In the summer of 1975, a group of scientists, engineers, and researchers gathered at Stanford University and NASA’s Ames Research Center to tackle an ambitious question: Could humans build permanent settlements in space? Over the course of 10 weeks, this team developed detailed plans for how to construct and sustain a large-scale space colony housing 10,000 people. Their work, documented in NASA report SP-413, provides a fascinating glimpse into the technical challenges and creative solutions involved in extending human civilization beyond Earth.
While space colonies remain in the realm of science fiction for now, the concepts explored in this study continue to influence thinking about long-term human presence in space. This article examines the key elements of the space colony design proposed by the NASA study group, the rationale behind their choices, and some of the alternatives they considered. It offers a window into how scientists and engineers approach the complex challenge of creating a livable human habitat in the harsh environment of space.
The Overall Vision: A Wheel in Space
The centerpiece of the proposed space colonization system is a large, wheel-shaped habitat orbiting the Earth at a special location known as the L5 Lagrange point. This point, located about 60 degrees behind the Moon in its orbit, allows objects to remain in a stable position relative to both the Earth and Moon.
The habitat itself would be a massive structure, with a diameter of nearly 1.8 kilometers. It would rotate to produce artificial gravity for the inhabitants, completing one revolution per minute. The main living areas would be located in a toroidal (donut-shaped) tube, 130 meters in diameter. Six spokes would connect this outer ring to a central hub where spacecraft could dock.
Large mirrors would be positioned to reflect sunlight into the interior of the habitat, providing illumination and energy. Within this structure, the colonists would live, work, and cultivate crops in Earth-like conditions, protected from the vacuum and radiation of space.
Why Build Space Colonies?
The study group envisioned space colonization as a way to expand human civilization, exploit the resources of space, and potentially alleviate problems on Earth. Some key motivations included:
- Access to abundant solar energy
- Utilization of lunar and asteroid resources
- Development of new technologies and industries
- Creation of new societies and ways of living
- Potential for long-term expansion of human presence in the solar system
While acknowledging the enormous technical challenges, the study group believed that space colonization could become feasible with near-term technology, given sufficient investment and effort.
Choosing a Location: The Benefits of L5
The decision to locate the colony at the L5 Lagrange point was driven by several factors:
- Stable position: Objects at L5 can maintain their location relative to Earth and Moon with minimal fuel expenditure.
- Access to resources: L5’s position allows relatively easy access to both Earth and lunar resources.
- Continuous solar power: Unlike low Earth orbit, L5 experiences no eclipses, allowing uninterrupted solar energy collection.
- Room for expansion: The L4 and L5 points can theoretically host many large structures without interference.
While other locations like low Earth orbit or the surface of the Moon were considered, L5 offered the best combination of stability, accessibility, and growth potential for the envisioned colony.
Designing for Human Needs in Space
Creating a livable environment for 10,000 people in space presents numerous challenges. The study group identified several key requirements for the colony:
Artificial Gravity
Extended exposure to zero gravity causes numerous health problems, including bone and muscle loss. To avoid these issues, the colony would rotate to produce artificial gravity through centrifugal force. The study group specified a gravity level between 0.9 and 1.0 times that of Earth, requiring a rotation rate of one revolution per minute.
This rotation rate was chosen as a compromise between providing adequate gravity and minimizing potential discomfort from Coriolis effects. At higher rotation rates, colonists might experience dizziness or nausea when moving between areas of different radii. The one rpm rate allows for a reasonably-sized habitat while keeping these effects manageable.
Atmosphere
The colony would need to provide a breathable atmosphere at a comfortable pressure. The study group proposed a total pressure of about half that at sea level on Earth, with normal oxygen levels but reduced nitrogen. This lower pressure reduces structural requirements while still preventing fires and respiratory problems.
The specific atmospheric composition recommended was:
- Oxygen: 26.5% (compared to 21% on Earth)
- Nitrogen: 73.5%
- Total pressure: 50.8 kPa (0.5 atm)
This mixture provides the same partial pressure of oxygen as Earth’s atmosphere at sea level, ensuring normal respiration, while reducing the total mass of gas needed to pressurize the habitat.
Radiation Protection
Space is filled with harmful radiation from the Sun and cosmic rays. The colony design includes a thick layer of material surrounding the habitable areas to shield the inhabitants. This shield would likely be constructed from processed lunar soil.
