China successfully builds megawatt-scale space nuclear reactor

Recently, the US website "Space News" reported a major achievement in China's aerospace industry: A nuclear reactor used to provide power and propulsion in outer space has passed the international comprehensive performance assessment.

According to Space News, the high-power nuclear reactor, designed by the Chinese Academy of Sciences, can generate 1 megawatt of electricity to power the spacecraft's propulsion engine. However, the report did not provide technical details of the nuclear power system, nor did it reveal plans for future applications. According to the South China Morning Post, the project was launched in 2019 and a prototype design was completed last year.

The significance of this megawatt-scale space nuclear reactor is enormous : it is one of the necessary technologies for human activities in deep space. Especially for missions such as building a base on Mars, if existing chemical-fueled rockets are used, Long March 5 - China's largest heavy-lift launch vehicle - will be able to launch about 6 tons of cargo to Mars at a time. This is because, for deep space missions, the specific impulse of the rocket is more important than the thrust. The higher the specific impulse, the less fuel is needed, and the lower the specific impulse, the more energy will be consumed.

According to a paper published in China's academic journal "Atomic Energy Science and Technology" in 2019, the country is developing a high-power Hall electric propulsion system based on a 1-megawatt nuclear power source. Normally, hydrogen-oxygen engines only have a maximum specific pulse of less than 400 seconds, while the specific pulse of the high-power Hall electric propulsion engine developed in China is nearly 4,000 seconds.

According to the newspaper's description, sending 30 tons of cargo to Mars will only consume 3.9 tons of fuel, much lower than current technology. One of the characteristics of electric propulsion is large specific impulse and small thrust, the thrust generated by 1Mw power is only 25-50N.

China is developing a high-power Hall electric propulsion system based on a 1-megawatt nuclear power source.

According to the article's calculations, it takes 203 days for the Hall thruster to travel from Earth to Mars. The time from the launch of China's Tianwen 1 to entering Mars orbit is 202 days, and the difference in time between the two engines is basically not much different, but the difference in fuel is huge. And the farther the distance, the greater the electric propulsion power. If you want to explore more distant planets in the future, electric propulsion is almost the only choice. Last year, China announced a long-term plan for exploring Neptune's orbit using this propulsion scheme.

Space nuclear power is not a new concept. The US and the former Soviet Union have researched and applied a lot of space nuclear power, but their solutions have a maximum capacity of only a few dozen kilowatts.

China's path is to create space nuclear reactors.

According to the current level of human scientific development, there are two technical routes to provide nuclear power in space: one is to use radioisotope thermoelectric power generation and small power (in fact, this is the battery), from tens to hundreds of watts. These solutions have been widely used in the United States. China's "Jade Rabbit II" spacecraft and the rover it carries are also equipped with a plutonium 238-based thermoelectric isotope generator (battery); and the second is to use nuclear reactor power , the former Soviet Union and Russia have used nuclear reactor power for a long time, but the maximum power is only tens of kilowatts.

China is currently pursuing the second route, which is to create space nuclear reactors. Late last year, the China Shipbuilding Industry Corporation announced the successful production of a large-capacity Stirling engine - 300Kw, and said that the capacity will be increased to MW in the future.

There are still many problems to be solved in the practical application of nuclear reactors in space.

Of course, there are still many problems to be solved in the practical application of nuclear reactors in space, such as how to prevent nuclear fuel from causing pollution to the atmosphere and the Earth's surface due to accidents during launch. On January 24, 1978, the Soviet nuclear-powered satellite "Cosmos" 954 malfunctioned, gradually falling into the atmosphere and burning up. In January 1983, a similar accident occurred on the nuclear-powered satellite " Cosmos" 1402, and the nuclear reactor module was completely burned up when it re-entered the atmosphere over the South Atlantic.

This is a problem that needs to be solved when we launch space nuclear reactors in the future, because compared to the miniature nuclear reactors in the former Soviet Union with a maximum power of only a few dozen watts, this 1 megawatt nuclear reactor in China requires much more nuclear fuel. However, with the advancement of technology, the reliability of spacecraft will increase, and the probability of accidents will decrease to an acceptable level.