Since nuclear fusion was discovered, it has become something of a holy grail in the search for efficient and clean energy sources. While the technology remains in a developmental phase, scientists are looking for a revolutionary application - fusion drives for spacecraft.

Direct fusion drive (DFD), a concept rocket that is powered by low radioactivity nuclear fusion processes, both for propulsion and for providing the energy needed by the craft to function. Its mechanism follows the Princeton field-reversed configuration reactor (PFRC) - an experimental program that evaluates a potential fusion reactor setup - invented by Dr. Samuel Cohen in 2002. By 2018, the team developing the PFRC has begun development of its second iteration - the PFRC-2.

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The team of engineers and scientists at the Princeton Plasma Physics Laboratory are looking to develop a prototype equipped with the PFRC-2 as its primary drive.

Developing a DFD Spacecraft

Early studies of the PFRC were supported by the NASA Institute for Advanced Concepts (NIAC) program. In principle, the direct fusion drive will create thrust directly without an intermediary electricity-producing process. It uses a magnetic confinement and heating system - fueled by a mixture of deuterium (D), a hydrogen isotope, and the light isotope helium-3 - to generate the energy required.

Aside from the thrust directly generated, bremsstrahlung and synchrotron radiations emitted from the fusion plasma will be captured and used as the spacecraft's energy source, providing electric power for communications and maintenance. 

An analysis of the first PFRC predicts that a corresponding DFD would be able to generate some 5 to 10 Newtons of thrust for each megawatt of generated fusion power. It also revealed that the fusion power generated would be approximately divided as follows: 35 percent for thrust, 30 percent to electricity requirements, 25 percent accounting for heat losses, and about 10 percent recirculated for the spacecraft's RF heating.

Additionally, a modelling of the first PFRC, from Stephanie Thomas at Princeton Satellite Systems, can theoretically send a spacecraft with a mass of 1,000 kilograms, or 2,200 pounds, to Pluto in only four years. In comparison, NASA's interplanetary space probe New Horizons was first launched 2006 and took over nine and a half years to reach Pluto, travelling at about a million miles a day.


Revolutionizing Space Travel

It has subsequently been proposed for use on a Pluto mission. Also, it was proposed as a part of the Artemis program, intended for integration on the Orion spacecraft. Should it become reality, it is expected to cut a crewed mission to Mars from nine months, with existing technology, down to four months.

Another interesting target that would greatly benefit from a direct fusion drive spacecraft is Saturn's moon, Titan. The ringed planet's largest moon has been a point of great interest for scientists for its uncanny similarities to Earth - fuelling theories about its potential capability to support life as we know it. 

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A recent study, submitted to the online archive arXiv last September, estimates that a DFD-powered probe could get to Titan in a little over two years. The study, conducted by a team of physicists and aerospace engineers from the New York City College of Technology and the Politecnico di Torino in Italy.