Generation Ships

[ericthered]

Originally Posted by Astromancer

I'm with you here. The only logic in a TL8 starship is to flee the Earth's solar system. If you need to do that, society isn't going to hold together long enough to build a viable starship, period. Generation starships, without either supers, mages, or something else of that order, can't exist before TL9 or probably TL10.

of course, there is no guarantee that the actual TL 9 will look like GURPS TL9. We also in this case are drawing a hard line between TL 9 and 8. A high TL8, or a prolonged one, could build a generation ship that is viable.

[Flyndaran]

Originally Posted by ericthered

of course, there is no guarantee that the actual TL 9 will look like GURPS TL9. We also in this case are drawing a hard line between TL 9 and 8. A high TL8, or a prolonged one, could build a generation ship that is viable.

One that is TL 8 in all ways except space tech. That's how the future looked back before all of NASA's screw ups and defunding.

[Lamech]

Originally Posted by ericthered

of course, there is no guarantee that the actual TL 9 will look like GURPS TL9. We also in this case are drawing a hard line between TL 9 and 8. A high TL8, or a prolonged one, could build a generation ship that is viable.

This probably makes the most sense. Get to full TL 9 and generation ships start becoming too comfy. Fabricators, artificial wombs, AI, VR(?), all humans do is sit around and try not to touch anything important. But at TL 8 a generation ship is so expensive it would take a massive effort to produce a viable one.

[Johnny1A.2]

If you're fleeing the Solar System, then saying you're 'building a genship' is probably imprecise. Unless it's a scenario where the disaster can be seen coming way ahead (nova, stellar collision, whatever), a group fleeing the System would probably have to make do with what was at hand.

Thus if they have to build a genship, they won't be able to do it. But they might, just conceivably, be able to convert something extant to a genship. An O'Neil habitat, for example, might be converted into a genship more quickly than one could be built from scratch, in an emergency.

Of course, since it wouldn't be designed as a genship, it would be a makeshift, with endless problems, troubles, on-the-fly solutions, etc. Or to put it another way, a perfect role-playing situation.

A separate issue that applies to any genship attempt at interstellar travel is the time issue I alluded to upthread. Assuming you have a choice in the matter, how fast a drive do you need before you're ready to gamble that somebody leaving later won't get there ahead of you?

To use my .001c ship to Alpha Centauri as an example, they'll need 4500 years to get there. Even if civilization collapsed back to barbarism and pre-space technology right after they left, 4500 years is plenty of time to rebuild, regain space, and eventually be able to launch faster ships.

OTOH, a .01c ship can get there in 450 years. If the Solar System collapsed back to barbarism right after departure (maybe the escapees saw that coming), 450 years mght not be enough time to catch up the difference.

A .05c ship could get to Alpha Centauri in 90 years. That's only just technically a genship, since conceivably some of the younger voyagers could live to see arrival, even with unextended lifespans. If things collapsed as they left, they could probably reasonably assume they'll still be fairly collapsed 90 years later.

[Flyndaran]

5% of light speed would have to be one tiny ship strapped to a big honking fuel tank barring superscience. Can you get a generation ship that small?
I supposed when in doubt clone. But good human cloning just brings up TL9 again.

[Johnny1A.2]

Here's another consideration that might come into play for a genship running away from the Solar System: pursuit. A genship, almost by definition, is slow. It's big, massive, and won't be able to use much acceleration, we're more likely talking about a very very low acceleration over a long period, rather than a fast boost. Something maybe like .001G, but maintained over months, would get you out of the Solar System. (You'd reach 26 miles per second in about 7 weeks, by which point you'd have travelled some 56 million miles.)

But while .001G will get you out of the Solar System, it's easily outrun by missiles, lasers, etc. If whoever you're running from doesn't want to let you go, you're going to need defenses. How to defend against such threats is an interesting challenge.

BTW, if you can keep up that .001G all the way, you'll get to Alpha Centauri in about 133 years, acceleration/deceleration, with your peak velocity around .06c.

So, 133 years is genship time, all you need is a drive capable of producing an acceleration of .001G, which is trivial, and maintaining .001G for 133 years. Which is non-trivial.

[Flyndaran]

Good point. No matter how hopeless the home world situation seems to those of the gen ship, there will be some that demand not to throw away good resources on a fool's mission. And they will back that opinion up with force.
That could give a Battlestar Galactica feel even before the mission leaves the solar system.

[jeff_wilson]

Originally Posted by Astromancer

You tend to treat most of the other posters as backwards students in a physics class. Why can't they turn the tables and treat you as the backwards student.

I don't know about "most", but yes, I do challenge people to support their statements that I can't reconcile with what is taught in actual university physics courses, etc. Other posters are welcome to turn the tables since I can generally support what I post and this is not my first generation ship /space habitat discussion. I am also willing to own to being wrong, unlike certain other posters, and you can search the forums for me saying "I sit corrected" if that's what you're looking forward to.

Originally Posted by Astromancer

Actually, many of all moved on to the assumption that a generation starship was a tech level 10 project at least. Many, if not most of our statements assume the technology of either a standard GURPS TL10 or THS.

I reviewed the thread for that before posting, but didn't see such a transition.

[jeff_wilson]

Originally Posted by Fred Brackin

To look at some numbers from Spaceships a SM+15 vessel that might hold 20,000 to 40,000 in habitants supported by agriculture in Open Space modules (6-12 spaces) would mass 3 million tons and would require approx. 20,000 launches of a Saturn 5 in heavy lift configuration. You'd still only be in low orbit too.

Second is that there is no propulsion system that could be built before TL9 rolled around that would produce usable speeds. Even just the technical minimum of providing the 26 miles per second of Delta-V needed to achieve solar escape velocity is somewhere beyond merely impractical.

If long-term scaleable life support and moderate scale fabrication can allow human exploration and exploitation of the solar system and still be TL8, those can be done. The lifting problem is eliminated because materials already in space can be used for construction. IIRC, acceleration can be provided by using tethers to extract delta v from the energy of a rotating natural body. For example, every additional 5000 miles of space elevator height/length on Ceres provides 1 mile per second additional delta V for items turned loose.

[Astromancer]

A vast problem for a TL8 starship would be human bones. Without either a genetic engineering trick to prevent calcium loss, or artificial gravity (either superscience or spining part of the ship) everybody on broad gets brittle bone disease. And that's only a start because we don't know what DECADES of microgravity will do to humans. Moreover, we only have Sci Fi and speculation on human gestation and delvelopement in microgravity.

Another reason I assume that a society would need the space technologies and biotechnologies of Transhuman Space (or something as good) in order to build a viable generation starship.