Generation Ship SFV Exodus: Revised Designs

[DaveC426913]

If you want me to sketch this up, let's summarize all values here:

Overall
Silhouette: dumbbell - two spheres on either side of central core with rings
Length: 3km

Spheres:
Diameter: 1km
Inner compartments: spheres?
Number: 9?
Inner sphere diameter: 366m?

Backbone:
Length: 1km?**
Diameter: ?

Rings:
Number: 6
Major Diameter: 500m
Minor Diameter: 64m x ~20m?
Gap: 5m
Total length of rings: 6x (width+gap) = 410m**
Cross-sectional Shape: (rectangle? circle?)
Number of spokes: ?
Secondary structures (baby spokes/guywires)?

** note the rings only take up 410m, if the backbone is 1km long - that's 590m of naked backboneDrive:
Location: Backbone? Aft sphere?
Exposure: just the exhaust nozzle?This doesn't look like what I was expecting. Did I get the ring specs wrong?

 

[Strato Incendus]

Thanks a lot for all your time and effort again, @DaveC426913 !

But if you want one of them to contain a drive, then you should have at least one sphere on the ship's axis.
#9 is almost identical to #8, but with a ninth sphere. on the axis Up to you whether you want to go up or down the chart.

Number 9 seems ideal to me - as long as nothing speaks against the very concept of having the fusion drive in that location? Meaning, inside the sphere, on the axis? That's indeed where I placed the fusion reactor in my latest Campaign-Cartographer (Cosmographer) drawing. Meaning, not in the centre of the aft tank, but at the connection between aft tank and central pipe (not to scale):

Overall
Silhouette: dumbbell - two spheres on either side of central core with rings
Length: 3km

Spheres:
Diameter: 1km
Inner compartments: spheres?
Number: 9?
Inner sphere diameter: 366m?

Backbone:
Length: 1km?**
Diameter: ?

Okay, I'm glad we've clarified this: The spheres have a diameter of 1 km then, not (as in your very first original suggestion of this idea) a radius of 1 km (or rather, in your first suggestion, one sphere was twice as large as the other, with one having a radius of 1 km, the other one a diameter of 1 km).

Now both spheres have a diameter of 1 km. Which makes sense in relation to the size of the rings. Whether it's enough space to store all the fuel, or whether we need to store additional fuel in the central pipe, that's a different question. But both spheres are large enough to protect the rings against the radiation - and they both need to be, since the ship will be flipped eventually.

Now the obvious following question: How long is the central pipe in between the spheres?
Making it 1 km as well, and thus extending the overall ship back to its original length of 3 km in total, seems like a good starting point.

Now the question is: How much additional room, aside from what the rings take up (6 * 64 m + 5 * 5 m = 409 m) do we need?

I wouldn't lock-in the overall length of the central pipe at 1 km a-priori. It should only be as long as necessary, since every additional meter adds additional hull mass (an outer surface area of pi * 100 m * 1 m = 314 m², weight depending on the material the hull is made of) to the ship.

So, what else could we need the central pipe for?

1) additional fuel storage?

2) production spaces that might put the absence of gravity to good use (like for the creation of ball bearings)? This is a production facility which I used to place within the pipe, before and after the factory ring. However, that was when the rings were still 60 metres apart. With only 5 metres between the rings, that would be a factory inside a somewhat larger broom closet. ^^

3) sports facilities that put the absence of gravity to good use?

There's the gym on deck 3 of the public ring for all "standard" types of sports.
The swimming pool, which I initially wasn't sure about whether the ship could have one in the first place, is the one sports-thing I have placed on deck 2 of the public ring. That one is more of an "entertainment" floor, with a bar, a canteen etc.
One reason to put the pool on that same floor is that I also want people to be able to run laps around the entire gym floor, without having to pass through the swimming pool rooms in between).

But there might also be other kinds of sports which are specific to the ship / specific to space, which can only take place in zero or reduced gravity. I'm thinking of something between that Echo VR game that my father and my brother are playing at the moment, and "Quidditch without brooms".
(Then again, in the very first Potter novel, Harry describes Quidditch from an outsider's perspective as "basketball on brooms" - so in this case, you could simply think of a central-pipe-specific sport as "basketball while floating in the air" or something.)

Rings:
Number: 6
Major Diameter: 500m
Minor Diameter: 64m x ~20m?
Gap: 5m
Total length of rings: 6x (width+gap) = 410m**
Cross-sectional Shape: (rectangle? circle?)
Number of spokes: ?
Secondary structures (baby spokes/guywires)?

** note the rings only take up 410m, if the backbone is 1km long - that's 590m of naked backbone

What do you mean by "minor diameter"?
The inner diameter of the rings is 500 m, so that even on the top deck (deck 1), there can still be Earth-like gravity without requiring the ring to rotate too fast for human tolerance.
The outer diameter of the ring thus includes the total height of all five decks and ceilings combined, currently clocking in at 526 m.

