Building a Generation Ship: The SFV Exodus

[Filip Larsen]

The corridors on the inside are 32 m wide. Since I want the rings to dismantle and break down into their subsections A-D at the end

There are of course many ways this could be designed (at least for a story), but I would imagine that the doors (which has to be full pressure doors assuming the ring sections are to maintain pressure after separation) are not required take up the entire 32 m of depth with the additional design problem of where to store that door that this incurs. You could for instance have only the central part of each level, say 5-10 m being open for travel between the sections, with the remaining length is just being part the hull and being used to hold a sliding or hinged door. Assuming there is no requirement to have doors the same full height as the levels, you could just have the door hinged at the top, thus storing the door as part of the (slightly lower) ceiling near each section division at each level, which also seems to allow for nice fail-safe emergency deployment. By the way, note that having the doors stored internal (in air pressure) is probably needed since storing them outside will make a chicken-and-egg problem of deploying them to their sealed position without letting all the air out first.

Also, depending on when section separation is meant to occur and how fast it happens you may also want to consider using double doors to allow for some redundancy.

Does 60 m inter-ring distance still work if I change B from 32 m to 64 m? As far as I understood, the graph you made is specifically for B = 32 m.

Yes, the graph was made for B = 32m specifically, but let me stress again that such a moment of inertia calculation considers only the geometrical distribution of he bulk of the mass, so having some part of the structure protrude from the ring in various directions shouldn't matter much as long as the mass of these protrusions are small compared with the total. The various values used for the graphs just means that the bulk of the mass is assumed to be distributed equally within the geometric shapes these values indicate.

What may be more significant to rotational stability than have some doors protrude is the fact that I did not include the mass of the spokes in the calculation. Having spokes is, regarding rotational stability at least, a bit like having an "effective" inner ring diameter that is smaller than the geometric inner diameter, and in general the stability suffers a bit when making that "effective" inner diameter smaller. Again, if the mass of the spokes are small compared to the rings and central pipe, then the effect will be small. For instance, I assume the spokes does not have to be 32 meter deep, meaning even if they have same average density as the rings their total mass will like be a small part only. But of course, when in doubt a good engineer always verifies such assumptions by a calculation

The only places where the pipe does reach its full 100-metre ceiling height now (i.e., the full diameter) is at the hub of the rings. If the hub sections in the pipe rotate, too, I guess this would create some small levels of gravity in those sections of the pipe?

The level of rotational gravity scales linear with distance from the center. So if you have 1G at the outer ring radius, then at 0.2 times that radius you would have 0.2 G.

 

[DaveC426913]

The only places where the pipe does reach its full 100-metre ceiling height now (i.e., the full diameter) is at the hub of the rings. If the hub sections in the pipe rotate, too, I guess this would create some small levels of gravity in those sections of the pipe? They are obviously rotating too slowly to create Earth-like gravity, given their diameter is only 100 metres. But a little gravity in the hub sections of the pipe would actually be helpful to get people towards the elevators - since those four elevators would be rotating around you while you are standing / floating in the central pipe at one of the ring hub. The elevators A-D then travel down the four spokes of each ring.

It is important to keep in mind how "artificial gravity" actually works in this case.

The tendency is not toward the floor; the tendency is tangential to the floor underneath you, but as you move in that direction, the floor will rise up to meet you.

Things that can impart this are contact with the air around you, or contact with the floor or walls.

Without significant contact with any of these things, you will effectively float weightless.

Now, the above diagram is seen from an inertial frame of reference, so you see how it works.
The occupant doesn't see it that way from his rotating frame of reference. The differences are subtle but important.It's difficult to describe in a few paragraphs, but it would benefit your story to read up on it so you get it right.

 

[BWV]

With gene-editing techniques why would anyone care about inbreeding?

low velocity firearms like pistols or shotguns would not harm the hull - it would be expected to survive higher velocity impacts of particles from space. No one in the USN ever worried about a firearm discharge shooting through the hull of a battleship

 

[Melbourne Guy]

I fully agree - right now, I am just discussing what I consider the absolute basics, the bare necessities: I need to know how long my ship would reasonably be, how thick the central trunk etc., in order to even understand how much space I have to work with for all my scenes. It is far easier to decide this in advance, while a lot of the combat scenes are still rather vague in my mind, than to rewrite the whole thing because I made one conceptual mistake at the beginning.

I guess I'm wondering if you need it to be so correct, @Strato Incendus?

You are posting lots of words here and every one of them is a word that hasn't been written in your story. Good world building is necessary, and having written myself in a corner in one of my novels that led to rewriting a few chapters, I empathize with your planning, but I always come back to the fundamental question: will readers care?

It's science fiction, readers are willing to fill / ignore gaps and despite all the excellent physics detail being provided here, nobody has any experience with a ship like you are describing, so it's all theoretical anyway. You get to write it however you like and The Martian aside, too much in-depth technical guff is hard to make interesting.

 

[Strato Incendus]

The tendency is not toward the floor; the tendency is tangential to the floor underneath you, but as you move in that direction, the floor will rise up to meet you.

Thanks for stressing this again and adding a graphical depiction of it! I just checked out that one scene from The Expanse again (pouring water into a glass diagonally) to get an idea. Some people in the comments said the angle were exaggerated, but understanding the idea counts.

In my story, I have a couple of shower scenes that are relevant for the relationship between the leading couple. So I guess the water would fall diagonally in that shower, too? (The showers are part of every quarter and therefore on the habitat ring, of course.)

I guess this would be a good time to discuss water consumption on board in general. My natural intuition was that water would be scarce, so the amount of tab water to be used per person per day would be strictly limited. This is what led the main couple to take their showers together.

Isaac Arthur meanwhile suggested the main limiting factor in terms of recycling water would be the energy required, not the volume of water stored on the ship. And compared to the energy required from a fusion reactor to get a ship to 10% light speed, the energy required for recycling the water on board would be negligible. Any thoughts on this?

Of course, I could make it so that the reactor uses so much energy for propulsion that not much is left for everything else. But this could cause a bunch of plotholes elsewhere (why is computer usage not restricted too, then?). And furthermore, once the ship has accelerated to 10% light speed (which will have happened at the beginning of the journey), it can afford to just keep coasting, using all of the nuclear fusion power for countless other purposes.

This is just one example of the worldbuilding (and whether it is plausible or not) directly influencing the plot. Because without this external restriction, the shared showers don't make nearly as much sense.

With gene-editing techniques why would anyone care about inbreeding?

Another valid question that I have seen brought up in one or two articles, but haven't had the time yet to look into more deeply. I must admit I don't know too much about genetic printing yet. Is that something we can do reliably already by now? Or just one of those technologies we'd realistically extrapolate to have in the future (like nuclear fusion or lab-grown meat on an industrial scale)?

This also ties into what heritable medical conditions may or may not still occur on board. I recently joked "perhaps the unrealistic part about Star Trek: TNG will actually turn out to be Geordi, because we might not have replicators, transporters, and warp drives by the 24th century, but we might be able to heal blindness by growing replacement eyes". (I've already heard of one case right now of a formerly completely blind person who can now at least partially see again.) So far I don't have any blind characters in the story (I do not want to make this look too much like a Star Trek ripoff, there are already a bunch of references in the story). But other medical conditions become plot-relevant, in particular Duchenne muscular dystrophy and neuromyelitis optica. (My brother is a physician, so I have already asked him repeatedly "I need a medical condition that accomplishes X, Y, and Z in the plot", can you suggest one?)

low velocity firearms like pistols or shotguns would not harm the hull - it would be expected to survive higher velocity impacts of particles from space. No one in the USN ever worried about a firearm discharge shooting through the hull of a battleship

Good to know!

Spoiler

In the second book, according to my current plan, somebody gets shot by the antagonist at the end and is on the verge of death. (A choice has to be made between a painful emergency surgery or "painless release".) Right now, the three highest levels of the anti-organic guns cause instant death (level 10: annihilation, level 9: brain death, level 8: collapse of the respiratory muscles). This character gets shot at level 8, requiring a tracheotomy and intubation while still being fully conscious. But in the first version of that scene, the character just caught a regular bullet that had to be removed surgically. Now I would have both options! :)

Of course, if there are regular projectile weapons alongside the anti-organic ones, I would have to set that up with sufficient notice, and find a reason why both exist on board the ship. The anti-organic guns also have stun and shock modes, so they are more similar to phasers in Star Trek, or Stupefy in Harry Potter.

I guess I'm wondering if you need it to be so correct, @Strato Incendus?

Because my disbelief has become harder to suspend the more I learn about the scientific side of the topics that interest me. ;) As the lines between the fantasy and the sci-fi blur more and more, perhaps more readers will be accepting of authors who "just make some things up". But given that I try to write my story more in the tradition of 90s Star Trek, I would like to put the "science" back in "science fiction".

The Expanse is the only recent sci-fi show I am aware of that set out to do this. However, apparently then they still made mistakes that would have been avoidable easily. For example, I have heard that water would be the last resource to get scarce on Ceres, since it actually seems to have plenty of ice.

And with regards to the water supply on the ship, specifically, I might just be running into the same trap (see above), by potentially making it more scarce than it would reasonably be, given the available energy.

I am already taking some such creative liberties myself, with some of the most central points of the setting, in fact: Teegarden b might not be a habitable planet, after all, and the triple star system WR 104 most likely will not hit Earth with a gamma ray burst one day. (The confirmation of this threat is what leads to the construction of the generation ship in the first place.)

So wherever I can avoid further deviations from the current state of the science, I would like to do so. ;)

You are posting lots of words here and every one of them is a word that hasn't been written in your story.

I am familiar with this concern from other creative forums, like music forums. In fiction writing specifically, however, it reads to me like "every minute you spend doing research is a minute you don't spend writing". Yes - but if I don't research things properly first, I'll end up writing (and then deleting) even more.

Before this sci-fi story, I was working on a fan-fiction fantasy quadrilogy. That whole work already has over 240 pages of removed text (from all four books combined), simply because I kept varying stuff as I went along. However, that is a story that originally came into being via "pantsing"; I only made the outline later, and now have to fit what is already there with the overarching concept.

