How to Handle a Fire Onboard a Generation Ship?

[Strato Incendus]

The high surface gravity is due to the small radius of the star. At solar system distances the low mass of the red dwarf means its effect on other bodies is less (compared to more massive stars such as our sun).

Thanks for the quick reply; indeed, I didn't really expect the surface gravity to still have an effect this far out - I was just hoping to somehow justify the range of this Oort cloud (and by "hoping", I mean "grasping at straws" ;) ).

Is there any way to calculate how close to an M-type red-dwarf star you'd have to get before encountering its equivalent of the Oort cloud (if it has one)?

 

[DaveC426913]

Of course, they will be expecting to encounter Teegarden's Oort Cloud so it can't exactly catch them by surprise. It would be a mission planning flaw to wait until they were almost on top of the target system's outer cloud to do their turn around procedure.

Here is a question: if some fraction (50%?) of the journey is spent coasting, when is the optimal time to turn the ship, all factors considered? As soon as feasible, as late as feasible? Somewhere in the middle?

 

[Strato Incendus]

I'm glad you once again independently from myself came up with the same follow-up question that popped up in my head as I was writing this scene : Why not simply turn the ship around at the halfway point of the journey, in the interstellar medium, without having to brake right away?

The dust cloud can of course still be a problem, but only in the sense of "one speckle of dust might pierce the ship hull" - i.e., exactly what I had happen so far, except it would now not be happening while turning the ship around; rather, the ship would already be facing backwards, and the dust cloud would simply be so dense that it depleted the ship's own dust cloud, plus one speckle would also make it past the deflector lasers.

However, that once again restricts the damage the ship can take from the dust cloud to that of the impact of the speckle itself - the extra damage that turning the ship around too quickly would cause would now be off the table again, if the ship has already turned around several decades prior to that.


I guess I should have figured this idea sounded to good to be true... or rather, too good to actually work in the context of the story. Turns out, if you allow your characters to be smart within your head, they will try everything in their power to prevent the disaster from happening. I feel like a dungeon master who is constantly being outsmarted by the characters of his playgroup... and these characters don't even have other players steering them!

 

[ShadowKraz]

I feel like a dungeon master who is constantly being outsmarted by the characters of his playgroup... and these characters don't even have other players steering them!

Those darned players always screw things up! (long story about players outsmarting me by accident and completely ruining the dungeon)

As for the turn around...
the ship gets turned after the initial acceleration ends - it doesn't matter when, but we still have the issue with *something* going out of alignment and it doesn't get detected for the same reason as the kidney issue from post #49; it doesn't get detected because it doesn't look or act out of alignment with no acceleration applied. Once the braking acceleration is applied... it goes out of whack and crisis commences.
Yes, I know, design, engineering, and quality control are tight but errors and sabotage do happen even under the tightest regimes. Maybe sabotage during construction?

Yeah, I am kinda married to the idea. Tell me, however, to give it up and I will.

 

[gmax137]

As for the turn around...
the ship gets turned after the initial acceleration ends - it doesn't matter when

Maybe over the generations the "turn around" takes on a kind of religious or faith-based aura. Some people want to do it as soon as the coast period begins, others want to wait, others think it signifies a lack of trust in the grand plan.

 

[DaveC426913]

the ship gets turned after the initial acceleration ends - it doesn't matter when,

The mission would be planned to turn the ship around at the optimal time, whch is not necessarily right after the onset of the coasting leg.

The question is: what factors would or could arise duing that time that should be taken into account. Obviously, safety of the ship and crew are paramount, but what occurences could be anticipated that might require the ship to remain in Acceleration Mode? Are there alternate mission configurations? Say, a backup in case higher-rez data of the taget system shows it to be uninhabitable? Do they account for interlstellar dust couds and be ready to go around them? (Note that whether they do or not, isn't the point. The point is what would they be planning for in Mission planning?)


It's not a great analogy, but when I am out sailing, and it's time to come in to the harbour, I switch to my motor and drop the sails. Despite the fact that I won't be needing the sails, it is my habit to not lash down and store the sails until I am at-dock. The reason for this is as a backup, in case my motor dies at the worst possible moment. I need to be able to raise the sails at a second's notice if I suddenly find myself drifting toward a lee shore. That's the kind of precautionary wisdom that has kept sailors alive.

This can be generalized to a principle about any shipboard activity: what if I do this now? What is the worst that can happen? What if I do it later? What is the worst that can happen? If there is no upside to stowing my sails early, but a very definite downside (no matter how unlikely), then the advantage weighs in favour of holding off.

