Space Habitats

When humankind first went into space an early priority was the construction of space habitats. The first examples of such habitats were constructed with no attempt to provide artificial gravity; and zero gravity habitats continue to be very common, especially among the microgravity-adapted clades such as the Space-adapted Humans and associated subtypes. One useful type of zero-gee habitat was the Bigelow inflatable structure, made of flexible but strong cloth-like materials. However for the comfort of the majority of planet-dwelling peoples it was desirable to replicate the effects of gravity in some way. Centrifugal gravity produced by rotating the habitat was adopted early in the Interplanetary age, and continues to be the method used almost exclusively throughout the Terragen Sphere. Some habitats and spacecraft use utility fog and other mechanical forms of restraint to replicate some of the effects of gravity; this method does not provide any acceleration effects, so the medical effects of freefall are still apparent and need to be treated.

Although the archailects in the Orion's Arm have exquisite control over spacetime curvature and could produce a gravity field within a habitat or other vessel if they found such a thing necessary, there are very many physical and practical problems with such fields and in practice such effects are rarely used in habitats and vessels used by modosophonts.

Some Major Habitat Designs

Rotating paired Module Habitats
Stanford Torus
Bernal Sphere
O'Neill Cylinders
Bishop Rings
McKendree Habitat

	Rotating Paired Module habitats Centrifugal gravity is produced by rotation around a single axis. To reduce coriolis effects and for comfort's sake, most habitats rotate no more than 3 times per minute (3 rpm). To replicate one standard Earth gravity a habitat rotating at 3 rpm would need to be 99.3 metres in radius. In practice many small habitats use a lower gravity regime, and can therefore have a smaller radius or a slower rotation Because centrifugally produced gravity acts directly away from the axis of rotation, the designs used are limited to a few basic forms. Two modules can be linked by tether and rotated around a centre of gravity; this is the simplest form. If several such modules are connected together they form a ring, as shown here. Heaven Habitat (see left) was built in Earth Orbit in the late 21st century using expended heavy-lifter fuel tanks. The 36 modules were connected using polycarbon cables and rotated together in order to simulate 0.5 G.
	Stanford Torus A very simple form of continuous ring-shaped habitat is the torus; the classic design shown is the so-called Stanford Torus, which uses mirrors to illuminate the internal surface through a transparent roof. The original proposal for this type of colony was made in the Information age at Stanford University in the USA. The design called for a torus one 'mile' (1.6 kilometers) in diameter housing 10,000 people. In this image, of Chih Nii habitat in orbit around Penglai, the mirror collecting the sunlight is at the top, reflecting light to a semiconical mirror in the centre of the torus. Beneath the torus in the image is a radiator fin (introduced to cool the habitat because of the excess of collected sunlight), and two photoelectric arrays (of course the entire structure is in zero-gee except for the rotating torus itself, so has no real 'top' or 'bottom').
	This image shows the interior of a Stanford Torus. The transparent roof can be easily seen. In the original design the population density was intended to be similar to a suburban area of Earth, with mixed residential, recreational and agricultural areas. However in practice most Stanford Tori are not as densely populated, with many examples dedicated to recreational use or specialised agriculture. More elaborate arrays of mirrors can be used to collect sunlight if the habitat is far from the local star. Many other toroidal and ring shaped habitats do not have transparent sections and use artificial lighting throughout; these are generally more densely populated than true Stanford tori.
	Bernal Sphere In a very early proposal for a space habitat Dr J.D. Bernal described a rotating habitat consisting of a hollow spherical shell 16 km in diameter, with a population of 20,000 to 30,000 people. This was later modified by Gerard K O'Neill to become a smaller design, with a sphere only 500 m in diameter rotating at 1.9 rpm to produce a simulated gravity of one standard gee (the standard gee used widely throughout the Terragen Sphere is of course equivalent to the gravity of old Earth). The spherical design was chosen because of its strength; made of steel, the sphere could incorporate adequate radiation shielding. The spherical living accommodation in this version of the Bernal sphere is accompanied by several ring-shaped modules, illuminated by mirrors and dedicated to agriculture for food production. Sunlight is also directed into the sphere through windows near the axis. This concept would house 10,000 people in comfort. Several versions of the design have been built. In fact some modern versions use carbon buckyfibre in the construction and are up to a thousand kilometers in radius.
