1. Background on Space Habitat Concepts
AE 426, Lecture 5

2. Outline
History
NASA Designs

3. History
About 1970, Gerard K. O'Neill, an experimental physicist, was looking for a topic to interest his physics students, most of whom were freshmen in Engineering. He assigned them feasibility calculations for large space habitats.
Surprisingly, the habitats seemed to be feasible even in very large sizes: cylinders five miles (8 km) in diameter and twenty miles (34 km) long, even if made from ordinary materials such as steel and glass.
Also, the students solved problems such as radiation protection from cosmic rays (almost free in the larger sizes), getting naturalistic sun angles, provision of power, realistic pest-free farming and orbital attitude control without reaction motors.
O'Neill published an article about these colony proposals in Physics Today in The article was expanded in his 1976 book The High Frontier: Human Colonies in Space.
The result motivated NASA to sponsor summer workshops led by Dr. O'Neill. Several designs were studied, some in depth, with sizes ranging from 1,000 to 10,000,000 people.

4. History
The basic proposal by O'Neill had an example of a payback scheme: construction of solar power satellites from lunar materials. He, and others, presumed that once such manufacturing facilities were on-line, many profitable uses for them would be found, and the colony would become self-supporting, and begin to build other colonies as well.
These proposals much public interest. One result was the founding of the L5 Society in the U.S.
In this era, Dr. O'Neill also founded the Space Studies Institute, which initially funded and constructed prototypes of much of the new hardware needed for a space colonization effort, as well as number of paper studies of feasibility.
One of the early projects, for instance, was a series of functional prototypes of a mass driver, the essential technology to be used to move ores economically from the Moon to space colony orbits.

5. NASA Designs Bernal sphere Stanford torus O'Neill cylinder Lewis One
Kalpana One
“Bola”
Beaded habitats
Nautilus-X

6. Bernal Sphere
"Island One", a spherical habitat for about 20,000 people.
Bernal's original proposal described a hollow spherical shell 16 km (9.9 mi) in diameter, with a target population of 20,000 to 30,000 people. The Bernal sphere would be filled with air.
Ref: Bernal, John Desmond (1929). The World, the Flesh and the Devil

7. Stanford Torus
The Stanford torus is a proposed design capable of housing 10,000 to 140,000 permanent residents.
It was proposed during the 1975 NASA Summer Study, conducted at Stanford University, "Stanford torus" refers only to this particular version of the design, as the concept of a ring-shaped rotating space station was previously proposed by Wernher von Braun and Herman Potočnik.
It consists of a torus 1.8 km in diameter (for the proposed 10,000 person habitat described in the 1975 Summer Study) and rotates once per minute to provide between 0.9g and 1.0g of artificial gravity

8. O'Neill cylinder
The O'Neill cylinder (also called an Island Three habitat) was proposed by Gerard K. O'Neill in The High Frontier: Human Colonies in Space
O'Neill's project was not completely new. The German scientist Hermann Oberth, "Father of space travelling", described in his 1954 book "Menschen im Weltraum – Neue Projekte für Raketen- und Raumfahrt" the use of gigantic habitable cylinders for interstellar travel.
An O'Neill cylinder would consist of two counter-rotating cylinders, each 5 miles (8.0 km) in diameter and 20 miles (32 km) long, connected at each end by a rod via a bearing system.

9. Lewis One
A cylinder of radius 250m with a non rotating radiation shielding. The shielding protects the micro-gravity industrial space, too. The rotating part is 450m long and has several inner cylinders. Some of them are used for agriculture.

10. Kalpana One
A short cylinder with 250 m radius and 325 m length. The radiation shielding is 10 t/m2 and rotates. It has several inner cylinders for agriculture and recreation.

11. “Bola”
"bola": a spacecraft or habitat connected by a cable to a counterweight or other habitat. This design has been proposed as a Mars ship, initial construction shack for a space habitat, and orbital hotel. If some of the equipment can form the counter-weight, the equipment dedicated to artificial gravity is just a cable, and thus has a much smaller mass-fraction than in other designs.

12. Beaded Habitats
Small habitats would be mass-produced to standards that allow the habitats to interconnect.
A single habitat can operate alone as a bola. However, further habitats can be attached, to grow into a "dumbbell" then a "bow-tie," then a ring, then a cylinder of "beads," and finally a framed array of cylinders.
Each stage of growth shares more radiation shielding and capital equipment, increasing redundancy and safety while reducing the cost per person.

13. Nautilus-X
Nautilus-X (Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration) is a multi-mission vehicle imagined by the Technology Applications Assessment Team of NASA.
Designed for long duration (1 to 24 months) exo-atmospheric space journeys for a six-person crew. The spacecraft would be equipped with a centrifuge.
The spacecraft itself is proposed to be relatively cheap by space system standards as it is projected to only cost US$3.7 billion.