The generation-ship story writes itself much more fluently, because here I actually started with the theme and the outline - and the outline keeps evolving as I write, so it is still not set in stone.
As Scrivener tells me, though, I am already at 186,354 words right now, and the book is nowhere near finished yet. (I only started writing the book in the middle of September last year, and no, I did not do NaNoWriMo.)
In short: Getting the word count up does not seem to be my primary problem. If anything, I seem to be a massive overwriter.

I just checked how long some of the more extensive popular books in sci-fi and fantasy are. Brandon Sandersson's "The Way of Kings" clocks in at 383k words. The longest Harry-Potter novel is No. 5 with around 250k; one of the longest books I have personally ever read is Terry Goodkind's "Stone of Tears" at 393k. Robert Jordan topped even that with some of his books (396k).

This is not me trying to get up to that many words, btw; this is me trying to stay below that word count. :)
I aim to keep my individual chapters below 5,000 words. But sometimes you just need more. Robert Jordan often has chapters 2-3 times this length.I would like the story to be shorter in the end, but I would rather have it be long than too rushed:

- On the plot level, I need to depict a very gradual slide towards tyranny first, before the rebellion / mutiny at the end even has a plausible reason to begin. Each centimetre further down the slippery slope needs to seem entirely reasonable to the people making those decisions at that point in time.

Spoiler

This is different from a fantasy story, where the inciting incident is usually clearly identifiable as "the moment when the protagonist's home gets destroyed and they have to venture out into the world". Such a moment does not exist here: The crew is on the ship the entire time. Some might say the inciting incident is already in the first chapter; others might say it only comes several chapters later, when the commander doubles the number of children each couple is allowed to have (which then later becomes the number of children each couple must have).

- On the theme and character-development level, where the conflict is between the values of survival, well-being, and freedom, I need to lead the reader to some very unintuitive conclusions (or, if they disagree, I should at least make them understand why my characters are coming to these conclusions), and therefore have to make sure they can follow along with the logic step-by-step.

 

[DaveC426913]

Thanks for stressing this again and adding a graphical depiction of it! I just checked out that one scene from The Expanse again (pouring water into a glass diagonally) to get an idea. Some people in the comments said the angle were exaggerated, but understanding the idea counts.

In my story, I have a couple of shower scenes that are relevant for the relationship between the leading couple. So I guess the water would fall diagonally in that shower, too? (The showers are part of every quarter and therefore on the habitat ring, of course.)
coming to these conclusions), and therefore have to make sure they can follow along with the logic step-by-step.

The problem is, it's very circumstance dependent.
It depends on constants such as radius of the ship and the speed of rotation, but also on variables, such as what direction the target object is moving and what way the observer is facing.

Throwing a baseball spinward will cause it to fall way short.
Throwing a baseball antispinward will cause it to fall long.
Dropping a baseball vertically from your hand will show very little deflection.
A longer vertical drop will show more deflection than a shorter drop.

I've seen this last one used to neutralize (i.e. kill) a lethal enemy* who was not familiar with the subtleties artificial gravity.

*(Kzin Warrior. Kzin have generated artificial gravity and know nothing of Coriolis)What I'd suggest is to make a reference sheet with some samples for your specific constants that span the range of the variables. Maybe someone here can help with that.

 

[Melbourne Guy]

But given that I try to write my story more in the tradition of 90s Star Trek, I would like to put the "science" back in "science fiction".

But there is no science in Star Trek! It's all ad hocium, added after the fact to (somewhat) substantiate the plot. And you should include science and especially speculative science, that's half the fun of writing the stuff, but it is the degree of detail I am questioning.

I used a spinning cylinder to simulate gravity in one novel, even had a shower scene, but the protagonist didn't bother commenting on how the water fell on an angle. Who cares about that when he's just come home battered and bruised and doubting himself after a pivotal fight scene? I did use the slow motion sloshing earlier when the protagonist was trying to figure out where he had awoken, but it's a few words then a reaction, I never bothered calculating how the water sloshed so I could describe the motion exactly correct.

If I could find it, I'd send you the title of a horribly written novel where the author basically added characters to a technical manual about orbital mechanics as a huge asteroid plummets toward Earth. It was execrable, so much tedious detail that just got in the way of the emotional tone and left the characters floundering as they described delta v and specific impulses. Meanwhile, in the story, the world was ending, and as a reader, I wished for it to happen faster because the author made it all so interminable!

In short: Getting the word count up does not seem to be my primary problem. If anything, I seem to be a massive overwriter.

I go for 110,000-ish words in my novels, that's usually around 350 - 400 pages of a 6*9" paperback (the variation depends on chapter length). So, break it into separate books...or expect an editor to come in lopping because unless you're nailing the emotional tone, they're going to eviscerate those 186,000++ words

And irrespective of all my thoughts, given you've written novels before and presumably gotten the brutal feedback of reader reviews, you know what you should be doing, so carry on...

As an aside:

I've seen this last one used to neutralize (i.e. kill) a lethal enemy* who was not familiar with the subtleties artificial gravity.

I vaguely recall a scene in Ringworld where someone with an AG pack falls to their death because the material of the ring did not provide sufficient 'anti' for the device to work. That was a pretty neat surprise!

 

[Strato Incendus]

What I'd suggest is to make a reference sheet with some samples for your specific constants that span the range of the variables. Maybe someone here can help with that.

Happy to! :) Glad I can contribute something to the calculating work, even as a layman:

Using SpinCalc as a reference, since it was suggested here:

Spoiler

Ring Radius: 250 m
Inner Ring Diameter: 500 m
Outer Ring Diameter: 526 m
Inner Ring Circumference: 1,570 m
Outer Ring Circumference: 1,652 m
Inner Ring Thickness: 32 m
Outer Ring Thickness: 64 m
Angular Velocity: 1.9380115679324463 rotations per minute
Tangential Velocity: 50.737024203238406 meters per second
Centripetal Aceleration: 1.05 g

The radius of the pipe is 50 m (diameter 100 m), as we have established earlier in this thread.

Don't worry, the "most technical" details like angular velocity and tangential velocity probably won't end up in the book. ;) Rather, I need to show how physics on board behave as a result of these variables. But in order to be able to do that, I first need to have an idea myself of what these effects would look like in practice.

Throwing a baseball spinward will cause it to fall way short.
Throwing a baseball antispinward will cause it to fall long.
Dropping a baseball vertically from your hand will show very little deflection.
A longer vertical drop will show more deflection than a shorter drop.

I've seen this last one used to neutralize (i.e. kill) a lethal enemy* who was not familiar with the subtleties artificial gravity.

Another great point I had not thought of!

Given that I have already introduced the terms "pipeward" and "ringward" to replace "up" and "down" in many contexts, "spinward" and "antispinward" could easily be added, too, especially if they make such a difference.

Will readers care about that? Well, obviously not if it is just an info dump the author uses to show "hey, look, I've done my research!" But if it becomes plot-relevant, and more specifically, the characters actually use this to factor into their plans, it should both make the story look more plausible and make the characters come off as smart, without having to give them any special abilities, just their human intelligence and combination skills to use their natural environment to their advantage.

Baseballs most likely will not be thrown on the ring, the ceiling is too low in most places. However, basketballs will be (the ceiling is also too low for official Earth-based basketball rules, but at least it is not physically impossible to play on the gym ring).

What happens when somebody drops something vertically while standing on one of the rings, that will be the most common occurrence.
Security officers might shoot their guns on the rings occasionally. Now it depends on whether they use projectile weapons, or these anti-organic guns that give of energy blasts. I assume centrifugal force affects both differently?

In terms of longer vertical drops that are potentially lethal:
Indeed I am planning one scene where the characters take the lift to the pipe in an attempt to get to the bridge. The antagonist stops the lift, so they open the ceiling lid and try to climb up the rest. One person slips and falls back down, only to be saved last second by the elevator coming to meet them (with the ceiling lid still open), since the artificial intelligence on board is tasked to preserve human life at all costs. Then the lift tries to take them back down to the ring again, which means the characters have to break it, attempt to climb up the rest of the distance again (which should be shorter now than initially), and this time they all make it up to the pipe safely.

The deflection is one factor that plays into this scene, but of course, there is also the fact that gravity itself increases as the character falls down the lift shaft. It should thus not be the same as falling down a 200-metre shaft on Earth: Initially, closer to the top, the drop shut be slower. This should allow the character to survive a higher drop, i.e., fall a longer distance before the lift comes up to save them. (Obviously, they do not fall the entire 200 metres, I am pretty sure that would still be lethal.)

But there is no science in Star Trek! It's all ad hocium, added after the fact to (somewhat) substantiate the plot. And you should include science and especially speculative science, that's half the fun of writing the stuff, but it is the degree of detail I am questioning.

Two points about this:
1) Of course we know (today) that a lot of things in Star Trek are in opposition to science. But the question is: How much of it was anti-science at the time of the series' creation (TOS and TNG are two decades apart, after all)? Did the authors themselves already ignore or minimise the then-current state of the science deliberately? Or have we just found out more in the meantime, so that we now look back at Star Trek with much more disbelief than we would have done back when it first came out?

2) It is a commonly repeated advice that the author should know much more about their world than actually shows up on the page. Not just when it comes to physics (or in fantasy: rules of a magic system etc.), but also about character motivations. What I describe on the page are then often just the effects of those factors at play in the background: I will usually not spell out a character's motivation directly - but I will know it in "explicit / declarative terms", and the reader then has to infer it from the character's behaviour using their implicit / non-declarative memory. (That's one of the psychological aspects behind "show, don't tell".)

Just as in the example above with the lift: I am not going to list physical parameters in that action scene - all you are going to read about in it is the panic of the other characters for their friend falling down the shaft. But they will see this person fall down the shaft, so I need to describe the trajectory of the fall accurately if it differs from what Earthen readers would expect: Is the person slowly moving towards the wall of the shaft, or falling down right in the middle?

Which reminds me I haven't commented on this here yet:

or instance, I assume the spokes does not have to be 32 meter deep

Indeed, the spokes are much thinner. I only want the lift shaft in the middle of the corridor on the ring, halfway through each section as depicted in the graphic I uploaded. Good to know that this actually makes a difference for the physics! :)

And irrespective of all my thoughts, given you've written novels before and presumably gotten the brutal feedback of reader reviews, you know what you should be doing, so carry on...