But that works the other way for other tasks. Some tasks you want to do right away in case something unexpected happens. For example, reefing the sail (ie. shortening it) in anticipation of high winds. It is always better to reef early and decide to take it out if winds don't build (big upside, small downside), than it is to wait and have to reef in rising winds (small upside, very big downside).

 

[ShadowKraz]

The mission would be planned to turn the ship around at the optimal time, whch is not necessarily right after the onset of the coasting leg.

The question is: what factors would or could arise duing that time that should be taken into account. Obviously, safety of the ship and crew are paramount, but what occurences could be anticipated that might require the ship to remain in Acceleration Mode? Are there alternate mission configurations? Say, a backup in case higher-rez data of the taget system shows it to be uninhabitable? Do they account for interlstellar dust couds and be ready to go around them? (Note that whether they do or not, isn't the point. The point is what would they be planning for in Mission planning?)


It's not a great analogy, but when I am out sailing, and it's time to come in to the harbour,

Excellent points and I think the sailing analogy is good. I used to sail under Capt. Bligh... um, I mean, my Dad. He was ALWAYS about doing, or preparing to do, things earlier than absolutely necessary, such as reefing the sails. The boat was an old O'Day Daysailer, but it was good practice for life.
"The best laid plans of mice and men oft go awry."

 

[Strato Incendus]

the ship gets turned after the initial acceleration ends

This would fit the goals of the youth rebel organisation in prequel 2, Turning Point, who are unhappy about having been turned into the first generation of unwilling crew members, and are trying to make the ship return to Earth.

Whether or not this goal is realistic or not is secondary (one forum user here has criticised a story with a plot like this as nonsensical in the past); Turning Point do not have to be guided by reason. In fact, their youthful passion may be the counterpoint to the ship's establishment, doing everything based on "the science".

However, even Turning Point understood that, if they wanted to have any chance at all to actually accelerate the ship back towards Earth, they'd have to turn it around before it reaches full coasting speed. After that, braking would merely cause it to get stranded in the interstellar medium.

Thus, their time of trying to make the ship brake and turn around early coincides with it traversing the actual Oort cloud. Therefore, a lot of the things we've discussed so far are not irrelevant - they might merely become crucial for the second prequel, rather than for the first main book. :)


If the ship turns around right after leaving the Sol system, the question is whether this happens as an intentional action on part of the ship's commanding officers - or if this is the consequence of Turning Point's actions: They may have succeeded in flipping the ship early (and perhaps, faster than they should have, given they were about two dozen plucky teenagers and twenty-somethings), but were stopped by security before they were able to complete their plan.

Then again, this doesn't make sense, as turning the ship around while it's accelerating will make it veer off course. This is one crucial difference to flipping the ship at the end of the coasting phase, since there is no continued acceleration as the ship is being rotated.

Thus, the more straightforward and believable explanation would be that the ship was rotated on purpose by the ones in charge, early after leaving the Oort cloud - which is simultaneously shortly after ending the acceleration phase - once they had entered the interstellar medium, where a lot less space dust could get in their way.

If they don't flip the ship right there and then, the question is indeed, as @DaveC426913 has asked:
What would be the upside of flipping it at the midpoint of the coasting phase, or even later?
Or conversely, what would be the downside of flipping it early?

 

[pinball1970]

So the question is:
1) How does fire behave in zero gravity vs. in an environment of centrifugal gravity (=on the ring sections of the ship)?
2) What safety technology would the ship have against cases like this (maybe starting with whatever the ISS has for preventing fires on board)?
3) What levels of casualties would you expect, assuming a bunch of people are sent in to extinguish the fire as quickly as possible?

Looking for holly wood portrayals I came across the Apollo 1 accident in 1967.
Not something I was aware of till I saw the Apollo 1995 film.

If you want to take from real life.

The craft was on the ground doing tests and the fire started, the crew were dead before engineers could get the doors off which was 5 minutes later.

V50 mentioned the sub fire, I cannot imagine many things more horrific, trapped in an enclosed space with a fire rapidly spreading.

The “Gravity” fire was pretty cool looking, imagining this was not.

 

[Strato Incendus]

Thanks for getting us back to the main topic! ;) After all, we have been talking more about the origin of the damage to the ship, rather than about what the damage occurring inside the ship will actually look like.

To recap: The dust-cloud explanation is a good way of justifying why a dust speckle may pierce the ship at this specific point in time (rather than at any earlier point over the course of the coasting phase) — namely, because the ship enters the outskirts of the Oort cloud of Teegarden’s Star. If I set this up properly, not only should it feel less like plot convenience, but actually more like straight-up realism:
(“Yes, of course, once they enter the new star system, the density of matter per unit of space will increase, compared to the interstellar medium, because of the star’s gravity.”) Thinking about it, re-entry into a star system at full coasting speed (0.125 c) should be more dangerous, compared to accelerating out of a star system into the interstellar medium from a lower speed (assuming the low g forces that we’ve established for the acceleration, which is 0.048 m/s2).

