Nuclear-powered robots can hunt aliens on icy solar system moons

In the following 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), due to launch in 2024 and 2023 respectively. When they arrive in the 2030s, they will study Europa’s surface with a series of flybys to find out whether the inner sea can support life. These will be the first astrobiological missions to an icy moon in the outer solar system, collectively known as “Ocean Worlds”.

One of the many challenges for these missions is how to mine through the thick icy crusts and obtain samples from the inner ocean for analysis. According to a proposal by Dr. Theresa Benyo (a physicist and principal investigator of the Lattice Confinement Fusion Project at NASA’s Glenn Research Center), one possible solution is to use a special reactor that relies on fission and fusion reactions. This proposal was selected for Phase I development by the NASA Innovative Advanced Concepts (NIAC) program, which includes a $12,500 grant.

The list of ocean worlds is long and varied, ranging from Ceres in the main asteroid belt, the moons of Jupiter (Callisto, Ganymede and Europa), Saturn (Titan, Enceladus and Dione), Neptune’s largest moon (Triton) and Pluto and other bodies in the Kuiper Belt. These worlds are all thought to have internal oceans heated by tidal bending due to gravitational interaction with the parent body or (in the case of Ceres and Pluto) the decay of radioactive elements. Additional evidence of these oceans and activity includes surface plumes and streaked features indicating exchange between the surface and the interior.

The main challenge to exploring the interior of these worlds is the thickness of their ice sheets, which can be up to 40 km (25 mi) deep. In the case of Europe, various models have given estimates of between 15 and 25 km (10 and 15 mi). In addition, the proposed probe will have to contend with hydrostatic ice of varying composition (such as ammonia and silicate rock) at different depths, pressures, temperatures and densities. It will also have to contend with water pressure, maintain communication with the surface and return samples to the surface.

NASA has investigated the possibility of using a heating or boring probe to pass through the icy cover to access the inner ocean. In particular, scientists have proposed using a nuclear-powered probe that would rely on radioactive decay to generate heat and melt through the surface ice. However, a team of NASA scientists led by Benyo has proposed a new method that would rely on something other than conventional radioactive isotopes – plutonium-238 or enriched uranium-235. Instead, their method would involve triggering nuclear fusion reactions between the atoms of a solid metal.

Their method, known as Lattice Confinement Fusion, was described in two papers published in the April 2020 issue of Physical Review C, entitled “Nuclear Fusion Reactions in Deuterated Metals” and “New Nuclear Reactions Observed in Bremsstrahlung-Irradiated Deuterated Metals.” As Benyo explained in a recent press release from the NASA Glenn Research Center:

“Scientists are interested in fusion because it can generate enormous amounts of energy without creating long-lasting radioactive byproducts. However, conventional fusion reactions are difficult to achieve and sustain because they rely on temperatures so extreme to overcome the strong electrostatic repulsion between positively charged nuclei that the process has been impractical.”

Conventional fusion methods usually come down to inertia or magnetic confinement. With inertial confinement, fuels such as deuterium or tritium (hydrogen-2 or -3) are compressed to extreme pressures (in nanoseconds) where fusion can occur. In magnetic confinement (tokamak reactors), the fuel is heated to temperatures exceeding those in the center of the Sun – 15 million °C (27 million °F) – to achieve nuclear fusion. This new method creates fusion reactions within the framework of a metal grid loaded with deuterium fuel at ambient temperatures.

This new method creates an energetic environment inside the lattice where individual atoms achieve corresponding kinetic energies at the fusion level. This is achieved by packing the lattices with deuterium at densities a billion times greater than in tokamak reactors, where a neutron source accelerates deuterium atoms (deuterons) to the point that they collide with neighboring deuterons, causing fusion reactions. For their experiments, Benyo and her colleagues exposed deuterons to a 2.9+MeV energetic X-ray beam, creating energetic neutrons and protons.

This process can allow fast fission reactions using grids built from metals such as depleted uranium, thorium or erbium (Er68) in a molten lithium matrix. The team also observed the production of more energetic neutrons, indicating that enhanced fusion reactions – also known as Screened Oppenheimer-Phillips (OP) nuclear stripping reactions – are occurring in the process. According to Benyo, both fusion processes are scalable and could be a path to a new type of nuclear-powered spacecraft:

“The resulting hybrid fusion fast fission reactor will be smaller than a traditional fission reactor where a lower mass power source is required and provide efficient operation using thermal waste heat from the reactor heat probe to melt through the ice shelf to sub-ice oceans.”

Artist’s concept of a proposed Europa lander spacecraft.Credit: NASA/JPL-Caltech

A bonus of this new process is the critical role of metal lattice electrons whose negative charges help “shield” positively charged deuterons. According to the theory developed by project theoretical physicist Dr. Vladimir Pines, this screening allows adjacent deuterons to approach each other more closely. This reduces the chance of them spreading while increasing the likelihood that they will tunnel through the electrostatic barrier and promote fusion reactions. According to NASA project principal investigator Dr. Bruce Steinetz, there are hurdles to overcome, but the project is off to a good start:

“The current findings open a new avenue for initiating fusion reactions for further study in the scientific community. However, reaction rates need to be significantly increased to achieve significant power levels, which may be possible using different reaction multiplication methods under consideration.”

These kinds of nuclear processes could be part of a Europa Lander, a proposed NASA mission that would build on the research done by the Europa Clipper and JUICE. With more study and development, this technology could also be used to create power systems for long-duration exploration missions, similar to NASA’s Kilopower Reactor Using Stirling Technology (KRUSTY) project. The same technology could enable new engine concepts such as the Nuclear-Thermal and Nuclear-Electric Propulsion (NTP/NEP) NASA and other space agencies are investigating.

Ultimately, this proposed method may have applications for life here on Earth, providing a new type of nuclear energy and medical isotopes for nuclear medicine. As Leonard Dudzinski, chief planetary science technologist at NASA’s Science Mission Directorate (SMD), said:

“Key to this discovery has been the talented, interdisciplinary team that NASA Glenn assembled to investigate the temperature anomalies and material transmutations that had been observed with highly deuterated metals. We will need that approach to solve significant engineering challenges before a practical application can be designed. “

This article was originally published on The universe today by Matt Williams. Read the original article here.

Leave a Reply

Your email address will not be published. Required fields are marked *