What Are Realistic Mid-Journey Disasters in Interstellar Travel?

[Strato Incendus]

Alright, thanks again for your many ideas!

Right now, I’m actually considering going back to the original idea of having some damage be caused by a tiny dust speckle that collides with / pierces the ship. In particular, while the shielding at the front and back of the ship protects it against speckles of this size, during the rotation of the ship (which it needs to perform in order to start braking), it would be more vulnerable to such speckles for a few seconds.

The main question is really:
How tiny does a speckle of dust, hitting the ship at 0.125 c, have to be so that it only pierces some ship walls, without destroying the entire ship due to impact?

The resulting leaks should be so small that air or water can’t even escape the ship particularly fast. This would give the crew some time to react, while still clearly being an urgent problem.

Also, whenever water pipes are pierced by such a tiny speckle, I wonder whether the water jets coming out of those tiny leaks would be able to cut through things, given the pressure on the pipes relative to the extremely narrow diameter of such a leak.

The commander tries to make the rotation movement safe (which the ship performs by rotating around its vertical axis) by firing a broadside of the deflector lasers right before initiating the rotation. This clears the path ahead of the ship for the next 1 million kilometres. 0.125 c equals 37,474 kilometres per second. So the ship has about 26 seconds until it has covered a million kilometres while traveling at this speed.

A million kilometres equals 3.3 light seconds. Assuming the ship’s sensors work at light speed, a speckle of dust a million kilometres in front of the ship would be detected by those sensors with a 6.6-seconds delay.

So if rotating the ship around its axis takes about 20 seconds, this delay could create a temporary blind spot, during which the sensors might fail to detect an incoming speckle of dust. It could then pierce a few of the rings, as well as the aft sphere and a few of the sub-tanks within it, within the short time window during which they are exposed to what’s directly in the line of the ship’s trajectory of motion.

 

[Drakkith]

How tiny does a speckle of dust, hitting the ship at 0.125 c, have to be so that it only pierces some ship walls, without destroying the entire ship due to impact?

Hard to say. That's a velocity of about 40,000 km/s, which is far above what we've been able to study here on Earth for anything outside of particle colliders as far as I know.

The resulting leaks should be so small that air or water can’t even escape the ship particularly fast. This would give the crew some time to react, while still clearly being an urgent problem.

Impactors small enough to not do serious damage to the ship would likely vaporize completely upon impact with the first surface they come across. You might do better to explain things away as a laser malfunction that incompletely vaporizes an incoming rock, resulting in a shotgun-like effect where many smaller impactors hit the ship in different locations. Perhaps the rotation of the ship leaves only one or two lasers capable of hitting the rock, leading to asymmetric heating and incomplete vaporization that blows it apart into many smaller fragments.

Also, whenever water pipes are pierced by such a tiny speckle, I wonder whether the water jets coming out of those tiny leaks would be able to cut through things, given the pressure on the pipes relative to the extremely narrow diameter of such a leak.

Unless they are pressurized to huge pressures then no. Waterjet cutters have pressures of 30,000 PSI or greater for comparison. There's no reason for general-use water pipes to have such pressure.

 

[Strato Incendus]

You might do better to explain things away as a laser malfunction that incompletely vaporizes an incoming rock, resulting in a shotgun-like effect where many smaller impactors hit the ship in different locations. Perhaps the rotation of the ship leaves only one or two lasers capable of hitting the rock, leading to asymmetric heating and incomplete vaporization that blows it apart into many smaller fragments.

Great alternative explanation, thanks! ;) I had indeed thought about incomplete vaporisation, however, I thought whatever debris would be left after that might still be too large (i.e., large enough to destroy the entire ship on impact)?

Unless they are pressurized to huge pressures then no. Waterjet cutters have pressures of 30,000 PSI or greater for comparison. There's no reason for general-use water pipes to have such pressure.

Alright, good to have that out of the way. The reason I'm asking is that two characters could have been killed by such a water jet; I watched a video yesterday where somebody demonstrated with a dummy head what would happen if a waterjet cutter came into contact with the human body.

So now, instead, the question is: What would happen if such a dust particle (or incompletely-vaporised piece of space debris) penetrating the ship hull would come into contact with the human body? Would it be like a bullet from a gun? Or an absolute splatter fest?