The 64 m are the outer width / thickness of the ring, which you correctly added up together with the 5-m gaps in between every two of them. So I don't know where you take the number 20 m from?
The inner width / thickness of the rings, i.e., the usable space for citizens, is 32 m, some of which is used for rooms, some for corridors.
That means the walls on each side are 16 m thick, containing all kinds of technical stuff (most importantly, water supply and sewage, electricity, and heating). Engineers sometimes have to climb into the walls, by removing the lids at the access points; much like climbing into a Jefferies tube in Star Trek. But usually, regular citizens won't go there (or aren't even allowed to).

The number of spokes is indeed four, as in your Blender models, and as in my cross-section of the rings.

Spoiler

Drive:
Location: Backbone? Aft sphere?
Exposure: just the exhaust nozzle?This doesn't look like what I was expecting. Did I get the ring specs wrong?

I think this looks fairly accurate to the previous depictions!
You did indeed go with the correct number of spokes (4), and also made them thinner than the overall corridor width, as we had already agreed on in the first thread:
The spokes mainly just serve as elevators, down to the rings, and between decks. So they should definitely not be as thick as the inner ring thickness itself, or the lift shafts would end up blocking the entire corridor.

The main specs that's still up for debate now, as explained above, is the overall length of the central pipe: How long do we need it to be?

This includes the question: Where do we place the bridge / command central?
On one of the rings? That would probably be the public ring, then. Though it would feel weird to a) have the command central so close to public places accessible to everyone, and b) to have the bridge in a rotating position.
So far, I'm leaning towards placing the bridge between the public ring and the fore tank. Which, in order to still have something resembling normal gravity on the bridge, would necessitate the magno-boots solution from The Expanse. And the people working on the bridge would have to do just as much daily exercise as people working in the central pipe, or spending their entire day in zero-gravity for other reasons.

 

[Algr]

Didn't you say at one point that it was complicated to get from one ring to another? If there is a "Habitat Ring" then every day most of the people in that ring would have to cross to other rings to get to work, or do public ring stuff. Wouldn't it make more sense to have habitats in each ring so that people could live near their jobs?

Also, perhaps you'd want a storage ring for materials brought from Earth that might run out, and for items that are hard to manufacture in the limited space. I know you'll be recycling, but accidents happen, and gasses like nitrogen and neon can get lost into space.

 

[DaveC426913]

Also, perhaps you'd want a storage ring for materials brought from Earth that might run out, and for items that are hard to manufacture in the limited space. I know you'll be recycling, but accidents happen, and gasses like nitrogen and neon can get lost into space.

Yeah, you'd want a supply of materials that get easily lost - or converted that it's expensive to recover.
But no reason to waste valuable ring space, the km radius spheres have plenty of room for materials storage.

 

[Strato Incendus]

Didn't you say at one point that it was complicated to get from one ring to another? If there is a "Habitat Ring" then every day most of the people in that ring would have to cross to other rings to get to work, or do public ring stuff. Wouldn't it make more sense to have habitats in each ring so that people could live near their jobs?

I think the difference in distance within the same ring vs. between different rings is deceptive:

- Since each ring has an inner diameter of 500 m, the ring circumference is, depending on which deck you are on, always something around 1,500 to 1,600 m. So potentially, if you were living on the same ring and deck where you work, your way to work would be 750 to 800 m at max (since you would take whichever route was shorter, rather than walking more than half a lap around the ring).

- In the central pipe, meanwhile, which only has a diameter of 100 m, the circumference of the rotating hub with the four lift shafts going through the spokes is only 314 m (pi * 100 m). So using the same logic, you’d walk a maximum of 157 m around the hub, if you need to get to the lift shaft on the opposite side than where you are when you arrive. And you would usually take the lift to the section where your workplace is, since the detour is much larger once you’re down on the ring (like running on the outer track of a race track vs. the inner track).

- Assume you’re living on a deck where the ring circumference is 1,600 m, then each of the four sections is 400 m long. The spokes with the lifts are in the middle of each section, as the image in my previous post shows (since between the sections, there are the doors that can seal off one section from another for the final dismantling process, or in case of a leak etc.). So even when your quarter is right next to a section door, your way to the closest lift is only 200 m. Then the lift journey itself is 200 m, but you don’t have to walk or climb that.

- Once you’re in the central pipe, the distance to the next ring is only 5 m.

So your way to work might be 200 m from quarter to lift + 5 m walking through the central pipe (if you’re working in the lab or the factory; it’s 10 or 15 m if you have to get to the farms) + 64 m for each ring hub you pass. That’s still less than the 750 to 800 m you might be forced to walk if your job is on the same ring as your quarter, but on the opposite side.

I’m not saying that working on a different ring is outright preferable in terms of sheer distance, but I hope I’ve illustrated why it isn’t objectively worse either.

