Emergency braking in space

• Strato Incendus
In summary, the Impulse Drive is described in the Voyager Technical Manual as 0.25 c (25% of the speed of light). It requires g forces to "immediately" come to a halt from that speed - which is beyond what the human body can take. If you don't have the luxury of handwaving this away with the (in)famous inertial damping system, you have to start wondering how fast a ship could brake in space without crushing its inhabitants, and how far the ship would keep on coasting in the meantime before coming to a stop.f

Strato Incendus

The two most unscientific words in Star Trek are probably "full stop". The Impulse Drive is described in the Voyager Technical Manual as 0.25 c (25% of the speed of light). Whatever g forces are required to "immediately" come to a halt from that speed - it's certainly way beyond what the human body can take. If you don't have the luxury of handwaving this away with the (in)famous inertial damping system, you have to start wondering how fast a ship could brake in space without crushing its inhabitants, and how far the ship would keep on coasting in the meantime before coming to a stop.

In my story, I need an "emergency brake" from 0.1 c to a full stop - even though this puts the entire ship's mission in jeopardy. The reason I cite is therefore a (an impending?) failure of the deflector systems: If the ship kept going at 0.1 c, they would eventually run into a dust particle that would blow up the entire craft.

Using the g-Acceleration Calculator from "rechneronline" (German website), braking from 0.1 c to 0 c at 4 g (anything beyond that would make humans black out, as far as I know) would take 213 hours, 42 minutes and 21.93 seconds. That's the way Data would put it - in simpler terms, this is almost 9 days.

Follow-up questions that arise from this:

1) Can humans withstand 4 g non-stop for 9 days?
Because that's obviously different from withstanding it for shorter time periods.

2) How to prevent the crew from getting smashed against the back walls of every room on the ship? Since the ship needs to turn around to brake, the counter-acceleration would still point towards the front of the ship; hence, the "weight" resulting from the acceleration would still point to the back of the ship, if I understand correctly?

3) My idea here was to use the magnetic-boots trick from The Expanse. However, that's not a cop-out to just have people walk around normally. Rather, walking on the ground would feel like trying to walk up a wall, while the g force from the braking would try to make you "fall back" onto the back wall of the room - at four times your actual weight. If you just want to do as much as leave a room, and the door of the room is pointing to the front of the ship, it will be like an overweight Spider-Man trying to run up a wall until he reaches a hole in the ceiling.

4) In a room facing the back of the ship, the wall which holds the door to the corridor is now effectively the ceiling. If one can't walk up to the door in a straight line, one might have to walk "on the ceiling" for a bit. This would mean hanging down from the ceiling with your head first, at 4 g. Not sure how the human body reacts to that.
This wouldn't be possible without the magnetic boots, of course - since even during regular coasting, it would equate walking on the wall that holds the door. But with the magnetic boots active, it does become possible in theory. Hence, if the magnetic boots enable that, I need to know whether the crew members could use "walking on walls", even when that wall turns into a ceiling and their weight quadruples.

5) How much of a deflector-system failure would I get away with here? Could the ship fly for almost 9 days, constantly slowing down from 0.1 c at 4 g, without crashing into some dust particle that would blow it up?
If not, I need to postulate some impending failure of the deflector system, or a gradual reduction of accuracy of the lasers, that for some reason can't be fixed in time.

6) Finally: The intended braking force at the target destination is much weaker - so that people do NOT have to turn on their magnetic boots. A lot of authors have their ships accelerate and brake at 1 G, because it seems "easy" and intuitive. But the implications of that are a mess, and I for one am still not convinced by the proposed solution of "turning every room on the ship by 90 degrees", as in Adam Oyebanji's "Braking Day". And if the ship could constantly accelerate at 1 G for extended periods of time, it would get to light speed within a year - which is way too fast for my generation-ship story. At that point, I could only refer to the response time of the deflector system as a reason for not going faster.

So instead, I'll have the ship accelerate to the maximum travel speed of 0.1 c at 0.1 g. Meanwhile, the rotating rings of the ship still produce 1 g of centrifugal force. That way, the issue of "walls turning into floors" shouldn't even occur in the first place. And I end up with my 125 years for 12.5 light years time frame that the story relies on.

According to the calculator cited above, this would take 353.79 days, so almost a year. And unless I've misunderstood something here, braking from 0.1 c to 0 at 0.1 g would take the same time.

What does braking / accelerating at 0.1 g feel like, though, and can humans withstand that for a year?
I know most trains are capable of braking with such strength, but that's a particularly harsh kind of brake, one that most passengers would not be fond of.

First, you are accelerating at ##1 \ g## on the surface of the Earth. And, in fact, ##1 \ g## is needed to feel normal (e.g. ship accelerating, decelerating or rotating).

How much force you can withstand depends on how it is applied. When you are standing, the force applied at your feet is enough to accelerate your whole body. This force reduces vertically through your body. Your neck, for example, is only accelerating the mass of your head.

If you were supported at various points (arms, hips and feet, say), then the force at your feet (and hips) would be less than when standing.

Theoretically, if a force could be applied evenly across your body, then you could sustain much greater acceleration. I think there are already ideas along these lines in SF and even fururistic spaceship design.

PS to see this imagine one hundred ##1 \ kg## masses stacked vertically. The bottom mass is supporting ##100 \ kg##, the second mass ##99 \ kg## etc. And the top mass is only supporting its own mass of ##1 \ kg##. If, however, you support each mass independently, then each mass is only supporting itself.

If you could achieve that arrangement with every atom in your body ...

To be honest, I'm really disturbed by the very idea of 'braking' in space.
I can understand emergency manoeuvrers and such. But braking - just something you do on ground.

In space, you have a ΔV budget and acceleration. Sometimes these two are not independent - more acceleration may have adverse effect on ΔV budget, so extreme acceleration (can be considered as braking rapid speed change) is to be avoided if possible.

But 'braking'...

BTW adverse effects of few G accelerations can be 'handled' (more like 'handwaved') by immersion (check Forewer War, acceleration shell).

A representative human population sustaining 4 g for 9 days non-stop is likely going to give all sorts of health issues perhaps even fatalities due to rupturing aneurysms or due to the limited options of treating other occurring medical issues that arise is such a population. Instead of 9 days non-stop, perhaps it can be done as like 4 hours at 4 g (or as much as a safe maximum would be) and then 1 g (or lower if they are not accustomed to 1 g) for 1 hour to allow everyone a break for food and bathroom.