I actually have not. ;) Well, not something that could be published at least, because it was fan fiction, as I said previously. Of course I spent countless hours writing the text, in addition to outlining the plot and developing characters. But one reason I suspended working on that fantasy story is precisely so I could finally get to work on something entirely of my own.

I still love the characters from that fantasy story, too (and "fan fiction" is a loose term, since they are really unknown characters from Dungeons and Dragons who have barely received any "official" attention in book form). But knowing you are not going to be able to publish something before you have swapped out all the names (thereby losing the connection to the original source of inspiration) can be an impediment to motivation. With my sci-fi story, I have no such copyright-based motivation problems - and therefore, no excuses either.

I go for 110,000-ish words in my novels, that's usually around 350 - 400 pages of a 6*9" paperback (the variation depends on chapter length). So, break it into separate books...or expect an editor to come in lopping because unless you're nailing the emotional tone, they're going to eviscerate those 186,000++ words

Yes, I am aware that publishers will be much less patient with debut novels in terms of sheer length alone: Even the first Harry Potter (which was rejected countless times) only has around 70,000 words, less than a third of what the fifth one amounted to.

But as your statement about the emotional tone implies: What matters much more is how you fill that specific word count.
Harry Potter 5 (257k words) dragged for me. But so did Harry Potter 6, which only has 168k. The reason is that both had sections that were extremely repetitive: Countless dream sequences in Harry Potter 5; countless Pensieve sequences in Harry Potter 6 to explain Voldemort's backstory.

Just like that, here we see the opposite side of the coin: Once authors have established themselves as big names, editors will get more and more hesitant about shortening their works - in this case not in terms of sheer word count, but by asking "do we really need that many scenes of the same type?" - than they would have been with a debut writer. And that is not necessarily for the better.
Some say the Star Wars prequels suffered for a similar reason, because George Lucas directed them himself, and nobody dared to object to the ideas of the "mastermind himself" - forgetting that he hadn't actually been the director of the original trilogy, only the writer.

The whole physics side of sci-fi does not come to me naturally - I have always been more into languages than into numbers. Yet, perhaps precisely because I consider myself lacking in that department, I want to put in more effort to do it properly.

The main things that "fill" the pages are character motivations, conflicts, and their emotional turmoil. However, not just for the main couple, but also for 1-2 side characters. Star Trek had the option of focusing on individual side characters per episode. Doing this in a single book will naturally make it longer. If I don't have small subplots for 1-2 side characters, though, then it would feel as if the Enterprise D had only had Picard and Riker as fully fleshed-out characters, and the rest being little more than (no longer literal) redshirts.

I have just read some of the self-published works by certain "Author Tubers", i.e., authors on YouTube.

Spoiler

Abbie Emmons's "100 Days of Sunlight" is below 100,000 words, but it was essentially a romance, so it only really needed to flesh out the two leads (and the actual protagonist was still much less developed than the love interest). I read hers first because her videos about thematic storytelling were what got my current story started in the first place.
She did a good job with what she worked with, but of course, the story is on a much smaller scale than what I have in mind. It's always good to do "easier" things well than to do hard things badly, of course. But just as it would have been wrong for her to artificially make her story more complex, it would feel wrong for me to simplify my current story, or force myself to write something else just to "get a short book out of the way".

Jenna Moreci's "The Savior's Champion" is 140,500 words, and many already seem to consider that too long. Then at the same time, others complain about it being rushed - since it follows this new trend that the inciting incident happens almost in the first chapter. (Moreci likes to use the analogy "don't start with their school day, start in the last lecture at the end of their school day"). As a result, I didn't really have any reason to care about the protagonist's family, even though its essential to his motivation.
Second, despite this word count, the only characters who are halfway fleshed-out are again the two leads. The entire rest of the 20 competitors are flat as cardboard cutouts. Sure, there is a fast-paced "plot", but that plot has the depth of a mediocre videogame: Just have one challenge follow the next, with brief periods of rest in the "sanctuaries" in between.

If those two books have lead characters I still consider "too flat", despite both authors clearly having put a lot of thought into at least their protagonists and romantic interests, then chances are that, in order to get to the character depth I would personally enjoy, I'll simply need more space. Especially since these are new characters.
With a character people have seen before, you can have the reader rely on previous knowledge, assumptions, and inferences much more. Not so with new characters, especially not if they live in an environment so different from our own, having spent their entire life on a spaceship.
Just establishing the baseline of their reality, the "ordinary world" of the hero's journey, takes some time: How do they feed the crew? Why are they not using incubators, but still resort to natural birth? Why did they leave Earth in the first place.

I see a strong disconnect between all the louder calls for character depth and complexity in recent years (complaints that go all the way up to big Hollywood productions, like the Disney Star Wars movies) and the reduced attention span of modern readers, who would like to have the inciting incident on the first page, yet if that happens, they have no reason to care about any of the characters, or about what they do and what's happening to them.

If the character depth I am shooting for requires more words, then it would be a disservice to the characters to shorten the story below a certain point. The main thing I am going to end up cutting will probably be info dumps. Some of those paragraphs are stuff I just write into the first draft for myself, to understand and remember how my own physics work. And then I can still remove that later and summarise the same thing happening in fewer sentences.

Luckily, with self-publishing becoming more and more popular, much like in music, we are no longer as dependent on the opinions of traditional publishers. That of course does not mean one can simply ignore those guidelines and think one knew it all much better. But the question of whether something has been published traditionally or self-published is no longer a clear indicator of its quality to me:

Despite the flaws e.g. "The Savior's Champion" has, I've still found it much more entertaining than many of Terry Goodkind's later works, all of which have been traditionally published, simply because he had established a loyal fanbase at that point.
I do want to get more into Sandersson's works, if only as an example of "how to write a lot of words and still make it popular", but even he won't get a free pass from me as a reader. Some of the reading samples on Amazon felt very info-dumpy to me, and did so in the first chapter.

In contrast, if you can hook the reader early, then they will be much more accepting of more world-building information later. I remember countless scenes in Harry Potter where the plot felt like it was coming to a halt, just to show Harry going to classes and bantering with his friends. It was almost like in a crime story, where you know the true perpetrator won't be found until the end; in HP, you know the final confrontation happens close to the end of each school year, so before that, you have more time with the characters as if you were one of their friends. Without that, we wouldn't have any reason to care about them when they get to the final confrontation.

 

[DaveC426913]

Don't worry, the "most technical" details like angular velocity and tangential velocity probably won't end up in the book. ;) Rather, I need to show how physics on board behave as a result of these variables. But in order to be able to do that, I first need to have an idea myself of what these effects would look like in practice.

Will readers care about that? Well, obviously not if it is just an info dump the author uses to show "hey, look, I've done my research!" But if it becomes plot-relevant, and more specifically, the characters actually use this to factor into their plans, it should both make the story look more plausible and make the characters come off as smart, without having to give them any special abilities, just their human intelligence and combination skills to use their natural environment to their advantage.

Sounds like you've got a handle on good writing techniques.

The deflection is one factor that plays into this scene, but of course, there is also the fact that gravity itself increases as the character falls down the lift shaft. It should thus not be the same as falling down a 200-metre shaft on Earth: Initially, closer to the top, the drop shut be slower.

Be careful here. This is an excellent example of a scenario where you don't want to confuse AG with real gravity.

There is no way a freefalling character will fall down an elevator shaft for any significant distance unless the shaft is impractically wide.

Remember, the character is not really being pulled downward; they are being pulled spinward tangentially - and the ship is rising in front of them to intersect them.

Without the constraint of an elevator shaft, their freefall path would look more like this:

And - for a freefalling character - gravity doesn't really "get stronger" the farther they fall. They effectively stay moving (slowly) with the momentum they started with, but the surfaces they encounter will have increasingly (horizontal) relative velocities the farther outward they go.

If they fall far enough to hit the floor, they will actually impact gently - but the flor will be moving spinward quite fast and they will skid up-to-speed. (see diagram 2, above)

The real danger is having a wall hit them.

 

[Filip Larsen]

Be careful here. This is an excellent example of a scenario where you don't want to confuse AG with real gravity.

Indeed. For the benefit of the OP, let me add a disclaimer to my earlier comments about "gravity level" that when talking about that gravity is such and such at this and that distance from the rotation center this almost surely always implies we are talking about something that is stationary or very nearly so relative to the rotating station. In the limit where this is true (i.e. for small speeds relative to the tangential speed at the given radius) a free-fall motion relative to the station will appear to match "normal" gravity. If you make a small jump on the 1G ring of large station the path relative to the floor will look like a parabola well-known from "flat gravity". If something drops from the ceiling it will to a good approximation accelerate towards the floor at around 1G. But if you let something drop for long it will gradually "blend" into this "curved" path Dave so nicely has illustrated.

Minimizing this and other similar "strange" effects caused by the rotation while keeping the overall engineering feasible are usually a key design trade-off in many real-world designs. For instance, I would be surprised if a design for a station with a full 1G for all crew would ever be implemented since its simply too impractical unless it later proves to be absolutely critical for some (yet unknown) medical reason. It seems much more likely to have a lower G-level (i.e. use slower rotation for a given station size) and then use a local "tower" or cabin section that can extend beyond the radius of the main level if special 1G training or similar is needed.

 

[DaveC426913]

For instance, I would be surprised if a design for a station with a full 1G for all crew would ever be implemented since its simply too impractical unless it later proves to be absolutely critical for some (yet unknown) medical reason.

It would likely be implemented for next generation space tourism hotels.

The 1st generation would be for those willing to "rough it", and those tourists would have to jump through health and medical hoops and then sign waivers for injury.

But the next generation would be built for all kinds of tourists, including children and seniors - as well as longer stays. That would require full gravity and negligible Coriolis effect. Too much risk of injury and too much risk of bone density loss.

 

[DaveC426913]

"Harry Potter 5 (257k words) dragged for me. "

I am not one for long novels, but I just started on with 194,000 words, knowing it has a sequel of 308,000 words. (Any Edward Rutherford book.)