Other factors at play are:
- noise (having your quarter on the farm where you work might be one thing; but having it next to the factory might get on your nerves pretty quickly)
- limited-access areas (it might be harder to keep regular citizens from entering certain spaces if they live close by, and therefore, a lot of areas would be like ”blocked but residents only” streets; also, these regular citizens might simply get in the way of transport etc. if they just happen to be strolling the corridors while people working on that same floor need to pass through there)
- the psychological benefit of having a clear separation of home and workplace (some of the more digital jobs enable “home office” anyway)
- in terms of child care: In terms of the space the habitat ring provides, I’ve already calculated I don’t need five decks to have enough quarters for all the families. Hence, the school and kindergarten rooms are on deck 2; the university rooms are on deck 1. This allows the parents to drop off their kids on deck 2 on their way to work, by just briefly hopping out of the lift on the way to the central pipe, if they work elsewhere. In turn, the teachers of course do indeed work on the same ring where they live.

That said, everyone has to leave the habitat ring at some point during the day, if only for lunch (the canteen is on deck 2 of the public ring) and/or evening exercise (the gym floor on deck 3 of the public ring).

But no reason to waste valuable ring space, the km radius spheres have plenty of room for materials storage.

Wait, wait, now we’re going back to having a 1 km radius for the spheres? I thought we had agreed on 1 km diameter? ^^

In either case, yes, there should be enough space between the sub spheres to store additional things.

The question is now about the contents of the sub-spheres themselves:
- just water, which serves as radiation protection for one and is split into hydrogen and oxygen for nuclear-fusion fuel?
- are there some sub-tanks containing just hydrogen (H2), or Deuterium, or other forms of nuclear-fusion fuel?
- if each individual sub-sphere is 366 m in diameter, as we’ve calculated with sphere-distribution pattern #9, would that already be large enough to serve as a sphere for a black-hole drive later? I don’t think we’d need the entire 1 km diameter big sphere for that, would we? Because then, we’d have no protective water left in the tank once the ship turns around.

 

[DaveC426913]

Wait, wait, now we’re going back to having a 1 km radius for the spheres? I thought we had agreed on 1 km diameter? ^^

Yes, sorry mistyped.

 

[Strato Incendus]

Ah, okay, then that is settled.

Back to the questions at hand, then:
Can we eventually put the artificial black hole into one of those 366 m-diameter spheres?
Does that sphere need to be on axis, or can it be any of the sub-spheres inside the big aft tank?

The question is now about the contents of the sub-spheres themselves:
- just water, which serves as radiation protection for one and is split into hydrogen and oxygen for nuclear-fusion fuel?
- are there some sub-tanks containing just hydrogen (H2), or Deuterium, or other forms of nuclear-fusion fuel?
- if each individual sub-sphere is 366 m in diameter, as we’ve calculated with sphere-distribution pattern #9, would that already be large enough to serve as a sphere for a black-hole drive later? I don’t think we’d need the entire 1 km diameter big sphere for that, would we? Because then, we’d have no protective water left in the tank once the ship turns around.

And the second question is about the best way to store the hydrogen on board that’s specifically for the fusion reactor.

We’ve already established that we can’t slow down the ship ”just to pick up something”.
However, vice versa would still work:
If the ship had to slow down prematurely for some emergency reason (like the deflector systems failing or the ice shield at the front depleting too quickly - the latter reason I just came up with, but I like it more, because slowing down would still take 1-2 months), this would require the ship to waste its braking fuel too early - and then that fuel would be gone.

The ship would be stranded in the interstellar medium, but at least the crew would survive.
In order to get moving again, it would have to replenish its tanks somehow. The question is: How?

- collecting ice from ice fields and store it as water in the tanks again?
- sucking up hydrogen from gas clouds / nebula etc.?
- diving into the upper atmosphere of a gas giant and suck up hydrogen from there? (I kind of want that to happen in the second book, to be honest… ^^ This would require the ship to get stranded in a different solar system than the target solar system, or encounter a rogue gas planet in between star systems.)

 

[DaveC426913]

Ah, okay, then that is settled.

Back to the questions at hand, then:
Can we eventually put the artificial black hole into one of those 366 m-diameter spheres?
Does that sphere need to be on axis, or can it be any of the sub-spheres inside the big aft tank?

What did you decide about how the drive works? Is it still just a way to heat up the reaction fuel? As long as the mass exits the ship along its major axis, it won't matter where the drive is.

We’ve already established that we can’t slow down the ship ”just to pick up something”.
...

The ship would be stranded in the interstellar medium, but at least the crew would survive.

Stopping is suicide. Suicide by being marooned in deep space merely takes longer than suicide by radiation poisoning...

I can see such a debate dividing the crew so strongly that they would be willing to go to war - to kill - over it.

The war would only end when someone came up with an alternative - a way to refuel.

Maybe that would be somehow tied to whatever stoke of luck also provided the resources to make the BH drive possible? (Because I don't think they have enough of an energy budget in the entire Exodus to do it otherwise.)

What if the creation of this drive required a critical sacrifice? Like, enough mass to make the BH or to drop into it? Like, say a large part of the ship? A few of the rings? Sacrifice a portion of the mission so that a minimum complement can survive?

 

[Algr]

Stopping is suicide. Suicide by being marooned in deep space merely takes longer than suicide by radiation poisoning...

