A hybrid fission/fusion reactor could be the best way to get through the ice on Europa

Within the coming years, NASA and the European House Company (ESA) will ship two robotic missions to discover Jupiter’s icy moon Europa. These are none aside from NASA’s Europa Clipper and the ESA’s Jupiter Icy Moons Explorer (JUICE), which is able to launch in 2024, and 2023 (respectively). As soon as they arrive by the 2030s, they’ll examine Europa’s floor with a sequence of flybys to find out if its inside ocean might assist life. These would be the first astrobiology missions to an icy moon within the outer solar system, collectively often known as “ocean worlds.”

One of many many challenges for these missions is the best way to mine by way of the thick icy crusts and acquire samples from the inside ocean for evaluation. In accordance with a proposal by Dr. Theresa Benyo (a physicist and the principal investigator of the lattice confinement fusion venture at NASA’s Glenn Analysis Heart), a potential resolution is to make use of a particular reactor that depends on fission and fusion reactions. This proposal was chosen for Part I improvement by the NASA Modern Superior Ideas (NIAC) program.

The record of ocean worlds is lengthy and various, starting from Ceres within the Fundamental Asteroid Belt, the moons of Jupiter (Callisto, Ganymede, and Europa), Saturn (Titan, Enceladus, and Dione), Neptune’s largest moon (Triton), and Pluto and different our bodies within the Kuiper Belt. These worlds are all believed to have inside oceans heated by tidal flexing on account of gravitational interplay with their father or mother physique or (within the case of Ceres and Pluto) the decay of radioactive components. Additional proof of those oceans and exercise contains floor plumes and striated options indicating exchanges between the floor and inside.

The principle problem for exploring the interiors of those worlds is the thickness of their ice sheets, which could be as much as 40 km (25 mi) deep. In Europa’s case, totally different fashions have yielded estimates of between 15 and 25 km (10 and 15 mi). As well as, the proposed probe might want to take care of hydrostatic ice with various compositions (corresponding to ammonia and silicate rock) at totally different depths, pressures, temperatures, and densities. It would additionally should take care of water stress, preserve communications with the floor, and return samples to the floor.

NASA has explored the opportunity of utilizing a heating or boring probe to go by way of the icy sheet to entry the inside ocean. Particularly, researchers have proposed utilizing a nuclear-powered probe that will depend on radioactive decay to generate warmth and soften by way of the floor ice. Nonetheless, a group of NASA researchers led by Dr. Benyo has proposed a brand new methodology that will depend on one thing aside from typical radioactive isotopes—plutonium-238 or enriched uranium-235. As an alternative, their methodology would contain triggering nuclear fusion reactions between the atoms of a stable steel.

Their methodology, often known as lattice confinement fusion, was described in two papers printed within the April 2020 difficulty of Bodily Overview C, titled “Nuclear fusion reactions in deuterated metals” and “Novel nuclear reactions observed in bremsstrahlung-irradiated deuterated metals.” As Dr. Benyo defined in a latest NASA Glenn Analysis Heart press assertion:

“Scientists are taken with fusion, as a result of it might generate monumental quantities of vitality with out creating long-lasting radioactive byproducts. Nonetheless, typical fusion reactions are tough to realize and maintain as a result of they depend on temperatures so excessive to beat the robust electrostatic repulsion between positively charged nuclei that the method has been impractical.”

Typical fusion strategies typically come right down to inertial or magnetic confinement. With inertial confinement, fuels corresponding to deuterium or tritium (hydrogen-2 or -3) are compressed to excessive pressures (for nanoseconds) the place fusion can happen. In magnetic confinement (tokamak reactors), the gas is heated till it reaches temperatures in extra of what happens on the middle of the sun—15 million °C (27 million °F)—to realize nuclear fusion. This new methodology creates fusion reactions inside the confines of a steel lattice loaded with deuterium gas at ambient temperatures.

This new methodology creates an lively setting contained in the lattice the place particular person atoms obtain equal fusion-level kinetic energies. That is completed by packing the lattices with deuterium at densities one billion occasions larger than in tokamak reactors, the place a neutron supply accelerates deuterium atoms (deuterons) to the purpose that they collide with neighboring deuterons, inflicting fusion reactions. For his or her experiments, Dr. Benyo and her colleagues uncovered deuterons to a 2.9+MeV energetic X-ray beam, creating energetic neutrons and protons.

This course of might enable for fast-fission reactions utilizing lattices constructed from metals like depleted uranium, thorium, or erbium (Er⁶⁸) in a molten lithium matrix. The group additionally noticed the manufacturing of extra energetic neutrons, indicating that boosted fusion reactions—aka. screened Oppenheimer-Phillips (O-P) nuclear stripping reactions—additionally happen within the course of. In accordance with Dr. Benyo, both fusion course of is scalable and could possibly be a pathway to a brand new sort of nuclear-powered spacecraft:

“The ensuing hybrid fusion quick fission nuclear reactor will likely be smaller than a standard fission reactor the place a decrease mass energy supply is required and supply environment friendly operation with thermal waste warmth from reactor heats probe to soften by way of ice shelf to sub-ice oceans.”

A bonus of this new course of is the important position that steel lattice electrons whose negative charges assist “display screen” positively charged deuterons. In accordance with the idea developed by venture theoretical physicist Dr. Vladimir Pines, this screening permits adjoining deuterons to method each other extra intently. This reduces the prospect that they’ll scatter whereas growing the probability that they’ll tunnel by way of the electrostatic barrier and promote fusion reactions. In accordance with NASA venture principal investigator Dr. Bruce Steinetz, there are hurdles to beat, however the venture is off to a great begin:

“The present findings open a brand new path for initiating fusion reactions for additional examine inside the scientific group. Nonetheless, the response charges must be elevated considerably to realize considerable energy ranges, which can be potential using numerous response multiplication strategies into consideration.”

This sort of nuclear course of could possibly be a part of a Europa Lander, a proposed NASA mission that will construct on the analysis performed by the Europa Clipper and JUICE. With extra examine and improvement, this expertise is also used to create energy methods for long-duration exploration missions, just like NASA’s Kilopower Reactor Utilizing Stirling Expertise (KRUSTY) venture. The identical expertise might allow new engine ideas just like the Nuclear-Thermal and Nuclear-Electrical Propulsion (NTP/NEP) NASA and different space businesses are investigating.

Lastly, this proposed methodology might have functions for all times right here on Earth, offering a brand new form of nuclear vitality and medical isotopes for nuclear medication. As Leonard Dudzinski, the Chief Technologist for Planetary Science at NASA’s Science Mission Directorate (SMD), mentioned,

“The important thing to this discovery has been the gifted, multi-disciplinary group that NASA Glenn assembled to analyze temperature anomalies and materials transmutations that had been noticed with extremely deuterated metals, We are going to want that method to resolve important engineering challenges earlier than a sensible utility could be designed.”