 

[Melbourne Guy]

1) Of course we know (today) that a lot of things in Star Trek are in opposition to science. But the question is: How much of it was anti-science at the time of the series' creation (TOS and TNG are two decades apart, after all)? Did the authors themselves already ignore or minimise the then-current state of the science deliberately? Or have we just found out more in the meantime, so that we now look back at Star Trek with much more disbelief than we would have done back when it first came out?

We're off topic, but let's not romanticize Star Trek from the distance of decades. Gene Roddenberry was a script writer, not a sci-fi writer, and downplayed the sci-fi aspect to get the series sold. A lot of his work prior to Star Trek included police / detective shows and this thematic is clearly carried into Star Trek.

There were a some sci-fi writers who wrote a few Star Trek scripts - Robert Bloch (though sci-fi was not his primary genre) and Theodore Sturgeon, for instance - and D. C. Fontana wrote many sci-fi scripts after she worked on Star Trek, but whatever 'science' was in Star Trek was incidental to telling the story of boldly going where no man had gone before.

 

[DaveC426913]

Ring Radius: 250 m
Inner Ring Diameter: 500 m
Outer Ring Diameter: 526 m
Inner Ring Circumference: 1,570 m
Outer Ring Circumference: 1,652 m
Inner Ring Thickness: 32 m
Outer Ring Thickness: 64 m
Angular Velocity: 1.94 rotations per minute
Tangential Velocity: 50.74 meters per second
Centripetal Acceleration: 1.05 g

The radius of the pipe is 50 m (diameter 100 m), as we have established earlier in this thread.

Trying to figure out how many scenarios you'd need to cover all the bases.

I think you'd want fifteen trajectories modeled from the rotating FoR, thus:

For each of three radii:
1] outer ring floor,
2] pipe floor and
3] halfway between
you want
A] High speed spinward
B] Low speed spinward
C] At rest wrt floor
D] Low speed antispinward
E] High speed antispinward

Maybe someone who knows the math better can fill in the numbers.

But, if you are so inclined, it could be done diagrammatically the way I did on post 44.

 

[DaveC426913]

Oh. If you have projectile weapons of any sort, you should probably figure out their deflection as well. Yes, slugs are fast - meaning Coriolis will have a very small chance to act on them - but a matter of inches could mean life or death.

Raising the question: how many crew have sufficient training in AG marksmanship? That could be a big advantage.

I can see a cool scenario where security teams are trained in AG marksmanship but rebels are not.

Spoiler: A skirmish in AG

So, in the first skirmish, rebels take a heavy loss because they are shooting spinward. They didn't account for Coriolis Force and their slugs fall short, hitting the deck in front of security.

Then, in the next skirmish, the rebels think they've figured it out and compensate by shooting slightly high. Except the security forces know that -HAHAH! - in this encounter, the positions are reversed the rebels are now shooting antispinward. Security ducks and the rebels' slugs go right over their heads! The rebels take heavy losses again.

The rebels can be as smart and adaptable as they want, but if they're not trained and experienced, they may still lose to a much smaller force.

Remember the lesson of Khan in the Mutara Nebula:

That's how I was taught to write science fiction. Science fiction is not just OK Corral in space; science fiction has science as an integral vehicle of the story.

 

[Strato Incendus]

Thanks again for all of your answers! :)

@Melbourne Guy : ...in your case for the more detailed behind-the-scenes info on who wrote what for Star Trek! ;)

I can see a cool scenario where security teams are trained in AG marksmanship but rebels are not.

Referring to your spoiler: That is awesome! I really want to make this plot-relevant now. Indeed, the security officers are supposed to be more experienced, and though quite a few of the rebels have or obtain weapons (including some of the security officers joining their cause), so far I was lacking a way to show this difference in expertise.

The protagonist was taught how to shoot by her father, by she never had to use it, and did not really want to, either. Perhaps her training only consisted of shooting across the width of the ring in a practice room, rather than up or down the ring.
Although it would not really make sense to set up the practice shooting rooms this way if this is so relevant for the actual training of real security officers.

"Losses" are relative in this regard; both sides have an incentive not to deliver lethal shots, since they all know they might be the last survivors of humanity. (Contact to Earth and the other inhabited worlds of the Sol system has been interrupted at this point - so far, I blame that on a solar storm, but given that this would only hit Earth, for example, while leaving the rest of the planets in the same system unharmed, I might need a better justification within the story.) "Losing" in these battles means "being stunned and captured by the commander's forces, which might lead to the captives becoming unwilling participants in the continuation of the human species".Talking about spinward and antispinward in general, I have a few more quick questions regarding sports on the ship. Especially since @Filip Larsen said it might actually be more plausible if some parts of the ship do not have full 1G (or 1.05 G even, in my case, so that the crew adapt to the gravity of Teegarden b). So far, there is only 1.05 G (on the rings) or 0.21 G (in the central pipe). Of course I am aware that it gradually shifts from the outside of the ring to the first deck of the ring, all the way up the elevator shaft on the spokes. But if there are sections that have something in between 1.05 G and 0.21 G, a lot more people would be affected by the need for a daily 2-2.5 hours exercise routine.
So far, someone spending all day on one of the rings could theoretically get by with just as much exercise as one would recommend on Earth, while someone working all day in the central pipe would have to do the 2-2.5 hours that ISS inhabitants do per day.

Here come the sports questions:
1) My initial mental image for the sports scene during the third chapter (to show how it is mandatory / necessary for survival on board) included swimming. So the first big question is: Would it be possible for the ship to have a swimming pool somewhere on the rings? Size-wise, this would not be a problem: Competitive swimming pools are 50 metres long, 25 metres wide (remember the inner corridor width on the rings is 32 m). But how would the water behave? The ring circumference, depending on the deck the pool would be placed on, is always around 1.6 kilometres.

2) The current sports scene has the characters run two laps around the ring instead, which amounts to about 3.2 kilometres. This is just for warming up, so it takes most of them 12-14 minutes to complete. Except for one particularly unsportive character, who would need twice the time (I actually have some of the other characters lap him close to the end of his first round). The rest of the 90 minutes (slightly less than on the ISS, since most characters do spend quite some time on the rings with normal gravity each day) is spent on bodyweight exercises. The question here is: Would they run spinward, or anti-spinward? Would this make a difference, and if so, what would it look like?

3) While they are running around the ring, I describe what the rest of the gym floor looks like, including fields for various kinds of ball sports - basketball, among others. I imagined the field to be perpendicular to the ring circumference, i.e. across the 32 metres of the corridor width. I can already tell this way wise, since otherwise, the rules (of physics) would not be the same for the team playing spinward vs. the team playing antispinward. But now it might make a tactical difference whether you attack on the left vs. the right side of the field - and of course, simply during ever pass that occurs in the game. An actual basketball game is not described in the first book, but there will be one at the beginning of book 2.

4) At one point later in book one, the main character runs away from someone else on the lab ring - so she has to choose a direction: spinward or antispinward. What difference does this make (now talking about sprinting rather than long-distance running, i.e. potentially higher speeds)?
If she ran anti-spinward and vaulted forward (=jumped) at one point, would she partly fall back into the direction she came from?
If she ran spinward and jumped, would she smash into the floor coming up to meet her?

 

[DaveC426913]

If she ran anti-spinward and vaulted forward (=jumped) at one point, would she partly fall back into the direction she came from?

Definitely would not fall back, no. She'd float higher and longer than normal. If she gets enoguh speed, she could conceivably go quite high and long (unless the ceiling is too low.

The thing is that can be a curse as well as a blessing.

While you're floating you have no traction, and cannot speed up.
You need traction to get up to full speed.
It would be tricky the find the right balance of straying on the deck long enough to get speed but not waiting so long that you don't weigh enough to get that traction.

If she ran spinward and jumped, would she smash into the floor coming up to meet her?

She wouldn't smash into the floor but it would come come faster than expected, she is danger of tripping unless she knows what she's doing. But, if she doesn't trip, she would get excellent traction for sprinting.

 

[Filip Larsen]

Would it be possible for the ship to have a swimming pool somewhere on the rings?

That should be feasible. A little care has to be taken in the design regarding the mass it represents, but nothing that is not also the case with areas of heavy machinery and such.

Overall, a good design for the mass distributions on the rings will probably try to ensure that mass in general is distributed fairly evenly so each ring has a center of mass is very near the geometric center allowing for a pure rotation without too much torques between transferred between the rings. Exactly what what type of dynamics one would see if for example one of the rings becomes very unbalanced is not really clear to me, but I would be surprised if such unbalance would not in some way result in troublesome loading of the structure at some point. Luckily, if the center of mass from the ring structure is designed to be near the geometric center from start it is fairly easy to include some water tanks (which is needed anyway) at difference sections and pump water around to fine-tune that center of mass.

Would they run spinward, or anti-spinward? Would this make a difference, and if so, what would it look like?

If they run spinward they would feel a little bit heavier, and if they run anti-spinward they would feel a little bit lighter. This was covered in another thread with some detail: https://www.physicsforums.com/threads/walking-around-the-ring-on-a-spinning-space-station.1008798/

So if running on a <1G ring level to train muscle mass it will probably make sense to run spinward to get that extra load. On the other hand if you run for "fun", then running anti-spinward may be more entertaining in some sense.

There is an effect here that may play into a low-G competition scenario. If you need to accelerate hard (including changing direction fast) on the flat ground you need good friction between the floor and your shoes, so, with everything else being equal, being heavier allows you to accelerate faster for situations where this friction dictates your acceleration limit. I assume normal athletes in 1G do not usually hit this limit, but if you have muscles for 1G and then try to accelerate at lower and lower G's then at some point you will likely experience that you start to slip. Around that G-level there will probably be noticeable difference on how to change running direction depending on if you are running spinward or anti-spinward to begin with. Coupled with the Coriolis forces this could make for some pretty interesting patterns of movement the athletes would have to adapt to.

If she ran anti-spinward and vaulted forward (=jumped) at one point, would she partly fall back into the direction she came from?

