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As the U.S. President Trump signed a directive in December 2017 to send Americans to the Moon and eventually to Mars “America will lead in space again and the world will marvel”, NASA’s 2018 strategic planning committee identified four main goals to strengthen NASA’s ability to accomplish the President’s vision. The four major themes identified in the 2018 plan are each characterized by a single word reflected through the agency’s activities 1) Discover, 2) Explore, 3) Develop, and 4) Enable.
One of the key strategic goals is to “Extend Human Presence Deeper into Space and to the Moon for Sustainable Long-Term Exploration and Utilization”, in which the Marshall Space Flight Center (MSFC) is the leader for the space transportation, design, development and manufacturing. This charges MSFC to provide specific functions for our deep space crew, with an ultimate objective of extending the human presence into the solar system
In this project, our major objective is to optimize the process of forming structural Martian regolith-bricks, suitable for autonomous construction technologies, which will be utilized to build the necessary infrastructure for deep space extended exploration missions. The novelty of the proposed approach is utilizing ILs to partially digest in situ Martian regolith particles, allowing the regolith particles to bind together and form predetermined construction suitable shapes (tiles or bricks). To be clear, no binder or adhesive or cement is used in this technology. Microwave and possibly CO2 exposure will be the primary proposed chemical mechanisms to cure the resulted bricks, utilizing the environmental resources and possible available energy sources. The pre- shaped bricks could be further optimized and assembled to construct and evaluate structural elements or systems. This process is also applicable to lunar materials.
The proposed IL technology concept will evaluate a variety of acidic ILs to chemically convert the surface (to a depth on the order of 10 microns) of particles of silica/alumina-bearing rocks and minerals into silicic acid (hydrated silica), which consists of reactive Si-OH groups. This treatment is to permit bonding of the particles to one another after the treated particles are pressed together and the excess ionic liquid (containing solubilized metal salts) is washed away. After removal of the IL the Si-OH groups of silicic acid react with each other under mild heat and compression to form Si-O-Si linkages and thereby harden the material between the particles of rock and rigidize the structure. The recovered IL is recycled to treat more regolith. The treated regolith powder can be shaped or formed into useful geometries such as tiles or bricks prior to the hardening treatment. A form of chemical sintering is thus produced and, if desired, the treatments can be extended to large structures if the IL recovery and hardening can be carried out in a timely manner despite the scale-up.
This innovative proposed research will be transformative in its utilization of a unique multi- physics holistic approach (synthesis, characterization, and computational) to scale up and to expedite in situ additive construction. In accordance with the NASA CAN program, it will build on the existing foundation established by Additive Manufacturing Research and Education Cluster (AMREC) for an intensive integrated experimental research program and leverages several partnerships with NASA centers, and K-12 local schools, in addition to the UM interdisciplinary team of researchers. The research is aimed at overcoming some of the current technology barriers and challenges in the field of in situ additive construction, through IL construction binder(s)’ extraction from a Martian simulated regolith. Moreover, the utilization of such studies to understand the materials behavior under Martian severe environments compared to Earth is becoming a demanding research necessity in order to reach NASA’s MEP mission by 2030.
To fulfill the key strategic goals, NASA mission-supportive research has focused on in situ resource utilization for Earth-independent missions on Mars. Ionic liquids (ILs) are among candidate element/compound separation platforms with unique physical, thermal, and mechanical properties, such as extremely low vapor pressure, low flammability, and structural integrity in the extreme Martian environment (extreme temperatures, near-vacuum pressures, and Galactic Cosmic Ray (GCR) radiation). Researchers at Marshall Space Flight Center (MSFC) have investigated the use of ILs for the in situ extraction of oxygen and metals from dissolved Martian regolith, as well as in situ CO2 capture from the Martian atmosphere followed by an electrochemical reduction of CO2 and water to methane with promising results.
This project is comprised of synergistic holistic integrated synthesis, including experimental and computational activities, utilizing the research expertise of four junior faculty within the School of Engineering (SoE) at the University of Mississippi (UM) who formed a Additive Manufacturing Research and Education Cluster (AMREC), and the Additive Construction with Mobile Emplacement (ACME) & ILs groups at NASA-MSFC. The overarching goal of the project is to utilize some of the main facilities and personnel expertise among AMREC faculty and MSFC research groups to develop a comprehensive space research and educational program within the UM’s SoE that work closely with NASA 2018 Strategic Plan.
This research program would enable us to: 1) build the necessary basic research infrastructure for NASA-related experimental and computational research in a top-notch national field, Additive Manufacturing, for in situ construction binders; 2) increase the competitiveness of the UM in general, and the SoE in particular, in acquiring external funding from NASA and other federal agencies by demonstrating successful peer-reviewed publications and preliminary data emanating NASA research Grants and collaboration; and 3) recruit and train students underrepresented within the STEM disciplines to pursue academic or industrial careers in the areas of interest to the NASA space program. To achieve the overarching goal, we propose fundamental research relevant to the NASA Mars Exploration Program (MEP).
The primary goal of this NASA 2018 CAN Grant is to develop an integrated multiscale- holistic research and educational program devoted to advancing fundamental knowledge on extraterrestrial additive construction technologies. Utilizing in situ resources for the construction of habitat structures on Mars will increase the efficiency of the long duration space missions and will reduce the number of launches from Earth necessary, thus reducing cost. Hence, there is a critical need to understand the transformation of in situ materials, such as Martian regolith and any respective atmospheric constituents, into revolutionary superior construction materials. This proposed research will address the Human Exploration Destination Systems Technology Area 7 roadmap through the In Situ Resource Utilization (ISRU) Technology Area 7.1.
