View Full Version : Multi generation spacecrafts

10-10-2004, 08:51 PM
I've been trying to learn a little bit about the science behind multi-generation spacecraft for a short story I'm working on. While this is all backdrop to my main story, I just wanted the technical details to support the story in a meaningful way.

Some considerations for a multi-generation craft:

1) really small rooms
2) really big fuel tanks
3) recycling of organic material
4) ?

Any other thoughts or resources? I'm planning to read The Dazzle of Day by Molly Gloss and Heinlein's Orphans of the Sky.

Any brainstorming would be much appreciated!

10-11-2004, 08:24 AM
In his book, How to Write Science Fiction & Fantasy, Orson Scott Card describes "generation ships" as one solution to inter-stellar travel without resorting to the bolognium of FTL. I recommend you look this up (in addition to other resources).

In part he says:
...the problem with sublight voyages is that they take a long time. And you have to carry all your fuel with you. The good news is that you can coast most of the way--there's little friction in space, and once you reach a certain speed, you should continue traveling at that speed in the same direction until something happens to turn you or slow you down. So most of the voyage needs no fuel at all.

The bad news is that your fuel is part of the mass that your fuel [sic] has to lift. There comes a point where the fuel to accelerate any more will add enough weight that you either can't lift it or can't design a sturdy enough ship to hold it. ...If you work out the fuel problem, he says, you might achieve 10% of the speed of light--about 67 million miles an hour--but even at that rate, it will take more than 300 years to get to a star system 30 light years away. He explains:
Assuming that the ship is a completely self-contained environment, with plants to constantly refresh the atmosphere and grow food, a whole human society lives aboard the ship. People are born, grow old, and dke, and the elements of their bodies are processed and returned to the ecosystem within the ship. This idea has been well-explored in many stories--particularly stories about ships where the people have forgotten their origin, forgotten even that the ship is a ship--but it has a lot of life left in it.Card goes on to recommend Rebecca Brown Ore's debut story, "Projectile Weapons and Wild Alien Water."

10-11-2004, 08:57 PM
I'm not really certain that a multi-generation craft is any less bolognium than travel at the speed of light. Here on our multi-generation space craft called Earth, there are billions of microorganisms and plants for every living human or animal. These plants and microbes live even where humans can't, producing oxygen and decomposing waste. A space ship would have to be Huge in order to meed the needs of even a small number of humans.

As Pthom pointed out, the fuel required to lift such a huge craft would make it so heavy that escaping earth's gravity would be well-nigh impossible. And though moving the craft along once in space would not require much food, what about the lights required to grow the food? Once out of the orbit of a sun, all of that light would need to be generated by using fuel...

I think there has been an experiment where some scientists created a completely self-contained environment here on earth and had three or four volunteers live there for a year or so. They came out emaciated -- alive, true, but not in any shape to carry the experiment out for much longer. (Does anyone have more information on this?)

So, IMHO, it's gonna be bolognium whichever way you go (faster-than-light, or generation ships). So choose your poison and come up with some neat-o original ideas as to how it could work, then write your story. (Or write your story first, then figure out how it could work...)

Oh, and I second the recommendation for Card's book. Good stuff in there.

10-12-2004, 03:55 AM
Great advice, Ruth and Pthom.

So I should embrace the story's inner bolognium and run with it?:grin

The story is already written, so I'll just have to soft-pedal on some of the technical stuff. I guess I'm writing 'rubber' SF!


10-12-2004, 06:52 AM
So I should embrace the story's inner bolognium and run with it?

That's what I'd do.

A good story is a good story, and as long as the science isn't too far out, most people either won't realize it, or won't care. The story's the main thing.

Flawed Creation
10-12-2004, 09:06 AM
they aren't possible with pour current technology, but are less bolognium than FTl, because we understand ways in which they MIGTH work.

I think they would undoubtably be assembled in space, making lifting them from earth moot.

for feul, rather than huge fuel cells i would try to figure out a way for them to replenish or recreate their fuel.

various stories have featured solar sails, nets to collect hydrogen from space, and so on. a bigger problem than energy is mass. rockets depend on having something to throw away behind you, so the ship would definitely need some way of collecting more stuff.

of course, one book i recently read featured an interesting piece of bolognium. they ended up creating a jetless drive that somehow made use of some energy that isn't normally perceivable. something to do with the expansion of the universe...

it's called "the reefs of space" but that wasn't genereational or interstellar, and that was definite bolognium.