Regarding the magnetic boots I don't see why you are talking about those? In movies they are used in low-g environments because it is too expensive or complicated to depict everyone in free fall all the time. The only place I can imagine mag boots might be of some value would be on the exterior of a non-accelerating ship to allow moving around without a tether and without having to spend a lot of reaction mass.

Regarding making (or planing) an emergency deceleration in the first place, I would wonder where all the fuel comes from. Planing a delta-V budget of 4 times 0.1 c rather than 2 times 0.1 c (without possibility of mid-stop) or even 2 times 0.2c (and spend roughly half the time in transit) is a critical part of the design. I mean, even for the most efficient rocket propulsion (MAR photon rocket) the fuel/payload ratio will be severely impacted by such decisions.

Regarding the combination of rotational gravity rings and normal linear acceleration, one could imagine that rings done in segments can be made to rotate or pivot and change rotation speed to maintain 1 g at the floors for all linear accelerations in the 0-1 g range.

You say you need a story reason for a generation ship to stop mid-transit, but I cannot help thinking a failed deflector sounds as a bit contrived, at least if its hard sci-fi. If the deflector fails without hope of repairing why stop at all? And if it is reparable within some time, why would anyone knowing this in advance plan for stopping instead of making sure (e.g. using redundancies) that the deflector system are never down that long?

Having the acceleration of the ship be relative to a wall is weird. I can't see why this would be done. It should be relative to the floor. If the ship accelerates, then you get heavier.

The magnetic boots won't help you. The crew would have to be lying down in special beds like our astronauts do.

If propulsion is an ordinary rocket then all the fuel would be used up doing this, so you are pretty much hosed anyway.

And if the ship could constantly accelerate at 1 G for extended periods of time, it would get to light speed within a year
You cannot reach the speed of light. Your calculator (I assume this one?) is not good for relativistic velocities. Use this one instead.
What does braking / accelerating at 0.1 g feel like, though, and can humans withstand that for a year?
When you brake normally with a car - for a red light, for example - you do it at about 0.3g. A hard emergency stop where you have to hold on to your seat begins at around 0.7g. So I don't think 0.1g would be noticeable in your everyday life. You would weigh 0.5-1.0 kg more, would that really impact your body that much?

Strato Incendus
I think it is very important to examine
• exactly what they hope to accomplish by braking
• relative to what, exactly, are they stopping?
Because, for almost all intents and purposes, they are already stationary in space.

Thanks for your many replies! :)

In another thread, we already briefly speculated about within-story reasons for the ship to slow down or come to a halt. Personally, I'd be fine with both - full stop, or slowing down from 10% to 2.5% light speed.

The point for the story is that the incentive to have children on the ship suddenly switches from "colonising the planet in 25 years" to "replenishing the crew size (since a bunch of people died in the catastrophe) and maintain it until we get to the planet in about another 100 years". Having kids goes from merely being a part of the mission to becoming a struggle for survival for the entire crew.

Due to the braking, the perspective changes because the current crew can no longer look forward to landing on the planet themselves; they're now living with the same perspective the previous generations had: That neither themselves nor their own kids will ever get to see the new planet with their own eyes.

Here is one external cause that @DaveC426913 suggested in that other thread: A hydrogen cloud blocking the ship's path.

DaveC426913 said:
What if all the actions taken were driven by a single cause? What if they ran into a hydrogen cloud first and that's what made them have to stop (a suicide move) so they didn't get cooked? And then, after sitting for a generation or two (because all options are suicide), they decide to try some of the more outlandish solutions (because they have little left to lose) that require such a huge amount of work and invention and sacrifice?

We didn't get to explore this hydrogen-cloud explanation much further, though, before that thread went on to different things. Among others, I didn't get what you meant by "so they didn't get cooked". How exactly would the hydrogen cloud do that when a spaceship passes through? ;) And would flying through it at, say, 2.5% light-speed be any safer than flying through it at 10% light-speed?

Second, could a deflector even be used to locally disperse hydrogen clouds, allowing the ship to pass?
If not
- if the deflector is only useful against debris, and the water tanks and ice shield in front of the ship protect against radiation, but gas clouds are a problem - then we don't even need to include a deflector failure in the premise for emergency braking. They could simply detect the gas cloud about a week in advance, and then conclude they have to slow down before getting there.

Alternatively, instead of slowing down before the gas cloud, they could try going around it. Which, if they're headed towards the target planet in a straight line, would mean a detour - at 10% light-speed. This could throw them so far off-course that they need much longer to get to their destination.

Going around the cloud is probably something they should at least entertain. They might find out the cloud is too large to steer the ship past it in time, given the momentum it already has. In either case, the ship should at least stay close enough to the cloud, so that I can have it fly into the cloud in book II to replenish its hydrogen supplies and accelerate from there again.

@jack action : Thanks for putting the g forces into perspective, and for linking this other calculator! ;) Indeed I end up getting similar numbers, though:

acceleration: 0.1 g
target velocity: 0.1 c
total distance: 12.5 light-years
whole trip ship time: 125.3462 years
whole trip Earth time: 125.9711 years
cruise ship time: 123.4023 years
acceleration ship time: 0.9720 years (=354.78 days)
acceleration Earth time: 0.9736 years (=355.364 days)
Earth minus Ship Time: 0.6249 years (I was working with half a year, give or take)

That's precisely our 123 years cruise time + 1 year acceleration / deceleration on both ends.

If the ship kept going at 0.1 c, they would eventually run into a dust particle that would blow up the entire craft.
How do you detect a dust particle far enough out to know you need to brake? But if you can, why not just move the ship laterally a minuscule amount and avoid the dust particle entirely?

Edit...

I can now see in your other reply, @Strato Incendus, that it's a gas cloud the ship is trying to avoid. But my question remains. It is unlikely that the ship can't detect a threat like this far enough out to avoid it via course correction, rather than stopping, and surely that has to be baked into the trip mechanics? This type of event is going to be predictable, if it's not accounted for, the designers lacked imagination.

