The recent launch of the worlds first commercial manned spacecraft by enterprenuer Elon Musks company Spacex represents a step change heralds a new era of cheaper access to the solar system. This follows from an earlier launch of Musks cherry red tesla roadster which was sent into space in an earlier test flight. However, these events do lead us to ask the question. If travel to space is going to become increasingly feasible and affordable, where are people going to go and where are they going to live when they get there?
One intriguing possibility comes from another of Musks’ ventures, “The Boring Company”. Why not shelter underground?
The Boring company (TBC) aims to make “boring” more interesting. Tunnelling beneath the earth is a slow and expensive process. TBC aims to speed this process up via number of technological improvements to tunnel boring machine technology. This can be achieved by increasing the machines power whilst improving cooling systems. Typically, in soft soil a tunnelling machine will spend 50% of the time tunnelling and 50% of the time shoring up the walls of the tunnel. Doing these two things at the same time would increase speed and efficiency and allow continuous tunnelling. Automating the whole process would eliminate the current need for several operators and replacing the diesel motors with electric motors could lead to further efficiency gains.
Whether Elon Musk intends to use the tunnel boring technology in space is unclear but if his tunnel boring machines could be put on a rocket, the possibilities are vast. Living underground may seem dangerous but it’s actually quite the opposite. On Mars potential hazards include radiation solar flares, dust storms and extreme swings in temperature from day to night. Going underground is a way of avoiding all these problems and tunnels are known to be one of safest places to shelter in the event of an earthquake. On earth there are some places where people live quite happily underground. One example is the Australian outback town of Cooper Pedy. Residents in Cooper Pedy have built houses, shops, churches swimming pools and an underground cinema all to escape the scorching heat above.
Recently researchers at the University of California, SanDiego have found it possible to create bricks from compressed simulated Martian soil. These bricks were found to have strengths greater than concrete. These could be used to seal the walls of the tunnel. This is probably the simplest conceivable way to build a shelter on the surface of another planet. The tunnels could be sealed and then pressurised to provide a breathable atmosphere. If deep enough, the possibility of leaks would be small. The walls of the tunnels could be treated to suppress dust which would be a potential hazard if not managed. The positive air pressure would help drive dust particles to any tiny leaks where it would soon plug them up. Impregnating the walls of the tunnels with fungi which grow and plug tiny gaps which may appear over time is another possibility. This technique has been trialled here on earth as a way of building strong, durable, self-healing concrete structures. A cleverly designed tunnelling machine which was able to turn sharply enough could build larger structures such as amphitheatres, hallways, lightwells, water reservoirs or fuel storage tanks by twisting around on itself and removing excavated rock and soil. Alternatively, the excavated material could be used to 3D print staircases, doorways shelving or other useful structures within the tunnels.
Mars is not the only place that this technology could work. Tunnelling on the moon could also be a cheap and effective way of building. Another exciting possibility is on asteroids. Some asteroids are full of important metals and resources. The economic value of asteroid resources is truly staggering since many contain large amounts of valuable materials such as gold, platinum, iron, nickel cobalt, hydrogen and ammonia. Some of these could be bought to earth but they could potentially be more valuable if utilised in space. The economic value of a mineral rich asteroid is typically estimated in the 100s of billions or even trillions of dollars more than enough incentive for Musk or another entrepreneur to put a tunnelling machine on a rocket.
Once these minerals were removed the resulting hollowed out asteroids has long been suggested as a way of building space colonies. Giving the colony, a spin could produce a centripetal force which could act as a type of artificial gravity allowing people to live and work in a kind of inside out version of the earth. Utilising tunnelling technology gives us the possibility of “living off the land” throughout the inner solar system. This means less materials need to be brought from earth, speeding up the process of colonisation.
Not all underground habitats would need to be built from scratch. Just as caves exist on earth they are also likely to occur on other bodies in the solar system. The Japanesespace agency JAXA has already identified lava tubes on the moon from ‘skylights’, collapsed sections of cavern open to the sky. Similar caves have also been identified on Mars. Calculations have shown that under the moons low gravity allows these caves to be structurally stable at much larger sizes than here on earth. The Japanese team has discovered caves 50 km wide and 100km long. This is more than large enough to hold a large city. Such caves could possibly hold water ice deposits which could be used to sustain life or for rocket fuel. These could be filled with air (produced from the lunar soil) and lit with skylights and/or LED lights powered by solar panels (again easily manufactured from the silicon in the lunar soil). Protected from micrometeorites, solar flares and swings in temperature such places would comfortable places to live. Perhaps one day there will be vast cities, replete with gardens perhaps even lakes under the surface of Mars, the moon or the hollowed-out interiors of asteroids all built on the proceeds of mining.
Whilst sending a cherry red roadster and a manikin into deep space may be an excellent advertising stunt, sending a tunnel boring machine, with the possibilities of extraterrestrial mining and opening vast areas of habitable real-estate would have a return on investment which is difficult to overestimate.