 

[DaveC426913]

during the rotation of the ship

I dunno. It seems to me that smacks in incompetence. It was an avoidable disaster and they didnt avoid it.

 

[Strato Incendus]

Thanks for your impression; that's indeed something I'm always worrying about. I want the commander to come off as competent - not just so that she's earned the position, but also, because she's the antagonist. Antagonists need to be competent to be intimidating.

So how would you go about avoiding this while rotating the ship? Clearing the path ahead of the ship through a preemptive deflector broadside before initiating the rotating sequence to me already sounded like doing everything they could.

I will of course have a less tech-savvy officer ask (on behalf of the reader) why they didn't shield the entire ship to the same degree as the front of the fore and aft sphere. But a technician could then dismiss that by reminding them how much extra mass that would have added to the ship. Mass which would not only have reduced the maximum coasting speed it could accelerate to; but also, mass which would have been useless for 99.9% of the journey.

I mean, in another thread, we already talked about how the rings wouldn't need as much radiation shielding, because for the most part, they're protected by the two spheres in front of and behind them. Even though of course, during the rotation sequence, the rings will indeed be exposed to such radiation for a few seconds, during which neither the fore sphere nor the aft sphere is in front of the rings.

 

[jrmichler]

There is a book, Structural Failure by Wierzbicki and Jones, with Chapter 2: Debris-Impact Protection of Space Structures. It discusses the impact of meteoroids at velocities on the order of 20 km/sec. That's far slower than your speeds, but the basic principles should be of interest. It was published in 1989, and is still available: https://www.amazon.com/dp/0471637335/?tag=pfamazon01-20. This book is well written, and recommended if you like to read about smashing, crushing, denting, bending, or breaking things.

This chart from that book shows the probability of impact on space vehicles in Earth orbit. The probability is of course much lower in interstellar space, but the concept of larger size equals lower probability should hold.

Most of the chapter is about what happens when a particle impacts at high velocity. This figure summarizes the chapter. The particle hits and vaporizes itself and part of the wall. The cloud of vapor retains most of the particle's momentum. That momentum can punch a hole through the next layer. I do not know if this would extrapolate to your velocities, which are about three orders of magnitude faster. Keep in mind that kinetic energy is proportional to speed squared.

For comparison, a lead bullet at about 0.3 km/sec hitting a steel plate will splatter similar to a drop of water hitting a windshield. The splatter will be parallel to the surface of the steel plate, which is not dented. The base of the bullet, with about 15% of the bullet's mass, will fall to the ground. A lead bullet at 0.6 km/sec hitting a thick steel plate will make a crater the size of the tip of your little finger. Some of the lead splatter from that will come straight back.

 

[DaveC426913]

So how would you go about avoiding this while rotating the ship?

If a risky maneuver were a calculated risk but that was combined with a statistically improbable event, they could be forgiven.

I.e. The maneuver is designed to be safe up to 99% of worst case scenario, but then they get hit with an anomalous, rogue rock that is way outside their worst expectations.

But not just a fabulous bad coincidence. That might seem too coincidental.

What if, I dunno they did a plot of enountered debris and determined that they were entering a relatively free volume of space,meaning this is a good low risk time to perform the maneuver, but then get hit with something outside their predictions. Afterward, they realize that the initial drop in encounters wasn't because it was empty space, as they'd thought, but because a central body had cleared the volume, and they ran into the undetected central body.

 

[Strato Incendus]

What if, I dunno they did a plot of enountered debris and determined that they were entering a relatively free volume of space,meaning this is a good low risk time to perform the maneuver, but then get bit with something g outside their predictions. Afterward, they realize that the initial drop in e counters wasn't because it was empty space but because a central body had cleared the volume, and they ran into the undetected central body.

That central body sounds like a much larger object, though. Like a mini-asteroid. Not only would that be more likely to destroy the entire ship again; the larger it is, it would also be less likely to go undetected.

If a risky maneuver were a calculated risk but that was combined with a statistically improbable event, they could be forgiven.

I.e. The maneuver is designed to be safe up to 99% of worst case scenario, but then they get hit with an anomalous, rogue rock that is way outside their worst expectations.

But not just a fabulous bad coincidence. That might seem too coincidental.