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Strato Incendus
Yes, that‘s why I did propose the alternative solution of a course correction that leads the ship so far off track that the travel time is extended considerably. Basically, because of the gas cloud, the ship suddenly has to take a massive detour.

Of course, if the mid-point plot twist represents the arrival at the gas cloud (that is, the beginning of the phase of going past it), the presence of the gas cloud would already be known in advance. So in order to keep this as a twist, I‘d have to place the gas cloud further away. Rather than arriving at the cloud and getting stranded in it at the midpoint, the twist would be in the detection of the gas cloud and the ensuing need to course-correct - with the full awareness that this extends the journey by (since that‘s about the time frame I need) by 100 years.

The massive time extension could also happen precisely because the ship maintains its high speed of 0.1 c. Meaning, a minor change of the course, because it has to happen so far in advance, takes them so far away from the straight line between the solar system and Teegarden b, that they later have to cover that distance again in the opposite direction to get back to their original destination.

In other words: That gas cloud needs to be at least 5 light years in diameter, probably more. If the ship then has to steer 5 light years “sideways” to get past the cloud, those are 5 light years it will have to make up for again once it has passed the cloud. 2 x 5 light years at 0.1 c means 2 x 50 additional years.

Course-correcting by itself shouldn‘t do any damage to the ship, though. I still need something to happen to the reactor in the process, so that there is a ship-internal repair mission requiring lots of strong hands to fix it, and fix it urgently. :D

In other words: That gas cloud needs to be at least 5 light years in diameter, probably more.
It's a big number, @Strato Incendus, and something you'd expect future astronomers to notice (Hubble might already, but JWST certainly should), but what does that do to average density? Surely, knowing this cloud is in the way, the trip designers would have either allowed for the density in the ship's structure such that it would not slow them down, or allowed for avoidance in the trajectory.

I'd say you're at one of those author points where you either have to hope your audience won't know enough cosmology to accept this, or backtrack and create a different problem for the ship because a 'surprise' gas cloud between Earth and Teegarden stretches credulity.

Course-correcting by itself shouldn‘t do any damage to the ship, though. I still need something to happen to the reactor in the process, so that there is a ship-internal repair mission requiring lots
Havent thought this through fully but...
An emergency course correction would require turning the ship 90 degrees.

That puts the ship broadside to the hard radiation sleet - which thus is no longer being blocked by the radiation shield.

I think 'damage' would be a pretty reasonable consequence.

Strato Incendus
It's a big number, @Strato Incendus, and something you'd expect future astronomers to notice (Hubble might already, but JWST certainly should), but what does that do to average density? Surely, knowing this cloud is in the way, the trip designers would have either allowed for the density in the ship's structure such that it would not slow them down, or allowed for avoidance in the trajectory.
Yeah, unfortunately, that’s what I suspected, too. Anything requiring a 10-light-year detour would be big enough to be noticed in advance.

Unless maybe it’s all dark matter, rather than gas? ^^ Then again, even if you couldn’t see it, you could easily observe the gravitational effects of such a massive object.
An emergency course correction would require turning the ship 90 degrees.

That puts the ship broadside to the hard radiation sleet - which thus is no longer being blocked by the radiation shield.
Good point, that is something I had not thought of yet! That still leaves the question of what kind of object could possibly be blocking the path (and do so suddenly) to require such an emergency turn.

Perhaps I should rephrase the question even more generally: What type of thing could occur during the last 25 years of the journey that would unexpectedly extend the journey by another 100 years? It doesn’t necessarily have to involve braking or taking a detour - I’m open to any alternative suggestions at this point.

What type of thing could occur during the last 25 years of the journey that would unexpectedly extend the journey by another 100 years?
As they get closer to their destination it seems prudent the will start observing it more, so perhaps they discover something that will make them choose an alternative destination? I assume here the set of possible destinations have been chosen based on only remote sensing (i.e. no active probes first), so as they get closer they should have a chance to discover something new, and that destination candidates are more or less along their path requiring only little change in direction. Regarding what they discover it doesn't have to be catastrophic as such, just something that will make selecting the "next destination" a better option all things considered. For instance, perhaps more precise measurements reveal some of the planetary orbits are unstable, just enough of a risk that it is deemed safer to continue rather than committing to this destination by beginning the break maneuver.

Strato Incendus
Unless maybe it’s all dark matter, rather than gas?
Please don't go there, @Strato Incendus, there's a Netflix sci-fi show I started watching, it was TERRIBLE across the board, but I stopped watching when their spaceship had to slow down because of a cloud of dark matter. The reason it's dark is the reason a cloud of it would be literally immaterial to a spaceship.

Anyway...

What type of thing could occur during the last 25 years of the journey that would unexpectedly extend the journey by another 100 years?
With apologies, I've lost track of whether the crew / passengers are awake or asleep? If they are awake, it is a long time for ship resources to support them unless such a long duration was part of the design parameters. Asleep, well, that creates different problems (I used that two novels ago, hibernation for a couple of hundred years, the ship was a grubby mess by the time they were saved!).

But it is hard to imagine an unforeseen external event, unless it is a close-by supernova that fries ship electronics and it takes time to repair them? Teegarden is not far enough that 'things in the way' of any size would not have been already spotted and planned for, so it would probably have to be something on or in the ship itself. Any failure that could not be repaired en route is going to be fatal, so that's a stretch, but can the drive fail in some hard but not impossible way to repair and restart? I'm struggling for ideas, to be honest, adding a century of travel that does not include adding to the route distance or considerably slowing the ship is not immediately obvious.

Strato Incendus
As they get closer to their destination it seems prudent the will start observing it more, so perhaps they discover something that will make them choose an alternative destination? I assume here the set of possible destinations have been chosen based on only remote sensing (i.e. no active probes first)
This in turn is something where I think exploration of the system with unmanned probes would definitely be part of the planning stage. Simply sending an expensive ship somewhere and hoping for the best does not only seem irresponsible towards the crew, it’s also an easy way to waste all the money that went into building the ship.

Hence, in my story I’ve postulated that Breakthrough Starshot 3 sent a bunch of solar sails to different stars, including Tau Ceti, 82 G. Eridani, Teegarden’s star, Trappist-1 etc., and Teegarden proved to be the best candidate. (The probe to Trappist-1 is still on its way when the story starts, given that Trappist-1 is 40 light-years from Earth.)

