How do you convey electrical energy to your lunar base? With a concrete tower a number of kilometers excessive
It sounds like science fiction, but building a huge tower several kilometers high on the lunar surface may be the best way to harness solar energy for long-term exploration of the moon. Such towers would raise solar panels over disruptive geological features on the lunar surface and expand the surface area available for power generation.
A successful future moon base of any size requires two key resources: water and electricity. Ever since evidence of frozen water ice was discovered in the depths of permanently shadowed craters near the moon’s south pole, the polar region has become NASA’s primary target for future moon landings. Water can of course be used to drink and grow plants, but it can also be used as rocket fuel or separated at the molecular level to produce breathable oxygen. While the moon’s waters are deep in the crater basins, power generation will likely come from above over the crater rims, where “peaks of eternal light” are known to exist. These peaks almost never experience shade and would be ideal places to place solar cells on the moon for water extraction.
The “tips of Eternal Light” are small, however, and to get the most out of them it can make sense to build on top of them vertically – which dramatically increases the usable surface area for unhindered generation of solar energy.
While it will take many decades for such a construction to be seriously attempted, researchers at Harvard University have already begun to work out the possibilities and limitations of such a project. At the end of February, they published a preprint paper on ArXiv examining the physics and materials science that would determine the construction of such giant lunar towers.
Water near the moon rods. Photo credit: NASA.
The tallest building ever built, the Burj Khalifa, is 828 meters high. It is possible to build much higher on the moon as the lunar environment has three main advantages.
First, the moon’s gravity is only 1/6 that of the earth, which means that buildings at much greater heights can hold under their own weight. Second, the lunar environment lacks an atmosphere, meaning that builders on the moon don’t have to consider the exposure of high winds as they do on Earth. And finally, the moon’s serene seismic environment means that lunar tower builders needn’t worry about the effects of earthquakes, or rather moonquakes.
Taking these parameters into account, the researchers were able to calculate that a minimum wall thickness of 20 cm is required to safely build a concrete tower several kilometers high. Building taller is possible, but the cost and amount of concrete required increases dramatically beyond two kilometers.
The Burj Khalifa, the tallest building on earth, is 828 meters high. Photo credit: Donaldytong, Wikipedia.
The researchers chose concrete as a building material because it can be made fairly easily from lunar soil (regolith). The cost of transporting steel girders (for example) from Earth would be prohibitive, so it is important to be able to build the towers from lunar resources. The researchers also measured the compressive stress of the weight of the concrete, as well as its buckling strength, to determine how tall such a structure could possibly be built.
While towers up to 17 km could theoretically be possible, the team concluded that “the mass and volume of the regolith, which must be converted into concrete in a reasonable amount of time, is likely to be the limiting factor for some time. If we need a construction time of 1 year, a 2 km long tower would have to process 11 m / day. A 1km tower would require 80% lower rates. Those numbers seem plausible in a decade or two. “
So towering lunar skyscrapers are not only possible, but also the most practical solution for generating electricity on the moon in the long term. The day a lunar building will cross the height of the Burj Khalifa is still a long way off, but with the Artemis program planning to return to the moon this decade, the foundation for such a project could be laid in the not-too-distant future.
Find out more: Sephora Ruppert, Amia Ross, Joost Vlassak, Martin Elvis, “Towers on the Moon: 1. Concrete.” ArXiv Preprint.
Feature Image: Earthrise captured by the Apollo 8 crew. Photo credit: NASA.