Inward Bound: How Should We Colonize the Earth?

Atlas Towers, Terrariums, Space Hotels, and Futuristic Cities

3D animation of a Karmen Tower (also known as an Atlas Pillar). This video was created by Jarred Eagley who is also a member of the SFIA production team.


For those of you who are unfamiliar with this concept, a Karmen tower is an ultra-tall tower whose top exceeds 100 kilometers above the Earth's surface. The 100 kilometer mark is known as the Earth's Karmen line and represents the boundary between space and Earth's atmosphere. Solar panels would be attached near the peak of these towers; electricity produced by these solar panels could get sent down the tower through conductive cables and subsequently used to power a city. A Karmen tower could be used if we wanted to provide power to only one city. The source of power could come from space-based solar panels attached to the top of the tower.

But here's an alternative scheme. The Karmen tower could be attached to an asteroid; a nuclear power reactor could process helium-3 and deuterium (which come from the asteroid itself) in order to produce nuclear energy which could be transmitted down the length of the Karmen tower to the city. If that asteroid was hollowed out and its materials put off to the side, then a rotating cylindrical habitat like the so-called terrariums envisioned in Kim Stanley Robinson's 2312 could be built inside of the asteroid. This "terrarium" would essentially be a smaller version of an O'Neil cylinder where cities, homes, lakes, forests, and roads are located on the inner surface of the cylinder; the rotation of the cylinder produces artificial gravity (centrifugal forces, to be more precise) which keeps everything on the "ground." Any humans living in a such a structure could peer upwards (through, say, a telescope) and see people on the opposite side of the cylinder "walking upside down." (That might sound strange but it actually isn't too terribly unusual when you consider the fact that if (somehow) you could "see through the Earth" and watch people on the opposite side of the Earth, you'd see them upside down too.) Ultimately, the asteroid, the Karmen tower, and the arcology could be connected into a single super structure.

That is possible and indeed the idea of attaching a mega-skyscraper to an asteroid has been seriously considered. But hauling an entire asteroid into Earth-orbit is something that we probably wouldn't want to do. We could, instead, attach the tower to a space hotel (like the one proposed by Shimizu) and that tower could extend beyond the space hotel to an orbital ring, which would, eventually, become a system of multiple orbital rings; but the prospect of a multiple orbital ring system for communication, planetary transportation, interplanetary transportation, and combating global warming is something which we'll discuss in more detail in a future lesson. Deuterium, helium-3, and other useful material could be mined from an asteroid or other celestial body in situ and transported to a space-based nuclear reactor; that reactor could, like in the previous example, produce power which could be transmitted across the length of a graphene cable and used to power a city such as an arcology. 

Depiction of arcologies located on the surface of the sea. (Click image to enlarge.) Image credit:

The nuclear reactor would produce a lot of heat during this process. If the Karmen tower was located above the sea near a costal arcology (see image above), then that heat could be pumped down pipes and used to power water desalinization plants which could be used by the local inhabitants of the arcology city. Indeed, directly beneath the arcology on the sea, we could build some kind of underwater city such as the Ocean Spiral which is essentially a vast spiral-shaped structure with orb-shaped structures situated in between the spiral that extends from the sea surface to the sea floor and this city could also be powered using aforementioned space-based nuclear reactors. Essentially, what I am describing is a system of cities, power generation sites, and other facilities which stretches from above the Earth's atmosphere in space to down deep in the ocean and eventually to the sea floor (and, indeed, to eventually below the sea floor as we shall soon discuss). Such a structure would be immense. 