The proposed shielding consists of a 4.5 meter thick layer of moon rock, providing protection equivalent to Earth’s atmosphere. This massive shield accounts for a significant portion of the colony’s total mass – over 10 million tons.
Psychological Considerations
Living in an entirely artificial environment could be psychologically challenging. The design incorporates features to make the colony feel more Earth-like and spacious:
- Large windows and mirrors to provide natural light and views of space
- Open spaces and long sight lines to reduce feelings of confinement
- Parks, lakes, and other natural features
- Variety in architecture and layout to avoid monotony
The designers recognized that the psychological well-being of the colonists would be crucial for the long-term success of the settlement. They aimed to create an environment that balanced the need for efficient use of space with the human desire for beauty, variety, and connection to nature.
Community Design
The study group devoted considerable attention to the layout and organization of the colony’s interior. They estimated space requirements for various functions based on terrestrial standards, including:
- Residential areas: 30 m² per person
- Commercial and office space: 25 m² per person
- Industrial zones: 40 m² per person
- Agricultural sections: 20 m² per person
- Public spaces and recreation areas: 25 m² per person
The overall design aimed to create a community that would feel familiar and comfortable to Earth-born inhabitants while taking advantage of the unique possibilities of a space-based habitat.
Harvesting the Resources of Space
A key aspect of the space colonization concept is the ability to utilize extraterrestrial resources, reducing reliance on supplies from Earth. The study group developed plans for mining and processing materials from the Moon and potentially asteroids.
Lunar Mining
The Moon would serve as the primary source of raw materials for constructing the colony. Key resources available on the lunar surface include:
- Oxygen (bound in lunar rocks)
- Silicon (for glass and electronics)
- Aluminum
- Titanium
- Iron
The plan calls for establishing a lunar base and mining operation to extract and process these materials. This lunar outpost would be staffed by a crew of about 300 workers, operating on rotating shifts to maintain continuous production.
Mass Driver
To efficiently transport lunar materials to the colony construction site, the study group proposed using an electromagnetic catapult called a mass driver. This device would launch payloads from the lunar surface at high speed, to be collected in space. This approach avoids the need for large amounts of chemical rocket fuel.
The mass driver concept involves accelerating small (20 kg) packets of lunar soil to escape velocity (2.4 km/s) using a series of electromagnetic coils. These packets would be launched at a rate of about 30 per second, allowing for the transport of millions of tons of material per year.
Processing in Space
Raw lunar materials would be refined and processed at the colony location. The study group developed concepts for extracting metals, producing glass, and manufacturing structural components in the space environment. These processes would take advantage of abundant solar energy and the vacuum of space.
Some key processing steps include:
- Electrolysis of molten lunar rock to extract oxygen and metals
- Vapor deposition techniques for producing large structural components
- Solar furnaces for high-temperature processes
The ability to process materials in space is crucial for making the colony largely self-sufficient and reducing the need for imports from Earth.
Power Generation and Economics
To make the space colony economically viable, the study group proposed that it could manufacture and deploy large solar power satellites. These satellites would collect solar energy in space and beam it to Earth using microwaves, providing a new source of clean, abundant electricity.
The production and sale of these power satellites could potentially generate enough revenue to offset the enormous costs of establishing and maintaining the colony. This concept of space-based solar power remains an active area of research and speculation today.
Key features of the proposed solar power satellite system include:
- Each satellite would measure 5 x 10 km and generate 10 gigawatts of power
- Microwave transmission to Earth with 70% end-to-end efficiency
- Annual production of 1-2 satellites by the colony
- Potential to supply a significant fraction of Earth’s energy needs
Transportation System
Moving thousands of people and millions of tons of material between Earth, the Moon, and the colony location requires a sophisticated transportation system. The study group outlined a network of specialized vehicles:
- Heavy-lift launch vehicles to reach low Earth orbit
- Interorbital transfer vehicles for trips between Earth orbit, the Moon, and L5
- Lunar landers for surface access
- Local tugs and shuttles for operations around the colony
The plan emphasizes reusable vehicles and propellant production in space to reduce costs. The transportation system represents one of the most challenging and expensive aspects of the space colonization concept.