That is indeed how I try to frame it in the chapter: We've cleared the path ahead of us for 1 million km, the rotation only takes a couple of seconds, all should go well. And then, there's just one tiny little thing that sneaks through - so tiny in fact that they don't even notice the damage right away, but only realise some sub-tanks have been pierced after the aft sphere (the big one surrounding the smaller sub-spheres) starts filling up with hydrogen and water.

That would also be a nice demonstration of the purpose of the big spheres surrounding the smaller ones. Because for me as an author, that purpose was primarily an aesthetic one.
But I can justify it by saying that the big spheres do not only provide additional shielding on the front and back, where it is most needed (thereby justifying the extra mass): They also prevent the contents of the sub-spheres (hydrogen, water, deuterium, and whatever else) from escaping directly into space and being lost, in case any of the sub-spheres break. It's just an additional level of redundancy, which does double duty by also acting as the primary shield on both ends of the ship.

In your first post, you said this scene would make the commander come off as incompetent. Now it sounds to me more like you'd be criticising such a course of events as plot convenience - meaning, the commander would be particularly unlucky, but not incompetent.

So who's to blame now: The commander, or the universe and quantum randomness?

 

[Drakkith]

So now, instead, the question is: What would happen if such a dust particle (or incompletely-vaporised piece of space debris) penetrating the ship hull would come into contact with the human body? Would it be like a bullet from a gun? Or an absolute splatter fest?

It's... very bad. See here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5014777/
A 5.6 mm steel ball was shot at pig hind limbs at varying velocities from 1,000 m/s to 4,000 m/s in 1k m/s steps. There was a clear increase in damage with increasing velocity. Exit wound size, contusion range, and palor area all increased as impact velocity increased. However, at 4,000 m/s the steel ball completely vaporized itself upon impact with the limb, leaving no exit wound.

Past 2,000 m/s the animals showed damage to areas of the body other than the hind limb. At 3,000 m/s the abdominal and thoracic organs showed damage, and at 4,000 m/s they were severely injured. The brain, which is about as far away from the hind limb as it is possible to be, began to show damage at 4,000 m/s.

So, at least for velocities around 4 km/s, being hit by a hypervelocity object is similar to having an explosive detonate inside you. Whether this damage proportionally increases with speed all the way up to 0.1c I can't say. I wonder if at at a certain point the velocity is so high that the vaporizing projectile simply has no time to expand before it crosses through the body, reducing the potential damage.

Thanks for your impression; that's indeed something I'm always worrying about. I want the commander to come off as competent - not just so that she's earned the position, but also, because she's the antagonist. Antagonists need to be competent to be intimidating.

To be fair, she's probably just following pre-written procedures on how to operate the ship, including the turn around. Whatever goes wrong can't really be blamed on her unless she's doing something she herself thought of or not following the instructions. Navigating and maneuvering a large ship is not something usually done without planning things out ahead of time.

 

[Drakkith]

In your first post, you said this scene would make the commander come off as incompetent. Now it sounds to me more like you'd be criticising such a course of events as plot convenience - meaning, the commander would be particularly unlucky, but not incompetent.

So who's to blame now: The commander, or the universe and quantum randomness?

Well, SOMETHING has to happen in order to get the plot going. That something is either due to randomness or human intervention (or a combination of) and it is up to you to choose which one and lay it out in such a way as to make it believable (or at least palatable) to the audience. And, really, the initial reason often isn't that important since it usually only makes up a small portion of the story. What really matters is how the characters react. They're the ones the story is about after all.

 

[Strato Incendus]

Thanks a lot for that study!

This of course takes us back to the question about the size of the particle, which is hard to estimate given current means, I understand. I would suspect that 5.6 mm hitting at 0.125 c would already do plenty of damage to the ship as a whole, not just to individuals standing in the way.

But if we have this hypothetical dust speckle of less than a millimetre, which can pierce the ship without destroying it as a whole, and it passes through two people on its way, I am basically free to make the result of that as gory as I want?

Not that I'm actually all that keen on that; in fact, part of me wants to tell this story without any "bloodshed" in a classical sense, but more creative forms of human cruelty. Then again, in this particular scene, it's the universe we're talking about, and since most people seem to underestimate the universe's capability to cause destruction, compared to that of humans, a little more "drastic" show-don't-tell may be in order here.