The Karmen tower (which is essentially a giant skyscraper), the arcology on the sea's surface, and the spiral structure loosely attached to orb-shaped structures extending deep down below the ocean surface could all incorporate cities, homes, recreational centers, and power production sites. Whereas the orbital rings system would consist of nuclear reactors and arrays of solar panels for production of energy, the length of the Karmen tower could perhaps incorporate wind turbines; the arcology on the sea's surface could also be powered by offshore wind farms and bobs which tap into the oceans tidal energy. Lastly, a boring machine could be used to bore a tunnel from the ocean bottom to the mantle; then, a graphene cable could extend from the mantle through the tunnel and up to the bottom of the Ocean Spiral. Graphene is one of the best thermal conductors known to science and would be able to transmit heat, for all practical purposes instantly, from the mantle to the underwater city structure. It is in fact the ambition of the entrepreneur billionaire, Manoj Bhargava, who created the documentary Billions in Change, to bore a tunnel to the Earth's mantle and, using a graphene cable, to tap into the Earth's geothermal energy and to use that energy to power the world. 

One of the big advantages of orbital rings is that we can build multiple of them around the Earth and at any orientation around the Earth; this means that the space elevators descending down from the orbital rings to the Earth's surface could in fact terminate at any point on the Earth's surface of our choosing. And this is true for any planet. Thus, you could have many Ocean Spirals, arcologies, and Karmen Towers which connect to the orbital ring. This is handy because an orbital ring system is probably the best planetary transportation system that we know of.


This infographic depicts the Ocean Spiral: a vast helical-shaped structure which would extend from the surface of the sea to the sea floor. (Click image to enlarge.)

Image Credit:

All systems including the space hotels and orbital rings in Earth-orbit, the Karmen/Atlas towers, the terrestrial arcologies and the arcologies on the sea surface, and the Ocean Spirals (and possibility other kinds of underwater cities) could all be connected into a single super structure. A boring machine, perhaps one like that used by Elon Musk's Boring Company, could be used to bore a tunnel to the Earth's mantle. A graphene cable would extend from the mantle to the Ocean Spiral which could provide geothermal power that could be converted into electricity. Elon Musk has proposed using his boring machines to bore underground tunnels on Mars\(^{[5]}\) which could connect underground cities; his proposed method of transportation between cities is rockets. It is worth mentioning that such a scheme would also be feasible on the Earth. Using this machinery, a network of tunnels could be bored underneath the sea floor; using either rockets like those proposed by Elon Musk or maglev trains (maglev would be preferable; see article), passengers could be transported from one Ocean Spiral to another, or indeed to underground cities that are below the sea floor.

Everything that we have discussed up to this point is in fact technically possible for the simple reason that it obeys the known laws of physics and nature; the caveat though is that such a project would be a formidable engineering project of epic proportions. However, given the extraordinary progress in scientific and technological understanding in the last century, to our descendants a few centuries from now such a task might not seem so daunting. Indeed, millennia from now, unless they destroyed themselves they would have, inevitably, visited other exoplanets in other star systems. Such infrastructure, extending from above the planets atmosphere down through its sea and even underneath its sea floor, might in fact be incorporated by our descendants on other nearby Earth-like exoplanets and perhaps even non-Earth-like planets, though this is purely me just speculating.

 Illustrations of a floating city concept.  Images Credit:

Illustrations of a floating city concept. Images Credit:

Thus far we have discussed the prospect of using space-based solar power and nuclear power to provide electrical energy to terrestrial, coastal, and underwater cities called arcologies (or, to a larger kind of city known as an ecuomonopolis). We have discussed the use of such power sources to power a planetary transportation system, even more efficient than the one proposed by Elon Musk, which would incorporate a system of orbital rings, space elevators, and maglev trains. After millions of years the planets Venus and Mars could be fully terraformed and also incorporate cities and these same planetary transportation systems. Indeed such a system is scalable to many worlds including planets like Proxima B in the Alpha Centuari system or other Earth-like planets (natural or artificial) in other star system. Such space-based solar panels could be used to power an ultra-powerful array of lasers which could be beamed on numerous solar sail spacecraft, like those proposed by Project Starshot. We have discussed how this system could be used to create an "interstellar highway" between the stars; but it could also be used to create an "interplanetary highway" between planets. These spacecraft could travel at relativistic speeds between Venus, Earth, and Mars in a matter of hours. Thus people living on, say, Venus could receive materials from Mars in under one Earth day. Therefore, space-based power might not only be the key to creating an "interstellar highway" for voyages from one star system to another. but it might also be the key for making interplanetary trade and travel feasible, cheap, and convenient.