Some key elements of the proposed transportation system include:
- A fleet of reusable “space freighters” capable of carrying 300 tons of cargo
- Passenger vehicles accommodating up to 200 people per trip
- Use of lunar-derived oxygen as propellant for spacecraft operating beyond Earth orbit
- A “space port” at the colony for docking and servicing various vehicles
Construction Process
Building a kilometer-scale structure in space presents unprecedented engineering challenges. The study group developed a conceptual construction sequence:
- Establish a small construction base at L5
- Begin lunar mining and material delivery
- Construct the main structural framework
- Install radiation shielding
- Pressurize the interior and install internal structures
- Gradually expand the habitable volume and increase population
They estimated that the process of establishing the initial colony might take 20-30 years and require a workforce of thousands of people working in space.
The construction would likely involve a combination of techniques, including:
- Assembly of prefabricated modules launched from Earth
- On-site manufacturing of large structural elements using lunar materials
- Robotic systems for dangerous or repetitive tasks
- Inflatable structures for rapid deployment of pressurized volumes
Life in the Colony
The study group envisioned the space colony as a largely self-sufficient community with a diverse population. Some key aspects of life in the colony include:
Governance
While the initial construction would likely be managed by space agencies or corporations, the study group suggested that the mature colony would develop its own system of governance. They speculated on various possible political structures but did not prescribe a specific system.
The governance system would need to address unique challenges of the space environment, such as:
- Managing shared life support systems
- Allocating limited resources
- Coordinating with Earth-based organizations
- Balancing individual freedoms with the needs of the community
Economy
The colony’s economy would initially focus on the construction of solar power satellites. Over time, it might diversify into other space-based industries, scientific research, and tourism. The unique environment of space could enable new manufacturing processes and products.
Potential economic activities include:
- Microgravity materials processing
- Asteroid mining and resource extraction
- Space-based observatories and research facilities
- Maintenance and servicing of satellites and spacecraft
- Development of advanced propulsion technologies
Agriculture
A significant portion of the colony’s volume would be dedicated to agriculture to provide food for the inhabitants. The controlled environment would allow for highly efficient farming techniques. The agricultural areas would also serve as part of the life support system, recycling air and water.
Some innovative agricultural approaches proposed include:
- Hydroponic and aeroponic systems to maximize yield and minimize resource use
- Carefully controlled lighting and climate to allow multiple harvests per year
- Use of genetically engineered crops optimized for the space environment
- Integration of food production with waste recycling systems
Recreation and Culture
The study group recognized the importance of providing recreational and cultural opportunities for the colonists. They proposed sports adapted to the low-gravity environment, arts centers, and educational facilities. The unique setting of the colony might also lead to the development of new forms of art and entertainment.
Some specific ideas for recreation in the colony include:
- Three-dimensional sports taking advantage of the large, open spaces
- Virtual reality systems for simulating Earth environments or fantastic worlds
- Observation decks for viewing Earth, the Moon, and deep space
- Artistic projects utilizing unique properties of the space environment, such as microgravity sculpture
Challenges and Limitations
While the study group developed detailed plans for the space colony, they also acknowledged numerous challenges and areas requiring further research:
Cost
The enormous cost of establishing a large-scale space colony remains a major barrier. While the study group proposed potential economic justifications, the initial investment would be tremendous. Some estimates suggest a total cost on the order of trillions of dollars.
Technology Development
Many of the proposed systems, such as the mass driver and large-scale life support systems, would require significant technological advancement. Key areas needing development include:
- Closed-loop life support systems capable of sustaining thousands of people
- Reliable, long-duration space transportation systems
- Large-scale in-space manufacturing and construction techniques
- Efficient systems for extracting and processing lunar resources
Human Factors
The long-term physical and psychological effects of living in an artificial space environment are not fully understood. More research is needed on issues like:
- The impact of partial gravity on human health and development
- Psychological adaptation to isolated, confined environments
- Social dynamics in a small, closed community
- Reproduction and child-rearing in space
Political and Legal Issues
The establishment of large, semi-independent communities in space would raise complex political and legal questions about sovereignty, resource rights, and international cooperation. Some key issues include:
- Ownership and use rights for extraterrestrial resources
- Jurisdiction and law enforcement in space settlements
- Environmental protection for celestial bodies
- Coordination of space activities among multiple nations and private entities
Alternatives and Variations
The study group considered various alternatives to their baseline design:
Different Shapes
While they settled on a toroidal design, they also examined spherical, cylindrical, and more complex geometries for the habitat. Each shape offers different trade-offs in terms of structural efficiency, radiation protection, and internal layout.