Agreed. I can't see any reason why they would want to slow down. Remember that once they stop accelerating, they would perceive themselves as simply floating in space while while the galaxy moves around them. There would be no external forces vibrating them or knocking them around. They only need energy to keep the lights on.

Even if the ship was stationary relative to the Earth, or destination, you would still need radiation shields and deflectors. It would just make the direction of incoming objects less predictable.

 

[DaveC426913]

Even if the ship was stationary relative to the Earth, or destination, you would still need radiation shields and deflectors. It would just make the direction of incoming objects less predictable.

Well, only a nominal amount of shielding. Out in interstellar space, the chances of an incoming object are effectively nil, and the radiation is minimal, and it's not blue-shifted.

 

[Strato Incendus]

What did you decide about how the drive works? Is it still just a way to heat up the reaction fuel? As long as the mass exits the ship along its major axis, it won't matter where the drive is.

Isaac Arthur's concept of a black hole drive was to find a balance between the Hawking radiation pushing the ship forward (requiring the gamma-ray-reflective panels to direct that impulse into the same direction, since otherwise, the radiation would be given off into all directions), and the gravity of the tiny artificial black hole keeping it attached to the ship (rather than pushing the ship away once, with the black hole remaining in its position).

Hence, he then concluded that a demisphere at the back of the ship was not enough, but a small Dyson sphere surrounding the entire miniature black hole would be required. (Not remotely comparable in size to a "traditional" Dyson sphere around a star, of course, given the tiny size of that artificial black hole.)

In other words: If the impulse that propelled the ship forwards came from the Hawking radiation, then the black hole would probably have to be on-axis, wouldn't it? Otherwise, it would be pushing at the ship slightly from one side.

Stopping is suicide. Suicide by being marooned in deep space merely takes longer than suicide by radiation poisoning...

Well, the ship has to be autonomous in terms of everything it produces anyway. The only thing limiting its lifetime is the durability of the fusion reactor, as well as the risk of running out of hydrogen eventually.

Hence, if I had them strand within a nebula, wouldn't that allow them to keep replenishing their hydrogen supplies for a long time, using only the gas clouds surrounding them?

(Perhaps "stranding inside a gas cloud" is a better way to put it, since nebula would be so much larger in size that the ship could be passing through a single one for several generations. Also, this would require checking with the "real universe" whether we have any evidence of actual nebula existing anywhere close to Teegarden's star.)

Maybe that would be somehow tied to whatever stoke of luck also provided the resources to make the BH drive possible? (Because I don't think they have enough of an energy budget in the entire Exodus to do it otherwise.)

Well, yes: If the lasers that are supposed to create the artificial black hole are powered by the nuclear-fusion reactor, ultimately the same hydrogen would be required for both. The difference between the "cautious" and the "risky, visionary" side would then merely be: Do we replenish our hydrogen supplies just to keep the lights on for a little longer? Or do we invest the energy into powering those lasers, so that we can get out of this trap we stranded in during book I?

What if the creation of this drive required a critical sacrifice? Like, enough mass to make the BH or to drop into it? Like, say a large part of the ship? A few of the rings? Sacrifice a portion of the mission so that a minimum complement can survive?

Using actual matter to create or at least contribute to an artificial black hole of such a small size sounds much harder to my layman ears than doing the same just by using light. How do we squash the entire mass of a ring into such a small space? Fusing hydrogen to helium seems like a cakewalk in comparison.

The premise of having to sacrifice a portion of the ship is interesting, of course (even though it would fit better into a story like The 100, where it's often "life vs. life", meaning, the survival of one group against that of another - rather than the more fundamental, abstract debate about "life vs. liberty vs. happiness"). But just like with my own premises, I need to make sure the physics actually support that premise. So that we don't end up with another "there-would-have-been-enough-space-for-Jack-on-that-door-next-to-Rose" plothole that ruins the reader's suspension of disbelief.

 

[Algr]

Isaac Arthur's concept of a black hole drive

Please let my clone ships get out of the solar system before you start trying to make your own black holes. By the time such a thing is possible we'll know how to harness dark matter and do who-knows-what with it.

---

::Arrives at the planet. The black hole eats it. ::

Hence, if I had them strand within a nebula, wouldn't that allow them to keep replenishing their hydrogen supplies for a long time, using only the gas clouds surrounding them?

The nearest nebula is the Helix Nebula. It is 700 light-years away in the constellation Aquarius. Also, check if nebula are dense enough for their hydrogen to be gathered like that.

 

[DaveC426913]

In other words: If the impulse that propelled the ship forwards came from the Hawking radiation, then the black hole would probably have to be on-axis, wouldn't it? Otherwise, it would be pushing at the ship slightly from one side.

Yes.

But you've already had to grant the existence of these "gamma-ray-reflective panels". (If you don't have reflecting panels then your BH will radiate omni-directionally, making it useless as a direct drive).

So, with the existence of those panels, it is not critical that the drive be centred - you simply have more routing of the exhaust.

However, I agree, the best arrangement is to have the drive axially aligned.

Really though, with a drive that's spewing hard gamma radiation, what you really want to to place it - not only at the very stern of the ship - but even very far astern of the ship. The farther the better, for the sake of radiation.