If I have this tiny high-speed dust particle rip two people to shreds, though, this question becomes important:

I wonder if at at a certain point the velocity is so high that the vaporizing projectile simply has no time to expand before it crosses through the body, reducing the potential damage.

So far, I assumed that a particle of this tiny size would simply pass through the ship, tearing holes of about equal size into each layer it penetrates. This also relates to @jrmichler 's post, who also raised the question "how well does the behaviour of bullets or other standard projectiles translate to relativistic speeds?"

That's why I thought the particle would only kill these two characters if it passed right through a vital organ. Or why I would have liked to use the waterjet-cutter explanation instead, where the particle causes pipe leakages so thin that the water comes shooting out at sufficient pressure to cut through tissue. With the waterjet ruled out, the particle itself could still act as such a "miniature bullet".

However, if the particle is indeed too fast and does not expand while crossing through the body, given that it's also really small, how much damage could it even do to the human body, then? It might not be lethal at all.

At worst, it might cause minor brain lesions that go undetected for a while, or cause blindness in one eye, etc. Best case scenario, it would pass through an arm, perhaps doing less damage to the muscle tissue than a syringe, since the latter is much thicker in comparison.

 

[DaveC426913]

That central body sounds like a much larger object, though. Like a mini-asteroid. Not only would that be more likely to destroy the entire ship again; the larger it is, it would also be less likely to go undetected.

That's the unlucky part: the body was small enough - just a few yards across - to have evaded the detectors - at least until it was too late in our turnover process to engage in our standard evasive maneuver.

Lucky it was a glancing impact and not a direct hit. It wasn't the body that hit, it was the plume of superheated steam blown off from the shield that got us...

 

[Drakkith]

I would suspect that 5.6 mm hitting at 0.125 c would already do plenty of damage to the ship as a whole, not just to individuals standing in the way.

It has about 285,000 MJ. Which is a substantial amount of KE. How much energy it takes to severely damage a large spaceship I don't know, nor do I know how the KE will be partitioned. We might be talking about it punching a hole through the whole ship, or we might be talking about a breach of several compartments before the remaining material is too spread out to punch through further walls.

 

[pinball1970]

It has about 285,000 MJ. Which is a substantial amount of KE. How much energy it takes to severely damage a large spaceship I don't know, nor do I know how the KE will be partitioned. We might be talking about it punching a hole through the whole ship, or we might be talking about a breach of several compartments before the remaining material is too spread out to punch through further walls.

This discussion is reminiscent of the Columbia disaster. The leading edge of the left wing was hit by a 'suitcase sized' portion of insulating foam.
This was calculated to be moving at 500mph so much slower than the speeds you guys are discussing.
The piece was much larger but still just foam that exploded into fine dust particles once it struck that area of the wing, which was reinforced carbon fibre. That part of the wing was crucial as it would have to be able to withstand heat extreme temperatures on re-entry.
This presentation shows footage of the foam strike as it happened and a reconstruction of the event using an air powered gun.The damage to the wing was not visible on the shuttle at the time so they assumed this would not be significant. From about 28.30

 

[jrmichler]

It has about 285,000 MJ.

Which is the energy released from 67 tons of high explosive. For comparison, the Oklahoma city bomb, which killed 168 people, was the equivalent of 2.5 tons of TNT: https://en.wikipedia.org/wiki/Oklahoma_City_bombing.

An explosion releases energy in all directions. A kinetic strike has momentum into the space vehicle, which would increase the damage.

 

[Drakkith]

An explosion releases energy in all directions. A kinetic strike has momentum into the space vehicle, which would increase the damage.

If all of the energy is dissipated into the ship, sure. It's also possible that the projectile and its spalling passes through the ship completely before it expends all of its KE.

 

[256bits]

So if rotating the ship around its axis takes about 20 seconds

From where does the 20 sec come from?
Is that an add hock timeframe - it must come from somewhere.
How much is the mass of the end spheres?
Have you calculated the velocity and acceleration needed for a 20 sec rotation maneuver?
And the burn cycle?
Can the ship infrastructure handle the stress?

As an aside, is the living quarters still rotating, or brought to a standstill while doing this maneuver?

