Ceres megasatellite settlement that could grow bigger than Earth
The universe outside Earth has unlimited material and energy. If people were not confined to living on Earth but could somehow live in the vast universe, resources and the standard of living could increase. A Ceres megasatellite is a new and ambitious extraterrestrial settlement concept. The concept was originally developed to address the shortcomings of previously known modes of habitation, which include Mars settlements and free-space O’Neill-type cylindrical settlements. The megasatellite paints a potential future where a larger mankind lives in paradise-like conditions, without natural disasters, without resource competition and maybe without conflicts.
Other settlement concepts
The first problem, and most imminent regarding long-term habitation on Mars, is that Mars’ gravity is only 38% of Earth’s. This might have such a result that children that have grown up on Mars could not move to Earth as adults, making them and their offspring effectively prisoners of Mars, or other low-gravity environments. O’Neill-type rotating cylindrical settlements provide a better environment regarding gravity as here it is possible to create earthlike 1 g artificial gravity. However, the major problem with O’Neill cylinders is that they have a size limit due to the fact that the tensile strength requirement of the walls is proportional to the cylinder’s radius. For hosting a significant number of people — millions — more than one cylinder is then required. However, as the cylinders are not physically connected, they tend to drift apart due to orbital dynamics. The distance would make travel between the settlement islands inconvenient regarding time, and also due to radiation exposure and propellant. If the settlements were to orbit the Sun then they would eventually be distributed evenly along the orbit. If they were to orbit another body, such as an asteroid, then the distances would be shorter; however, if the number of settlements would be large, there would be a risk of mutual collisions and the settlements would also shadow each other. Full radiation shielding would be feasible in the settlement itself, but not in the transfer vehicles because it would make them too heavy. Hence, in addition to being slow and boring, inter-cylinder travel would also increase the travellers’ radiation dose and, therefore, it would probably decrease the life expectancy of the passengers. Finally, large daily use of rocket propellant would not be sustainable in the long run, because propellants are non-renewable resources of our Solar System.
The megasatellite architecture and materials
The megasatellite settlement concept is a further development of the O’Neill cylinders idea. For the megasatellite settlement, several O’Neill cylinders are attached by magnetic bearings to a rigid frame, creating a megasatellite.
This would solve the problem of free-space O’Neill cylinders drifting apart. The geometry could be made such that the megasatellite can grow in a self-similar way. This means that the satellite, shaped like a disc, can grow larger at the edges. As for any city, the old city centre does not need to be demolished when new suburbs are built on the outskirts.
The remaining questions are where to place the megasatellite and where to get the building materials at low cost? For this, one possible solution could be the dwarf planet of Ceres. Ceres is the largest body of the asteroid belt and it has a significant amount of nitrogen, which is necessary for creating an earthlike atmosphere in such a settlement. If the megasatellite were to be built in Ceres’ orbit, the raw materials for expanding the settlement would not run out in the foreseeable future. It would be possible to lift the materials from Ceres at low cost by using a space elevator. The elevator’s feasibility on Ceres (< 1000 km diameter) is much higher than on Earth (12× larger than Ceres). Due to the low gravity of Ceres, standard engineering materials such as carbon fibres could be used for the elevator cable. A space elevator works by synchronising a planet’s rotation with a station’s orbital velocity. Since objects move faster in lower orbits, a planet or asteroid with a higher rotation rate would require a shorter elevator. In the case of Ceres, a space elevator would be established by connecting a location on the Cererian equator with a station that is stationary with respect to the ground location. Because Ceres rotates relatively fast, the stationary orbit is rather close and the elevator cable would be no more than 1024 km long. Rockets could be used as well, because Ceres has abundant water to make hydrogen–oxygen rocket fuel. Reusable rockets may be simpler than the space elevator, although the space elevator is an order of magnitude more energy-efficient. An electromagnetic catapult might also work, as proposed originally by O’Neill for the Moon.
Ceres has so many potential building materials that the megasatellite could eventually have more living area than Earth. For example, a 10¹⁸ kg megasatellite would be able to host 100 billion people and, in material terms, only 0.1% of Ceres’ mass would be utilised in order to build it.
A megasatellite could also be built in Mars’ orbit, using Deimos as the source of materials. The mass of Deimos is 1.4 × 10¹⁵ kg, so the population here would be limited to around 100 million people. If it turns out that the Martian moons have insufficient nitrogen, it would be possible to import it from the Martian atmosphere, which is 2.8% nitrogen. Incidentally, Deimos’ resources and Martian nitrogen would be exhausted at approximately the same time that a ~100 million population is reached.
The cylindrical habitat design
There are various ways the megasatellite could be designed. A recently published paper describes a version in which each cylinder has a radius of 1 km and length of 10 km consisting of two 5 km halves.
Not all cylinders need to be of the same size. A large cylinder has room for more people and provides a higher quality of artificial gravity due to the smaller Coriolis component of the acceleration field.
