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Space HabitatLife in habitats (includes the terms space colonies, settlements or stations) floating in space has been visualized by scientists and science fiction for a good part of the 20th Century.Some of these space structures were envisioned as being built entirely out of manmade materials. Others were carved out of asteroids. In 1963 Dandridge Cole suggested hollowing out an ellipsoidal asteroid about 30 km long, rotating it about the major axis to simulate gravity, reflecting sunlight inside with mirrors, and creating on the inner shell a pastoral setting as a permanent habitat for a colony.Most of the visions in the Wikipedia article on space habitats are far more intriguing than the actual structure constructed in the space above earth's atmosphere. Videos have been created that convey to the viewer a sense of what it could be like to live in one of these space habitats. Orion's Arm is good overall source of possible future space habitats.Space Habitat FAQActual Space StationOther than the Soviet/Russian Space Station Mir, which fell to earth in a planned de-orbit in 2001, the International Space Station (ISS) is the only significant (weighing more than 100 metric tons) space habitat ever constructed. Neither it nor its precursors were designed to generate artificial gravity by rotation.The International Space Station now orbiting the earth began construction in 1998. Station assembly completion slated for 2012, far beyond the originally contemplated 2004 completion date. The estimated cost by the ESA is €100 billion for the entire station over 30 years - far beyond original projections. Probably most important, its construction resulted in the relinquishing of alternative paths (moonbase, etc.) into space that those billions could have financed. The ISS is funded until 2020, and may operate until 2028. Given the International Space Station experience, where do we go in the future evolution of habitats in space? If the intention is for humans to live in space for more than temporary periods of six months or less, what will be the shape of future habitats designed to generate artificial gravity?Innate Advantages of Space Habitats These advantages assume future habitats designed to make full use of the unique capabilities associated with them. Such habitats were visualized by NASA in the 1970s, back when visionaries were encouraged by the agency. Artificial habitats in outer space have a number of advantages over terraforming planets and moons for human habitation. Some advantages are: Feasibility - Creation of space habitats is more feasible than terraforming planets and moons, given resources and technology reasonably available in the next 200 years.Gravity - Habitats could be created with artificial gravity equivalent to the surface of the earth. Terraforming of Venus, the only solar system world with a gravity equivalent to earth's, would not be possible at a cost and timescale we can contemplate in our current state of scientific and technical knowledge.Resource Availability - Access to vast resources, including the moon via mass drivers, asteroids and the energy resources of the Sun.Expandibility - Given the nature of outer space, there is no practical limit to the habitable space that could theoretically be created.Artificial GravityThe consequences of extended exposure to weightlessness are undesirable physiological adaptations that increase the difficulty of returning to an environment with gravity. The longer the period of weightlessness, the greater the difficulty.Although countermeasures such as daily periods on a spinning wheel, diet and exercise can reduce these physiological adaptations, they are not entirely effective. The perfect solution would be to create artificial gravity, enabling humans to better maintain their health in space.Studies show that people get motion-sick in centrifuges with a small rotational radius (generally less than 100 meters) or with a rotation rate above 2 rotations per minute (rpm). To generate a rate of spin of 2 rpm or less and produce a gravitational force equivalent to the surface of the earth, the radius of rotation would have to be 224 meters (735 ft) or greater. For the same gravitational force, a rate of spin of 1rpm would virtually eliminate motion sickness and require a radius of rotation of 894 meters (2933 feet). By comparison, the ultimate dimensions of the ISS will be 108 by 74 meters. Obviously, future space habitats able to generate artificial gravity would need to be much larger than space stations constructed to date.This calculator determines the radius and rotation speed necessary to create various levels of artificial gravity.WheelThe image to the left is the classic space habitat from the movie 2001:A Space Odyssey, directed by Stanley Kubrick in 1968. The movie based its space station concept on former German scientist Wernher Von Braun's model. Kubrick's station in the movie was 900 feet in diameter, orbited 200 miles above Earth, and was home to an international contingent of scientists, passengers, and bureaucrats.The spoke design shown in the movie was a popular concept at the time. The shape combined with the revolution speed created simulated gravity in space. The more scientists learned, however, the more they became aware of the physical hazards and the costs necessary to avoid those hazards. As indicated above, to create an artificial gravity similar to earth's and turn at a speed slow enough to not trigger motion sickness would require a very large wheel. Large meant expensive, which