A hybrid fission/fusion reactor could be the best way to traverse the ice in Europe

A hybrid fission/fusion reactor could be the best way to traverse the ice in Europe

This reprocessed color view of Jupiter’s moon Europa is from images taken by NASA’s Galileo spacecraft in the late 1990s. Credit: NASA/JPL-Caltech

In the coming years, NASA and the European Space Agency (ESA) will send two robotic missions to explore Jupiter’s icy moon Europa. These are none other than NASA’s Europa Clipper and ESA’s Jupiter Icy Moons Explorer (JUICE), which will be launched in 2024 and 2023 (respectively). Once there by 2030, they will study Europa’s surface with a series of flybys to determine whether its inner ocean could support life. These will be the first astrobiology missions to an icy moon in the outer solar system, known collectively as “Ocean Worlds.”

One of the many challenges of these tasks is how to drill through the thick ice crusts and obtain samples of the inner ocean for analysis. According to a proposal by Dr. Teresa Benio (physicist and principal investigator of the confinement-lattice fusion project at NASA’s Glenn Research Center), a possible solution is to use a special reactor based on fission-and-fusion reactions. This proposal was selected for Phase 1 development by NASA’s Innovative Advanced Concepts (NIAC) Program.

The list of ocean worlds is long and varied, starting with Ceres in the main asteroid belt, the moons of Jupiter (Callisto, Ganymede, and Europa) and Saturn (Titan, Enceladus, and Dione), and the largest moons of Neptune (Triton), Pluto, and other Kuiper belt bodies. These worlds are all thought to have inner oceans that are heated by tidal flexion due to gravitational interaction with its parent body or (in the case of Ceres and Pluto) the decay of radioactive elements. Additional evidence of these oceans and activity include surface plumes and striped features that indicate exchanges between the surface and the interior.

The main challenge for exploring the interiors of these worlds is the thickness of their ice sheets, which can be up to 40 km (25 mi) deep. In the case of Europa, different models have yielded estimates of between 15 and 25 km (10 and 15 mi). In addition, the proposed probe would need to handle hydrostatic ice of different compositions (such as ammonia and silicate rock) at different depths, pressures, temperatures, and densities. It will also have to deal with water pressure, maintain contacts with the surface, and return samples to the surface.

NASA has explored the possibility of using a heating or boring probe to pass through the ice sheet to reach the inner ocean. In particular, the researchers proposed using a nuclear powered probe based on radioactive decay to generate heat and melt surface ice. However, a team of NASA researchers led by Dr. Benio has proposed a new method that relies on something other than a traditional radioisotope – plutonium-238 or enriched uranium-235. Alternatively, their method may involve stimulation Nuclear fusion reactions between atoms of a solid metal.

Their method, known as grid-entrapment fusion, is described in two papers published in the April 2020 issue of physical review centitled “Nuclear fusion reactions in corrosive metals” And “New nuclear reactions are observed in minerals that have been exposed to radioactive radiation. As Dr. Benio explained in a recent NASA Glenn Research Center press release:

“Scientists are interested in fusion, because it can generate huge amounts of energy without creating long-lived radioactive by-products. However, traditional fusion reactions are difficult to achieve and sustain because they rely on extremely intense temperatures to overcome the strong electrostatic repulsion between the positively charged nuclei that the process was improper. proces “.

Traditional fusion methods generally come down to inertial or magnetic confinement. With inertial confinement, fuels such as deuterium or tritium (hydrogen-2 or -3) are compressed to extreme pressures (for nanoseconds) where fusion can occur. In magnetic confinement (tokamak reactors), the fuel is heated until it reaches temperatures greater than what occurs at the center of the sun – 15 million degrees Celsius (27 million degrees Fahrenheit) – to achieve Nuclear fusion. This new method creates fusion reactions within the confines of a metal lattice loaded with deuterium fuel at ambient temperatures.

This new method creates an energetic environment within the lattice where individual atoms achieve equivalent kinetic energies at the fusion level. This is achieved by filling the lattices with deuterium a billion times more dense than in tokamak reactors, where the source of neutrons accelerates the deuterium atoms (deuterons) to the point where they collide with neighboring deuterons, causing fusion reactions. For their experiments, Dr. Benyo and her colleagues exposed deuterons to a beam of 2.9 + MeV X-rays, which created energetic neutrons and protons.

This process can allow rapid fission reactions using gratings made of metals such as depleted uranium, thorium, or erbium (Er).68) in the molten lithium matrix. The team also noticed the production of more energetic neutrons, which indicates an increase in fusion reactions — aka. Nuclear stripping reactions examined by Oppenheimer-Phillips (OP) – also occur in this process. According to Dr. Benio, either fusion process is scalable and could be a path to a new type of nuclear-powered spacecraft:

“The resulting FHPR will be smaller than a conventional fission reactor as it requires a lower mass power source and provides efficient operation with thermal waste heat from the reactor heating probe to melt through the ice shelf into the icy oceans.”

A reward for this new process is the critical role played by electrons in the metallic lattice negative charges Help “screen” positively charged deuterons. According to a theory developed by the project’s theoretical physicist Dr. Vladimir Pines, this screening allows neighboring deuterons to approach each other more closely. This reduces the chance of them scattering while increasing the likelihood that they will tunnel through the electrostatic barrier and promote fusion reactions. According to NASA project principal investigator Dr. Bruce Steinitz, there are hurdles to overcome, but the project is off to a good start:

A hybrid fission/fusion reactor could be the best way to traverse the ice in Europe

Artist’s concept of the proposed Europa space probe vehicle. Credit: NASA/JPL-Caltech

The current findings open a new path to start Fusion reactions For further study within the scientific community. However, reaction rates must be significantly increased to achieve appreciable power levels, which may be possible using the various reaction doubling methods under study. ”

This type of nuclear operation could be part of the Europa Lander, a proposed NASA mission based on research by Europa Clipper and JUICE. With further study and development, this technology could also be used to create power systems for long-duration exploration missions, similar to NASA’s Kilopower Stirling Technology (KRUSTY) project. The same technology could enable new engine concepts such as nuclear, nuclear, and electric thermal propulsion (NTP/NEP) that NASA and other space agencies are researching.

Finally, this proposed method could have applications for life here on Earth, providing a new type of nuclear energy and medical analogues for nuclear medicine. As Leonard Dudzinsky, chief planetary science technologist for NASA’s Science Mission Directorate (SMD), said,

“Key to this discovery was the talented multidisciplinary team that NASA Glenn had assembled to investigate the temperature imbalances and material transformations observed with highly corrosive metals, and we will need this approach to solve significant engineering challenges before a practical application can be designed.”

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