Well, the ship has to be autonomous in terms of everything it produces anyway. The only thing limiting its lifetime is the durability of the fusion reactor, as well as the risk of running out of hydrogen eventually.

I think this is optimistic. It would be a pipe dream to expect a ship to operate indefinitely. Critical materials will run out. Gene pools will dry up. Minds will turn to mush. Factions will form and rebel.

In fact, if it were designed to survive indefinitely, then you wouldn't have needed to aim for only 12.5 light years - you could have aimed anywhere in the galaxy. Thus, by corollary, I'd suggest that an unspoken premise of your story is that the gen ship has a limited lifetime to make Teagarden a logical target.

Hence, if I had them strand within a nebula, wouldn't that allow them to keep replenishing their hydrogen supplies for a long time, using only the gas clouds surrounding them?

Do you actually have a way to harvest hydrogen? Unless that was part of the original design, that's another technology your crew is going to have to cut from whole cloth. Even if they have access to hydrogen, will they be able to gather enough and compress it to a high enough pressure? Your tanks were meant to hold water, not pressurized gas.

I am beginning to wonder if there's too many implausible things needing to happen along the way in the story to drive all these risky and desperate modifications.

What if all the actions taken were driven by a single cause? What if they ran into a hydrogen cloud first and that's what made them have to stop (a suicide move) so they didn't get cooked? And then, after sitting for a generation or two (because all options are suicide), they decide to try some of the more outlandish solutions (because they have little left to lose) that require such a huge amount of work and invention and sacrifice?

So that we don't end up with another "there-would-have-been-enough-space-for-Jack-on-that-door-next-to-Rose" plothole that ruins the reader's suspension of disbelief.

Yes. I suspect you are going to spend a lot of time testing exactly this.
You want to force the crew to take specific outlandishly risky actions that they never never otherwise consider - but at the same time, you don't want to have so many independent external forces that it looks like they're just being toyed with by the universe.

The mess they find themselves in needs to be a balance between dire and plausibly simple.

 

[Strato Incendus]

Arrives at the planet. The black hole eats it.

Correct me if I’m wrong, but given how small these artificial black holes made of light would be, I’m pretty sure the Schwartzschild radius of one of those would be way too small / narrow for that to happen. Also, these tiny black holes evaporate much faster than their real, “natural” cousins. They could time it in such a way, i.e. create a black hole of appropriate size, that it would have fully evaporated by the time they reached the target planet.

The nearest nebula is the Helix Nebula. It is 700 light-years away in the constellation Aquarius. Also, check if nebula are dense enough for their hydrogen to be gathered like that.

Thanks for that! ;) That takes anything I’ve written in the book about nebula thus far out of the picture (it wasn’t much and nothing essential, though, so no big loss here). Changing it to “a small gas cloud” will most likely accomplish everything I need it to.

But you've already had to grant the existence of these "gamma-ray-reflective panels". (If you don't have reflecting panels then your BH will radiate omni-directionally, making it useless as a direct drive).

So, with the existence of those panels, it is not critical that the drive be centred - you simply have more routing of the exhaust.

Good to know! So this is one solution that would work for them in a pinch. :)

However, I agree, the best arrangement is to have the drive axially aligned.

Really though, with a drive that's spewing hard gamma radiation, what you really want to to place it - not only at the very stern of the ship - but even very far astern of the ship. The farther the better, for the sake of radiation.

If I recall correctly, sphere-in-sphere design #9 only had one sphere on the axis. So would we need design #11 or #12 to have two spheres on axis (one containing the fusion reactor, one containing the black hole)?

In fact, if it were designed to survive indefinitely, then you wouldn't have needed to aim for only 12.5 light years - you could have aimed anywhere in the galaxy. Thus, by corollary, I'd suggest that an unspoken premise of your story is that the gen ship has a limited lifetime to make Teagarden a logical target.

Well, the obvious caveat here is that the technology could be more durable than the human minds. ;) It’s about giving the crew sufficient hope and a positive perspective to even join such an endeavour. The psychological factors are precisely why I’m writing this story, since I get the impression these are the first things that get overlooked, once people start focussing on the physical details:

With a 125-year-long journey, Generation One (the first one born on the ship) at least knows their grandchildren will still get to see the new planet (even those grandchildren will be middle-aged by then, or will already have grandchildren themselves). If I sent the Exodus on a 400-year-long journey to Trappist-1 at 0.1 c (since it’s 40 light years from Earth), there is no longer a personal connection between those who board the ship and those who get to leave it at the end.

Do you actually have a way to harvest hydrogen? Unless that was part of the original design, that's another technology your crew is going to have to cut from whole cloth. Even if they have access to hydrogen, will they be able to gather enough and compress it to a high enough pressure? Your tanks were meant to hold water, not pressurized gas.

One argument for why the ship could have such technology is that the nuclear-fusion reactor should ideally continue to be used after the ship’s arrival. At least for the first couple of decades of establishing the colony. If the settlers had to restart in the stone age after their landing on a habitable but “primordial” world, why would anyone ever want to leave the comfort of the ship?

