Strato Incendus
- 188
- 23
Alright, time to turn to something I've neglected for far too long, but which I cannot afford leaving unaddressed:
My generation ship Exodus (accelerating and braking at 0.048 m/s2 over 25 years, maximum coasting speed 0.125 c) needs to decide on a specific type of nuclear-fusion reactor. This doesn't just refer to what type of fusion reactor would work the best in zero g vs. on Earth, but also what type of fusion reactor you personally consider the most likely to become a reality first, just in general.
For starters, I've included a few of the most commonly proposed fusion mechanisms in a poll. Notably, I've added the Boron-Hydrogen reaction, as @John Strickland proposed it to me (taken from a story of his) in the very first thread on the Exodus ship in this post.
Suffice it to say, I don't think I can simply put a plain old Tokamak or Stellarator into one of the 21 spherical tanks inside the 1-km-large aft sphere of the Exodus (sphere packing in a sphere) and call it a day. Anyone familiar with the problems the Tokamak and Stellarator are currently facing will be unconvinced, and thereby pulled out of the story quickly, if that's all I have to offer in terms of how both my ship engines and the general power supply for all the electricity on board work.
Recently, I watched a video from Real Engineering about the Helion design (using the Deuterium + Helium-3 reaction, which was also the one I had chosen for the Exodus thus far). For me, as a layman, this design seemed to be using the heat energy more efficiently, rather than heating water to hit a turbine as an interim step. However, I've also heard some of the criticisms of the Helion approach, such as the Deuterium + Helium-3 reaction being less efficient in general than Deuterium + Tritium.
So now, I'm of course somewhat confused and uncertain about how to proceed. Especially because it's still not fully clear whether the exact workings of the nuclear-fusion reactor will end up becoming plot-relevant (to book 1 or any of the planned sequels and prequels) or not.
Obviously, there is some creative liberty as long as no particular approach to nuclear fusion has been successful yet (in terms of becoming a reliable source of energy that can be upscaled to industrial levels). At the same time, that also makes it easy to "bet on the wrong horse" here, and postulate a type of fusion reactor for my ship that's of a different kind than the one that actually ends up becoming viable one day.
Keep in mind my ship is shaped like a dumbbell (credit to @DaveC426913), and that the spherical tanks inside the fore and aft sphere of my ship double-act as radiation protection from the front and back. Hence, so far, I would presume these tanks include "heavy water", i.e. liquid deuterium oxide.
Personally, I'm confident enough about the themes of my story to consider that part "timeless", so that the story doesn't become worthless immediately if any of its assumptions about the universe are disproved. That's because the thematic conflict and the character psychology is still at the heart of the story - it's not just speculative fiction about "what would life on a generation ship be like". You can still enjoy "The War of the Worlds" while fully knowing that Mars is neither inhabited by aliens, nor covered by a Red Weed.
However, I acknowledge that there is a subgroup of readers that approaches fiction this way - especially in sci-fi, and especially the "harder" sci-fi gets. And given how much time I (with your help) have already spent on designing the ship itself, so far it's pretty "hard" sci-fi; much harder at least than the works of fiction in the spirit of which it is written (such as Star Trek).
Thus, I can't just handwave the nuclear-fusion reactor away, after having already dedicated a large amount of attention on getting the details of artificial gravity via centrifugal force, acceleration to relativistic speeds, protection against radiation and space debris etc. right. Or rather, if I handwave something as integral as the fusion reactor now, the hard-sci-fi crowd will probably be quick to dismiss the story as a whole. Because some of them may end up being drawn to it for what they consider the speculative-fiction aspect.
If they end up being disappointed by the focus being more on theme an character psychology, that's one thing; however, I don't just want to lose them simply because I refused to do my homework on the technical aspects of the ship design. It's not something I care for in a story in and of itself; rather, I care enough about immersion in a story that I want to do this "chore" properly.
I even find myself applying this standard to other sci-fi works as a reader / viewer; for example, whenever I encounter a setting in which Mars has been terraformed (such as Elite: Dangerous), I must assume the author "kind of forgot" about Phobos and Deimos, the fact that Mars's gravity won't change, etc.
A terraformed Mars is kind of to sci-fi what the "one-handed longsword" is to fantasy: An often regurgitated trope that has little to do with actual research from physics or history / HEMA (historical European martial arts), respectively. Sure, every piece of fiction needs to handwave some things; but I prefer to handwave in areas about which fewer people have expert knowledge - so that the overall number of readers pulled out of the story by a disruption of their suspension of disbelief will hopefully be kept to a minimum.
So, without getting into controversial real-world speculation too much, but instead focusing on the fictional context of a hitherto overly ambitious project like a 3-km-long interstellar generation ship:
What type of nuclear-fusion reaction would you choose, and which type of reactor to go along with it?
My generation ship Exodus (accelerating and braking at 0.048 m/s2 over 25 years, maximum coasting speed 0.125 c) needs to decide on a specific type of nuclear-fusion reactor. This doesn't just refer to what type of fusion reactor would work the best in zero g vs. on Earth, but also what type of fusion reactor you personally consider the most likely to become a reality first, just in general.
For starters, I've included a few of the most commonly proposed fusion mechanisms in a poll. Notably, I've added the Boron-Hydrogen reaction, as @John Strickland proposed it to me (taken from a story of his) in the very first thread on the Exodus ship in this post.
Suffice it to say, I don't think I can simply put a plain old Tokamak or Stellarator into one of the 21 spherical tanks inside the 1-km-large aft sphere of the Exodus (sphere packing in a sphere) and call it a day. Anyone familiar with the problems the Tokamak and Stellarator are currently facing will be unconvinced, and thereby pulled out of the story quickly, if that's all I have to offer in terms of how both my ship engines and the general power supply for all the electricity on board work.
Recently, I watched a video from Real Engineering about the Helion design (using the Deuterium + Helium-3 reaction, which was also the one I had chosen for the Exodus thus far). For me, as a layman, this design seemed to be using the heat energy more efficiently, rather than heating water to hit a turbine as an interim step. However, I've also heard some of the criticisms of the Helion approach, such as the Deuterium + Helium-3 reaction being less efficient in general than Deuterium + Tritium.
So now, I'm of course somewhat confused and uncertain about how to proceed. Especially because it's still not fully clear whether the exact workings of the nuclear-fusion reactor will end up becoming plot-relevant (to book 1 or any of the planned sequels and prequels) or not.
Obviously, there is some creative liberty as long as no particular approach to nuclear fusion has been successful yet (in terms of becoming a reliable source of energy that can be upscaled to industrial levels). At the same time, that also makes it easy to "bet on the wrong horse" here, and postulate a type of fusion reactor for my ship that's of a different kind than the one that actually ends up becoming viable one day.
Keep in mind my ship is shaped like a dumbbell (credit to @DaveC426913), and that the spherical tanks inside the fore and aft sphere of my ship double-act as radiation protection from the front and back. Hence, so far, I would presume these tanks include "heavy water", i.e. liquid deuterium oxide.
Personally, I'm confident enough about the themes of my story to consider that part "timeless", so that the story doesn't become worthless immediately if any of its assumptions about the universe are disproved. That's because the thematic conflict and the character psychology is still at the heart of the story - it's not just speculative fiction about "what would life on a generation ship be like". You can still enjoy "The War of the Worlds" while fully knowing that Mars is neither inhabited by aliens, nor covered by a Red Weed.

