Space nuclear energy device, this can have

  According to Xinhua News Agency, the Russian National Aerospace Corporation initiated the development of an "orbital nuclear power plant" that uses lasers to charge satellites in orbit, which was questioned. In fact, nuclear energy has been widely used in space and is expected to become the core power source of space exploration in the future.

  Both chemical energy and solar energy have limitations.

  Both manned spacecraft carrying astronauts into space and unmanned aerial vehicles such as satellites and detectors are equipped with many electronic devices. Stable and sufficient power supply is the basic condition for the normal work of spacecraft.

  Most of the early spacecraft used chemical batteries as the power source. The basic principles of these chemical batteries are basically the same as those of dry batteries and mobile phone batteries used in our daily life, and the time for continuous power supply is not long. When the battery is exhausted, the spacecraft has to stop working because there is nowhere to charge. China’s "Dongfanghong-1" satellite has only worked in space for 28 days, which is limited by the battery power.

  Today’s spacecraft, when working in orbit, will stretch out a device shaped like a wing. For example, shenzhou spaceship, which we are familiar with, has a pair of such "wings" on the propulsion cabin at the rear. This "wing" of the spacecraft is a solar array. Its function is not to fly, but to convert solar energy into electric energy. With the continuous progress of solar energy technology, the power supply efficiency of solar panels is getting higher and higher, and it has become the main power source of spacecraft working near the earth. Although solar energy is inexhaustible, it will not be enough to support the spacecraft’s work if it is to go out into space like New Horizon flying over Pluto and Voyager flying out of the solar system. With the increase of the distance from the sun, the sunlight will be weaker and weaker, and the electric energy generated by solar panels will be less and less.

  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 reaction to generate electricity, and built many nuclear power plants to convert nuclear energy into electricity needed in our daily life. In space, nuclear energy has also been widely used and is expected to become the core power source for space exploration in the future.

  Mainstream power supply for deep space exploration of isotope thermal battery

  The requirement of spacecraft for power supply is that it can not only provide stable power supply, but also require it to be small in size and light in weight, and it can work reliably for a long time without failure. In order to realize this requirement, the United States and the Soviet Union chose two different technical routes: at that time, the Soviets miniaturized the nuclear reactors used in ground nuclear power plants and installed satellites with powerful functions. Americans, on the other hand, prefer isotope thermal batteries which are safe, reliable and simple in structure.

  The principle of isotope thermal battery is not complicated, and its basic structure is similar to that of a coal stove. Isotopic thermal batteries are generally cylindrical with nuclear fuel in the middle, which can generate heat through spontaneous decay reaction, like pieces of burning honeycomb coal. The isotope thermal battery can convert the heat released by nuclear fuel into electric energy because the outer wall of the battery wrapped with nuclear fuel is unusual. 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 different, it can generate electricity and convert thermal energy into electrical energy. This phenomenon of voltage generated by temperature difference is called "Seebeck effect", which is named after the German physicist Thomas John Zeebek who discovered it. As the decay of nuclear fuel continues, the temperature difference between the inside and outside of the isotope thermal battery can persist, thus generating stable electric energy through thermocouples.

  In nature, there are many isotopes that can produce spontaneous decay, and there are some stresses on which one to choose as the nuclear fuel of isotope thermal batteries. First, the decay rate of this element cannot be too fast. Elements that decay too fast will release most of their energy in a short time and cannot support the spacecraft for a long time. Second, the energy generated by nuclear fuel per unit mass must be enough, so that the spacecraft can meet the needs with only a small amount of nuclear fuel, so that more weight can be used to carry the payload for mission. Third, the types of radiation emitted by nuclear fuel decay should be absorbed by thermocouples as easily as possible.

  After screening by scientists according to these three standards, plutonium-238 stands out as the most used nuclear fuel in space isotope thermal batteries. The half-life of plutonium-238 is 87.7 years, and the power of releasing energy per gram of plutonium-238 is 0.54 watts, which can meet the first two requirements. What’s more commendable is that when plutonium 238 decays, almost all the radiation produced is easily absorbed by thermocouples α X-rays, which have strong penetrating power and are not easily absorbed by thermocouples β Ray. In this way, the radiation of plutonium 238 during decay can almost be absorbed by the thermocouple itself, so there is no need to set an additional shielding layer outside RTG to block β Radiation hazards of rays to other equipment.

  Plutonium 238 has few sources and complicated preparation process, so it has high cost and low output. At present, the United States can only produce 1.5 kilograms of plutonium-238 a year. However, due to its excellent properties, it is difficult to find other isotopes that can completely replace it.

