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Bigger Than Worlds
Just because you've spent all your life on one planet, doesn't mean that everyone always will. Already there are alternatives to worlds. The Apollo spacecraft have an excellent record; they have never killed anyone in space. The Soviet space station may have killed its inhabitants, but the American Skylab didn't.
Alas, they all lack a certain something. Gravity. Permanence. We want something to live on, or in, something superior to what we've got: safer, or more mobile, or roomier. Otherwise, why move?
It's odd how much there is to be said about structures larger than worlds, considering that we ca
The Multi-Generation Ship
Robert Heinlein's early story "Universe" has been imitated countless times by most of the writers in the business.
The idea was this: Present-day physics poses a limit on the speed of an interstellar vehicle. The ships we send to distant stats will be on one-way journeys, at least at first. They will have to carry a complete ecology they couldn't carry enough food and oxygen in tanks. Because they will take generations to complete their journeys, they must also carry a viable and complete society.
Clearly we're talking about quite a large ship, with a population in the hundreds at least: high enough to prevent genetic drift. Centrifugal force substitutes for gravity. We're going to be doing a lot of that. We spin the ship on its axis, and put all the things that need full gravity at the outside, along the hull. Plant rooms, exercise rooms, et cetera. Things that don't need gravity, like fuel and guidance instruments, we line along the axis. If our motors thrust through the same axis, we will have to build a lot of the machinery on tracks, because the aft wall will be the floor when the ship is under power
The "Universe" ship is basic to a discussion of life in space. We'll be talking about much larger structures, but they are designed to do the same things on a larger scale: to provide a place to live, with as much security and variety and pleasure as Earth itself offers—or more.
Gravity
Gravity is basic to our lifestyle. It may or may not be necessary to life itself, but we'll want it if we can get it, whatever we build.
I know of only four methods of generating gravity aboard spacecraft.
Centrifugal force looks much the most likely. There is a drawback: coriolis effects would force us to re-learn how to walk, sit down, pour coffee, throw a baseball. But its effects would decrease with increasing moment arm, that is, with larger structures. On the Ring City you'd never notice it.
Our second choice is to use actual mass: plate the floor with neutronium, for instance at a density of fifty quadrillion tons per cubic foot, or build the ship around a quantum black hole, invisibly small and around as massive as, say, Phobos. But this will vastly increase our fuel consumption if we expect the vehicle to go anywhere.
Third choice is to generate gravity waves. This may remain forever beyond our abilities. But it's one of those things that people are going to keep trying to build forever, because it would be so damn useful. We could launch ships at a million gravities, and the passengers would never feel it. We could put laboratories on the sun, or colonize Jupiter. Anything.
The fourth method is to accelerate all the, way, making turnover at the midpoint and decelerating the rest of the way. This works fine. Over interstellar distances it would take an infinite fuel supply—and by God we may have it, in the Bussard ramjet. A Bussard ramlet would use an electromagnetic field to scoop up the interstellar hydrogen ahead of it—with an intake a thousand miles or more in diameter—compress it, and burn it as fuel for a fusion drive. Now the multi-generation ship would become u
The Bussard ramjet looks unlikely. It's another ultimate, like generated gravity. Is the interstellar medium sufficiently ionized for such finicky control? Maybe not. But it's worth a try.
Meanwhile; our first step to other worlds is the "Universe" ship—huge, spun for gravity, its population in the hundreds, its travel time in generations.
Flying Cities
James Blish used a variant of generated gravity in his tales of the Okie titles.
His "spindizzy" motors used a little-known law of physics (*Still undiscovered) to create their own gravity and their own motive force. Because the spindizzy motors worked better for higher mass, his vehicles tended to be big. Most of the stories centered around Manhattan Island, which had been bodily uprooted from its present location and flown intact to the stars. Two of the stories involved whole worlds fitted out with spindizzies. They were even harder to land than the flying cities.
But we don't really need spindizzies or generated gravity to build flying cities.
In fact, we don't really need to fill out Heinlein's "Universe" ship. The outer hull is all we need. Visualize a ship like this:
(1) Cut a strip of Los Angeles, say, ten miles long by a mile wide.
(2) Roll it in a hoop. Buildings and streets face inward.
(3) Roof it over with glass or something stronger.
(4) Transport it to space. (Actually we'll build it in space.)
(5) Reaction motors, air and water recycling systems, and storage areas are in the basement, outward from the street level. So are the fuel tanks. Jettisoning an empty fuel tank is easy. We just cut it loose, and it falls into the universe.
(6) We're using a low-thrust, high-efficiency drive: ion jets, perhaps. The axis of the city can be kept clear. A smaller ship can rise to the- axis for sightings before a course change; or we can set the control bridge atop a slender fin. A ten mile circumference makes the fin a mile and a half tall if the bridge is at the axis; but the strain on the structure would diminish approaching the axis.
What would it be like aboard the Ring City? One gravity everywhere, except in the bridge. We may want to enlarge the bridge to accommodate a schoolroom; teaching physics would be easier in free fall.
Otherwise it would be a lot like the Generation ship. The populace would be less likely to forget their destiny, as Heinlein's people did. They can see the sky from anywhere in the city; and the only fixed stars are Sol and the target star.
It would be like living anywhere, except that great attention must be paid to environmental quality. This can be taken for granted throughout this article. The more thoroughly we control our environment, the more dangerous it is to forget it.
Inside Outside
The next step up in size is the hollow planetoid. I got my designs from a book of scientific speculation, Islands in Space, by Dandrige M. Cole and Donald W. Cox.
STEP ONE: Construct a giant solar mirror. Formed under zero gravity conditions, it need be nothing more than an Echo balloon sprayed with something to harden it, then cut in half and silvered on the inside. It would be fragile as a butterfly, and huge.