We’ve look at cylinders and toroids–popular shapes for large space vessels using artificial centrifugal gravity. These shapes obey the canon that form follows function. Almost everything humanity has learned to do has been learned in Earth’s gravity well. The human body itself relies on gravity in ways we are still discovering.
There are other options. Assuming no breakthrough in gravity physics, a variety of differently-shaped spacecraft can have spinning compartments for human occupation. A single compartment attached by a spoke would do the trick.
The Ares mission Hermes spacecraft in the Andy Weir novel and movie The Martian is a modified toroidal vessel, with several separate compartments attached through tubes and ladders.
One NASA concept in 1969 consisted of one spoke, spinning around an axis, looking somewhat like a giant, spinning cotton swab, with centripetal force creating artificial gravity as it does in a spinning cylinder or toroid.
Basically, for artificial gravity created by centripetal acceleration, anything that spins or rotates around an axis will do.
Another option is to go weightless. The International Space Station is a seemingly weightless environment for its occupants. The ongoing project continues to provide a wealth of information about operations in microgravity. Of course, ISS personnel have no intention of staying there forever, and for that reason, exercise machines and other measures are taken to keep their bodies “gravity ready” for their return to Earth. Muscle atrophy, decreased bone density, and other effects of microgravity are a concern largely because of their effect once an astronaut returns to Earth. But if a return to a gravity well is not in the forecast, then adaptation to weightlessness might be more practical than holding on to artificial gravity. Without a concern for creating centripetal force, the “form follows function” idea takes on new meaning. Any shape is possible.
The 1988 Nebula award winning novel, Falling Free, by Lois McMaster Bujold, features genetically modified humans with four arms, rather than two arms and two legs, as an adaptation to weightlessness. In the story, the modified humans were created as a cheap zero-g labor force, and the story develops around an unmodified human’s interaction with them and his growing concern with how they are treated (or mistreated) as a form of property by the corporate interest that created them.
Humanity is not at the point where it can implement genetic modifications of that scale. But adaptation remains a possibility, with the greatest adaptations probably occurring in mere functionality. Everything behaves differently in weightlessness. Without an “up” or a “down,” many human behaviors and activities must change and many deeply ingrained habits must be overcome.
Other options require some advancement in science. For instance, gravity can be simulated by direct acceleration (rather than centripetal acceleration). This isn’t too hard to manage at the outset. A ship must accelerate at about 32 ft./sec. to provide a simulation of Earth gravity. However, the energy required to maintain that acceleration for a long period of time is enormous, and if it could be managed, it would not take long before relativistic effects would be significant.
another option, one that we are working on and that many science fiction stories assume, is the creation of localized, stationary artificial gravity. Star Trek, Star Wars, and almost any popular space-based science fiction in which the characters walk the decks of space ships like they are floors in buildings, are evoking a fictional form of artificial gravity. Even the spherical Star Wars Death Star has a top and a bottom. The gravity in these various stories is created by a “gravity generator,” “gravity plates,” or any number of other hypothetical devices and technologies, often completely unexplained.
Can it be done? Probably. Can it be done soon? Maybe. There are far more things that we don’t understand than do understand. Whether modifying gravity requires a refinement of what we already understand, or a paradigm shift, is unclear. Nevertheless, gravity modification is being studied. For example, Benjamin T. Solomon’s book An Introduction to Gravity Modification tackles the subject in a big way. Solomon has also published Super Physics for Super Technologies, and various articles, including Honda’s Gravity Modification Research (Huffington Post).
For the most part, anything goes. Large space vessels do not face a great deal of friction or other aerodynamic concerns. Gravity is something we can simulate or do without. Time will tell what shapes and designs humanity will employ in its perpetual reach for the stars.