For a ring that rotates with a tangential speed much larger than anyone's running speed you can with good approximation understand it from the rotating system simply as running in a normal gravity with but with gravity that slightly depends on your speed and direction. Running spinward (anti-spinward) will increase (decrease) the effective gravity and the faster you run the more this "effective" gravity will vary from standing still. So if she runs anti-spinward and jumps, she would be able jump a bit higher and further than if she did the same jump in spinward direction.

 

[Filip Larsen]

if the center of mass from the ring structure is designed to be near the geometric center from start it is fairly easy to include some water tanks (which is needed anyway) at difference sections and pump water around to fine-tune that center of mass.

Let me add that in addition to adjusting the position of the center of mass such "balancing tanks" or trim tanks would, if also placed at different depths, allow for adjusting the direction of the principal momentum axis of each ring, which then allow for minimizing the dynamic loads at various points in the ring structure, which again allow designing for an overall lighter structure without having it flexing too much during normal use. Constructing an extended rotating structure that rigidly can absorb some degree of mass imbalances without flexing (i.e. without giving the crew the feeling they are on a rolling ship at sea) is not a trivial task.

The above is mostly hand-waving for saying there is a design tradeoff between comfort of the crew and the bulkiness of the ring, and a mechanism such at trim tanks can be one way to ease up on this trade off. Depending on the exact geometry and placement the pools you mention could also be part of such a trim system, perhaps only used in extreme situations.

 

[Strato Incendus]

Alright, let's get back to this thread again. I want to revisit a question that was brought up earlier, namely the duration of the journey:

To recap the parameters so far:
Target destination: Teegarden b (12.5 light years from Earth)
Travel speed: 10% light speed
Travel time: 125 years

Somebody pointed out that this of course does not sound like constant acceleration, but like a short burst of acceleration at the beginning, and a similarly sudden stop at the end.

If the ship were to use constant acceleration, though, how long would it take to get it up to 10% light speed?

I wouldn't actually mind if the journey took a little longer than 125 years, since that way I could comfortably get five generations to live on the ship before the plot starts (the main characters are all members of Generation Five, where Generation One is the first one born on the ship, meaning the original crew was Generation Zero).

I won't change the starting time of the story to a later date (that will remain on 1st January 2475, with 25 years left to go until arrival). But I could set the ship's departure from Earth to an earlier time than exactly 100 years earlier. Right now, the ship is set to have left on 1st January 2375. (Granted, currently there's a minor Star Trek reference hinging on this fact, since this is the year in which the story of Deep Space 9 ends. But there would be ways to reference that elsewhere, I'm sure.)

 

[jedishrfu]

You can use a classical computation:

##v = a * t## with ##v = 0.1 * c## and you get to pick "a" to find the time in seconds "t". I would choose a = g so that the passengers experience Earth like gravity.

##a = g = 9.8 m/s^2##
## c = 3.0 * 10^8 m/s ##
## v = 0.1 * c = 3.0 * 10^7 m/s ##
## t = v / a = (3.0 * 10^7) / (9.8) = 3.06 * 10^6 secs = 354 days##

 

[Melbourne Guy]

You can use a classical computation:

Or, you can do what I do and plug it into an online calculator!

I find https://math-physics-calc.com/acceleration-speed-distance-calculator is useful, as it includes a number of acceleration, distance, and speed options, which helps when you're musing over questions like the duration of the journey.

 

[jedishrfu]

You forget that I am a robot with no need for such online tools. ( psst I used the Google calculator)

 

[DaveC426913]

## t = v / a = (3.0 * 10^7) / (9.8) = 3.06 * 10^6 secs = 354 days##

This is one-way acceleration? So just shy of one year to get up to .1c?This raises a question: how much time is saved via dilation at .1c?** Is there really any motivation for trying to take advantage of relativity if it only shaves 5/1000ths of the trip off?

**answer: .1c = a dilation factor of 1.005 - that's 8 months saved over a 125 123 year coasting journey.

So, it sounds like the only factor driving coasting velocity and trip time is total fuel (divided by 2) (i.e. they can only carry enough for 2 years of burn).

Knowing that in the design phase, is it possible the designers might have made different decisions?

Is it possible this results in a plot manipulation so obvious as to jeopardize story plausibility?

 

[Filip Larsen]

it sounds like the only factor driving coasting velocity and trip time is total fuel

Usually propulsive mass and energy is indeed the limiting factor for any kind of transport, also in space

And for interstellar travel this is no exception, but here with the added bonus challenge provided by the rocket equation, i.e. the insanely high fuel-to-payload mass ratios required if you want to go there in a timescale that makes human sense. I have yet to hear about a generation ship concept that both is feasible in engineering and sensible for its passengers.

 

[DaveC426913]

Usually propulsive mass and energy is indeed the limiting factor for any kind of transport, also in space

Yes but does it take the same or similar amount of fuel to get there in 200 years as 125 years?

Correct me if I'm wrong but a slower transit would save fuel. So a fuel constraint, if considered in isolation, would drive the duration of the trip up.

This means the upper limit duration of the journey might be determined by a secondary factor, such as only room for 125 years of supplies and resources, or failure lifetime of critical parts.

 

[Filip Larsen]

Correct me if I'm wrong but a slower transit would save fuel.

Yes, that is what is what I meant by fuel in general being the limiting factor on how quickly you can travel anywhere really. To me you just sounded somewhat surprised to discover this holds for interestellar travel, so I didn't want to miss the oppertunity to make a teasing remark about its generality

 

[John Strickland]

I have no idea if this discussion is ongoing or not.
You seem to need to know some more basic physics so that any description of an accident on the ship would make sense. This does not need to affect the characters as much unless it is in the story design. I used 3 colonization ship designs in a non-fiction book published in 2021. Here are some basic rules.

For nearby stars, the majority of an interstellar voyage using fusion power or similar method would be under thrust, with a shorter period of cruise (no thrust). For distant stars, the cruise phase would be the majority of the trip. Most past starship designs seem to use only a small amount of fusion fuel, while in reality the mass of fuel should be 25 to 100 times the dry mass of the ship, such as a 10 million ton ship with a 1 billion ton fusion fuel mass. As you accelerate, (probably at 1-1000 of a G), for year after year, there is little stress on the ship's structure.

The main issue your design seems to be ignoring is protection from cosmic radiation: CGR and "pseudo-radiation "sleet" caused by the ships high speed hitting atoms in interstellar space. If the fuel is in front of the passengers and cargo, it can protect them from the sleet, and the cargo can protect them from the CGR which comes from all directions. Thus the rotating habitat rings need to be INSIDE the ship. You do need pairs of habitat rings which rotate in the opposite direction to prevent ship spin.

A buffer mass of water ice can be in front of the ship to protect it from moderate size impacts, but some impacts will wipe the ship out without a laser system to vaporize the particles. Yes the bearings need to be able to be repaired while in use, so they also must be in pairs. A narrow ship is better than a wide one to reduce chances of impacts. Hitting a sand grain at that speed would be catastrophic.

The better the fusion process, the faster the ship can reach cruising speed. We do NOT know how efficient any given fusion engine design will be! There are multiple engine designs and multiple fusion processes which could be used. Good progress is now being made in fusion.

After the cruise phase which could be very short, the ship must decelerate to get rid of the huge speed and kinetic energy. Depending on the ship's mass and thrust, the deceleration phase might take 1/6 as long as the acceleration phase, but the amount of deceleration would be significantly higher, perhaps starting at 1/100 G, as the bulk of the fuel is no longer on board. You do need to get to zero velocity when you reach the target star system or your voyage will never end! You need lots of cargo mass, and volume to grow food.

A reasonable colonization ship would carry 1000 or more passengers, but some of these could be in true hibernation, once we figure out how to do it. You will also probably need equipment to terraform the destination planet, or the equipment to build it.[Moderator's note: promotion removed]

 

[Strato Incendus]

You can use a classical computation:

Okay, so according to this calculation, the acceleration time would just add about a single year to the overall journey, am I right?
In fact, it's already established as of now that the crew spent an entire year on board the ship while it was still in the orbit of Earth, to test how well they could handle that lifestyle.

**answer: .1c = a dilation factor of 1.005 - that's 8 months saved over a 125 123 year coasting journey.

I'm not sure if I understand this correctly: Does this mean the estimated journey would be two years shorter overall? Or 8 months shorter?

I am aware of time dilation, but I kind of blurred the lines on that a little bit. In the inciting-incident scene, the crew receives some messages from the Sol system. The commander says "So let's hear what (person X) had to say to us about 10 years ago... give or take half a year due to time dilation." So it's not actually clarified whether this message is 10-and-a-half or 9-and-a-half years old. ;) Not that it particularly matters to the crew anyway, given that they have no way to physically interact with Earth.

Knowing that in the design phase, is it possible the designers might have made different decisions?

Is it possible this results in a plot manipulation so obvious as to jeopardize story plausibility?

That would of course be a major plothole. Can you elaborate on what you mean by that?

So far, the plans were just "we launch the ship in 2375, the journey takes about 125 years at a constant 10% of light speed, so by 2500, the crew should arrive at Teegarden b".

This means the upper limit duration of the journey might be determined by a secondary factor, such as only room for 125 years of supplies and resources, or failure lifetime of critical parts.

One of the reasons I currently cite in the story for why the ship can't afford to go faster, even if it had more energy resources, is the response speed of the deflector systems to get rid of space debris in the ship's path. Loosely referencing an Isaac-Arthur video here where one of the fictional officers says "We can go as fast as we want, but if we go e.g. twice as fast, we'll encounter larger space debris twice as often / twice as quickly" etc.

In terms of failure lifetime of critical parts, that's indeed another problem I've been thinking about: As far as I am aware, current concepts for nuclear-fusion reactors would only last a few decades, not over a century. So if they went with a 21st-century nuclear-fusion reactor, chances are it would fail after less than half of the journey. They might already be coasting at 10% light speed at that point, but they still need the reactor for electricity, air- and water recycling, and pretty much everything else.

Then again, I've already established that I need some sort of disaster to occur in the reactor (in a separate thread). So far this is connected to a minor collision (also partly involving human failure on part of one weapons officer), but I could just chalk it up to regular wear and tear instead. This would seem more "mundane", but at the same time, perhaps also more realistic for precisely that reason.