	O'Neill Colony (Island Three) Gerard O'Neill also produced detailed plans for a larger colony, based on the cylinder. A cylindrical form gives the maximum possible habitable space in a rotating habitat, but long cylinders are prone to tumbling in orbit, so O'Neill proposed that cylinders could be linked together in counter-rotating pairs to stabilise their orientation. By managing the rotation rates of each of the cylinders, the long axes could be oriented in any chosen direction. O'Neill proposed that the orientation of the cylinders could be managed so that they permanently pointed towards the Sun, and mirrors could then be used to illuminate the interior surface through long, strip like windows. Each cylinder in a classic O'Neill colony is 3km in radius, and 30km long. Such a colony can support up to 10 million people. Each cylinder is divided into three sections by the window strips, with parkland and agricultural land providing a complete closed ecology. To simulate night the mirrors are adjusted to reduce the amount of sunlight coming in.
	Conchobor Habitat in Tau Ceti orbit; this modified O'Neill design is relatively remote from the local star, so uses larger (inflatable) mirror arrays to collect more sunlight. This type of colony is sometimes known as the Mirror Petal design. O'Neill's original design included two rings of small agricultural modules, each module rotating just enough to allow the crops to grow under low gravity conditions. In lower light conditions such agricultural rings require larger sunlight collection surfaces, so often orbit separately from the inhabited cylinders.
	Bishop Ring When carbon buckyfibre cable became readily available through nanofacturing techniques, the size of rotating habitats could be increased considerably. The largest rotating habitats possible using this material can be slightly more than one thousand kilometers in radius. In the Information Age Forrest Bishop proposed a ring-shaped open ended habitat, with the atmosphere retained by centrifugal force and tall atmosphere walls. Any stray molecules of air which might wander out of the ring could be recovered by a very thin membrane, preferably transparent. In most versions of the Bishop Ring design the local star is permanently obscured from the point of view of someone standing on the ring-floor; this means the ring requires artificial lighting, generally provided by a central artificial sunlet called a luminaire. Power for this luminaire can be collected by photovoltaic cells on the outside of the ring; if the ring is distant from the star, the p-v arrays can be extended beyond the ring floor in both directions, and/or other sources of energy can be utilised.
	McKendree Cylinder Closed cylindrical habitats were proposed many times in the Information age, but the largest concept was described by Tom McKendree of NASA in 31 a.t. Constructed (like a Bishop Ring) using carbon buckyfibre, these cylinders could be a thousand kilometers in radius and ten thousand kilometers long. To combat instability, pairs of these giant constructs could be coupled together to make giant sized O'Neill habitats, or alternately a counter-rotating cylinder could be nested inside the outermost shell. Some McKendree cylinders have several such shells inside, giving a living space comparable to a typical Gaian class planet. More information
Larger Artificial Worlds Even larger artificial worlds have been built in the Orion's Arm civilisation; these worlds are generally too large to be considered habitats, but are worlds in their own right. See the following pages for more details; Dyson Spheres (includes links to Ringworlds, Topopoli, Supramundane Worlds and Kepleria among others) Ederworlds, Symmes Worlds and Dyson Trees See also Infrastructure Space Habitat Illumination with non-imaging optics external links Open Air Space Habitats ; a proposal by Forrest Bishop Wikipedia entries; O'Neill Habitat :: Bernal Sphere and Stanford Torus
Celestia Information (cel:URLs) If you have downloaded Celestia, the free space modelling and display program, you can download models of various Bishop Rings here at the Orion's Arm section of the Celestia Motherlode Once you have unzipped the Bishop Ring add-on into the 'extras' folder inside Celestia, you can travel to a number of these objects by clicking on the links below (Celestia will open automatically) Elsirac Ring at Arkab Prior B (A desert Ring) Rendell Ring a temperate ring Frunobulax Ring a largely maritime ring there are several other rings at various stages of construction in the Arkab Prior system; for a novel set in this system, see here; Betrayals