 

[DaveC426913]

if rotating the ship around its axis takes about 20 seconds

Yeah wait what?

No way. The rotation HAS to be on the order of many, many minutes, like, some fraction of an hour. The ship will not stand transverse forces any stronger.

That means they MUST arrange an Intermediate shield configuration. Doesn't matter how long it takes to set up and break down - it could be in the works for a year - it's got to be done.

 

[Drakkith]

That means they MUST arrange an Intermediate shield configuration. Doesn't matter how long it takes to set up and break down - it could be in the works for a year - it's got to be done.

I don't agree. The ship already has a defense system for larger pieces of debris, so the only thing they're dealing with is gas, near-microscopic dust particles, cosmic rays, and EM radiation, all of which is easily withstood by the ship for the time it takes to rotate the ship. The crew is probably safe too, but it would be easy to make everyone go stand inside a shielded area for an 20 minutes to an hour while the ship turns.

 

[DaveC426913]

I don't agree. The ship already has a defense system for larger pieces of debris, so the only thing they're dealing with is gas, near-microscopic dust particles, cosmic rays, and EM radiation, all of which is easily withstood by the ship for the time it takes to rotate the ship. The crew is probably safe too, but it would be easy to make everyone go stand inside a shielded area for an 20 minutes to an hour while the ship turns.

OK, sure. That works.

Still, the end-over rotation MUST take much, much longer than 20 seconds.

 

[Strato Incendus]

Alright, thanks for the unanimous feedback regarding the time it would take the ship to rotate. I really just shot for a number. Let’s go with 20 minutes, rather than 20 seconds!

Now, the question is indeed whether they need an intermediate shield configuration, as @DaveC426913 suggested, or whether the deflector lasers can continue to do the job, like @Drakkith said.

 

[DennisN]

@Strato Incendus:

I haven't read the entire thread but I wanted to put in a couple of cents.
Interstellar travel has not been done (caveat: by humans at least ), so you would have to look elsewhere for ideas.

I would personally look at the history of long ship voyages (let's say between ca 1400 - 1900), since there are a number of accounts of things going wrong, e.g. :

• infighting among crew
• disobedience
• mutiny
• food/water shortage (turn it into cannibalism if you want to go wild )
• diseases
• accidents (e.g. I think there was a famous ship that hit an iceberg )
• fire breaking out onboard
• piracy (though it may not be applicable to your story?)

One example of a disastrous journey in history is Franklin's lost expedition (1845-). It was an utter catastrophe and extremely tragic.
I remember seeing an absolutely fascinating documentary about it.

Edit: Better yet faulty maintenance on the journey. The the culprit is still onboard. Sabotage, incompetence, bad management, false accusations, distrust amongst the crew...?

I think those were excellent suggestions.

 

[gmax137]

How long is the voyage? If it is more than a few decades, a very plausible scenario is: the people operating the ship make some kind of fix, or change, that they think will be an improvement - not knowing that the original design feature had some basis. In other words, they have forgotten why something is the way it is; and their change leads to failure/disaster...

 

[DaveC426913]

I like that. A very real risk when changes are made without a detailed understanding of the original design.

The 1981 Hyatt Recency collapse is a textbook study in how redesigns can result in disaster.

https://en.m.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse

The engineers who reviewed the initial designs of this short 120 foot pedestrian walkway made what they thought was a simple minor change to a throughbolt fitting. That small change resulted in a catastrophic failure that killed 114 people and injured another 100.

Nevermind the neglect that led up to it, look at the point of failure - the nut and thread design - and how they failed to analyze the original specs in full.

"...the company objected that the whole rod below the fourth floor would have to be threaded in order to screw on the nuts to hold the fourth-floor walkway in place. These threads would be subject to damage as the fourth-floor structure was hoisted into place. Havens Steel proposed that two separate and offset sets of rods be used: the first set suspending the fourth-floor walkway from the ceiling, and the second set suspending the second-floor walkway from the fourth-floor walkway.

This design change would be fatal."

 

[256bits]

I don't agree. The ship already has a defense system for larger pieces of debris, so the only thing they're dealing with is gas, near-microscopic dust particles, cosmic rays, and EM radiation, all of which is easily withstood by the ship for the time it takes to rotate the ship. The crew is probably safe too, but it would be easy to make everyone go stand inside a shielded area for an 20 minutes to an hour while the ship turns.