The drawback of a bigger cylinder is that the fraction of structurally strong tensile material is larger, since the centrifugal tension of the walls increases linearly with the rotation radius. If the radius of the cylinder is 1 km, 5% of the total mass is structural, at least in the case that steel is used as the structural material. The radiation shield and soil would comprise most of the mass (94%) and both could be mined from Ceres without much processing. The majority of the production energy would go into making the structural material. The remaining 1% of the settlement mass would be mainly air. The rigid megasatellite frame and the traffic and mirror systems would be less than 1% of the mass. The rigid frame and the mirrors would be lightweight because they would be built and utilised in microgravity. Only the spinning cylinders would experience artificial gravity, hence the tensile strength requirement.
There would be a tradeoff between soil thickness and manufacturing energy. The baseline concept includes a 1.5 m thick inner-soil layer under the cylinder’s artificial gravity and a 2.5 m layer of outer soil outside the spinning cylinder. The inner soil would be available for plants, but needs structural support mass to overcome the centrifugal force. The manufacturing energy would be proportional to the structural mass. Both types of soil contribute to radiation shielding, and, for sufficient shielding, their total thickness would need to be 4 m.
Living conditions and diurnal cycle
In the baseline configuration, each cylinder offers 1100 m² per inhabitant of ‘rural’ area and 900 m² per inhabitant of ‘urban’ area. The rural area is 63 km² in total and has room for 57,000 inhabitants.
The rural area would be illuminated by natural sunlight, which is concentrated to earthly intensity by parabolic mirrors placed at the cylinder end. It has the same gravity as Earth.
The urban area would be illuminated artificially by LEDs and the gravity is 81% of the earthly value. The settlers could easily travel between the rural and urban areas, getting full g, necessary sunlight and other outdoor benefits.
Travel between the cylinders would take place using vehicles resembling autonomous electric cars. During the trip, the passengers would not experience weightlessness because the road tunnel can be curved into a spiral providing artificial gravity thanks to the centrifugal force. As a backup, there could be an elevator-type mobility system between the cylinders where passengers would experience trip-time weightlessness. The final backup escape route is that each cylinder has two docking ports for spacecraft to enter and leave.
An earthlike diurnal cycle would be simulated by dividing the habitat into three time zones that differ from each other by ±8 hours. The sunlight consumption would be constant so that no light would be wasted. In the baseline concept, seasons are not included but could be considered in detailed studies.
The mean solar distance of Ceres is 2.77 au, so that sunlight is 7.7 times dimmer than for Earth. This longer distance would be compensated for by parabolic reflectors that concentrate the sunlight. A parabolic reflector surface would not cost much, because in zero gravity the reflectors can be made lightweight. Ceres’ heliocentric orbit is rather circular, which simplifies the thermal design.
Some practical considerations
Moving to outer space could be expensive for the first settlers. One solution could be that they would take a bank loan for buying the right to live in the megasatellite. After moving in, they would then pay the loan back by extending the settlement and selling the newly created space to immigrants. Because the settlers would be on site, they could teleoperate the building robots in real time with no signal delay and also fix the robots if needed.
Why would someone prefer Ceres over Earth? The permanent benefit of living in an artificial settlement is the absence of natural catastrophes such as volcanic eruptions, earthquakes, hurricanes and tsunamis. The fact that it would be possible to grow crops all the time without the need to store food would make life easier as well. There would also be no need to store energy, because outside the megasatellite, the Sun would shine all the time and solar panels would generate constant power.
Could the Martian gravity problem be solved by placing spinning habitats on Mars? In principle yes, but the magnetic bearings would have to compensate for Mars’ gravitational force and they would become more expensive than in microgravity. The stationary radiation shields around the spinning habitats would need additional structural support in Martian gravity. In orbit, for habitats to obtain concentrated sunlight is easy as it would rely on pointing the megasatellite mirrors towards the Sun. The same method cannot be used on Mars though, because the Sun moves in the sky. Thus, habitats on Mars would probably have to use artificial illumination. Letting sunlight in through normal windows would entail the problem of also letting in cosmic radiation. On the megasatellite, this problem would be avoided by reflecting the sunlight in concentrated form through a narrow slit. No cosmic radiation would enter the habitat through the slit, because it is covered by shields and cosmic rays travel straight without bending around corners or reflecting from mirrors.
Building artificial-gravity habitats on the surface of Mars would be possible, but would have several drawbacks relative to building a megasatellite in Ceres’ orbit — or in Mars’ orbit.
The only downside of building a megasatellite in orbit relative to building on a planetary surface is that the material would need to be lifted by either a space elevator, by rockets or by electromagnetic catapult. But lifting material from Ceres or Deimos by elevator or catapult would be energetically cheap compared to making the habitats themselves.
It seems to be the case that Earth is the only planet where people can meaningfully live. But that does not prohibit people — even the majority — from living outside Earth, and to live better than they ever could or have done on Earth.
Author: Pekka Janhunen
Editors: Andris Slavinskis and Silvia Kristiin Kask
Design: Anna Maskava and Rute Marta Jansone
Proofreading: Robert B. Davis
Attribution (text): Space Travel Blog / FMI (Janhunen)
Attribution (images): see captions
