ShellStar 2020

ShellStar 2020 in orbit around the Earth.
  • 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.
ShellStar Drawing 1 of 2.
Figure A. Earth-Moon construction orbits.
  • 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. ShellSTAR spherical construction system diagram.
  • 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. ShellSTAR cylindrical construction system diagram.
  • 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. Moon base support facilities.
  • 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.
ShellStar Drawing 2 of 2.
  • 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.
  • An alternative is to use the concentrated light energy to generate heat for power production.
  • 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.
  • The waste heat could be used to drive a heat engine for power production.
  • The solar collectors could be placed on all external surfaces and sized to provide all the power requirements.
Solar collection and power production areas.
  • See design update recommendation at Figure C.
Propellant production and raw materials processing facilities.
Vehicle transfer areas.
Primary residential, commercial and recreational areas.
Agriculture and livestock areas.
  • 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.



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David Smitherman

David Smitherman


Retired from NASA. Architect, space architect and writer on science, technology, travel, and social issues. See the “Reading List” for introductory Greetings.