The “insufficiently explored target solar system” is used in Adam Oyebanji’s ”Braking Day” to reveal new information about it as the ship gets closer to arrival. But precisely for the reasons stated above, I find this idea rather unconvincing. They don’t need to know every last planet in the destination system, but at least the destination planet should have been confirmed to be habitable before the mission even started.
Please don't go there, @Strato Incendus, there's a Netflix sci-fi show I started watching, it was TERRIBLE across the board, but I stopped watching when their spaceship had to slow down because of a cloud of dark matter. The reason it's dark is the reason a cloud of it would be literally immaterial to a spaceship.
Alright, then let’s scrap that idea as quickly as it came. :) I was just brainstorming.
With apologies, I've lost track of whether the crew / passengers are awake or asleep? If they are awake, it is a long time for ship resources to support them unless such a long duration was part of the design parameters.
They are awake; sleeper ships are the next stage in development after the story is over.

The durability of all the parts of the ship, including the reactor, is a general problem. Any type of delay, even if just by a couple of years, could be fatal if the ship was only designed to last 125 years. Then again, if the ship is designed with enough redundancy in mind in all other areas, it would make sense that it has also been designed to be at least a little more durable than for just the planned duration of the mission.
But it is hard to imagine an unforeseen external event, unless it is a close-by supernova that fries ship electronics and it takes time to repair them? Teegarden is not far enough that 'things in the way' of any size would not have been already spotted and planned for, so it would probably have to be something on or in the ship itself.
Close-by supernova was indeed an option I had considered - specifically, one that might throw the ship off course. However, that won’t catapult it 8-10 light-years away (and if it does, the g forces will be so strong that all the crew members get squashed by them).

Aside from that, though, we’d face the same problem with supernovae as with gas clouds: A star large enough to go supernova, somewhere between Teegarden and Earth, would be known in advance, including the fact that it’s in its final stage. Also, given the close proximity of 12 light-years at max, both Teegarden b and Earth would probably be rendered uninhabitable by a supernova occurring so close by.

For Earth, I could indeed use that, since at the 2/3rd mark of the story, the crew on the ship needs to have plausible reason to assume they are now the last human beings in the universe (without that actually being the case). Currently I explain that via a massive solar storm hitting Earth and disrupting all communication with the ship for almost two decades (factoring in the time it takes for the first message from Earth after the solar storm to reach the ship that is now over 10 light-years away). A supernova would be a more convincing reason to suspect Earth may have been wiped out, but only if that supernova comes from a different direction. Meaning, the ship would have to be 10 light-years further away from the source of the supernova than Earth itself.
I'm struggling for ideas, to be honest, adding a century of travel that does not include adding to the route distance or considerably slowing the ship is not immediately obvious.
I must admit I’ve grown somewhat attached to Teegarden b as the target destination, including the eventual landing there. But I can of course at least look for other candidate planets that are in turn 10 light-years away from Teegarden - or within that range.

That is one upside of the “cliche” target destination Tau Ceti - 82 G. Eridani is 20 light-years from Earth, but only 8 light-years from Tau Ceti. So if Tau Ceti were to prove itself uninhabitable, the crew could more easily decide to “spontaneously” travel on to 82 G. Eridani.

The problem with that is: The known planets in the Tau Ceti system range in mass between 1.5 and 4 times the mass of Earth. Meaning, even on the smallest one of them, a person weighing 60 kilograms would suddenly weigh 90 kilograms. And this is something we already know now. Which again makes the idea that somebody would first send a ship to Tau Ceti, only to then experience the “surprising” revelation that even the smallest planet may not be suitable for humans, less believable.

I must admit I’ve grown somewhat attached to Teegarden b as the target destination, including the eventual landing there.
Just spitballin' here but what if Teegarden wasn't the initial destination, but became the destination because of events in the story? That changes your Act I but not your Act III.

Strato Incendus
That would raise the question: What other potentially habitable candidates lie somewhat on the way to Teegarden b? The other candidates (Tau Ceti, 82 G. Eridani etc.) are all in different directions, as far as I can tell.

There is no nearer star in Aries.

Strato Incendus
A star large enough to go supernova, somewhere between Teegarden and Earth, would be known in advance
It does not need to be between Teegarden and Earth, it just needs to be directed such that the ship is in the way.

Potentially, the crew could be informed that conditions at Teegarden are not habitable during their journey, and that could be found out via Solar System telescopes and sent to them via radio. Perhaps signs of life are detected? Morally, should the ship still go there? If not there, what's the fallback? That could be a large moon in a different system, it does not need to be a planet, and surely the crew weren't expecting to find another Earth at Teegarden that they could just land on and start their new lives? They must have tools to dig in and survive on a hostile surface.

Strato Incendus
There is no nearer star in Aries.
Thanks for confirming; that’s what I feared. I checked last night with a top-down map of the nearest stars, but the only stars that were depicted as close-by to Teegarden ”from above” are apparently on a different horizontal plane than Teegarden’s Star. And thus, they were still about 30 light-years away from Earth.
Potentially, the crew could be informed that conditions at Teegarden are not habitable during their journey, and that could be found out via Solar System telescopes and sent to them via radio. Perhaps signs of life are detected?
A general question is whether the ship could have its own telescopes on board. Given that it’s 3 kilometres long, the tanks on both ends have a diameter of 1 km, and the rings in between an inner diameter of 0.5 kilometres, that’s larger than any man-made object sent to space so far. So could they use on-board telescopes to look for other planets themselves (radial velocity method, transit method etc.)? I guess the main problem with that is that the ship is moving, so the point of reference keeps changing constantly?

In my setting so far, thanks to the unmanned probes sent by Breakthrough Starshot 3, plant life has already been detected on Teegarden b (in different colours than on Earth, ranging from various brown tones all the way up to black, to soak up the energy from the dimmer red dwarf star). No animals have been observed yet, though.