If the tanks are only large enough to contain fuel for the journey, it could be part of the plan to replenish hydrogen supplies from a gas giant in the target planet’s solar system. I’ve postulated that this system has been confirmed to have at least two gas giants - since those are probably needed anyway in order to protect the habitable planet from too-frequent meteor impacts (again, just working off of what we know from our own solar system, where Jupiter does that job, and Saturn prevented Jupiter from wandering inwards and kicking out the smaller planets during the early days of the solar system). So the ship could refuel the tanks from the outer gas giants before heading further inward to the habitable zone and landing on the target planet.

At the same time, the fact that the on-board fusion reactor won’t last forever may also be a reason why the new settlers might pass through various “outdated” form of generating electricity (coal / gas, propped up with solar / wind / water etc.) as a bridge technology, until they’ve built a second, new fusion reactor all by themselves on the surface.

What if all the actions taken were driven by a single cause? What if they ran into a hydrogen cloud first and that's what made them have to stop (a suicide move) so they didn't get cooked? And then, after sitting for a generation or two (because all options are suicide), they decide to try some of the more outlandish solutions (because they have little left to lose) that require such a huge amount of work and invention and sacrifice?

That actually sounds like an ideal plan to me (from a story-writer’s perspective; obviously it’s not ideal for the crew)! What would this look like? They’d still need 1-2 months to slow down once they encounter the gas cloud, wouldn’t they?

What do you mean by “so they didn’t get cooked?” The exhaust would heat up the hydrogen to such levels that it would threaten the ship? Would the protective ice shield at the front of the ship melt? Would there simply be too many particles per volume that the ship could collide with at 0.1 c?

The mess they find themselves in needs to be a balance between dire and plausibly simple.

Fully agree! :) I don’t want to create the fatalistic impression of “everything that can go wrong will go wrong”. Rather, I want to demonstrate the extreme volatility of any space mission: ”If only one thing goes (really) wrong (enough), the entire mission can be in jeopardy.” So a “domino” effect of a single problem causing a bunch of other ones would be ideal for the story, in my view.

 

[Algr]

I’m pretty sure the Schwartzschild radius of one of those would be way too small / narrow for that to happen.

Well if it eats the ship first, that would help it eat the planet later.

 

[DaveC426913]

Soooo I am currently reading an Adam Oyebanji novel called Braking Day, about gen5 characters on a genship with 8 hab rings headed for Tau Ceti...
... designed to be broken up and sent down for construction materials...

 

[Strato Incendus]

Well if it eats the ship first, that would help it eat the planet later.

But why would it eat the ship first to begin with? Isn't the Schwarzschild radius too small for that, too? The sphere containing the artificial black hole shouldn't contain anything else, so that the black hole couldn't start "devouring" stuff, and therefore it shouldn't grow to sufficient sizes to become dangerous to the ship.

You're not creating the black hole to feed its "limitless hunger for matter"; you're essentially creating it just to let it die, by giving off its Hawking radiation to drive the ship forward, until the black hole has evaporated entirely.

(And if you hear any simile in my way of phrasing this, that is entirely on purpose. ;D )

Soooo I am currently reading an Adam Oyebanji novel called Braking Day, about gen5 characters on a genship with 8 hab rings headed for Tau Ceti...
... designed to be broken up and sent down for construction materials...

Great! :) That means the general premise of the ship design does not seem to be so outlandish that it were unbelievable to the average reader.

(Also, why is everyone going to Tau Ceti? That's where Isaac Arthur sent his fictional ship "Unity", too. Is that system somehow more promising than Teegarden's star? Anyway, I'm sticking with the latter; if fewer people have been using Teegarden b as a target destination thus far, all the better for the "uniqueness" of my own story. )

If this comment was meant to imply that my story is too similar, don't worry - I've just read the synopsis of Braking Day, and the plot seems to be about something completely different.

In fact, to such an extent that once again, based on the synopsis alone, I'm personally not really interested in that story - I might only read it to learn about the setting.

(But then again, maybe I shouldn't, so that I don't start copying stuff from there; I'd always rather base the worldbuilding on physical reality first, like a fantasy author getting inspired by real-world history, rather than taking things from other novels and simply assuming that they're scientifically accurate - relying on the assumption that this other author did their research properly.)

Because from the synopsis, it looks to me like another case of the generation ship merely serving as a setting, for a story that promises to be supernatural (like the Force in Star Wars); rather than the story being about the inherent problems of the premise itself.

I'm not saying one is better than the other, just that I prefer the latter. The Swedish movie Aniara attempted to go there, but it simply had an awful story structure, and the characters were either bland or off-putting; in either case, I didn't find any of them relatable.

Star Trek Voyager sometimes brings up these issues, but of course, since they can jump between inhabited star systems much more easily, most episodes are still about something else. And when I watch Voyager, that's fine for me, because I don't primarily expect generation-ship questions to begin with.