 

[DaveC426913]

Okay, so according to this calculation, the acceleration time would just add about a single year to the overall journey, am I right?

One year at each end. You need another year to decel.

I'm not sure if I understand this correctly: Does this mean the estimated journey would be two years shorter overall? Or 8 months shorter?

Sorry. Out of 125 years total, The ship spends a year acceling and another deceling. The intervening 123 years are shortened subjectively by a total of about 8 months - due to the time/length dilation factor of 1.005.

Technically, the accel and decel years are shortened too, but the effect on journey duration is miniscule. I think it's less than 1 day each.By the way, I am using no complex math to figure any of this out. This calculator tells me the dilation factor at .1c is 1.005. Everything else is just simple arithmetic.

The "one year accel" is entirely premised on the excellent @jedishrfu's post #56 that concludes 1g accel will get you to .1c in 354 days.

I am aware of time dilation, but I kind of blurred the lines on that a little bit. In the inciting-incident scene, the crew receives some messages from the Sol system. The commander says "So let's hear what (person X) had to say to us about 10 years ago... give or take half a year due to time dilation." So it's not actually clarified whether this message is 10-and-a-half or 9-and-a-half years old. ;) Not that it particularly matters to the crew anyway, given that they have no way to physically interact with Earth.

If Earth set up a clock that sent a laser pulse New Year's Eve, the pulse would appear to arrive late. Every year that passes, it would be later by 1.825 days. By the half-way mark of the journey (that's after 75 years), the pulses and messages would be about 4 months out-of-date. It would not be until the 112 year of ship-time that messages would be 6 months late.

That would of course be a major plothole. Can you elaborate on what you mean by that?

No need. You plugged it:

One of the reasons I currently cite in the story for why the ship can't afford to go faster, even if it had more energy resources, is the response speed of the deflector systems to get rid of space debris in the ship's path. Loosely referencing an Isaac-Arthur video here where one of the fictional officers says "We can go as fast as we want, but if we go e.g. twice as fast, we'll encounter larger space debris twice as often / twice as quickly" etc.

Thats a perfectly valid reason to limit the top speed.

 

[John Strickland]

Maybe you have a table somewhere in the past posts that give the ship's dry mass. For the ship sizes I am seeing, I assume the ship is over 1 million tons dry. If you want to reach a cruising speed of 0.1 C (30,000 km/sec) in 1 year, that means you must gain over 820 km/sec every day (300,000 meters per second div by 365 days = 821 m/sec. with 9.5 meters per second average at a constant acceleration of about 1/3 G (821,000 meters/sec div by 86,400 seconds per day). This would be an Expanse-sized engine system. Figure out the total continuous energy output requirement for such an engine system - it would be scary. Do you have an anti-matter generator powered by the engine itself, to use the anti-matter up as fast as it is created? That is one method that has been suggested to avoid going boom.

With the same thrust, the time to decelerate would be a fraction of the acceleration mass since all of the acceleration fuel mass, the majority of the mass, is no longer on the ship. Note that for all such interstellar ships under thrust, the turnover point is normally much closer to the target star system.

If you go twice as fast along exactly the same path, you would hit exactly the same number of interstellar particles, but you would hit each one with twice the velocity, which means something like 4 times more damage per hit. I assume there will be extensive trials with large, thin cross section ships to test the number of such particles before humans try such a voyage.

John Strickland

 

[Strato Incendus]

You seem to need to know some more basic physics so that any description of an accident on the ship would make sense. This does not need to affect the characters as much unless it is in the story design. I used 3 colonization ship designs in a non-fiction book published in 2021. Here are some basic rules.

Thanks for your input! Some of these things I have indeed addressed in past posts, others I have not. I will get to them one by one.

For nearby stars, the majority of an interstellar voyage using fusion power or similar method would be under thrust, with a shorter period of cruise (no thrust). For distant stars, the cruise phase would be the majority of the trip. Most past starship designs seem to use only a small amount of fusion fuel, while in reality the mass of fuel should be 25 to 100 times the dry mass of the ship, such as a 10 million ton ship with a 1 billion ton fusion fuel mass. As you accelerate, (probably at 1-1000 of a G), for year after year, there is little stress on the ship's structure.

The target destination has been established: Teegarden b, 12.5 light years away from Earth. Now it depends on what you mean by "nearby" or "distant", since that is relative.

The main issue your design seems to be ignoring is protection from cosmic radiation: CGR and "pseudo-radiation "sleet" caused by the ships high speed hitting atoms in interstellar space. If the fuel is in front of the passengers and cargo, it can protect them from the sleet, and the cargo can protect them from the CGR which comes from all directions.

I was indeed working with Isaac Arthur's suggestion of having the water on board act as the main radiation shield. This is why I widened the rings: Not just to be able to hide the security doors in these 16-metre-thick walls, but also to have the water run through them. As far as the trunk of the ship is concerned, at times I indeed imagined the central pipe surrounded by water, like in a tunnel for visitors at an aquarium. I thought that might look kind of cool. Though it would probably look better from the outside, through a window.

And precisely because of radiation, it has already been established that the ship does not have any windows - only screens pretending to be windows. Meaning, their default mode is to depict whatever the cameras on the outside are showing. But you can switch them to show landscapes, or other things that might make life on the ship resemble life on Earth more closely. For example, in a passenger's quarter, a common use is to get the "window" screen to imitate a sunrise in the morning.

The passengers are also receiving regular anti-radiation treatments in medical form (this is established in the second chapter). But I fully admit even more protection might be in order, especially at the front of the ship.

Thus the rotating habitat rings need to be INSIDE the ship.

That takes us back to the cylinder vs. rings debate that we had at the very beginning. Hiding the rings inside the ship would make it look more sleek from the outside. However, it would also blow up the "central pipe" to the same diameter at the rings themselves (500 m). Or rather, there would be an "inner central pipe" around which the rings rotate, and the outer hull. The main problem with this approach is that it increases the ship mass drastically, because its surface would be much larger with that, too.

You do need pairs of habitat rings which rotate in the opposite direction to prevent ship spin.

This is something we have already discussed above. My suggested solution was to have some of the five rings rotate in one, others in the other direction. And since five is an odd number, the farm ring, which extends further inwards and therefore is greater in mass, could amount to the mass of two rings.

We have also discussed at length the distance between the rings, and ended up bringing them down to 60 metres - which is less than the outer thickness of a ring itself (64 metres). So any two of them could be construed as a pair of rings, the distance between them is equal.

Can we now use this to specify which ring turns into which direction?
Reminder: From front to back, it's public ring, lab ring, habitat ring, factory ring, farm ring

If the farm ring rotates clockwise, would the next two rings (factory and habitat ring) have to turn counter clockwise? Then lab ring clockwise again, public ring counter-clockwise?
Currently, on the page it says that the first and last ring rotate clockwise (public ring and farm ring), while the middle three (lab, habitat, factory) rotate counter-clockwise.

A buffer mass of water ice can be in front of the ship to protect it from moderate size impacts, but some impacts will wipe the ship out without a laser system to vaporize the particles.

Yes, the weapons are being used to vaporise particles, which is aided by the ship's AI. In the first act, one officer in this position (of course there are several, working in rotating shifts) is being set up as a potential source of disaster, since he's a less-than-ideal fit for his job. (Obviously, on a generation ship, you can't select people as thoroughly; you only have those to work with who are born on the ship.)

Normally, the AI is smarter and makes fewer errors than the humans anyway. But if, at the mid-point plot twist, the AI fails for some reason, and it is suddenly up to the human to compensate for that, this guy could be to blame for the disaster occurring.

Yes the bearings need to be able to be repaired while in use, so they also must be in pairs.

Do you mean the bearings for the protective ice mass in front of the ship here? Or the bearings for the lasers?

A narrow ship is better than a wide one to reduce chances of impacts. Hitting a sand grain at that speed would be catastrophic.

The Exodus is longer than wide (860 metres long, 100 metres in diameter for the central pipe). The rings of course have a diameter of 500 metres, but anything that passes in between the outer ring and the central pipe has a reduced chance of hitting the ship. (Of course, the elevator shafts in the spokes of the rings could still be hit.)

If the entire ship, including the rings, is surrounded by the hull, though, this wold make the ship almost as thick as it is long (500 metres), thereby increasing the chances of impact of something, in the off-chance case that some particle goes under the radar of the deflector system.

The better the fusion process, the faster the ship can reach cruising speed. We do NOT know how efficient any given fusion engine design will be! There are multiple engine designs and multiple fusion processes which could be used. Good progress is now being made in fusion.

Given that the ship is launched in 2375, I think we can safely assume that their fusion process will be far more efficient than anything we might be able to develop during the 21st century.

After the cruise phase which could be very short, the ship must decelerate to get rid of the huge speed and kinetic energy. Depending on the ship's mass and thrust, the deceleration phase might take 1/6 as long as the acceleration phase, but the amount of deceleration would be significantly higher, perhaps starting at 1/100 G, as the bulk of the fuel is no longer on board. You do need to get to zero velocity when you reach the target star system or your voyage will never end!

Yes, I am aware they need to slow down that much at the end. I've actually considered using the "ship spin" to their advantage: Making all the rings turn into one direction, causing the ship to flip over, then accelerate in the opposite direction to slow down. =D

You need lots of cargo mass, and volume to grow food.

The surface required to grow food is drastically reduced by a) the use of hydroponics for all the crops and b) in-vitro meat grown in the lab. There are no live animals on board, nor does the ship need to carry a lot of soil to create fields on the farming ring. If I remember the stats I've read correctly, hydroponics could bring down the required soil and water usage for farming by up to 90%, compared to traditional farming.

A reasonable colonization ship would carry 1000 or more passengers, but some of these could be in true hibernation, once we figure out how to do it.

1000 is indeed the average crew size: The ship started with 500 people (250 couples, at least one from each country on Earth), and they had children just a few years into the mission, thereby quickly bringing the population up to 1000. Potentially, there could be up to 1500 people living on the ship if all members of three generations live out their entire lives on it. But, as I mentioned earlier, there is the cultural component of the "exit pill" (like in Star Trek "Half a Life", as well as a similar Vulcan custom).