Other Locations
Alternatives to the L5 point included low Earth orbit, the lunar surface, and orbits around other planets or asteroids. Each location presents unique advantages and challenges in terms of access to resources, energy availability, and communication with Earth.
Smaller Scales
The group briefly considered smaller habitats or clusters of smaller units but focused on the 10,000-person scale as a minimum for a self-sustaining community. Smaller colonies might be more feasible as initial outposts but would lack the economic and social benefits of a larger settlement.
Legacy and Influence
While NASA did not pursue the development of large space colonies, the 1975 summer study has had a lasting impact on thinking about long-term human presence in space. Many of the concepts explored, such as the use of extraterrestrial resources and the potential for space-based solar power, continue to be active areas of research and development.
The detailed, systems-level approach to designing a complete space habitat has influenced later work on space stations, proposed lunar and Mars bases, and even the development of closed-loop life support systems for long-duration spaceflight.
Some specific areas where the study’s ideas have been influential include:
- The design of rotating habitats for artificial gravity, as seen in concepts for future Mars missions
- The use of in-situ resource utilization (ISRU) for sustainable space exploration
- The development of advanced life support systems for long-duration spaceflight
- Concepts for large-scale space manufacturing and construction
Current Relevance and Future Prospects
While the vision of large-scale space colonies remains far from realization, many of the underlying concepts and technologies explored in the 1975 study are becoming increasingly relevant as humanity expands its presence in space. Some current developments that echo themes from the study include:
- Growing interest in lunar and asteroid resource utilization by both government agencies and private companies. NASA’s Artemis program aims to establish a sustained human presence on the Moon, with in-situ resource utilization (ISRU) as a key component. Private companies have also shown interest in space resource extraction.
- Renewed focus on long-duration human missions, including plans for sustained lunar presence and eventual Mars exploration. NASA’s Gateway project, a small space station in lunar orbit, will serve as a staging point for both robotic and crewed exploration of the Moon.
- Advances in closed-loop life support systems, as demonstrated on the International Space Station. The ISS has provided valuable data on long-term human habitation in space and the challenges of recycling air and water.
- Continued research into space-based solar power and other space-based energy systems. While large-scale implementation remains challenging, organizations like the Japan Aerospace Exploration Agency (JAXA) and the China Academy of Space Technology (CAST) are actively pursuing space solar power research.
- Development of new space habitation concepts by private companies like SpaceX, VAST and Blue Origin. Moreover, SpaceX is designing spacecraft capable of supporting crews for long-duration missions to the Moon and Mars.
- Advancements in additive manufacturing (3D printing) technologies, which could enable more efficient construction of structures in space using locally sourced materials.
- Growing commercial interest in space, including space tourism and private space stations. Companies like Axiom Space are developing modules to be attached to the ISS, with plans for independent commercial space stations in the future.
As technology advances and our experience with long-duration spaceflight grows, some of the challenges identified in the 1975 study are being addressed:
- Radiation protection: New materials and shielding concepts are being developed to better protect astronauts from cosmic radiation.
- Artificial gravity: While no large-scale rotating habitats have been built, research continues on the potential benefits of artificial gravity for long-duration spaceflight.
- Psychological factors: Studies on the ISS have provided valuable insights into the psychological challenges of living in isolated, confined environments for extended periods.
- Resource utilization: Advances in ISRU technologies are making it more feasible to use space-based resources for life support and construction.
However, significant challenges remain before large-scale space colonization becomes feasible:
- Cost: Launching materials and people into space remains extremely expensive, though reusable rocket technology is helping to reduce costs.
- Political and legal frameworks: The governance and ownership of space resources and habitats remain contentious issues in international law.
- Long-term health effects: The impact of long-duration spaceflight on human health, particularly with regard to radiation exposure and reduced gravity, is still not fully understood.
- Technological gaps: Many of the technologies required for self-sustaining space colonies, such as large-scale space manufacturing and efficient closed-loop life support systems, are still in early stages of development.
Despite these challenges, the concept of space colonization continues to inspire research and development in space technologies. As our capabilities in space expand, the ideas explored in the 1975 study may serve as a foundation for future large-scale human presence in space. The coming decades are likely to see incremental progress towards more permanent and self-sustaining human habitats beyond Earth, even if they fall short of the grand vision of 10,000-person space colonies envisioned in the original study.
