For future missions to the moon, in order to construct a permanent settlement there, in space construction is extremely important. It is very inefficient to transport construction materials from Earth's gravity well. The two main challenges in space construction are:
- Material transport/acquisition
- Construction process
Since only 6t of mass has been transported to the moon with landings so far, on site construction and additive manufacturing are important keywords in making permanent habitation on the moon possible.
Additive manufacturing is basically the overarching name for 3d-printing and allows creation of complex geometries with relatively simple processes. On site resource utilisation and construction promises to greatly reduce the need for material transport. On the moon the available material is lunar regolith, of which two general types exist: highlands, and maria (lunar sea) regolith. These differ in composition and thus application.
Two papers utilising lunar regolith will be discussed.
Determining the feasible conditions for processing lunar regolith simulant via laser powder bed fusion
The problem is in determining the best methods to be used for materials processing on the moon. More specifically the characteristics of Laser Powder Bed Fusion suitable for lunar regolith will be identified, and the resulting material will be analysed.
The first step is selecting a base plate for the LPBF process, since the base plate can react with the material placed on it due to the intense heat of the laser process. Two types were tested, firstly metal, which turned out to react with the regolith in a negative way, and refractory clay, which was found to be suitable, and used for further processes.
The process of determining the LPBF characteristics themselves simply involves comparing different laser powers and scanning speeds to find a combination that results in the best powder adherence and production speed combination. These tests were iterated, starting from larger steps in the characteristics, and "zooming in" on the best determined combinations and going over the range with lower steps.
The resulting material was then tested for compressive yield strength, which was found to be ~32.5 MPa, about half that of copper. These results are 2x better than other similar methods such as extrusion printing or solar 3d printing, but 8x worse than thermal sintering, where as thermal sintering is a much more complex and delicate process.
Simply put this paper explores using lunar regolith for creating brick-like material on the moon, and shows promise in the field.
In-situ resource utilisation manufacturing of optically transparent glass from lunar regolith simulant
Where as the previous paper concerns a more rough construction material, this one explores glass manufacturing for various applications. The aim is to determine if it is feasible to create transparent glass from lunar regolith for use in solar panels, containers, windows, etc.
Here the regolith composition is very important. On Earth most glass used is synthetic, and natural basaltic glass is not widely used. On the Moon however, regolith composes generally of 1-25% of basaltic glass depending on the region. This is where composition comes in, as glass colour and opacity is very sensitive to impurities, with more metal generally making it more opaque and the type of metal determining the colour. On the moon the colour is mainly Titanium and Iron influenced.
The researchers used 6 different regolith simulants, 5 from lunar seas and 1 from highlands, highlands signifying lower iron content. They had 200 g of each to start.
The first step of the process is beneficiation starting with drying and sieving, to remove all the water content and separate the larger granular material from the finer. The resulting materials were then run through an electromagnetic separator used by geologists to remove as much metallic content as possible. It was found that the lunar sea regolith had an extremely low, sub 10 g, yield. Thus the best samples came from the highlands regolith.
After beneficiation, the hot process was started. This involves melting the samples in a crucible and casting them. The processing temperature was 1550 C after which the glass was annealed at 700 C.
Once the rough samples were poured the cold process was lapping and polishing, to provide an even and smooth glass. The results were a relatively good transparent glass from the highlands regolith, and some farily opaque samples from the lunar seas regolith due to impurities and lingering metal content.
The samples were tested for surface profile, comparing to a microscope glass slide, showing still great drawbacks for the samples. Then spectral passthrough analysis was done to determine suitability for solar panel use and the higlands sample showed promise.
Overall the two papers show that lunar regolith can be used in additive manufacturing processes to generate both rough and delicate construction materials on the Moon for a permanent habitation.
Lunar regolith - https://curator.jsc.nasa.gov/lunar/letss/regolith.pdf
Moon missions - https://en.wikipedia.org/wiki/List_of_missions_to_the_Moon
Artemis mission - https://www.nasa.gov/specials/artemis/
Project Olympus - https://www.ubm-development.com/magazin/en/project-olympus-on-the-moon/
Additive manufacturing - https://additivemanufacturing.com/basics/
Lunar maria - https://courses.lumenlearning.com/astronomy/chapter/the-lunar-surface/
Spectral irradiance - https://en.wikipedia.org/wiki/Irradiance
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