In the third book, when the ship does eventually land on the planet, they send down their android as a vanguard, who also takes a dive into the ocean in the “belt” around the planet’s vertical equator. (Teegarden b is tidally locked, so life is only possible in the twilight zone between the day and night side.) There the android discovers some aquatic species, eventually gets pulled down into the depths by some octopus-like creature, but his consciousness is uploaded to the ship server.
Morally, should the ship still go there? If not there, what's the fallback? That could be a large moon in a different system, it does not need to be a planet, and surely the crew weren't expecting to find another Earth at Teegarden that they could just land on and start their new lives? They must have tools to dig in and survive on a hostile surface.
The fallback for Teegarden b is Teegarden c. Both have similar masses, much closer to the mass of Earth than any other nearby candidates in other star systems. Though I’d expect Teegarden c to be much colder, more comparable to Mars.

Indeed, they aren’t expecting Earth-like conditions on Teegarden b: Slightly higher gravity (1.05 g), eternal sunrise / sunset, slightly warmer than Earth, and much shorter ”years” (Teegarden b just needs about 5 days to orbit its star once). Also, the atmospheric composition is slightly different, but still a breathable mixture of oxygen and nitrogen. In short: They aren’t expecting any outright “dealbreakers”. If they wanted to live underground, they simply could have stayed on Earth - where the majority of people are moving under the surface because of the impending gamma ray burst.
It does not need to be between Teegarden and Earth, it just needs to be directed such that the ship is in the way.
That’s great news, thanks a lot! ;) To me, this sounds like the most workable solution at the moment, so let’s continue down that train of thought:

Where and at what distance could we position a red-giant star in such a way that
- it doesn’t harm the Teegarden system
- it doesn’t harm Earth or the solar system
- it still creates a supernova cloud that would end up “blocking” the path in between the two systems (=making it unsafe to travel through)?

As far as I know, everything in a range of up to 30 light-years is in the danger zone of a supernova. Thus, the “area of effect” would certainly be big enough to warrant such a long “detour” as I need it: An evasive route of 5 light-years into any direction, which then means another 5 light-years that have to be covered at the end again to make it back onto the main route to Teegarden b.

Since @Vanadium 50 already said that there are no nearer stars than Teegarden b in Aries (I assume that means “no stars in general”, not just “no potentially habitable ones”?), do we know of any red giant stars of sufficient size in, say, about a 35 light-year radius of Teegarden’s star?

Because the supernova star needs to be far enough away from both Teegarden and Earth themselves to not damage them significantly, but the fastest route in between Earth and Teegarden would have to lead through the danger zone.

Of course, I could just “postulate” such a star within my story, but it can’t just pop into existence out of thin air (thin vacuum? ). It would have to be a star that already exists now, and if we don’t know of one yet, I would have to claim it hasn’t been discovered yet. Which is hardly believable, given the size a future supernova star would be required to have. It should be impossible to overlook for us in the 21st century.

Within the story, it’s actually good if the supernova star is known in advance. Then I can set up this plot twist properly, rather than having it happen out of nowhere: When it‘s said that Teegarden b is a safer home than Earth (because Teegarden b is not in the line of the gamma ray burst), somebody could ask whether Teegarden b is safe in general. (I’ve already “postulated” two gas giants in the Teegarden system that could avert asteroids, much like Jupiter and Saturn.) And then someone else could answer that the closest dangerous star to Teegarden’s Star is this red giant, which will go supernova soon, but it has already been confirmed that both Earth and Teegarden b are outside the supernova’s reach.

Finally, if there are no known objects in Aries currently that would fulfil these criteria, I could always have a “wandering star” end up there. But then I usually think of rogue brown dwarfs, comets, and asteroids - not of red supergiants.

Sorry, @Strato Incendus, what is the motivation for the additional journey? You have worked out a series of books, is there a compelling reason that the first one can't just be the story of an arduous interstellar trip? Why does it need what is a difficult to engineer detour?

Any...

A general question is whether the ship could have its own telescopes on board. Given that it’s 3 kilometres long, the tanks on both ends have a diameter of 1 km, and the rings in between an inner diameter of 0.5 kilometres, that’s larger than any man-made object sent to space so far. So could they use on-board telescopes to look for other planets themselves (radial velocity method, transit method etc.)? I guess the main problem with that is that the ship is moving, so the point of reference keeps changing constantly?
Yep, that's good enough for a serious telescope, and it's not moving fast enough that you can't image in high resolution.

Since @Vanadium 50 already said that there are no nearer stars than Teegarden b in Aries (I assume that means “no stars in general”, not just “no potentially habitable ones”?), do we know of any red giant stars of sufficient size in, say, about a 35 light-year radius of Teegarden’s star?
You can try https://stars.chromeexperiments.com/ and see if there are any red giants around, but from my stellar database, there aren't any. However, Groombridge 1830 is a super flare (I used it in my last novel to scarify a few hundred million people who lived in a series of orbitals!) so how about you stretch physics a touch and have a super flare erupt that fires off line of sight of the ship? The electronics would of course be hardened, but eject a sizeable amount of a red dwarf flare star at the ship, and it would take a hit!

Strato Incendus
Sorry, @Strato Incendus, what is the motivation for the additional journey? You have worked out a series of books, is there a compelling reason that the first one can't just be the story of an arduous interstellar trip? Why does it need what is a difficult to engineer detour?
A shift of perspective for the current Generation Five - from the optimistic attitude "we'll arrive in 25 years, and our kids will be the first grownups to walk on the planet" to "we will never get to see the planet ourselves, nor will our kids". In other words: The perspective the first generations started out with.

Yes, one could tell that story with the first generation on board - and I plan to do that in a prequel. However, their motivations are entirely different:

- For Generation Zero, the first one that boarded the ship,
the story starts out on Earth, and the focus is at least as much on why they want to get away from Earth (and their respective home countries) as it is about what they're hoping to find on the generation ship. (Push and Pull factors)

- For Generation One, their natural "teenage rebellion" against their parents overlaps with their struggle of being the first ones born on the ship
- the first involuntary members of the crew. In contrast to Generation Five, however, they are still fairly close to Earth. In fact, Earth is still much closer than Teegarden b at this point, so it's the path of lesser resistance. Generation One's struggle is with those who want to make the ship turn around and return back home; they have an idealised view of Earth (based on the stories their Earth-born parents told them as children, where they naturally left out the worse parts), since they've never been there themselves.

