A Space Settlement Design Concept
April 15, 1989 with 2022 updates.
By David Smitherman
ShellStar 2020 is the name of this spherical habitat for three thousand people. It is an inside-out world that rotates at about two revolutions per minute (rpm) to generate an artificial 1-gravity force that is equivalent to Earth’s gravity. The name ShellStar is derived from the acronym ShellSTAR for “Shell System Technology and Advanced Robotics.” It is proposed that this type of construction method be developed for all major facilities on the Moon, Mars and free space.
Project Update Notes
- The name ShellStar also refers to its appearance in that the pressure vessel is a large spherical shell that will look like a star when viewed from Earth. The 2020 numbers on the side of ShellStar were thought to be the approximate date this technology would be feasible. Progress is being made as noted in the References section at the end of this article.
- The pressure vessel size for this design is about 600 meters in diameter, and is roughly equivalent to the smallest spherical pressurized volume that can provide a one gravity living area while rotating at no more than 2 rpm. The stated population of 3000 is approximate and needs to be refined through more detailed design and analysis.
- Since designing this work in 1989 for the National Space Society’s Space Habitat Design Contest I have found several possible construction methods and design improvements which will be mentioned in this article and hopefully explored in more depth later with updated designs.
Drawing 1 of 2
The center drawing shows ShellStar 2020 and a neighboring vessel in orbit around the Earth. On the back side of the vessel is a parabolic mirror facing the Sun that collects and transfers light to the interior by fiber optics. Next is a group of radiator rings for removal of waste heat surrounding a pressurized cylinder enclosing a nuclear power facility. The center section is a pressurized sphere which encloses the primary habitable volumes, surrounded by a ring of solar collectors along its outer edge. On the front side of the sphere is a cylindrical landing ring which operates much like a conventional airport. Extending from the sphere’s axis of rotation is a pressurized tube beam connected to a fuel production facility.
Figure A shows an Earth-Moon construction orbit for ShellStar 2020 to provide for better access to materials and convenient construction crew rotations. During construction all personnel will rotate between ShellStar 2020 and the Moon several times before returning to Earth from their tour of duty. A Moon base is proposed as a combination scientific outpost and mining camp to provide the bulk of the mass to be used in the construction of the ShellStar vessel. From Earth all prefabricated materials and robotic machines will be provided to construct and equip the large pressure vessel. The final location is shown trailing the Moon in its orbit around the Earth.
Orbital Update Notes
- The cyclic orbit proposed for construction in Figure A will likely take too much propellant to be practical. The best orbit for ShellStar 2020 would depend primarily on where most of the materials are coming from for construction and ongoing operations. If the Earth, then perhaps an Earth orbit up to a geosynchronous altitude, and if the Moon, then perhaps a lunar orbit up to and including the Lagrangian Earth orbits in proximity to the Moon.
Figure B shows ShellStar 2020 under construction as a robotic arm rotates from the center point of the tube beam gradually building up layer after layer of a concrete-like material to form the spherical shell. On Earth a glass fiber reinforced concrete spread by a slip-form or extrusion process would best describe the characteristics of the material proposed. Two spherical shells are constructed, one inside the other, each between one and two meters thick, and set about ten meters apart, as illustrated in the section on Drawing 2 of 2. A trussed bracing system between the two forms a rigid double wall sphere. This double wall construction provides for good environmental protection and convenient utility distribution. At each end of the tube beam are space station modules used for temporary living and working quarters for the construction crew. The system is automated such that raw materials enter each end of the tube beam and are processed, mixed, and extruded out the rotating arm.
Construction Update Notes
- A concrete shell between one and two meters thick will require a lot of material and be incredibly massive. This approach was selected for radiation protection and not structural integrity. So if another solution can be found to protect permanent residents from galactic cosmic rays then a thinner and lighter weight system would be preferred.
- Alternative radiation protection systems could include water (still massive), electromagnetic fields (high power requirements), and medical breakthroughs that repair damaged cells from cosmic rays (possible cancer cures).
- Concrete may not be feasible because there is no practical binder available in the lunar materials that have been found so far. Alternate structural systems include aluminum plates welded robotically into a geodesic sphere, rigidized inflatable systems, and perhaps inflatable bladders in combination with reinforced frozen water.
- The least massive solution would be the aluminum plate geodesic sphere in combination with medical solutions for the radiation issues.