So how does the ship save itself from debris after the ship has turned with the defense mechanism on the now rearward of the ship. Some ship re-configuration would need to be performed in any case for the deceleration phase.

 

[DaveC426913]

So how does the ship save itself from debris after the ship has turned with the defense mechanism on the now rearward of the ship. Some ship re-configuration would need to be performed in any case for the deceleration phase.

That is a good point. That should have been obvious.

Originally, as I thought, only the shield was needed as a defense, and therefore it was the only thing that needed to be reconfigured. But if this ship also has a laser defense system, that too needs to be reconfigured to work as effectively in the targetward direction.

And now we have to reexamine the whole ship design from the top - we have to see if it's really worth reconfiguring so much of it. After all, it might now be more efficient to leave the ship in the original orientation and just move the propulsion component (which I think might have been SI's original plan).

Note: this is an excellent exemplar of the lesson learned in my post 94. After any design changes - even apparently small ones - it is critical to re-analyze the project from the top.

 

[256bits]

Alright, thanks for the unanimous feedback regarding the time it would take the ship to rotate. I really just shot for a number. Let’s go with 20 minutes, rather than 20 seconds!

Now, the question is indeed whether they need an intermediate shield configuration, as @DaveC426913 suggested, or whether the deflector lasers can continue to do the job, like @Drakkith said.

A failure occurring during the turning around movement from a strike would be for me be a 'saw that one coming. A strike, with the crew safe in their pod shield, but the ship not coming out OK doesn't lend itself to a successful mission being certain. I would think the designers of the ship would have had to have done some analysis on possible outcomes of such an event. If any simulation gave a what to do in this situation of 'put you head between your legs and kiss your a.. goodbye', they would have gone back to the drawing board.
What is the chance of a debris hit?
Or the earth being hit by a killer asteroid?
By comparison, what is the chance of your ticket being the winning lottery ticket? and yet someone does win.

Addendum
Of say ten ships launched, yours might be the unlucky one.

 

[DaveC426913]

256b: I think you inadvertently double-posted some of your response....

 

[Drakkith]

So how does the ship save itself from debris after the ship has turned with the defense mechanism on the now rearward of the ship. Some ship re-configuration would need to be performed in any case for the deceleration phase.

I was under the assumption that the protection (lasers + shielding) was on both the fore and aft portions of the ship.

 

[256bits]

256b: I think you inadvertently double-posted some of your response....

Erased the duplicate sentence(s) in post 97. Tks

 

[256bits]

I was under the assumption that the protection (lasers + shielding) was on both the fore and aft portions of the ship.I

It could be.
Devils in the details - maybe budget constraints, or sky is the limit funding.

 

[Strato Incendus]

Thanks again for your many ideas!
Let's start out with a lightning round:

• infighting among crew
• disobedience
• mutiny
• food/water shortage (turn it into cannibalism if you want to go wild )

Well, that's what the main story is about (not the cannibalism, but people anticipate food shortages and rationing once the population increases beyond the ship's intended capacity ). But what we're talking about right now is intended to be the mid-point plot twist. In other words: An external, physical problem that causes of amplifies all of the psycho-social problems above.

diseases

I'm already worried about people misreading my story as an allegory on the pandemic, when it's not intended as such, merely because some of the ethical questions overlap (specifically with regards to bodily autonomy). So having disease play any major role in the plot (with all the expected consequences, i.e., quarantines etc.) would only increase that risk.

The crew are aware of the "War of the Worlds" risk, though (meaning, the danger of infection once they land on the new planet). Which is why they do have a biolab on board to constantly create artificial viruses, in order to keep everyone's immune systems sharp. Yes, that feature of the setting could serve as a setup for a sub-plot about a virus (especially because I mention it in the very first chapter). But so far, this is just a red herring.

accidents (e.g. I think there was a famous ship that hit an iceberg )

Guess what: The parallels to the Titanic have indeed been there from the beginning of the story - from the title song I wrote for it, all the way up to a scene in which Titanic is shown during movie night.

