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The National Aeronautics and Space Administration (NASA) has begun developing the 'first nuclear-powered interplanetary spacecraft' with the goal of launching it to Mars in 2028. This project, named 'Space Reactor-1 (SR-1) Freedom', is expected to provide efficient mass transportation capabilities in deep space by being equipped with a nuclear electric propulsion system.

This plan, announced this week by NASA Administrator Jared Isaacman, is attracting attention because it goes beyond simply reaching Mars and could be the fruition of more than 60 years of nuclear propulsion tests and failed projects.

Why is this important?

Currently, most deep space probes rely on chemical propulsion engines. Chemical propulsion provides explosive thrust, but its low fuel efficiency limits long-distance interplanetary travel. On the other hand, nuclear electric propulsion has a much higher thrust efficiency compared to fuel, so it can be a game changer in deep space exploration.

The SR-1 Freedom is equipped with a miniaturized nuclear fission reactor similar to nuclear power plants on Earth. This method uses the power produced by this nuclear reactor to drive the ion engine. Ion engines obtain thrust by ionizing and accelerating gases such as xenon or krypton. Although the thrust itself is weak, it can operate continuously for a long time, so its cumulative speed surpasses that of a chemical engine.

Historical context of nuclear-powered spacecraft

The use of nuclear energy in outer space has been attempted since the early days of the space age. In the 1950s, 'Project Orion' was an unconventional concept that gained propulsion from the shock waves of continuous nuclear explosions behind a spacecraft. In the 1970s, the British Interplanetary Society's 'Project Daedalus' also proposed a nuclear fusion engine.

In fact, one that has been used for a long time is a radioisotope thermoelectric generator (RTG). RTG converts the radioactive decay heat of plutonium-238 into electricity. The half-life of plutonium-238 is about 88 years, so it can provide stable power to spacecraft for decades.

NASA first put RTG into space in 1961 under the 'SNAP-3' project. At the time, 96 grams of plutonium-238 produced only 2.5 watts of power. Since then, technology has advanced dramatically, and RTGs have been installed on Pioneer 10 and 11, Voyager 1 and 2, New Horizons, Viking Mars Landers, and Curiosity and Perseverance rovers.

In particular, the Mars exploration rovers Spirit and Opportunity relied solely on solar panels, but suffered from a sharp decline in power supply due to Mars dust. This experience clearly demonstrated the need for RTG.

Difference between nuclear electric propulsion and RTG

The RTG is a power 'source', providing electricity to the spacecraft's equipment and communication systems, but does not directly generate propulsion. On the other hand, nuclear electric propulsion obtains actual propulsion by driving an ion engine with the power produced by a nuclear fission reactor.

Ion engines work in two ways. One is a method of accelerating ions using the 'Hall effect' using an electromagnetic field, and the other is a 'grid ion thruster' method that accelerates and sprays positively charged ions toward a negatively charged grid. When operating, it emits a characteristic blue light.

In inner solar system exploration, 'solar electric propulsion' is used, which supplies power to the ion engine with solar panels. However, since the efficiency of solar power decreases rapidly the further away you are from the sun, nuclear electric propulsion is essential for exoplanet exploration.

Future outlook [AI analysis]

If SR-1 Freedom is successful, it is highly likely that the paradigm of interplanetary space travel will change. Nuclear electric propulsion can become a foundational technology for the exploration of not only Mars but also exoplanets such as Jupiter and Saturn, and even for the construction of interstellar outposts.

In particular, as the era of manned Mars exploration approaches, the need for bulk cargo transportation is increasing. The high fuel efficiency of nuclear electric propulsion is suitable for cargo ships and supply ships, and is expected to play a key role in building manned exploration infrastructure.

However, operating a nuclear fission reactor in space poses many technical challenges. Challenges that need to be addressed include radiation shielding, heat management, and securing long-term reliability. In order for the 2028 launch goal to become a reality, intensive technology development is expected to take place over the next three years.