuclear fuel for isotope thermal batteries. First, the decay rate of this element cannot be too fast. Elements that decay too quickly will release most of their energy in a short period of time and cannot support the spacecraft for long periods of time. Second, the mass of nuclear fuel produced must have enough energy so that the spacecraft needs to carry only a small amount of nuclear fuel to meet its needs, so that more weight can be used to carry the mission payload. Third, the type of radiation emitted during the decay of nuclear fuel should be as easily absorbed by the thermocouple as possible.
After the scientists screened according to these three criteria, the é’š238 emerged as the most used nuclear fuel for the current isotope thermal battery. The half-life of 238 is 87.7 years. The energy released by 238 gram per gram is 0.54 watts, which can satisfy the first two requirements. What is even more commendable is that when the cesium 238 decays, the radiation generated is almost always Î±-rays that are easily absorbed by the thermocouple, and it does not produce beta rays that have strong penetrating power and are not easily absorbed by thermocouples. In this way, the radiation of the crucible 238 in the decay can be absorbed by the thermocouple itself, so that no additional shielding layer is provided outside the RTG to block the radiation hazard of the beta radiation to other devices.
The source of cesium 238 is less, and the preparation process is more complicated, so the cost is high and the yield is low. At present, the United States can only produce 1.5 kilograms of plutonium 238 a year. However, due to its excellent properties, it has been difficult to find other isotopes that can completely replace it.
On June 29th, 1961, the world's first nuclear-powered spacecraft â€œMeridianâ€ 4A military navigation satellite was launched and successfully operated in orbit. Its isotope thermal battery output power was only 2.6 watts. After that, isotope thermal battery technology boomed. In addition to the aforementioned â€œNew Horizonsâ€ and â€œTravellerâ€ numbers, the â€œCassiniâ€ detector that had recently completed its mission and crashed into Saturn and orbited Jupiterâ€™s Galileo. The No. 2 probe, the curious Mars vehicle that landed on the surface of Mars, and so on, all use isotope thermal batteries. The isotope thermal cells they use can already output several hundred watts to one kilowatt.
In addition to power supply, isotope thermal batteries sometimes use the "excess heat" of power generation to make a true "furnace" to "heat" spacecraft in an extremely cold space, so that the equipment on the spacecraft is not frozen. In the movie "Mars Rescue," the protagonist Matt Damon had also ventured to dig out an abandoned isotope thermal battery in the Mars to heat himself.
Space nuclear reactor high-power space power supply
Although isotope thermal batteries have many advantages, they also have their inherent defects. On the one hand, its electrical energy conversion efficiency is low, and generally only less than 10% of the radiant energy is converted into electrical energy. On the other hand, the maximum output power is generally about one kilowatt, and there is no way for a spacecraft with a greater demand for electrical energy. Moreover, with the depletion of nuclear fuel, the output power of isotope thermal batteries will continue to decline.
The Soviet Union also successfully designed and manufactured isotope thermal battery power in the 1960s, but it may be that the fighting nation is naturally craving for a more powerful power source. The spacecraft that uses nuclear power in the Soviet Union almost all use space nuclear reactors. The space nuclear reactor is like a reduced version of a nuclear power plant. It also uses nuclear chain fuel fission reactions to heat substances and generate steam to drive turbine generators. It can also control the operation of the reactor by inserting and removing control rods. Unlike the general use of steam on the ground to propel turbines, space nuclear reactors typically use steam engines for metal vapors. In the 1960s, the Soviet Union successfully developed the BES-5 space nuclear reactor with an output of 3 kW, and later developed a TOPAZ reactor with an output of 6 kW.
