To colonise the solar system we need to figure out how to build settlements on alien surfaces, and, according to Professor Matthias Sperl, a material scientist from the German Aerospace Center (DLR), our best bet rests on 3D-printed bricks made from moon dust.
Your EU-funded project, RegoLight, uses lunar dust, or regolith, to 3D print bricks that could be used to build settlements on the moon. Why do we need buildings on the moon?
‘There are many scientific questions about the moon itself, for example, about the heat flow coming from it, its origin and history. Having a more permanent base would allow geologists and astronauts to go on missions way longer than in the past. They could learn far more about the moon than (what) was done during the Apollo mission.
‘Technologically, now that humankind has established a quite permanent foothold in orbit, the natural next step is to see how we can build on another planet's surface. Now we need to explore what the challenges are there, and this brings us much closer to potentially reaching Mars.’
What would these buildings look like?
‘One of the defining features of a lunar habitat, other than its unique gravity conditions, is the powerful radiation coming from the sun. This means that buildings, machinery and astronauts themselves would need to be equipped with radiation shielding.
‘Any lunar building would need a metres-thick layer of protective dust, a major additional load (weight) that typically no-one would have considered when designing a building on earth.
‘Regarding the bricks themselves, they would probably come in an interlockable or self-stabilising shape very similar to Lego toys. This is because you wouldn’t have the mortar you use on earth to keep bricks together.’
How will you power the 3D printer and where exactly will the materials for the bricks come from?
‘It makes sense to use the sun as a source of energy. For all the other materials you may need you can dig into the soil, where you would likely find hydrogen and oxygen with which you can produce water.
‘When you then use solar energy to bake together the grains of soil, there is the natural question of how sturdy anything built from the lunar dust blanket would be.’
How can you make sure the lunar buildings are safe?
‘With DLR we study granular materials in “microgravity”. Microgravity is also known as weightlessness and describes the absence of the force of gravity. With the help of tools that use the principle of free fall to create weightlessness such as parabolic flights, drop towers or sounding rockets, we do very fundamental and basic research on the behaviour of granular material.
‘Having a more permanent base would allow geologists and astronauts to go on missions way longer than in the past.’
Professor Matthias Sperl, German Aerospace Center (DLR)
‘But we also worry about the big picture, and to begin with we just did a proof of principle assessing if our combination of solar light and regolith can make any material worth studying at all (for settlements). After that was ticked off positive, the next step was trying to produce the brick, and with that you can study how that behaves in comparison with a building material like concrete.’
Why is it better to build directly on the moon?
‘If you consider reaching the space station from the ground, you pay quite a lot of money to bring each kilogram from the ground to an orbit. We call this quite literally payload, as you pay for all the load you bring from the confines of gravity to something that is more loosely confined to gravity, say a space station.
‘The problem becomes ever more significant the further you go out, and in that respect if you want to do more sustainable and long-lasting things on the moon than (just) landing a couple of tons there and returning back to earth, you (will) want to consider using the resources that are available.’
How much would we save by using 3D printing on the moon?
‘If you bring something up to the space station you may think about a cost between EUR 5 000 to EUR 10 000 to bring one kilogram of material. To such an order of magnitude you can easily add a factor of 10 if you go to the moon.
‘Imagine that you have a machine that you put on the lunar surface to build the bricks, something similar to the rovers we put on Mars. Such machines weigh about 200 kilograms, which would cost you roughly EUR 20 million. If you need to bring additional infrastructure such as shovelling devices, you can assume a cost of EUR 100-200 million.
‘Now imagine building bricks and other elements worth 10 tons of upload (material taken to space) on earth, as you will easily need a couple of thousand bricks for one building. To ship all of that to the moon, the estimated cost would be EUR 1 billion.
‘This estimate is slightly unfair because if you were shipping something from earth you would not go for a material as heavy as brick. On the other hand you need to work with materials that are fortified against shield radiation. There are a number of trade-offs. In the end, the best solution is a good mixture of parts that are launched from the ground and pieces that are assembled and produced on site.’
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