The Economics of Space-Based Solar Power

Humanities current power consumption is roughly 18 terrawatts per year. This means that, on average, each person on the Earth consumes about 2,400 watts every year. One of the biggest problems with modern civilization is that our current method of acquiring that power involves burning enormous amounts of hydrocarbons and fossil fuels. This releases vast quantities of greenhouse gasses into the Earth's atmosphere which traps infrared radiation (heat) causing our planet to warm. But would it be possible to meet all of our energy needs (roughly 18 terawatts per year) by using solar power satellites? And would it be economically feasible? To think about the answer to the first question, let's try to get a rough idea of just how much surface area of solar panels that we would need to get the job done. The best solar panels in the world produce roughly 600 watts per square meter. Assuming that we used such solar panels, we would need roughly 30,000 square kilometers of space-based solar panels to receive 18 terawatts per year of solar energy. Indeed, that still wouldn't be enough because a certain fraction of the Sun's solar energy gets lost as it gets converted from solar energy to electrical energy, and from electrical energy into electromagnetic energy, and from electromagnetic energy back into electrical energy. But this result does give us a sense of scale of just how immense such an engineering project would be. It might sound like a daunting task to manufacture more than 30,000 square kilometers of solar panels—and indeed it is—but it is certainly possible. The materials necessary to manufacture this vast array of solar power satellites could be transported form the Earth to space using an Earth-based space elevator or those materials could be extracted from the Moon and sent to low-Earth orbit by using a variety of launch system including a lunar electromagnetic launch loop or a lunar space elevator.

From an economic standpoint, it is very expensive to send things into space. At current launch costs, it would cost you about $10,000 per pound to transport materials from Earth's surface to space. Even at this expensive cost, space-based solar power could still be potentially economically competitive with ground-based solar-power. Because ground-based solar panels are exposed to the elements including wind, rain, and dust, those solar panels suffer much more wear and tear than space-based solar panels since there is no wind, rain, and dust in space. Due to wear and tear from the Earth's elements, ground-based solar panels require several trillion dollars per year just in maintenance. Space-based solar panels are expected to last 20-30 years and would not require the expensive maintenance fees. 

Another economic advantage of using space-based solar panels is that these solar panels could be exposed to perpetual sunlight unlike Earth-based solar panels which do not produce electricity on cloudy days. And because Earth-based solar panels are unable to produce electricity on certain days (namely, days when it is cloudy with little sunlight), battery storage systems must be installed. Indeed, Jeremy Rifkin imagined that sometime within the next few decades humanity will derive all of its power from renewable energy sources; but, as he argued, because some forms of renewable energy (such as solar and wind) are intermittent, a post-hydrocarbon civilization would need to install expensive batteries and super capacitors within its electric grid. What's nice about space-based solar power (as well as certain other renewable power sources such as geothermal power) is that we need not worry about outfitting our electric grid with these expensive energy storage systems because the power generated by space-based solar panels is constant and perpetual, not intermittent.

This article is licensed under a CC BY-NC-SA 4.0 license.


1. Puiu , Tibi . (2018, June). How much renewable energy does the world use. Retrieved from

2. Stone, Maddie. (2014, June). Life inside an asteroid: The plausibility of 2312. Retrieved from

3. Tate, Karl. (2013, October). Shell-Worlds: How Humanity Could Terraform Small Planets. Retrieved from 

4. Kramer, Miriam. (2013, October). Incredible Technology: How to Use 'Shells" to Terraform a Planet. Retrieved from



4. Warmflash, David. (2016, April). How to Harvest Terawatts of Solar Power on the Moon. Retrieved from

5. Strange, Adario. (2017, July). The secret behind Elon Musk's Boring Company may be out of this world, literally. Retrieved from