However, ultimately, the damage done to the ship must probably occur from the dust speckle alone, rather than from the rotation process. Since my conclusion from the comments so far is that the ship would realistically be rotated at an earlier point in the story, while it is somewhere in the interstellar medium, so the risk of damage is lower. In fact, the exact point in time when to rotate the ship could be determined by noticing, “We’re in a particularly empty pocket of space right now, let’s use the opportunity to flip the ship!”

The ship’s range of vision is fairly limited, though, due to its own travel speed (0.125 c) compared to the speed of its sensors (1 c).

Hence, as far as how quickly the crew notices the higher density of the dust cloud:

1. With the ship coasting at 0.125 c, they would cover 1 light-minute of distance within 8 minutes of ship time. The sensor signals can only work at light speed, so for any given speckle of dust in front of the ship, it would take one minute for the sensor signal to reach it, another minute for the reflected signal to get back to the ship. That would only leave the ship crew a time window of 6 minutes between first noticing the dust cloud and entering into it, right? Of course, they will expect the dust to get denser in general as they approach the target system. However, it may not be until they get the sensor data that they realise it’s denser than they anticipated.
2. The deflector laser beams obviously can’t move faster than light either, so even if they failed completely, after having vaporised everything perfectly up to that point, the ship would have 8 minutes of reaction time left before encountering further dust speckles, correct?
3. The higher density of the dust cloud as they enter the target star system no longer requires a failure of the deflector lasers in order for something to slip past, as @DaveC426913 pointed out. However, if the density of dust alone is what causes the problems now (rather than flipping the ship within such a dust cloud), I need an explanation why the ship doesn’t keep getting hit by more and more dust particles over the course of the story from then on.
   1. Perhaps some genius engineer makes a modification to the deflector lasers on the fly — perhaps within that critical time span of 8 minutes, before further impacts occur? Bonus points if the engineer sacrifices himself in the process. Perhaps he has to go to the back of the ship (which is now pointing forward) to manually adjust something on the deflector lasers?
   2. Spacewalks at this speed aren’t really possible, I’ve heard — however, that’s assuming a spacewalk that a character would survive. If he has to go outside to do something manually, he could die by radiation (because he’d be in front of the protective water tanks in the forward-pointing aft sphere), he could get pierced by the incoming barrage of dust speckles (even just a single one of them piercing his helmet would be enough), he could get fried by the engines as they turn on to brake (though in this scenario, there’s no reason to start the 25-year-long braking process while a crew member is still working outside), or he could simply slip and float away from the ship (which is kind of the biggest cliché, but of course an omnipresent danger in space).

For the rest of the crew, we need to get back to the question what exactly gets damaged on the inside, by the dust speckle that pierces the ship hull. I could have someone get ripped to shreds by the dust speckle passing through them — depending on whether this is the fate that befalls the engineer or not (I don’t wanna pull this twice in the same event, because “law of diminishing returns” in writing :D ). But either way, the speckle alone isn’t going to cause mass casualties, because the ship isn’t sufficiently densely populated for that.

I still like the idea of the speckle piercing some tank or pipe that contains an explosive gas. All it has to do on top of that is to also damage some wiring close to it, then you get some sparks, and boom, fire onboard galore. The obvious candidate here would be hydrogen, but pure hydrogen is of course hard to store, and not what you would want for the nuclear-fusion reactor anyway.

So I guess we’ll finally have to dig into the specifics of different types of nuclear-fusion reactors next.
But first, let’s address the remaining questions about the dust speckle listed above.
Once we know how the dust speckle got into the ship, then we can focus on the inside and imagine all the damage it can cause on its way through the ship.

 

[DaveC426913]

so even if they failed completely, after having vaporised everything perfectly up to that point,

Um. Vaporizing everything doesn't make it disappear. The vaporized components contain the same kinetic energy as the unvaporized components (minus whatever the laser pulse imparted on them). Ideally, you'll want both the radiative energy and the physical components to disperse, out of the ship's path. Hopefully, what's left will be spread over a wider area of the ship's proximal defenses. Just one more headache for you.

 

[pinball1970]

Apologies if this has already been mentioned.

Another example of a fire on a space craft.

https://www.nasa.gov/history/25-years-ago-fire-aboard-space-station-mir/

This was a happy ending. Note how long it took to remove toxic fumes from the craft. The escape capsule Soyuz has no fire extinguishers apparently according to Tim Peake. They depressurize the vessel extinguishing the flames.