That's why I've always liked / still like any type of accident that includes a collision. Only in this case: With a particularly small object. The problem is that, at 0.125 c, even collisions with small particles might still result in the equivalent of the Titanic ramming a nuclear bomb instead of an iceberg. That's why I'm wondering how small such a particle would have to be in order to only cause smaller levels of damage to the ship.

Titanic as a story for a movie was only interesting because some people managed to survive, and thus, the ethical conflict arises who gets to survive. If all passengers had drowned together with the ship, there wouldn't have been any dilemmas or choices left to make for the characters.

fire breaking out onboard

This is indeed a very flexible solution, although it would probably only lead to a few casualties, given the size of the ship. The most damage a fire could do would probably be close to the hydrogen tanks.

I already have a scene in which one character gets burned from a leak in one of the hydrogen tanks. The question is how much hydrogen has already escaped into the surrounding spherical tank at that point, and how I can prevent that spark from setting the entire sphere on fire.

piracy (though it may not be applicable to your story?)

Indeed not applicable, as there are no aliens in my story. Well, perhaps some primitive animal life forms on the target planet at the very end, given that the whole point of the journey is that this is the most Earth-like planet we know of so far: Teegarden b. Which answers the next question:

How long is the voyage?

125 years (Teegarden b is 12.5 light years from Earth).

Originally, I simply had the ship travel at 0.1 c to make this equation work. But that would have required the ship to accelerate to this coasting speed pretty quickly (i.e., probably at g forces too high, especially since the ship has rings for artificial gravity, not a "skyscraper-like" structure, as it has been proposed for constant-acceleration ships). Constant acceleration also wouldn't provide any gravity anymore once the ship has reached its coasting phase - which will be the majority of its voyage no matter what.

Therefore, we decided here on the forum that 0.125 c would work better: A slightly higher coasting speed (travel at full speed for 75 years), but a longer acceleration and braking phase of 25 years each.

So how does the ship save itself from debris after the ship has turned with the defense mechanism on the now rearward of the ship.

I was under the assumption that the protection (lasers + shielding) was on both the fore and aft portions of the ship.

Indeed, there are deflector lasers on both ends. Part of the reason for this is also that, if the ship had to send a probe back to Earth, such a probe would be equipped with solar sails - and then, the lasers on whatever end of the ship is currently facing backwards could be used to accelerate that probe (the same concept as Breakthrough Starshot).

The expected use for this was of course if something happened to the ship - then at least the crew could send a last "message in a bottle", even in physical form, if regular communication (radio waves etc., which travel at light speed) failed. Instead, it's Earth which suddenly stops communicating about 2/3rds through the story (meaning, in reality, they've stopped sending signals about 10 years ago). One officer proposes to launch the probe to see what's up at home - but that probe would take 50 years to get there (10 light years at 0.2 c), and they would only get the first data after 60 years. Hence, the commander decides not to expend the materials for the probe, since any matter that leaves the ship is lost forever.

Devils in the details - maybe budget constraints, or sky is the limit funding.

Of say ten ships launched, yours might be the unlucky one.

Those two points seem mutually exclusive to me: If there was enough funding to build several generation ships (an "Exodus fleet", as Isaac Arthur called it - which is coincidence, because my ship is called "Exodus"), it would be a hard sell to make the reader believe that somehow, there wasn't enough funding to equip them with lasers on both ends.

Or rather: Why send ten ships with lasers only on one end, if you could send five with lasers on both ends? Especially since the latter increases the chance of survival for the individual crews? After all, human beings are K-type strategists, not R-type.

Hence, in my case, the expenses to build even just a single generation ship are already so literally astronomical that only the richest man in the world can even afford to get the project started (he still needs to recruit a bunch of investors for it, who mainly profit off of the marketing for the recruitment campaign - because of course, the ship itself will leave and not come back). So there is only one single generation ship - for the time being. There are plans to build further ones, but they will be sent to different star systems (Tau Ceti, 82 G. Eridani, Trappist-1, Ross 128 etc.).

Stories about Exodus fleets can show political / inter-crew conflicts between the various ships of that fleet (such as in Adam Oyebanji's "Braking Day"). However, such stories tend to require travel between the ships, perhaps also spacewalks (both are featured in "Braking Day", at least). And for all I have heard, spacewalks while coasting at relativistic speeds would be a non-starter (again, mostly due to radiation).