You will also probably need equipment to terraform the destination planet, or the equipment to build it.

Teegarden b is similar in mass as Earth (slightly heavier), and in the habitable zone of its star. The main issue is that it's most likely tidally locked, so people will have to live in the fertile "twilight zone" between the desert side facing the sun, and the ice side facing space. However, that isn't something terraforming can do a lot about.

Maybe you have a table somewhere in the past posts that give the ship's dry mass.

Since the measurements of the ship aren't finalised yet (the length might be, but right now we're back to discussing the diameter, because of rings vs. cylinder), we haven't tried to estimate the overall mass yet.

Do you have an anti-matter generator powered by the engine itself, to use the anti-matter up as fast as it is created? That is one method that has been suggested to avoid going boom.

So far, I've only established nuclear fusion as a power source. One way to show even to laypeople that this ship is much less ambitious than those in Star Trek: No anti-matter, no warp drives, not even light speed.

If you go twice as fast along exactly the same path, you would hit exactly the same number of interstellar particles, but you would hit each one with twice the velocity, which means something like 4 times more damage per hit. I assume there will be extensive trials with large, thin cross section ships to test the number of such particles before humans try such a voyage.

In the backstory, there has been a Breakthrough Starshot 3 mission sent to Teegarden b - an unmanned probe launched towards it with a giant laser (like in the actual plans for missions to Proxima Centauri right now), at close to the speed of light, to create images of the surface and examine the make-up of the atmosphere.

How these unmanned probes slow down at their destination is still being discussed by the Breakthrough Starshot researchers at the moment, as far as I know. They could just fly by and create some images, then vanish back into the interstellar medium. If they're supposed to drop a landing rover or something similar, slowing down and getting into the orbit of the planet is probably a must, though.

 

[John Strickland]

I am glad to see other people interested in what I refer to as "slowboats", realistic interstellar starships that are not FTL ships as in Star Trek, etc, but rely on the physics we know. I am not a physicist, engineer or mathematician, but merely a generalist who can ask the right questions and track down the answers with algebra and Excel! I can also think like an engineer. There is a good reason for my focus, since I know that a fusion powered vehicle can actually slow down to zero velocity at the target star system unlike most of the other concepts!

As I understand we can only communicate via text in this forum (no images apparently) and we cannot post contact info. I would like to be able to send you some examples of what I have done, and would like to see even crude sketches of what your vehicle looks like if we can get permission to communicate directly. A picture really can be worth many thousands of words!

Even after reading much of the text I find it hard to visualize what your ship looks like. I am imagining a set of tuna can shaped sections with the "rings" or habitat tori inside them, strung along the ships axis like fat beads. I strongly suggest that you create a baseline design, which is not the final design, but would then allow us to discuss the ship with actual numbers, such as dry mass, fuel mass, thrust, mass fraction, etc. Improving the baseline design leads to a final design as you can see how design changes improve it.

If I know these basic physical parameters, I can then cover additional issues which depend on them. Say you have a ship that has a dry mass of 4 million tons and a wet mass of 1 billion tons (fusion fuel). This puts the dry mass ratio into the same general range as chemical rockets. You want a high mass ratio and a low dry mass compared to the fuel mass.

As an example, my 3rd ship design takes over half of its voyage of 80 years to the Centauri system to accelerate, and the fusion engines are very large, so they do not melt from the fusion reaction (photons and particles both). (Fusion thrust is very good due to the high temperature of the exhaust, but the reaction also radiates heat and particles in all directions). Thus the engines are a significant part of the ships dry mass. It is hard for me to visualize a realistic slowboat that can accelerate to 0.1 C in 1 year without the whole ship being a giant engine.

The nice thing about the low acceleration on the ship is that there is little stress on the ship's structure. With a ship that has an initial mass of 1 billion tons, and a final mass at destination of about 4 million tons, the total fusion thrust of 7 huge fusion engines is only about 660,00 metric tons or to satisfy the physics purists, about 6.5 billion Newtons. Of this fuel mass, only about 6 percent is used to decelerate! Thus it is clear that the deceleration will be much stronger than the acceleration and will take much less time.

So with a baseline design, you can then calculate the optimal trip time and cruise period for your vehicle. Based on what I calculated for my designs, you might travel 40 years during acceleration, and 5 years during deceleration, so the cruise phase would be much longer than the acceleration. At 12 years distance with 0.1 C velocity, the trip spent at cruise phase (as a comparison value) would be 120 years, so the whole trip would take longer than that.

Shipshape:

Obviously narrow is better to reduce chances of collision. The chances of something hitting the sides of the ship at that speed are very low, so the best idea is to have all of the ships structure relatively close together behind the ice shield in front. The mass of the ice shield is much more than the side shielding so all of the tori would get a low dose from the “velocity sleet”. You only need the equivalent of 10 meters of water as side and rear shielding, so the tori rings should be relative close together to save mass and to act as shielding mass for each other. A lot of the dry mass of my design is in the form of supplies for use at the destination planet, and this dry mass is also used as shielding.

My ship design is very boring looking, it is just a giant cylinder, but it is very efficient in mass usage. Note that the habitat tori (what I believe are your rings), must be in a vacuum to rotate without drag, so the only drag is the magnetic bearing pairs for each torus hub. My tori are only 200 meters across with 20 meter wide torus tubes (the doughnut part) as there is only a fraction of the crew and passengers awake at any given time. I would put all of the tori inside a thin Whipple shield hull cylinder around all of them to protect from possible side hits (still unlikely due to the speed of the ship vs the speed of any local object).The shield could be 50 meters thick in layers to absorb any hits, with the ability to replace any spalled portions of the shield. The bearings which allow the tori to rotate can still be attached to the central tube which would not rotate. Some structure along the sides of the ship would be needed to support the edges of the ice shield. Note that the ice shield should be slightly wider than the widest diameter component such as the rings to prevent side collisions.

Which direction the rings or torus turn in is not significant, but the mass spinning clockwise must match the mass spinning counterclockwise. It is better to have all tori the same mass. The cargo does NOT need to be inside the tori. A small amount of energy would be used to counter any magnetic friction in the bearings.

Humans would not be able to react in time to vaporize any object fast enough. Let the computer do it. Human pilots could not land a Falcon 9 rocket, it takes a computer.

If you do not assume some fusion process has been developed and set an efficiency value for the engines, you simply cannot calculate the trip time accurately as you do not know the acceleration and thrust available.

Animals would be stored in hibernation or as embryos or DNA data that can be reconstituted back into DNA when there is a place for the animals. If you have artificial gravity, you can have live cats as cat boxes will still work even in low gravity! You would need a better cat litter recycling system.

It is unlikely that we will discover any truly Earth size planets with oxygen atmospheres, so atmospheric terraforming operations will probably be needed.

My anti-matter comment was slightly snide, but the reason I call these ships slowboats is also ironic, in that an FTL ship goes vastly faster (if the speed is measurable at all), then a realistic slowboat. See if you can decide on a realistic fusion reaction to use. I like the Boron-hydrogen reaction as the fuel can be Hydrogen boride liquid, which is not fully cryogenic and is denser than water (less tank mass).

Scout missions can be done without slowing down as the cameras and instruments can take images and measurements and then feed them back to Earth after the flyby just like the Pluto mission. Thus vehicles that cannot slow down are fine for this use.

 

[Strato Incendus]

In fact, we can use images here - just not anything that has been used for promotion already, as far as I understand it?

My ship is rather "boring-looking" from the outside, too: Just a long pencil shape with the five rings wrapping around it. So here is a very crude depiction of it (using the same public domain background as on the previous page of this discussion).

Since I made this image, the rings became wider and the distance between the rings shorter. So we'd probably have to imagine the ring width and the sections between the rings to be almost equal in length (64 metres ring width, 60 metres between-ring distance).

On the previous page of this thread, I have already uploaded a cross-section of one of the rings, with the central pipe in the middle.

This is not to scale yet, since we haven't decided on final measurements so far.
However, as it currently stands, the diameter of the trunk (central pipe) is 100 m, the inner diameter of the rings 500 m (given the height of the five decks etc. discussed previously, the outer diameter of the rings is 526 m).

Regarding the bridge section, I wanted it to remain in a fix position relative to the direction of movement. Hence, I could not place it on one of the rotating rings. So the question is how to ensure something that resembles regular walking on the bridge. In The Expanse, they have the magnetic-boots solution. This might work well for the crew working on the bridge normally. But for the rebels storming it at the end of the mutiny, it seems unlikely that they would all have access to such magnetic boots.

My tori are only 200 meters across with 20 meter wide torus tubes (the doughnut part) as there is only a fraction of the crew and passengers awake at any given time.

You mean a diameter of 200 metres? Or a radius of 200 metres?
For all I know, both seem to small. Meaning, they would have to rotate too fast to create Earth-like gravity, and then you get into troubles with the Coriolis effect.
A radius of 225 metres, or a diameter of 450 metres, for all I know, is the minimum required to have the ring rotate slowly enough while still producing 1 G.

Which direction the rings or torus turn in is not significant, but the mass spinning clockwise must match the mass spinning counterclockwise. It is better to have all tori the same mass.

Okay, so it is not crucial that each ring is directly followed by another ring rotating in the opposite direction, as long as the total mass of rings rotating clockwise vs. anti-clockwise evens out?
In my case, if mass (public ring) + mass (farm ring ) = mass (lab ring) + mass (habitat ring) + mass (factory ring), then everything should be fine.

Ensuring the same mass on all rings is difficult, though, especially when they serve different purposes. The habitat ring will have most of the people on it; the factory ring and lab ring will have fewer people, but a lot more gear etc.

The shield could be 50 meters thick in layers to absorb any hits, with the ability to replace any spalled portions of the shield. The bearings which allow the tori to rotate can still be attached to the central tube which would not rotate. Some structure along the sides of the ship would be needed to support the edges of the ice shield. Note that the ice shield should be slightly wider than the widest diameter component such as the rings to prevent side collisions.