Spoiler

And while Star Trek of course invents things that clash with actual science, especially given what we know today compared to what people thought they knew in the 1990s, within the setting, only few things that happen in Star Trek are framed as supernatural. (Whereas a lot of Star Wars fans complained when midi-chlorians were invented as a "scientific" explanation for the Force.)

Even telepathic abilities of species like Vulcans, Betazoids etc. are framed as abilities these species naturally evolved. The most supernatural thing that happens in Star Trek, aside from the Q, of course, is probably the whole mythology surrounding the prophets of the Bajorans. But even those have a basis in reality, since the wormhole is indeed inhabited by a real alien species.

To illustrate what I mean, for mere comparison, here's the synopsis / blurb (at least the current version) of the first book of my story (work in progress, so things might still change in the future):

Spoiler

2475. In 25 years, the generation ship SFV Exodus will reach its destination, the exoplanet Teegarden b.
Most young adults on board are looking forward to having children in the name of the mission —
24-year-old pharmacist Charlie Emerald would rather continue revelling in her juvenile love for her boyfriend Patrick a little longer.

But social pressure is rising: Commander Theresa Kendrick increases the number of children per couple from two to four, to prepare for the colonisation of the planet. In reality, birth rates on board have been falling. And the smaller the crew, the more offspring they will need to have.

To ensure humanity’s survival, Commander Kendrick starts getting more and more restrictive with each crew member’s personal freedoms. Charlie places herself at the forefront of those resisting the commander’s increasing obsession with micro-managing every aspect of their private — including their sexual — lives. But Kendrick is determined to see this mission through until its envisioned end, and individual suffering isn’t an obstacle factoring into her plans…

That is what I mean by "the story being about problems inherent in the premise itself". Others may disagree. If any of you are aware of a generation-ship story that does indeed go more into this direction, please let me know!

What's good to know from the first chapter of Braking Day is the apparent necessity to stop the ring rotation during acceleration. In terms of stowing away loose objects so that they don't turn into potentially lethal projectiles, my crew is already taught to be paranoid about that right now, even during the coasting phase. I'm not sure if that's necessary during coasting, though?

Conversely, when slowing down, would the ring rotation have to be stopped at that point, too?

I'm not sure how fast the Archimedes is traveling in Braking Day, but three weeks to slow down seems like a rather short time. As I've stated before, from 10% light speed, I'd expect it to be something between 1 and 2 months.

 

[Strato Incendus]

Okay, since there haven't been any replies for a few days, as I understand the rules, "bumping" is fine now. Especially since I have more to contribute than just a "bumping" post by itself. ;)

First of all, thanks to @DaveC426913 for recommending "Braking Day" to me. I'm about a tenth into the book so far, and as I've expected, I could care less about the story and characters (even though this is almost a five-star-rated book). But we're mainly here for the setting anyway.

So let's do a quick comparison of the Archimedes and the Exodus:

	my ship (SFV Exodus)	ship from "Braking Day" (Archimedes)
overall length	3 km	>20 km
number of rings	6	8
shielding	sphere shape	disk shape
number of decks per ring	5 (3 on the public ring)	>30
central section diameter	100 m	200 m
width of ring hubs	64 m	625 m (5,000 m : 8 rings)
gravity in the ring hubs	0.2 g (since the hubs have 1/5 of the diameter of the rings, which create 1 g)	none
population	500 - 1,500	>30,000

A few other noteworthy things:

1) The Archimedes is described to have windows. I deliberately removed any windows from my ship, replacing them with digital screens instead that only pretend to be windows to people on the insight. The reason of course being that people could get bombarded by radiation through those windows.
I'm not sure if having the shield / spheres on both ends would be enough to prevent that now, so that windows would be okay again. But as @DaveC426913 said, you must not see any starlight through them. So what would you look at? The other ring in front of or behind your own?
The upside of having a screen act like a window is that such a screen could simulate things like sunrise and sunset, too.2) Like on the Exodus, the Archimedes has the lifts in the spokes, four of them, and the entrance to those lifts are through their ceilings, through the holes in the hubs. So it seems like my design idea was pretty much spot-on in this regard. ;)
In addition to the regular lifts, though, the Archimedes is also described to have paternosters (constantly rotating lifts in which you can enter at any time; I know these from one particular building in Cologne). That sounds like a nice idea; though I would leave this as a specific feature of the Archimedes, rather than "stealing" it for my own design.3) The four-elevator construction, one in each spoke, seems to make intuitive sense. However, while a cylinder with a 100 m diameter (the ring hub) only has a circumference of 314 m, so the way from one elevator to the next isn't that long: For somebody down on the ring, which has a circumference of around 1,600 m, the distance between two elevator shafts is about 400 m (=one lap around a standard sports court with a race track). That seems quite long, especially if you have to get somebody from a room into a lift in case of emergency.
Therefore, would two lifts for each of the four sections make more sense? Then they'd only be 200 m apart, i.e. half a sports court. Since the lifts have to be between the section doors, that would divide each section the following way:
section door --> 100 m --> lift 1 --> 200 m --> lift 2 --> 100 m --> section door
The same pattern would repeat in the next section, so that between lift 2 of one section and lift 1 of the next section, there would again be 200 m in total.
Naturally, this would require the rings to have 8 spokes, rather than just 4.4) Also, the central section of the Archimedes is indeed just one big empty room, with the hubs rotating around it - rather than being divided into sub-pipes. That was also my initial design. As epic as that might look, though, it sounds like a waste of space: How much use would people have for a pipe of 100 / 200 m, respectively, into which you could fit an entire cathedral upright?
Having sub-corridors in a circular array around the pipe would allow these corridors to be smaller, separate civilians from tech transport etc., you'd have emergency routes for quick transport to the medical bay etc. Heck, you could even have separate sub-corridors for vehicles (most likely, floating ones, not "cars"), without running the risk of colliding with a "pedestrian" floating through the pipe.5) The claim that the ring hubs on the Archimedes rotate, but don't produce any (!) artificial gravity at all, seems like a comparatively "lazy" handwave on the author's part. Supposedly, they rotate "too slowly to make gravity". But how would the rings rotate faster than the hubs (=more rotations per minute) if they're connected by the spokes? That's precisely the reason why we need the hubs to rotate in the first place, isn't it? ;)