 

[Strato Incendus]

Um. Vaporizing everything doesn't make it disappear. The vaporized components contain the same kinetic energy as the unvaporized components (minus whatever the laser pulse imparted on them). Ideally, you'll want both the radiative energy and the physical components to disperse, out of the ship's path. Hopefully, what's left will be spread over a wider area of the ship's proximal defenses. Just one more headache for you.

Thanks for pointing this out! ;) On that note, let’s get back to the question of where the captain would send the crew members to be as safe as possible from the barrage, keeping the dumbbell-structure of the ship in mind: In case one or several dust speckles to pierce the ship hull, would citizens be safer in the central pipe, around which the rings rotate? Or would they be safer on the rings themselves?

The holes the speckles would punch into the ship hull are likely so small that they won’t allow a lot of air to escape into space that quickly, I assume? They would detect slowly dropping levels of air pressure, and would quickly send technicians to fix them.

If there are a bunch of speckles punching holes into the hull in different places, that would perhaps finally be one way of getting me to that “disaster which requires a lot of helping hands to fix, and is dangerous” scenario that I need, since it would incentivise the commander to send a lot of male officers “into battle against the universe”. Quite literally, in case some of them end up getting pierced by dust speckles themselves — getting hit by a bullet will seem harmless in comparison, given the speed of the speckles, and what they would do to the human body as a result (we’ve discussed that part before).

Apologies if this has already been mentioned.

Another example of a fire on a space craft.

https://www.nasa.gov/history/25-years-ago-fire-aboard-space-station-mir/

This was a happy ending. Note how long it took to remove toxic fumes from the craft. The escape capsule Soyuz has no fire extinguishers apparently according to Tim Peake. They depressurize the vessel extinguishing the flames.

In fact, it hasn’t! Thanks a lot for this real-world example! :) In particular, this is useful for thinking about “stuff that could ignite”.

The part about the route to the evacuation shuttle is not that useful in my setting, since getting to one of the generation ship’s landing shuttles is still a death sentence if you flee the ship while it’s still in the interstellar medium — you won’t arrive anywhere with those landing shuttles.

Even if the air inside them never ran out, you’d die of old age, much like the older generations on the generation ship itself — except you can’t raise your entire family inside such a shuttle. Even if several generations somehow could survive inside a shuttle, a single shuttle probably does not have enough fuel to decelerate it from the mothership’s 0.125 c coasting speed all by themselves, in order to eventually brake at the target star.

 

[DaveC426913]

...the question of where the captain would send the crew members to be as safe as possible from the barrage, keeping the dumbbell-structure of the ship in mind: In case one or several dust speckles to pierce the ship hull, would citizens be safer in the central pipe, around which the rings rotate? Or would they be safer on the rings themselves?

Def safer in the pipe.

The holes the speckles would punch into the ship hull are likely so small that they won’t allow a lot of air to escape into space that quickly, I assume?

At relativistic speeds, I'm not sure particles would drill holes so much as explode, vaporizing chunks of ablative shielding and leaving craters.

That is, after all, the point of shielding - to
1. absorb and spread the damage out laterally so it doesn't reach the inner hull
2. carry away the kinetic and heat energy with the ablated material.

 

[Strato Incendus]

Def safer in the pipe.

Perfect, thanks a lot! That allows me to keep my evacuation scene, where a security officer guides a bunch of school children away from the ring and to the elevators that lead to the central pipe.

At relativistic speeds, I'm not sure particles would drill holes so much as explode, vaporizing chunks of ablative shielding and leaving craters.

That is, after all, the point of shielding - to
1. absorb and spread the damage out laterally so it doesn't reach the inner hull
2. carry away the kinetic and heat energy with the ablated material.

Sure, and usually, the shielding works. The point is that the sudden increase in density at the outskirts of the star system becomes too much to handle for both the protective cloud in front of the ship (which is being depleted fast) and the deflector lasers, so something does get past.

"Craters", while more destructive than "tiny bullet holes", is still better than "micro-meteor", because the latter would probably be enough to destroy the entire ship. So perhaps, "craters" is exactly the level of destruction I need? How large exactly the craters would be will depend on the individual speckle, I assume - and since they're too small to be seen with the naked eye, the reader has no way of observing where the speckles are coming from.

Hence, I would conclude I can just place and shape my craters wherever I want on the ship, as long as the speckle trajectory makes sense? (Meaning, they should traverse the ship from aft sphere to fore sphere, since, as we established, the ship is already facing backwards at this point.)


Speaking of the ship's own protective dust cloud: How would this be used in conjunction with deflector lasers? Specifically, how can the ship stop its own deflector lasers from depleting its own gas cloud, rather than whatever natural interstellar dust is waiting beyond the ship's own protective dust cloud?