Having an ice shield of over 526 metres in width in front of the ship sounds quite ironic: In the chapter that currently discusses the danger of collisions, some obvious comparisons between the Exodus and the Titanic are being made. So far, it's just that a collision with something much smaller than an iceberg would be enough to destroy the ship completely. But if an iceberg is actually the thing protecting the ship from just that, that would make the analogy even more curious.

Of course, collecting ice would have a different purpose, too: Restocking water supplies on board in case some of it gets lost. At the start of the plot, water consumption on board is quite strictly regulated (mainly when it comes to showers, though).

This is another question I'm not sure about: Isaac Arthur argues the main constraining factor for water recycling on board a spaceship would be energy, and the amount required for water recycling would be negligible, compared to the amount of energy required to accelerate the ship.

In either case: One officer detects a nearby ice cluster and suggests to take the ship on a detour to pick it up. This would allow the crew to loosen the restrictions on water consumption quite a bit - which would make the crew happier and improve the commander's standing with them, too.
However, it would also make the ship heavier, and they'd have to slow down to pick up the ice (the question is: How much and how fast?). The commander rejects the request, stating she won't take the ship on a detour of over half a year, just so that her crew could live a more decadent lifestyle.

The point of the scene is to show that the commander places the success of the mission above the well-being of her crew members.

If the ice could also be used to repair the protective sheet in front of the ship, though, this would give her more of an incentive to go on the detour and pick up the ice reserves, as suggested. It would no longer make sense for her to regard this as a mere "luxury problem". In other words: It would either destroy the scene - or make her seem irresponsible for letting the opportunity slip.

Then again, she could be arguing that the present ice shield works just fine. This hubris would then be analogous to the Titanic leaving the harbour with only half the suggested number of life boats.

Humans would not be able to react in time to vaporize any object fast enough. Let the computer do it. Human pilots could not land a Falcon 9 rocket, it takes a computer.

Yes, that's what I mean by "AI assistance": Normally, the computer does the job. The question is what room there is for human failure to lead to a disaster, then. Perhaps the "inattentive officer" is responsible for keeping an eye on the computer, rather than the deflection of particles itself - and he overlooks an impending malfunction.

The main catastrophe happens at the reactor, though. So I could just have the reactor fail for other reasons, without any collision or partial collision happening (because most likely, such collisions would be strong enough to annihilate the entire ship anyway). This moves over into the parallel thread I created on which disasters to use. The main reason I need the catastrophe to affect the reactor is because the plot requires the ship to lose speed for some reason, extending the journey as a result.

Potentially, the following sequence of events could happen:
- The inattentive officer overlooks the impending malfunction of the deflector system. The system would keep working, but catch fewer objects in time if the ship kept going at 10% light speed.
- To save the crew, the commander orders the ship to slow down - to a quarter of the speed (2.5% light speed), where the deflector can keep up despite performing at lower efficiency now.
- The sudden stop then in turn is what causes damage to the reactor, because of the high amounts of energy needed to slow down this quickly.
- A bunch of damage would occur inside the ship, too. The question is how fast the ship could reasonably slow down from 10% to 2.5% light speed (=i.e. not to 0) with humans still being able to withstand the forces at play here (even if only for a short while).

It is unlikely that we will discover any truly Earth size planets with oxygen atmospheres, so atmospheric terraforming operations will probably be needed.

Yes, I know the chances of the atmospheric composition matching our requirements is low. I've been to Teegarden b in Space Engine, and there it also shows the atmospheric composition, which isn't suitable. However, I don't quite understand yet to what extent the atmospheric composition of exoplanets can be known at this point?

I have a vague layman understanding of how researchers infer the number of planets around a star, their respective masses, and their distance to the star (habitable zone or not). But as long as we don't know anything specific about any given exoplanet's atmosphere, sci-fi authors are still free to simply "postulate" these factors. =D For example, I also postulate that Teegarden b has a magnetosphere - which isn't necessarily a given, either. Especially tidally locked planets seem to be less likely to have magnetospheres, but tidal heating can still create one - taking Ganymede as an example (tidally locked with Jupiter).

Advanced terraforming abilities would open up a bunch of plotholes, since the obvious question is: If the crew has the means to terraform a planet with inadequate atmospheric composition, potentially also one without a magnetic field, if they could basically turn any given piece of rock out there which lies in the habitable zone of its star into a second Earth - why not pick a destination much closer than Teegarden b? They could give Proxima b a shot instead. (In fact, originally the plan was to send the ship there, and it would have traveled much more slowly. But Teegarden's star is a much calmer red dwarf than Proxima Centauri. The frequent eruptions of Proxima Centauri were a knockout argument against it.)

See if you can decide on a realistic fusion reaction to use. I like the Boron-hydrogen reaction as the fuel can be Hydrogen boride liquid, which is not fully cryogenic and is denser than water (less tank mass).

Thanks for this specific suggestion! ;) I'll look further into that specific reaction!

Scout missions can be done without slowing down as the cameras and instruments can take images and measurements and then feed them back to Earth after the flyby just like the Pluto mission. Thus vehicles that cannot slow down are fine for this use.

For images of the surface from space, sure. What about dropping landing rovers to actually explore the surface? If they're launched from a probe zipping by the planet at close to light speed, the direction and velocity of the dropship containing the rover would also be influenced by that, wouldn't it? ;)

I need to plausibly demonstrate in the story that Teegarden b has been sufficiently explored by unmanned missions, so that people on Earth are absolutely certain it will be habitable for humans, before they invest the enormous material effort to actually send a generation ship there.

 

[John Strickland]

This physical design means that all of the habitable space is outside the protection of the ice shield (on the front of the ship) and is also unprotected from the "velocity sleet" radiation by the mass of the fuel. Is the fuel for your ship stored in the central cylinder? What is the mass ratio for your ship. It should be at least 100 ( wet mass over dry mass). I assume that each habitation ring has a torus inside. If so, the Major diameter of your tori is about 500+ feet and the minor diameter is the thickness of each torus tube, Like a huge bicycle tire. I also assume that you have shielding around each torus. This almost doubles the shielding mass needed, making the mass ratio much less. You need a ring shaped ice shield in front of all of the rings and the rings should be close together so that one rings radiation shield mass can partly shield the adjoining ones. The fuel can also be in a ring of tanks between the ice shield and the habitat rings. The ice shield and fuel tanks to NOT need to rotate. This can reduce the core cylinder to a structural cylinder with a non-rotating navigation section also behind the ice shield.

The problem with this design is that the struts that attach the rings to the core are exposed to impacts at 30,000 km/sec. That is why it is much better to have a narrower habitat design with everything behind an ice shield, and preferably behind the fuel tank section. A 500 meter wide habitat ring is over 1500 feet in diameter, This is what you would build in the target system, not for use in an interstellar vehicle. That is more like a "Worldship" concept. Getting to the target star system sooner is more important than a huge habitat.

My first designs were wide like this but I shrank them down to get a huge mass ratio value. The tori for design 3 have a radius of about 100 meters, a Major diameter of 200 meters, and a tube cross section (minor diameter) of 20 meters. The coriolis effect would only be noticed in certain circumstances, such a jumping sports, etc.

Do not worry about microgravity in the ships bridge. The bridge crew would spend most of their time in the rotating sections. It would make the story more realistic and interesting.

The ice shield is made of water ice filled with anti-spall fibers, to prevent loss of larger chunks of ice if it is hit. Ice shields are a standard concept. If a particle ruptures a fuel tank, how do you slow down? The ice shield is there to act as a shield. At these velocities, ice is as good as metal and water is better as a radiation shield than an EQUAL mass of metal. you could make the ice shield in the form of a giant Whipple shield with layers separated by shock struts. Then a strike on the front layer would not wipe out the layers behind it and the shock would be mostly absorbed in the shields own structure. Some of the shielding water stored in other areas can be used to replace lost material from the ice shield.

Yes, the water ice in the shield can also be melted and used as water! You cannot replace any water or gases during the trip so you must have a compartmentalized method of storing backup amounts of all such materials, which can also be used as CGR radiation shielding, You need shielding between the fusion engines and the habitation areas also due to the radiation they would create.

Yes, you CANNOT take on any supplies DURING the voyage, as you would have to slow down to zero velocity to do so, using up your precious deceleration propellant and leaving you stranded in deep interstellar space! Your ship could be designed to shed duplicate sections of materials in case too much propellant was lost in an accident. Such a detour is impossible to do if you want to reach your destination.,

Humans could detect malfunctions but the system would have multiple hardware backups. For the detection system to fail would require "a major malfunction".

An interstellar vessel cannot slow down or stop "suddenly" any more than a train can stop suddenly. It has a huge mass and a huge amount of kinetic energy which has to be reduced gradually, over a period of YEARS. You need to investigate the amount of thrust a given fusion engine can produce, In my design, the fuel tanks are like metal balloons to save mass, and they would be crushed by any high deceleration even if that were possible. The typical acceleration - deceleration ranges for a slowboat are between 1/10,000 G and 1/100 G. So in that one respect a slowboat is actually "slow".

You need life with photosynthesis to have a stable, breathable oxygen atmosphere with enough buffer gas like nitrogen. There are just so many factors that weigh against a living world that there may be less than half a billion such worlds in our entire galaxy. Fortunately there should be enough rocky planets between 0.5 and 1.2 Earth diameters to provide terraformable planets.

A "habitable" planet also assumes a "rock" large enough to have gravity strong enough to hold its atmosphere. The lowest such size is about that of Mars or slightly larger.

I agree that Proxima does not look very favorable right now, but Alpha Centauri A or B could have planets that are not visible to us due to the tilt of their orbital planes, (all random).

A scout mission that has an orbiter and/or lander must obviously slow down to near zero velocity. However, as there is no crew, its payload could be much smaller and the trip faster. Orbiters are far more valuable than landers, but a set of landers should be used to try to get samples of surface materials to make sure there are no high levels of toxic elements. Elemental abundances can vary from star to star. So both orbiter and landers are needed.
A super-AI would be required to make decisions on targeted surface locations and to control radio transmissions back to Earth. The main vehicle could stay in a high orbit so its signal would only rarely be blocked by the planet of interest. By this time, we might even have aware AI's.