  On June 29th, 1961, the world’s first nuclear-powered spacecraft "Meridian" 4A military navigation satellite was launched and successfully put into orbit. The output power of its isotope thermal battery was only 2.6W.. Since then, the isotope thermal battery technology has developed vigorously. In addition to the New Horizon and Voyager mentioned above, the Cassini probe that recently completed its mission and crashed into Saturn, the Galileo probe that traveled around Jupiter, and the Curious rover that landed on the surface of Mars also used isotope thermal batteries for power supply. The isotope thermal battery they use can already output power of several hundred watts to one kilowatt.

  In addition to power supply, isotope thermal batteries sometimes use the "waste heat" of power generation to make a real "stove" to "heat" the spacecraft in the extremely cold space, so that the instruments and equipment on the spacecraft will not be damaged by freezing. In the plot of the movie "Mars Rescue", the protagonist Matt Damon once ventured to dig out an abandoned isotope thermal battery and put it in the rover to keep himself warm.

  High-power space power supply for space nuclear reactor

  Isotopic thermal battery has many advantages, but it also has its inherent defects. On the one hand, its electric energy conversion efficiency is low, and generally only less than 10% of radiant energy is converted into electric energy. On the other hand, its maximum output power is generally around 1 kW, so it is powerless for spacecraft with greater power demand. Moreover, with the consumption of nuclear fuel, the output power of isotope thermal batteries will continue to decline.

  The Soviet Union also successfully designed and manufactured the isotope thermal battery power supply in the 1960s, but perhaps it was the fighting nation’s natural desire for a more powerful power supply. Almost all spacecraft using nuclear power in the Soviet Union used space nuclear reactors. The space nuclear reactor is like a scaled-down nuclear power plant. It also heats materials through the chain reaction of nuclear fission of nuclear fuel, and generates steam to drive the turbo-generator to generate electricity. It can also control the operation of the reactor by plugging and unplugging control rods. Unlike steam turbines that are generally driven by water vapor on the ground, space nuclear reactors generally use steam engines of metal vapor. In the 1960s, the Soviet Union successfully developed the BES-5 space nuclear reactor with an output power of 3 kilowatts, and later developed the TOPAZ reactor with an output power of 6 kilowatts.

  While the Soviets successfully promoted the space nuclear reactor technology, they accidentally created the first large-scale space nuclear accident. BES-5 reactor has been assembled on "RORSAT". The orbit height of this satellite is only 250 kilometers, and it is used to make a quick "scan" of the earth to monitor the movement of the US Navy. When a RORSAT satellite is about to reach its working life, it will eject its nuclear reactor into a 950-kilometer-high "discard orbit". There, abandoned nuclear reactors will always float in space to avoid nuclear pollution to the earth. The rest of the satellite body will fall into the earth under the action of atmospheric resistance after losing power. However, on January 24, 1978, an out-of-control RORSAT satellite, code-named "Cosmos 954", failed to eject the reactor into the "discarding orbit" normally, but fell into the earth with the nuclear reactor and scattered radioactive nuclear fuel on the territory of Canada. The Canadian government had to spend a lot of manpower and material resources to find and remove radioactive materials scattered over thousands of square miles. To this end, Canada also launched an international lawsuit with the Soviet Union, demanding that the Soviet Union compensate for the economic losses of 6.041 million US dollars. After that, the Soviet Union reformed the design of RORSAT satellite and installed a backup propulsion device on the reactor.When the main propulsion device fails, the reactor can still enter the discarding orbit normally. At the same time, in the face of the potential risk of nuclear accident in space, US President Carter signed an order prohibiting American spacecraft working near the Earth from using nuclear energy.

  Although the nuclear reactor using nuclear fission has such risks, it is the only source of high-efficiency and large-scale production of nuclear energy in space at present. In the future, to launch nuclear-powered rockets with more powerful power and better flight performance, we must rely on space nuclear reactors. At present, there are mainly two kinds of nuclear-powered rocket schemes that are fully demonstrated technically. The first type is a thermonuclear rocket, which 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 then ejects it to propel the rocket with a strong airflow. At this time, liquid hydrogen does not act as fuel like rockets used now, but only acts as propellant to generate momentum. It is estimated that when carrying the same weight of propellant, the carrying capacity of this rocket will be doubled compared with the chemical fuel rocket currently used. Another more advanced and effective nuclear rocket scheme is a nuclear electric propulsion rocket that combines emerging electric propulsion technology with nuclear technology. This rocket first uses the heat generated by nuclear energy to ionize liquid hydrogen and other propellants into a plasma state. Then, the electric energy generated by the nuclear reactor is reused to accelerate the plasma with electromagnetic force, resulting in huge thrust. Because the plasma can be accelerated to a very high speed under the action of electromagnetic force, even close to the speed of light, this rocket can quickly gain enough momentum and energy to accelerate to the speed required for interstellar travel.