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This article comes from Weixin Official Accounts: SF Chinese (ID: kexuejiaodian), author: SF

Nuclear-powered Orion spacecraft concept (Image: NASA) At present, human involvement in space is limited to the vicinity of Earth. Spacecraft is the main factor restricting human exploration of space. Existing spacecraft have to make tradeoffs between payload and power: if you want to carry more passengers and cargo, you have to sacrifice power and reduce fuel load; if you want to carry more fuel, you have to affect payload. For decades, scientists have been trying to figure out how to "maximize the benefits" of spacecraft payloads and power. Some space agencies and scientists are looking to nuclear power.

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Nuclear power, as its name implies, uses nuclear energy as a source of power. The earliest use of nuclear energy can be traced back to the eve of World War II. Today, nuclear-powered ships, nuclear power plants and even nuclear weapons have become one of the most promising sources of energy for mankind in the future, despite constant controversy.

At present, mankind uses nuclear energy to provide power, and the most successful example is nuclear-powered aircraft carriers, whose technology is quite mature. Nuclear power may also be needed to resolve the contradiction between spacecraft power and payload.

NERVA: A Nuclear-Powered Rocket Pioneer Halfway through Life As early as 1952, Los Alamos Laboratories in the United States began developing nuclear-powered rockets. In 1964, NASA began working with Los Alamos Laboratory to apply a nuclear-powered rocket developed by Los Alamos Laboratory to NASA's Nuclear Power Space Test Vehicle (RIFT) and completed the first test flight of RIFT.

The success of the Space Race and the RIFT experiment led to the establishment of the Space Nuclear Propulsion Agency (SNPO). Under the auspices of SNPO, Los Alamos began developing and manufacturing the Nuclear Engine for Rocket Vehicle Application (NERVA), with the participation of two private companies. After analysis and demonstration, the R & D team selected the KIWI engine-based scheme from many schemes and built two nuclear-powered rocket engines, NERVA NRX and NERVA XE.

On December 1, 1967, the NERVA XE underwent ground testing in Nevada, USA. The two nuclear-powered rocket engines were tested only in the laboratory, and scientists concluded from the test data that the nuclear-powered rocket engine is suitable for space flight and has twice the propulsion efficiency of a traditional rocket engine. However, due to the huge cost, the development of NERVA project was eventually cancelled by the U.S. government, these two NERVA engines never completed the space flight mission.

Nuclear-powered rockets are once again on the rise despite the cancellation of the nuclear-powered rocket program, but research in the field has not stopped. However, in the field of nuclear-powered rockets, there seems to be no breakthrough in decades. NERVA remains the only nuclear-powered rocket engine ever built.

Recently, the situation seems to have changed. NASA and the Defense Advanced Research Projects Agency (DARPA) plan to develop a nuclear-powered rocket engine that can travel to Mars. This project is called the Agile Earth Lunar Action Demonstration Rocket (DRACO) project. According to the plan, as early as 2027, the United States will test a nuclear-powered rocket in space. By the late 1930s or early 1940s, NASA will be using spacecraft propelled by nuclear rockets to send astronauts to Mars.

The DRACO program, which started in 2021, was joined this year by NASA, with Lockheed Martin and other private companies involved in the project designing, building and testing the nuclear-powered rocket.

NASA Deputy Administrator Pam Melroy said the partnership with DARPA and private industry would accelerate the development of technologies to send humans to Mars, and testing of future nuclear-powered rockets would be a key step toward landing humans on Mars.

How do nuclear rockets work?

Compared with traditional rocket engines, nuclear-powered rockets can be twice as efficient, which can carry less fuel, and nuclear-powered rockets perform better in terms of endurance. So how does such an efficient rocket work?

In fact, nuclear-powered rockets work differently. According to the principle of nuclear energy release, nuclear-powered rockets can be divided into three categories:

Radioisotope Decay Rocket Engine: Radioisotope decay produces radiation, which converts radiation energy into heat, heats the gas propellant, and the gas expands and exits the nozzle to create thrust.

Nuclear fission rocket engine: also known as nuclear thermal rocket, heating gas propellant heat from nuclear fuel fission reaction, similar to the working principle of nuclear power plants today. The DRACO project is based on the nuclear fission rocket engine concept.

Nuclear fusion rocket engine: Heat for heating gas propellants comes from nuclear fusion reactions. Because the nuclear fusion reaction is not easy to control, the research on controllable nuclear fusion is still in the preliminary stage, so the nuclear fusion rocket engine is only a theoretical idea.

In addition to the United States, other countries are trying or planning to develop nuclear-powered rockets, such as China and Russia. In March 2018, Liu Zhirang, president of the Sixth Academy of China Aerospace Science and Technology Corporation, said that they were cooperating with relevant research and design units of China's nuclear power to carry out demonstration of space nuclear power schemes and research on key technologies, and various schemes such as thermonuclear and nuclear power would be formed in the future. Around 2040, China will achieve a major breakthrough in nuclear-powered space shuttle.

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