Figure C shows the construction of a cylinder outside the sphere created by moving the rotating arm along the tube as each layer of the cylindrical shell is built up. A double wall construction is used here too, set about twenty meters apart and reinforced with a truss structure between the two cylinders similar to the spherical shells.
The inside face of the inner cylinder forms a landing ring for Shuttle and NASP (National Aero Space Plane) type vehicles as shown in the section on Drawing 2 of 2. As the vehicle touches down and brakes it accelerates with the rotation of the cylinder to about 1/2-gravity. The craft then pulls next to the spherical wall for passenger and cargo transfer in a near conventional style air terminal facility. Vehicle launch is accomplished by lowering the craft to the outside of the cylinder and releasing it from a robotic crane.
Inside the sphere each floor level is a cylinder too, constructed in the same manner as the outside landing ring. The construction sequence here is such that a habitable environment and slow rotation can be created soon after the closing of the first sphere. The construction crew can then work with minimal environmental suits in a low gravity construction area to assemble the truss and column structures between the spheres and cylindrical floor levels.
Design Update Notes
- The cylindrical landing pad concept will likely have some complex orbital mechanic issues that will require more propellant for landing operations than for simple docking operations. A solution is to add more docking ports along the pressurized tube beam for zero gravity passenger transfers and then use cranes to lower vehicles onto the inside of the cylindrical landing pad for docking to the pressure vessel or moving the vehicles into large airlocks for maintenance and cargo transfers where a low gravity environment is desired.
Figure D is a view above a Moon Base where the raw materials are mined and shot into orbit by an electromagnetic accelerator. Two dome structures are complete and one is under construction using the ShellSTAR system. Each capsule shaped package is launched on an orbit that will cross and catch up with the Earth-Moon orbit of ShellStar 2020. A maneuvering unit attached to the capsule provides assistance in making course corrections and final docking with the tube beam.
Materials Update Notes
- The Moon was selected for primary material supplies due to the large quantity required and the high cost for launching everything from Earth. With reusable rockets now available and less massive construction concepts possible, then a better solution might be to bring everything up from Earth.
Drawing 2 of 2
ShelStar 2020 has the potential of being a completely self contained city in space capable of traveling anywhere within the solar system. The modular design and structural characteristics of the pressurized tube beam allow the fuel production facility to be fitted with boosters located at either or both ends of the vessel. The spherical end of the fuel facility is designed to accept raw materials through an airlock. For small asteroid type objects the spherical shell can be opened into two halves. The facility separates and processes the various elements it takes in, transferring propellants to its storage tanks and the raw materials to the industrial areas inside the ShellStar vessel.
The two ShellStar vessels shown on Drawing 1 of 2 are in Earth orbit within close proximity to each other. This is the more common setup anticipated for ShellStar vessels. Groups of vessels flying in high Earth orbit, geosynchronous orbit, lunar orbit, and other orbits and stable regions in the Earth-Moon system. It is anticipated that most of the vessels will concentrate on production of only a few types of products and that trade and travel around the Earth-Moon system will be extensive.
The ShellSTAR constructed vessels can vary in size according to the needs of the various industrial function and required work force. As the population and economy grows, larger vessels are built as free fliers in parallel with their builders so construction crews can eventually become permanent residents in space.
Inside the ShellStar vessel is a city with residential, commercial, agricultural, industrial and institutional establishments overlooking a park lined river flowing around the sphere. The river has fishing and swimming areas and the parks have various facilities for outdoor recreation. There are two zero gravity domes at the sphere’s rotational axis. One is for industrial and research activities, and the other is a multipurpose facility for research, recreation and tourism.
ShellStar 2020 and the ShelSTAR construction concept has the potential of creating many future habitats in a variety of shapes and sizes. This proposal is just one of many possibilities.
ShellStar 2020 dimensions are as follows:
- Diameter of the spherical pressure vessel: 600 meters.
- Diameter of the ShellStar vessel including the solar arrays: 800 meters.
- Overall length of the ShellStar vessel: 1270 meters.
Keyed notes to cross section of ShellStar 2020.
1. Parabolic mirror: Reflective glass or polished steel on a concrete shell designed to reflect visible light to the light collector node.
2. Light collector node: Concentrated light energy is transferred by fiber optic cables to two interior Suns.
- An alternative is to use the concentrated light energy to generate heat for power production.