While the Soviets successfully promoted space nuclear reactor technology, they accidentally also created the first large-scale space nuclear accident. The BES-5 reactor is heavily assembled on the RORSAT radar. This satellite has an orbit altitude of only 250 kilometers and is used to do a quick "scan" of the Earth to monitor the movement of the United States Navy. When an RORSAT satellite is about to reach its working life, it will eject its nuclear reactor to a 950-kilometer high â€œdiscard trackâ€. There, abandoned nuclear reactors will always float in space to avoid causing nuclear pollution to the Earth. The remaining satellites will fall into the earth under the influence of atmospheric resistance after losing power. However, on January 24, 1978, an out-of-control RORSAT satellite codenamed "Universe 954" failed to eject the reactor normally onto the "discarded orbit". Instead, it leaped into the Earth with a nuclear reactor and spread radioactive nuclear fuel. Canada's national territory. The Canadian government has had to use a lot of manpower and resources to find and remove radioactive materials that are spread over thousands of square miles. To this end, Canada has also played an international lawsuit with the Soviet Union and demanded that the Soviet Union compensate for the economic loss of 6.041 million U.S. dollars. After that, the Soviet Union modified the design of the RORSAT satellite and added a backup propulsion device to the reactor so that if the main propulsion device fails, the reactor can still enter the discard track normally. At the same time, in the face of potential space nuclear accident risks, U.S. President Carter signed an order prohibiting U.S. spacecraft working near the Earth from using nuclear energy.
Although nuclear reactors using nuclear fission have such risks, they are the sole source of high-capacity and high-capacity production of nuclear energy in space. In the future, it is necessary to launch more powerful nuclear power rockets with better flight performance and rely on space nuclear reactors. At present, there are two main types of nuclear rocket programs that are technically justified. The first is a thermonuclear rocket that uses the heat generated by a nuclear reactor to heat the liquid hydrogen from the fuel tank to a temperature of nearly 10,000 degrees Celsius, and ejects it with a strong air current. At this point, liquid hydrogen does not act as a fuel like the rockets currently used, but only acts as a propellant that generates momentum. It is estimated that when carrying the same weight of propellant, the rocket's carrying capacity will be double that of the current chemical rocket. Another more advanced and effective nuclear rocket program is a nuclear energy electric rocket that combines emerging electric propulsion technology and nuclear technology. The rocket first uses the heat generated by nuclear energy to ionize liquid hydrogen and other propellants to the plasma state. Afterwards, the electric energy from the nuclear reactor was used again, and the electromagnetic force was used to accelerate the plasma and generate a huge thrust. Because the plasma can be accelerated to extremely high speeds, even close to the speed of light, under the influence of electromagnetic force, the rocket can quickly acquire sufficient momentum and energy to accelerate the speed required for interplanetary travel.
Alnico (AlNiCo) is the first developed a permanent magnet is made of aluminum, nickel, cobalt, iron and other trace metals composition of an alloy.According to different production process is divided into sintered Alnico (Sintered AlNiCo), and cast aluminum nickel and cobalt (Cast AlNiCo).Product shape of the round and square. Sintered products limited to the small size, their production out of rough tolerance is better than the rough cast product can be better workability.
Alnico alloys can be magnetised to produce strong magnetic fields and have a high coercivity (resistance to demagnetization), thus making strong permanent magnets. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico Magnets produce magnetic field strength at their poles as high as 1500 gausses (0.15 teslas), or about 3000 times the strength of Earth's magnetic field. Some brands of alnico are isotropic and can be efficiently magnetized in any direction. Other types, such as Alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico's remanence (Br) may exceed 12,000 G (1.2 T), its coercivity (Hc) can be up to 1000 oersteds (80 kA/m), its energy product ((BH)max) can be up to 5.5 MGÂ·Oe (44 TÂ·A/m). This means that alnico can produce a strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization. The field strength at the poles of any permanent magnet depends very much on the shape and is usually well below the remanence strength of the material.
Alnico alloys have some of the highest Curie temperatures of any magnetic material, around 800 Â°C (1,470 Â°F), although the maximal working temperature is normally limited to around 538 Â°C (1,000 Â°F). They are the only magnets that have useful magnetism even when heated red-hot. This property, as well as its brittleness and high melting point, is the result of the strong tendency toward order due to intermetallic bonding between aluminium and other constituents. They are also one of the most stable magnets if they are handled properly. Alnico magnets are electrically conductive, unlike ceramic magnets.
Alnico magnets are widely used in industrial and consumer applications where strong permanent magnets are needed; examples are electric motors, electric guitar pickups, microphones, sensors, loudspeakers, magnetron tubes, and cow magnets. In many applications they are being superseded by rare-earth magnets, whose stronger fields (Br) and larger energy products (BHmax) allow smaller-size magnets to be used for a given application.
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