- For Generation Five, they're already so close to the target star that turning around would never even cross their minds. They're looking forward to seeing the landing themselves - that is the promise they grew up with, and hence, the reader perceives that promise through their eyes, too. The detour then breaks that promise, forcing them to find a new purpose for spending their entire lives on board the ship.

I definitely want to start on that Star-Trek-like optimistic note (locus amoenus) before I introduce some of the darker themes of my story.
There is so much "dirty sci-fi" these days that it has become hard to draw the line between science fiction and dystopia. If it's all grim from the outset, even the disaster plot points don't hit as hard anymore. Conversely, if the story starts out in a hopeful place, the low points hit that much more. Doesn't mean the story has to stay there, of course. It simply makes the story more dynamic.
Yep, that's good enough for a serious telescope, and it's not moving fast enough that you can't image in high resolution.
Great, then I can leave that feature of the setting in there and give the astrophysicists on board a little more to do. Thanks a lot! ;)
You can try https://stars.chromeexperiments.com/ and see if there are any red giants around, but from my stellar database, there aren't any.
I think I've seen this website before; I struggled to find Teegarden's star somehow (or struggled to find a search function on the website? ^^). But I did find Groombridge 1830.

Regarding red giants, the closest one to Earth seems to be a star called Gacrux (Gamma Crucis), and it's 88 light-years away. Good news for us... bad news for my story.
However, Groombridge 1830 is a super flare (I used it in my last novel to scarify a few hundred million people who lived in a series of orbitals!) so how about you stretch physics a touch and have a super flare erupt that fires off line of sight of the ship? The electronics would of course be hardened, but eject a sizeable amount of a red dwarf flare star at the ship, and it would take a hit!
Great suggestion, many thanks!

I've been using this top-down map to indicate the important locations in my Campfire Pro file: https://gruze.org/galaxymap/10pc/

Groombridge 1830 is one of the stars I came across yesterday; on the map, it goes by its alternative designations CF UMa or HD 103095 (in the upper left corner, where it says "Aur Cloud").

I already use a solar flare from the sun itself at the disaster plot point - a flare much stronger than the Carrington Event, and according to Anton Petrov, indeed a type of flare we might have to expect more frequently in the future. That flare disrupts all communication between the ship and the solar system.

Now of course, I could flip this around and have the communication systems fried by a solar flare on the ship's side instead
. That would explain more easily why they can't contact the entire solar system, whereas a flare of our own sun would most likely only affect one of the colonised planets it happens to hit.

Then the question is what to do with Earth later on, to make the crew of the generation ship reasonably believe humanity may have died out in the solar system.

The easiest way to do that is to indeed have the gamma ray burst go off during the year of my plot. Even though another solar flare from our own sun would probably be much more likely.
From a story-writing perspective, meanwhile, the gamma-ray burst can be considered a Chekhov's Gun: If I introduce it in the beginning, it better go off later in the story. So far, however, the burst is only a MacGuffin: A reason to get the ship to leave the entire solar system, rather than just relocate to Mars or so.

Suppose I flip this around - a super flare at the midpoint, WR 104 going off at the disaster plot point, with the personal disasters for my protagonists following suit - how would the flare cause the ship to go on a detour?

With the supernova, the cloud would expand over a long time, and the crew would see it long before they reach it. So an early-enough course correction to go around it, even if it extends the journey by a century, would be doable.

Superflares meanwhile would last much shorter. Sure, I can have one hit the ship, and... then what happens next? Would it slow down the ship? Force it to brake? Force it to go on a detour?

Or alternatively: Would the flare damage the drive, so that they can't brake (by accelerating in the opposite direction), and zip right past the target star? Then the "detour" would consist of going back to Teegarden, rather than around some obstacle in the way...

Then the question is what to do with Earth later on, to make the crew of the generation ship reasonably believe humanity may have died out in the solar system.
They won't think this unless all the ship comms are fried, because they can pick up radio transmissions, so that's a puzzler. But humanity can be wiped out in more insidious ways than Sol misbehaving. It could be a geneered virus that knocks us back to the Stone Age, and that would percolate through the Solar System. Some bases might survive, but not so much that they would be beaming signals that the ship can hear.

Alternatively, why describe the Solar System disaster at all? Just have them go dark and let the crew's paranoia paint the picture(s) of malfeasance back home.

A shift of perspective for the current Generation Five - from the optimistic attitude "we'll arrive in 25 years, and our kids will be the first grownups to walk on the planet" to "we will never get to see the planet ourselves, nor will our kids". In other words: The perspective the first generations started out with.
Aha, that makes sense, but it's difficult to set up, as you're finding. But what would happen if the ship's engines had to be reduced in power due to 'technical difficulties' and the trip just took longer than expected? You can set up some dramatic twist for that if you wanted - sabotage, space junk, shoddy workmanship by the lowest bidder - you don't need the ship to detour, it just needs to slow down.

I've been using this top-down map to indicate the important locations in my Campfire Pro file: https://gruze.org/galaxymap/10pc/
I haven't come across this one, @Strato Incendus, thanks. I've been looking for a good visualisation and position app out to 300 LY for my current series, one that has a search function and which allows you to work out distances between stars, but can't find one. So, I've been messing around using 3D room design software instead. Stars as light globes with their galactic coords translated into millimetre X,Y,Z values...it's a work in progress that I am hoping pays off!

Strato Incendus
Aha, that makes sense, but it's difficult to set up, as you're finding. But what would happen if the ship's engines had to be reduced in power due to 'technical difficulties' and the trip just took longer than expected? You can set up some dramatic twist for that if you wanted - sabotage, space junk, shoddy workmanship by the lowest bidder - you don't need the ship to detour, it just needs to slow down.
Journey plan is one year accel and decel with 123 years coasting, so ship's engines are off i.e. reducing power is not an option.

I think the only reason we are looking at a detour at all** is because we've rejected any plausible reason to slow the ship. After all, it is effectively stationary in space wrt to anything. Doppler-hardened radiation is about the only thing the ship will encounter.

**right Incendus?

Anything else they might encounter will either be small enough to go around or big enough to be known ahead of time.

Strato Incendus
Journey plan is one year accel and decel with 123 years coasting, so ship's engines are off i.e. reducing power is not an option.
Thanks @DaveC426913, but if that's the case, the first gen crew are surely not expecting to arrive alive in the first place?