3. Light distribution Suns: The smaller Sun provides light to the agricultural volume, and the larger central Sun provides light to the city. Two half spheres on each side of the center Sun reflect and defuse the light throughout the sphere and help create the illusion of a bright sky overhead.
- Alternate designs should be considered for the center Sun because this location in the center of the sphere is also where the robotic construction systems for the sphere and floor systems are mounted.
4. Nuclear power facility: When the light collector is not oriented toward the Sun an alternative lighting system can be powered from this facility. It is also the city’s main energy source for power and interior lighting.
5. Radiators: Excess heat energy radiating from the two Suns, and all power equipment and lighting systems are pumped out of the facility and radiated into space.
- The waste heat could be used to drive a heat engine for power production.
6. Solar collectors: A backup system of collectors provides for low level emergency power and lighting.
- The solar collectors could be placed on all external surfaces and sized to provide all the power requirements.
7. Landing rings: This is part of the main transportation terminal for shuttles. An inbound shuttle or NASP can make a conventional landing by touching down on the inner rim and braking to accelerate with the cylinders rotation to about 1/2-gravity.
- See design update recommendation at Figure C.
8. Launching release: An outbound shuttle is lowered between the double walled cylinder and is transferred by an overhead crane for launching into free space. The velocity generated by the rotating cylinder allows for economical transfer between ShellStar vessels in close proximity.
9. Robotic cranes: Tele-operated cranes are used extensively to transfer shuttles and various vehicles at the transportation terminal along the tube beam in the industrial areas and at the fueling facility.
10. Fuel storage: Large propellant tanks store fuel for distribution through the tube beam to the transportation terminal, and directly to larger craft at the adjacent docking cranes.
11. Fuel production facility: Raw materials are separated and processed inside this facility, propellants are transferred to storage while other raw materials are transferred to the industrial areas in the sphere for processing or trade.
12. Materials transfer air lock: The spherical receiving end of the fuel production facility has a large air lock for receiving raw materials. Oversized objects can be processed too, by opening the two halves of the sphere.
13. Cargo vessel.
14. Lunar lander and transfer vehicle.
15. Shuttle / NASP.
16. Crew / cargo ship.
17. Vehicle transfer airlock: This large central airlock allows various types of vehicles and materials to be brought into the industrial area for servicing and processing.
18. De-spin coupling.
19. Passenger elevator tower.
20. Freight elevator tower.
21. Transportation terminal facility: 1/2-gravity.
22. Industrial area: 1/2-gravity to 3/4-gravity.
23. Office and commercial area: 3/4-gravity to 1-gravity.
24. Recreational area: 1-gravity.
25. Residential area: 2/3-gravity to 1-gravity.
26. Livestock and agricultural areas: 1/2-gravity to 2/3-gravity.
27. Agricultural areas: 1/2-gravity.
28. Industrial and research dome: 0-gravity.
29. Multipurpose dome: 0-gravity.
30. Utilities chase: The chase between the spheres provide space for equipment and distribution of power, air conditioning, sewage, industrial water, drinking water, and fire protection systems. Purified water is piped from the river through the chase to the beam tube for distribution from each side of the central sun. The spray effect creates and artificial rain shower for fire protection, periodic rinsing of the interior, and watering of vegetation on the deck levels below.
31. Pressurized tube beam: The central tube extending through the axis of the rotating sphere provides structural support and stability of the zero gravity domes and other components inside and outside the vessel. The interior of the tube provides a distribution rout for utilities and materials from the perimeter utility chase to the domes in the center and to the light collector and fuel facility at each end.
Design Update Notes
- An updated design should consider providing more main decks at one sixth gravity and one third gravity to simulate Lunar and Mars gravities.
- The double wall construction of the primary sphere was also intended to provide some backup protection in the event of a collision and breech of the primary pressure vessel. This is highly unlikely for the thick concrete concept presented initially but will be a primary consideration for lighter weight systems like the aluminum geodesic dome construction concept.
My plan is to produce a new design for maybe a ShellStar 2024 that may or may not be similar to this one. Questions and comments are welcome. You may respond with comments to this website or drop me an email at firstname.lastname@example.org.
- NASA surface construction technology: https://www.nasa.gov/oem/surfaceconstruction