I don't know the ring diameter of the Archimedes "wheels", as they're called. But if they're also twice as large as the rings of the Exodus (given that the central section is twice as wide), with the same number of rotations per minute at 1/5 the diameter, analogously to the Exodus, those hubs should be creating 0.2 g, shouldn't they? And that's already more gravity than on the moon (0.16 g)! So I wouldn't say that can simply be ignored.

If the Archimedes wheels themselves are only as wide as the rings on the Exodus, meanwhile, but the central section of the Archimedes is twice as wide, we'd be looking at a 500 m diameter for the rings vs. a 200 m diameter of the hubs, again with the same rotation speed. At that point, the hubs should even be creating 0.4 g with their rotation, which is more than the gravity on Mars (0.36 g).6) The author in Braking Day always uses the words "up" and "down" (sic!) in airquotes. That's why I've introduced the terms "pipeward" and "ringward" for my setting (and, after the input from the people on the last thread, "spinward" / "anti-spinward", too). Solves this "shameful" way of narrating ("I know up and down don't exist in space, but I lack a better term, so just bear with me") and also adds to the worldbuilding on top of that. But I'm glad the author of Braking Day didn't do this - it's just one more way for our settings to stand apart, which is a win-win!7) The population of the Archimedes is about 30 times as large as the population of the Exodus (30,000 vs. 1,000 to 1,500 at max), while the ship (20 km vs. 3 km) is less than 7 times as long. However, given the number of decks on the Archimedes (over 30 vs. just 5), as well as the assumed diameter of those rings (given that the central section is already 200 m in width), and the larger number of rings, that creates a lot more inhabitable surface. The majority of the Exodus's length is made up by the two 1-km spheres. Overall that still has me assume that the Archimedes is even less densely populated than the Exodus?8) The Archimedes seems to travel a little more slowly than the Exodus: It's headed for Tau Ceti, which is only 11.9 light years from Earth (whereas Teegarden's star is 12.5 away). Yet, it takes the Archimedes over 132 years to get there, whereas it would only take the Exodus 125.9) The quarters on the Archimedes all have the ability to turn by 90 degrees, for when the ship accelerates or decelerates at 1 g.
This looks like the most crucial point to me. Is this a feature my design, the Exodus, would reasonably need as well?
I already have my crew being obsessed with tightening any loose obejcts that might float around, bolting down every peace of furniture, students wearing seatbelts in class etc. But since we've established that the ship can't just "slow down suddenly", most likely this isn't actually (what's) needed?
We've also talked about when exactly the rings would dismantle - namely, after the ship has already come to a halt. At that point, they would also stop rotating.
However, Braking Day suggests the rings have to stop rotating for deceleration, and turn everything inside of them by 90 degrees on top of that. I can't just disassemble the ring and turn the entire ring by 90 degrees, since then, some quarters would be facing into other directions than others. Also, this would kind of require me to turn the whole central pipe by 90 degrees, while the ship itself turns by 180.

In short: Do we need this independent, "capsule-like" structure for the individual rooms on the rings?
You would basically be inhabiting a glorified elevator chamber, then, which is "hanging" on some sort of wires all the time, and has a larger, surrounding chamber around it, in which it could turn by 90 degrees.

The quarters on the Exodus have a square surface of 8 x 8 m. That's 64 m² for a couple, which is acceptable, but not much. With a ring circumference of about 1,600 m, this allows for roughly 200 rooms per deck. In reality, it's of course less, because you still have 0.18 m of wall between every two quarters, plus the doors between the sections, where there obviously can't be any rooms.

However, all of this of course assumes a standard ceiling height of 2.4 m (and a ceiling thickness of 0.2 m). If the rooms must rotate, it would make more sense for the rooms to have a cube-like shape.
But in order to maintain just a humble 64 m² of living surface, that would require a 8 m x 8 m x 8 m cube. (Who needs a quarter with a ceiling height of 8 m? )