With all the interest in returning to the Moon to build permanent human habitats, there is the question of what will be used for building materials. The Indian Institute of Science (IISc) and the Indian Space Research Organization (ISRO) have developed a sustainable process for making bricks on the Moon. It makes use of lunar soil, bacteria and guar beans to consolidate the soil into possible load-bearing structures. These space bricks could eventually be used to create structures for human habitation on the Moon’s surface.
Aloke Kumar is Assistant Professor in the Department of Mechanical Engineering, IISc and one of the authors of two studies recently published in Ceramics International and PLOS One. He said, “It is really exciting because it brings two different fields—biology and mechanical engineering—together.”
The current cost of sending a pound of payload to outer space is about ten thousand dollars. The process developed by the IISc and ISRO researchers makes use of urea which can be sourced from human urine and lunar soil as raw materials for constructions on the lunar surface. This would decrease expenditures for lunar construction a great deal. The process also has a lower carbon footprint because it uses guar gum instead of cement for support. The guar beans could be grown in greenhouses on the Moon.
Some micro-organisms can produce minerals. Sporosarcina pasteurii is a bacterium which produces calcium carbonate crystals through a metabolic pathway called the ureolytic cycle. Calcium and urea are consumed and crystals form as a byproduct of this metabolic pathway. Kuman says, "Living organisms have been involved in such mineral precipitation since the dawn of the Cambrian period, and modern science has now found a use for them."
The IISc and the ISRO teamed up to exploit this bacterium. First, they mixed the Sporosarcina pasteurii bacterium with a simulated lunar soil. Then they added the urea and calcium sources along with gum extracted from locally-sourced guar beans. The guar gum increased the strength of the material by functioning as a scaffold for the precipitation of carbonate. The mixture was incubated for a few days. After that time, it was found to have significant strength and machinability.
Koushik Viswanathan is an Assistant Professor in the Department of Mechanical Engineering at IISc and another author of the published articles. He said, “Our material could be fabricated into any freeform shape using a simple lathe. This is advantageous because this completely circumvents the need for specialized molds—a common problem when trying to make a variety of shapes by casting. This capability could also be exploited to make intricate interlocking structures for construction on the moon, without the need for additional fastening mechanisms."
The PLOS One study was conceived by Rashmi Dikshit who is a DBT-BioCARe Fellow at the IISc. The study also investigated the use of other locally available soil bacteria to replace the Sporosarcina pasteurii. Following tests on different soil samples in Bangalore, the researchers found an ideal candidate with similar properties. This bacterium is Bacillus velezensis. A small vial of Sporosarcina pasteurii costs almost seven hundred dollars while a vial of Bacillus velezensis is under seventy dollars.
The authors of the studies believe that this is the first significant step toward the constructions of building in space. Kumar said, "We have quite a distance to go before we look at extra-terrestrial habitats. Our next step is to make larger bricks with a more automated and parallel production process," says Kumar. "Simultaneously, we would also like to further enhance the strength of these bricks and test them under varied loading conditions like impacts and possibly moonquakes."