But it reinforces that @Strato Incendus is probably going to just have to invent an event and trust the readers willing suspension of disbelief...and lack of cosmological knowledge...to get them through.

Unless...

The cloud was known about, but people who did not want the ship's trip to be successful suppress the knowledge and it launches blissfully unaware?

Thanks @DaveC426913, but if that's the case, the first gen crew are surely not expecting to arrive alive in the first place?
Correct.
The cloud was known about, but people who did not want the ship's trip to be successful suppress the knowledge and it launches blissfully unaware?
That'd be a tough sell. It'd criminal negligence on a massive scale - sending them to their deaths.

Correct.
Okay, then you have to occasionally fire the engines for maintenance purposes. Maybe a routine run triggers a failure and they won't have sufficient thrust to slow down in the planned time, so go past Teegarden's Star, stop, and limp back?

That'd be a tough sell. It'd criminal negligence on a massive scale - sending them to their deaths.
Not such a tough sell, surely? The contractor might think there's redundancy so their crime is only a small one. Or, there could be a quality mix up in the supply chain, so the parts don't last as long as they're supposed to. Or, someone might just be heartless enough to pocket a LOT of cash for shoddy goods, because it's not like anyone is coming back to tattle on them. The news is full of such sociopaths, studies suggest this behaviour propels people (usually men) to the very top of business and political life!

Strato Incendus and DaveC426913
Maybe a routine run triggers a failure and they won't have sufficient thrust to slow down in the planned time, so go past Teegarden's Star, stop, and limp back?
For what it is worth I like that. It is fairly simple to understand and also sounds like a fairly realistic scenario.

The thrust reduction can of course happen in many ways (e.g. like one-time or periodic down-time with zero thrust available), but as a rough estimate using simple constant acceleration profiles then the total relative extra time ##\Delta t## spend on overshooting due to reduced constant acceleration (that is 3 constant acceleration segments instead of just one) should be around $$\Delta t = \frac{r+\sqrt{2r}}{1-r} t ,$$ where ##t## is the original deceleration time and ##(1-r)a## is the new reduced acceleration. So for example, a 38% reduction in acceleration will costs around 200% extra time so if the original deceleration phase was 50 years it will now take 100 years extra.

Strato Incendus and Melbourne Guy
Melbourne Guy said:
The cloud was known about, but people who did not want the ship's trip to be successful suppress the knowledge and it launches blissfully unaware?
---
DaveC426913 said:
That'd be a tough sell. It'd criminal negligence on a massive scale - sending them to their deaths.
--
In my old age, having lived to seen thousands if not millions sent to their deaths for the convenience and/or profit of others, I find this all too believable.

In my old age, having lived to seen thousands if not millions sent to their deaths for the convenience and/or profit of others, I find this all too believable.
I'd believe it too, @Hornbein, and find it sad that humanity seems to be wired that way.

But thanks for posting, I missed which of my comments @DaveC426913 was actually objecting to in my original reply and it's been too long now to edit. But, I do kinda agree with @DaveC426913, if his 'hard sell' refers to the likelihood of a conspiracy to keep the dangerous cloud a secret, sorry for a quick read of your post being a wrong read of your post.

Still, sci-fi is replete with conspiracy stories, I might have written one myself a while ago, but @Strato Incendus might have to jump through some narrative hoops to make that specific idea workable.

Well, this has taken an interesting turn, thanks for your many replies!

I've still been thinking about that superflare idea yesterday. Specifically, one coming from Groombridge 1830, also known as Argelander's Star. The problem is that it seems to be 30 light-years away from Earth. Even with a really massive superflare, could such a flare reach far enough to cross the route of a ship from Earth to Teegarden's star? Or is this the point where we'll have to "stretch physics" a bit? (And by "a bit", I mean several light-years, perhaps more than the entire distance between Earth and Teegarden b.)

Because if the flare can reach the ship somewhat plausibly, while the crew would know with sufficient prior notice, it would depend on the dimensions of that flare whether the ship could easily go around it or not, slow down in front of it, or accelerate briefly so that it makes it past the flare just before it would hit them.

For reference: The ship is about 3 km long. I looked up the size of solar flares and found anything ranging between 100,000 km and 500,000 km.
Now of course, that's just one dimension - I don't know how much space they take up in 3-dimensional space. But if the ship had to cover 100,000 km to get past the flare in time, at 0.1 c (or roughly 30,000 km per second), that would take a little over 3 seconds; getting past a 500,000 km flare would take between 16 and 17 seconds.

Speeding past the flare with a short-term acceleration boost is my current idea. Then I could indeed have some failure in the drive that requires a bunch of guys to fix (especially if that drive has been dormant for a century - in "Braking Day", even the heating system is deactivated in those rooms). They would be sent to the rear of the ship, behind the aft tank, where the drive is, and try to get it to fire up fast enough to accelerate past the flare. Because otherwise, the flare would hit the ring sections in the middle, including the habitats, where their families live. Meanwhile, the commanding officers would try to evacuate the rings closer to the rear of the ship to the lab ring and public ring, which are closer to the front.
Then I could have the ship barely escape the flare, but the flare damages the very rear end, including the drive, and the people who are still in the rear section of the ship.

Now, as far as I can tell, the main way a solar flare could kill someone would be through radiation, i.e. the people would get cancer afterwards. That is a "slower death"; the more spectacular variant would be if the ship is close to being hit by the flare, smack in the middle, and the commander eventually has to fire-up the now-repaired drive while some people are still working inside of it, to at least get the rings where the families live out of harm's way.
Then her justification could be "these people working on the drive would have died anyway, and much more slowly so, because they all would have been exposed to massive amounts of radiation from the flare hitting the rear of the ship."

It could be a geneered virus that knocks us back to the Stone Age, and that would percolate through the Solar System.
I generally try to avoid man-made reasons for extinction in this story; most people seem to be fairly aware of those. It also quickly gives a story a misanthropic spin, and as I've said previously, that is such an omnipresent attitude in "entertainment" shows these days that I actively try to go against the zeitgeist here, by keeping the story in Star-Trek / Orville tradition.

