How attractive are nuclear-powered rockets?

With the continuous advancement of manned space technology, landing on alien planets and creating new homes have become mankind's grand future goals. Among them, Mars, as the planet most similar to the Earth in the solar system, has the honor of becoming one of the first choices for human migration to alien planets.

However, building a home on Mars faces many challenges. For example, a spacecraft using a traditional chemical rocket engine will take at least two years to complete a round trip from Earth to Mars. The longer the flight time in space without an atmosphere to weaken the radiation, the more failures may occur, and the greater the risk of injury, illness, or even life-threatening situations. Therefore, manned Mars exploration missions require the flight time to be shortened as much as possible, and it is necessary to innovate aerospace propulsion technology.

Recently, NASA and the Defense Advanced Research Projects Agency announced that they will cooperate in the development of nuclear-powered rocket engines and strive to verify the technology in orbit in 2027. This technology is expected to significantly shorten the time it takes for astronauts to travel to and from deep space missions, and will lay the foundation for manned Mars exploration missions.

An illustration of a nuclear rocket under the "Agile Lunar Operations Demonstration Rocket" project released by the US media.

Generally speaking, nuclear-powered rockets are expected to have incomparable advantages over traditional chemical rockets in terms of power output or endurance.

Among all the future rocket propulsion schemes under discussion, nuclear-powered rockets have distinct advantages. They are expected to shorten spacecraft flight time, reduce astronauts' dangerous exposure to weightlessness and cosmic radiation, and be more conducive to maintaining health. They are also expected to simplify the design of spacecraft life support systems, reduce loads and system complexity, and thus improve reliability.

In addition, nuclear-powered rockets have strong continuous working capabilities, better mission adaptability, and are easy to adjust the start-up state. If the mission is temporarily suspended, it is expected that it will return to Earth safely without refueling after sailing in space for a period of time. In the future, when taking off from extraterrestrial planets such as Mars, nuclear-powered rockets are expected to simplify operations and embark on the return journey more reliably.

However, nuclear-powered rockets cannot be generalized. According to the different ways of releasing nuclear energy, nuclear-powered rockets can be divided into three types: radioactive isotope decay type, nuclear fission type and nuclear fusion type.

The working principle of the radioisotope decay rocket engine is to convert the radiation generated by the decay of radioisotopes into heat energy, heat the working fluid and form thrust. Research shows that it can continuously generate small thrust during missions lasting several months, but it is not suitable to serve as the main power unit for manned Mars exploration missions.

Nuclear powered rocket concept

Nuclear fusion rocket engines are the most fascinating for researchers in related fields. Their working principle is to use lighter atomic nuclei to fuse into heavier atomic nuclei, and release amazing energy in the process of this thermonuclear reaction. Unfortunately, the problem of nuclear fusion control has not yet been solved, and high-energy laser ignition technology is still not reliable enough, so this engine is still in the theoretical research stage and is mostly seen in science fiction works.

At present, the nuclear-powered rockets developed by the United States are based on the working principle of nuclear fission, also known as nuclear thermal rockets. They can be simply understood as nuclear power plants "going to the sky", which also consume nuclear fuel. After starting, the working gas flows through the nuclear reactor, absorbs heat, and then accelerates and ejects from the nozzle to generate thrust. In the future, nuclear fission rocket engines may be able to make the product present a plasma state, and the working gas is heated and ejected at high speed, generating more considerable thrust or specific impulse.

The use of nuclear-powered rockets does not mean that the manned Mars exploration mission is "safe and sound", but rather requires solving new problems. For example, as the number of astronauts and their daily necessities and work equipment increases, the spacecraft will significantly increase in weight, which will inevitably place higher requirements on the thrust of nuclear-powered rocket engines.

At the same time, the inherent safety hazards of nuclear power must be taken seriously, especially the threat of nuclear radiation to the health of astronauts. It is reported that the new generation of nuclear-powered rocket programs have made breakthrough progress in nuclear radiation safety.

In the near future, nuclear-powered rockets are expected to be put into practical use, and migrating to Mars will no longer be a dream, but a key leap in the history of human space exploration. (Author: Yu Haichuan)