gave pause to the politicians. The design difficulties worried the engineers. Unsurprisingly, no space habitats (stations) actually built include artificial gravity.TorusThe most extensive study on the options for space habitations grew out of a 10 week program held in California at Stanford University and NASA's Ames Research Center during the summer of 1975. The report on this summer program set forth in great detail the potential for creation of space habitats given technical knowledge at that date.The torus, although not the best design in many respects, seems to give the most desirable balance of qualities. Relative to the sphere and cylinder it is economical in its requirements for structural and atmospheric mass. Relative to the composite structures it offers better esthetic and architectural properties. The torus was adopted as the basic form of space habitat because of: good habitability properties, large volume, a variety of possible internal arrangements, the possibility of incremental construction, a clear circulation pattern, access to zero gravity docks and recreation at the hub, agriculture as an integral part of the living area, and a clear visual horizon for orientation, The Sun's rays in space are deflected by a large stationary mirror suspended directly over the hub. This mirror is inclined at 45 degrees to the axis of rotation and directs the light onto another set of mirrors which, in turn, reflect it into the interior of the habitat's tube through a set of louvered mirrors designed to admit light to the colony while acting as a baffle to stop cosmic radiation.The shielding masses required cannot be rotated at the same angular velocity as the habitat because the resultant structural stresses would exceed the strength of the materials from which the shield is to be built. Consequently the shield must be separate from the habitat itself and either rotated with an angular velocity much less than 1 rpm or not rotated. The space habitat image on the right above illustrates one way to construct the space habitat laid out in the parameters described above. It is called a Stanford Torus. On the left is shown a cut away view into the interior of the space habitat. To the lower right we see a possible interior view.The outer "tire" is a radiation shield built of compressed cinder-block-like lunar material or the remains of an asteroid. The central hub contains the docking station and communications antenna; six spokes connect the hub with the ring-shaped outer wheel and provide entry and exit to living and agricultural areas.To simulate Earth's normal gravity the entire habitat rotates at one revolution per minute about the central hub. The burnished disc that hangs suspended above the wheel is a floating mirror panel which reflects sunlight down onto the slanted panels and into the chevron shields that screen out cosmic rays.Bernal SphereA Bernal sphere is a type of space habitat intended as a long-term home for permanent residents, first proposed in 1929 by John Desmond Bernal. Bernal's original proposal described a hollow spherical shell 1.6?km (0.99?mi) in diameter, with a target population of 20,000 to 30,000 people. Gerard O'Neill proposed Island One, a modified Bernal sphere with a diameter of only 500m rotating at 1.9 RPM to produce a gravity at the sphere's equatorf equivalent to that of Earth. The interior landscape that would resemble a valley running all the way around the equator of the sphere. Island One would be capable of providing living and recreation space for a population of approximately ten thousand people. Sunlight was to be provided to the interior of the sphere using external mirrors to direct it in through large windows near the poles. The form of a sphere was chosen for its optimum ability to contain air pressure and provide radiation shielding.O'Neill also proposed Island Two with a diameter of 1800 meters, which provided an equatorial circumference of 6.5 kilometers (four miles). The habitat could house a population of some 140,000 people. This was a size considered economically feasible.Future ProspectsIn 1991 it was written in an article entitled, The Design and Visualization of a Space Biosphere, "There has been little published work on space settlement design in the last decade." Things have not changed much in the last 20 years. This hiatus in study of and planning for space habitats likely has one principal cause; the bad taste left by experience with the International Space Station.All material in the ISS was transported into space at great expense from the earth's relatively high gravity surface. Further progress on development of space habitats will be dependent on progress in two areas: (1) establishment of permanent bases on the lower gravity moon or asteroids which can provide material that can be transported more cheaply to potential space habitat orbits and (2) discovery of space-based technology that can process these materials into useable products in a cost effective manner. Current activity related to space habitats has been initiated by the private sector. Bigelow Aerospace has teamed up with SpaceX to offer rides for rich customers to private modular space habitats. Time will tell if this project developed beyond a publicity stunt. Then again, is not this how airplane travel began in the barn storming days of the early 20th Century?H Graem ? 2012Cool Youtube videos for space habitats: – the giant spoke – Troy Project – project SKYLON – Magnetoplasma Rocket – short space tech clips ................
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