And in the same breath, by showing the "indifference of the cosmos", rather than the "evils of humanity", I get to make people aware of some of the lesser-known ways humanity could die out. There are countless films about zombie apocalypses, nuclear warfare etc. But I have yet to see one depicting Earth after a gamma ray burst, or after a solar flare hitting a heavily digitised world.
Alternatively, why describe the Solar System disaster at all? Just have them go dark and let the crew's paranoia paint the picture(s) of malfeasance back home.
Well, if a gamma ray burst goes off in the Milky Way, and it would hit the solar system, I assume you would be able to see that from 10 light-years away? Would you see the beam from the side, if you're not in the line of fire yourself?
Journey plan is one year accel and decel with 123 years coasting, so ship's engines are off i.e. reducing power is not an option.
Correct.
I think the only reason we are looking at a detour at all** is because we've rejected any plausible reason to slow the ship. After all, it is effectively stationary in space wrt to anything. Doppler-hardened radiation is about the only thing the ship will encounter.

**right Incendus?
Yes, it seems hard to come up with a plausible reason for braking at this point. Unless the reactor / drive fails in some weird way where they can fire it up again briefly, but they'd have to do so right now - and if they don't, they would lose the drive, and thus the ability to brake at the end.

Perhaps that could be worked into a reason for slowing down to 2.5% light-speed at the moment, and then have an easier time decelerating from that reduced speed to 0 at the very end... but yeah, that explanation feels somewhat "manufactured".
Thanks @DaveC426913, but if that's the case, the first gen crew are surely not expecting to arrive alive in the first place?
No, Gen One doesn't expect that - but the first book will be about Generation Five, who were raised with precisely that perspective. Gen One will be explored in the prequels (should I ever complete them). But it's good that I've already started conceptualising them, since even if I never finish the prequels, they still serve as backstory for the main story. And indeed, some of that is directly relevant to the next point:
The cloud was known about, but people who did not want the ship's trip to be successful suppress the knowledge and it launches blissfully unaware?

That'd be a tough sell. It'd criminal negligence on a massive scale - sending them to their deaths.
The founder of the project that built the generation ship was an American billionaire who made his fortune by making what is basically my equivalent of the Holodeck available to individual customers: In small VR chambers the size of a closet or sound booth (every quarter on the generation ship has one of those). Yet, his wealth also eventually encouraged some have-nots to kidnap his firstborn son for ransom, and the son died when the police tried to free him.

As successful people tend to do, the billionaire internalises everything - both his successes and his failures - and thus, he has been asking himself ever since his son's death "how was this my fault?" And he arrived at the conclusion that, had his son not been born into a family has wealthy as his own, he probably would never have been kidnapped in the first place - the kidnappers wouldn't have had any incentive to do so.

Of course, his son couldn't choose which family he was born into - just like the people on the generation ship can't choose whether they want to be part of the crew or not (except for the very first generation). This is one of the core ethical problems built-into generation ships - yet sadly, all generation ship stories I've come across so far completely let the conflict potential of the premise go to waste.

The project founder indeed doesn't expect the mission to be successful. And his ideological opponent does accuse him of knowingly sending the crew to their deaths. However, the project founder does not actively sabotage the mission - on the contrary: He goes out of his way to ensure the crew is comprised by the best of the best he can find on Earth (not just in terms of expertise, but also character), that the society on the ship has division of powers, a reliable constitution etc.

In short: He had the ship designed as a "steelman", the best possible representation of a view he actually no longer endorses himself. To him, the generation ship is a scientific endeavour - but not so much in astronomical terms, but in terms of him trying to prove his own pessimistic world view wrong. If the mission succeeds, then humanity has proven itself worth saving from extinction, because without FTL travel, a generation ship could simply be what it takes to expand civilisation to another star. But of course, "success" is not only measured in terms of "do they reach the destination star or not?", but also "what kind of society does the crew of the ship turn into, what kind of civilisation is actually being exported there?"

The news is full of such sociopaths, studies suggest this behaviour propels people (usually men) to the very top of business and political life!
The "psychopaths make it to the top" principle is indeed one I use on the ship's commander in the first book (it's a woman, though). So when you then get to see the (male) billionaire who funded the generation-ship project in the prequels, you're inclined to perceive him through a similar lens. And in some ways, he is - but more like a "mad scientist", trying to prove something.

Meanwhile, he has to defend his principles and fight off a bunch of other sociopaths, who try to bribe him or to buy influence, to shape the future society of the generation ship according to their own visions - starting with who should make it aboard in the first place. And one of the people trying to influence him the most is his own son (his second one).
So for example, a 38% reduction in acceleration will costs around 200% extra time so if the original deceleration phase was 50 years it will now take 100 years extra.
That's a cool idea! But if I understand it correctly, this would have to happen at the very end of the journey? Meaning, during the last year, when the ship tries to brake, and then the crew realize their braking force is no longer strong enough?

if I understand it correctly, this would have to happen at the very end of the journey?
At any point during deceleration really, but if you are looking to add 100 years to the journey then one could try solve that equation to give ##r## as a function of ##t## (and ##\Delta t##). With that you could just plug in any given remaining time ##t## and get the reduction needed for that. As time goes by while following a nominal deceleration profile the "needed" acceleration reduction to give 100 year of extra time will of course then get closer and closer to 100% reduction.

And just like when bringing your car to a stop at the red light, it will be prudent for the crew to start decelerating early and not "slam on full brakes" at the latest possible movement, meaning they can absorb some reduction in maximum acceleration capability while staying on profile, and if so the relevant reduction is the actual maximum acceleration relative to the nominal acceleration, not relative to the nominal maximum acceleration. Like if you apply your car brakes 50% then even loosing up to two brakes you should still be able to break as planned by applying remaining brakes 100%. For a generation ship going for 50% safety margin sounds like too much time wasted, but a more sensible number depends strongly on the reliability of the actual rocket system and how easy it is to keep operational during deceleration.

In my old age, having lived to seen thousands if not millions sent to their deaths for the convenience and/or profit of others, I find this all too believable.
Yeah. In general, no doubt.

But it might require some footwork to set up a plausible scenario where so many contribute to an asset (and associated tech/resources/money) that is then sent away to its doom, never to be recovered. It's hard enough to get such a mission going anyway, any resistance might cause it to fail (thus saving the colonists' lives).

Not that it can't be done, just got to be thought through, and that eats up pages.