A preliminary set of acidic ILs have been selected for this work. One, Emim hydrogen sulphate, has been a workhorse for regolith dissolution experiments at MSFC and it also happens to be commercially available. Others are more aggressive or have different affinities for certain metal ions. All are viscous but not all are readily soluble in water at room temperature. All ILs are limited availability and most will be synthesized in the lab in both MSFC and at UM. Consider these ILs as powerful concentrated acids but with nil volatility and low chemical kinetics. These properties make them ideal for in-space processing.
Work at MSFC dissolving regolith and meteorites showed that certain ionic liquid recipes can dissolve regolith at 200 °C in 4 days. ILs differ in potential and kinetics and can be further diluted with water to reduce viscosity for ease of processing. Regolith particle size distribution will be critical to control. Together, for practical particle sizes from 20-120 um, these parameters will likely require 2-72 hours of process time at room temperature for moderate dilutions of the ILs. Pure ILs are highly viscous so without dilution, higher temperatures will be required to allow recovery of the IL. Add to these issues the strong possibility that microscopic fines will fully react (through and through) with the IL while the large particles develop only a few microns of treated surface. The lower chemical activity of the ILs and dilution levels will help with this. Chemical reactivity is strongly dependent on particle size. Therefore, it may be required to separately process fines less and then mix these back into less aggressively processed coarser regolith powder.
The ILs will likely be used in water solutions and moderate temperatures between room temperature and boiling water. Process time will directly depend on chemical activity, dilution, viscosity and temperature. If the process is automated, there will not need to be a high production rate so process time can grow too many hours with no loss in experimental productivity. Due to the small amount of IL material, higher dilutions (of the order of 20-80%) and longer process times will be needed for these initial screening experiments.
In order to increase contact point areas and strengthen bonds, the treated regolith particles should be pressed together with moderate pressure (more than sedimentation by gravity or manually wringing out water). This will densify the product as well. However, bonded regolith coupons require a certain (yet currently unknown) degree of porosity to enable recovery of IL possibly trapped between the particles. Careful adjustment of the particle size distribution and geochemistry will be needed to optimize the process. To be clear, the technology relies on connected porosity to enable processing through to finished solid product. Increased fines can close porosity and prevent recovery of trapped IL.
Metal ions (particularly Fe, Ni and Ti) in the regolith helps to efficiently couple microwave energy for heating. Since low temperatures (room temperature to boiling water) will be used for all stages of the process, microwave energy for heating will not have to involve high power levels. Certainly 1 kW magnetrons such as in a home microwave would suffice to heat a standard brick sized brick in a few minutes. Liquid water couples very well with microwaves so curing/drying the bricks will be very efficient; certainly, more so than solar or electric resistance heating. The CO2 curing is essential to predict the curing process in a Mars-like atmosphere, which is 95% carbon dioxide. An enclosed chamber filled with CO2 will be utilized to study the effect of CO2 on the cured samples. Use of CO2 to enhance curing has not been investigated to date and may play a small role in this proposed effort since the fundamental chemistry with the IL treatment of the regolith does not involve CO2.
Due to the nature of the ionic liquid action on the regolith, metal ions will be leached from the surfaces of the particles. These metal ions will need to be removed from the IL to recycle it. It is anticipated that multiple treatments of regolith batches by a single volume of IL will be possible before recycle processing. A measure of ‘consumption’ of the IL and of the loss in performance as it ‘wears out” is best obtained from the metal ion concentrations. It should be noted that a valuable ISRU byproduct from the recycle process will be extracted metals. Indeed, the process was already proven when dissolving regolith specifically for the recovery of these metals. Work in this task involves monitoring the metal ion concentrations in the individual IL being evaluated and relating this to the regolith geology (constituent chemistry).
For this technology to be viable, the ionic liquid will need periodic processing to recycle it and return its potency. Processes have been developed at MSFC for this purpose but due to the low Technology Readiness Level, the methods are not yet optimized. The IL will likely be employed as a solution with water, and water will be used to remove the IL from the processed regolith. The water is not consumed and will be recycled by distillation/evaporation which is a low temperature process. An alternative method to extracting the metals as salts, one can employ an electrolytic deposition method to plate out the metals with the possibility of separating them element by element with process controls. At this early stage of the project, minimal effort will be applied to the recycle issues since the main brick-making process has yet to be optimized. These are certainly to be addressed in follow-on years of the project.
To generate preliminary lightweight compressed structures for potential extraterrestrial additive manufacturing processes, AMREC and MSFC shall optimize the tiles/bricks regarding dimensions (aspect ratio) through demonstrating additively manufactured clay tiles and bricks. Minimal tile/ brick strength required to construct an overall stabilized compression structures will be analyzed via simulations in this task. Brick/tile design will also, focus on mold design including proper tapering to allow easy removal from the bricks, material selection for chemical compatibility and overall dimensions to ensure structural stability.
The expected outcomes of this project are: 1) Submission of original peer-reviewed journal articles; 2) Generating preliminary data yielding to successful proposals to NASA and other federal agencies for funding; 3) Increasing the state, regional, and national participation and recognition of the UM’s SoE in space-related research and in situ additive construction; 4) Establishing a local space research hub that would facilitate the recruitment and training of students in space research programs; 5) Cultivating collaboration with NASA researchers at the MSFC and other NASA centers; 6) Expanding the AMREC established undergraduate outreach program to promote education in STEM fields and space exploration related topics; and 7) Seeking industrial partnerships to nurture the proposed research activities and implement more applications.
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