For the same reason, my entire ship already has no windows, only cameras on the outside - and screens on the inside that show what these cameras show (like "the screen" in Star Trek). But every spacesuit has a visor.

After all, it might now be more efficient to leave the ship in the original orientation and just move the propulsion component (which I think might have been SI's original plan).

I think we even discussed the possibility of the ship having two drives? One in the fore sphere, one in the aft sphere? That would eliminate the need to move anything around, or turn the ship around. And it would also make sense, because redundancy is a huge asset, if not a necessity: Anything that breaks must be replacable or fixable on-board. There are no possibilities for a repair stop.

Conversely, that's why, whenever I need to get rid of some technology for plot reasons (artificial wombs, CRISPR, sperm bank with extra genetic material from non-crew members etc.), it's safer for me to postulate "the ship started with these things, but they got destroyed along the way". And then, the safer explanation for that is human sabotage, rather than an accident. Because accidents rarely destroy things completely - properly planned deliberate destruction can.

Basically, I always blame it on the one youth rebel organisation from Generation One (the first people born on the ship) whenever I need an explanation for why something has been destroyed that the ship used to have at the beginning . They had every incentive to make the mission fail, because they wanted to make the ship turn around and return to Earth before it had reached its full coasting speed (which, as the relativistic calculator told me, coincided with the ship passing the Oort cloud).
After that, braking would simply result in the ship getting stranded in interstellar space (because the remaining fuel was only intended to initiate braking once the ship approaches the target system).

Sure, the primary concern with anything I simply add to the ship is mass. But if there's one thing I have to handwave away, it's that. Not by pretending it doesn't matter, but by simply never specifying how much exactly my ship weighs.

I mean, I'm already content that the layout / internal map of my ship is comparatively clear-cut. Does anyone know exactly what the Enterprise looks like from the inside? Or the exact layout of Hogwarts?
(Trick question: it is established in the books that the interior of Hogwarts changes constantly, and a corridor that exists today may no longer be there tomorrow - because magic, duh.)

The worldbuilding of my ship is fairly "hard", in the sense that, once you understand the layout, you know exactly where characters can and cannot go. I can't just make up a new area on the ship out of thin air, whenever the plot would need me to.

That's why I've started digging deeper into the specific construction of the ship's central trunk (around which the rings rotate) in the neighbouring thread.

 

[Drakkith]

This is indeed a very flexible solution, although it would probably only lead to a few casualties, given the size of the ship. The most damage a fire could do would probably be close to the hydrogen tanks.

Only if the crew and passengers follow very, very strict fire safety protocols, which I doubt they would after decades onboard. Fire is possibly one of the most dangerous things that can happen on board in my opinion. Virtually everything in the ship other than the actual structure is potentially flammable. The rapid increase in air pressure from even a relatively small fire can blow open sealed compartments and seriously injure people, not to mention the danger from oxygen loss and smoke inhalation in small, constricted areas.

I'm sure I've said something like this before, but I think fire is by far the most likely catastrophic event that could occur on a spaceship, and the one that takes the most work to avoid given how many ways there is for a fire to start and how easy it spreads. Electrical issues, heating elements, sparks, kids playing with matches, adults playing with matches, chemical spills, hot exhaust or coolant flows, and many many other things can start a fire.

Leaks happen, equipment fails, people go crazy, but the one thing scarier than all of that is the fire alarm.

 

[DennisN]

Leaks happen, equipment fails, people go crazy, but the one thing scarier than all of that is the fire alarm.

If I remember correctly fire was/is one of the most (the most?) feared and potentially most dangerous thing on ship journeys (though I currently don't have a source for it).

Edit: And it was even weaponized (Fire ship).

 

[Drakkith]

If I remember correctly fire was/is one of the most (the most?) feared and potentially most dangerous thing on ship journeys (though I currently don't have a source for it).

Certainly, though it's a bit different when your ship's bones are flammable. You'd be amazed at what is flammable on a ship. Bunks, clothes, food packaging, the actual paint on the walls, electrical cable shielding, light fixtures, rugs and carpets, linen, plastic dishes and cups, upholstery on furniture, many electronic components, and many, many more things that I can't begin to think of.