Continuing my Grand Tour series here, working out to the habitats. I sketched out this great idea for an O'Neill-style habitat: two counter-rotating cylinders set in a zero gee frame with docking ports on the sides, solar arrays on top and radiators on the bottom. Then I remembered reading something about wobble and tumble problems with cylindrical habitats. It turns out that a stable hab can is a very short hab can. (If you really want to know see: http://alglobus.net/NASAwork/papers/2007KalpanaOne.pdf ). So, the length of the cylinder should be no more than 1.3 times the radius. There's detailed math in the appendix of the article. Damn you Angular Momentum! Kinda ugly, but I decided to try to do it right. So each of these hab cans is 800 m in radius (1600 m or a mile in diameter) and 1040 m long. At a density of 5,000 people per square kilometer (about average for a city, but only a fifth of Manhattan -- and they managed to squeeze in a nice park) then each can will hold about 25,000 people. Note: the big window-looking things on the spokes are my attempt to portray some sort of mirror angling device to reflect light into the hab. They're much too big to be windows at that scale. If you look hard at the smaller images, you should see some windows on or near the docking terminals. For scale, my 2001 rip-off lunar sphere lander from the previous Grand Tour posting is on the far left of the big picture. --- Space is an inhospitable place. The other worlds of the solar system are harsh homes for humanity. But with the aid of technology that is really not too different from that which allows vast arcologies on the surface of Earth, outer space can be enclosed and tamed. Floating free in space, protected from vacuum and radiation by armored plates and magnetic fields, spun to generate a full Earth gravity, a habitat is the most inviting home beyond Earth. In many ways, living in a habitat is better than living on the surface of the hot, crowded and polluted Earth, even after a century of Commonwealth recovery projects. Situated at a point equidistant from the Earth and the Moon, Harmony is one of the oldest habitats, built in the first decade of the Commonwealth to provide refuge and hope for a devastated world. Nearly fifty thousand people descended from many nations and cultures live and work together in the two habitat cylinders, producing enough food and technology to sustain themselves against the harshness of space. Outside, the habitat may look imposing and mechanical. But inside Harmony East and West, lush landscapes of neo-village-styled homes, shops and fields build a world even better than our own. --Grand Tour 2150: A Guide to the Solar System, Euphoria Press