However, I acknowledge that there is a subgroup of readers that approaches fiction this way - especially in sci-fi, and especially the "harder" sci-fi gets. And given how much time I (with your help) have already spent on designing the ship itself, so far it's pretty "hard" sci-fi; much harder at least than the works of fiction in the spirit of which it is written (such as Star Trek).
Thus, I can't just handwave the nuclear-fusion reactor away, after having already dedicated a large amount of attention on getting the details of artificial gravity via centrifugal force, acceleration to relativistic speeds, protection against radiation and space debris etc. right. Or rather, if I handwave something as integral as the fusion reactor now, the hard-sci-fi crowd will probably be quick to dismiss the story as a whole. Because some of them may end up being drawn to it for what they consider the speculative-fiction aspect.
If they end up being disappointed by the focus being more on theme an character psychology, that's one thing; however, I don't just want to lose them simply because I refused to do my homework on the technical aspects of the ship design. It's not something I care for in a story in and of itself; rather, I care enough about immersion in a story that I want to do this "chore" properly.

I even find myself applying this standard to other sci-fi works as a reader / viewer; for example, whenever I encounter a setting in which Mars has been terraformed (such as Elite: Dangerous), I must assume the author "kind of forgot" about Phobos and Deimos, the fact that Mars's gravity won't change, etc.
A terraformed Mars is kind of to sci-fi what the "one-handed longsword" is to fantasy: An often regurgitated trope that has little to do with actual research from physics or history / HEMA (historical European martial arts), respectively. Sure, every piece of fiction needs to handwave some things; but I prefer to handwave in areas about which fewer people have expert knowledge - so that the overall number of readers pulled out of the story by a disruption of their suspension of disbelief will hopefully be kept to a minimum.

So, without getting into controversial real-world speculation too much, but instead focusing on the fictional context of a hitherto overly ambitious project like a 3-km-long interstellar generation ship:
What type of nuclear-fusion reaction would you choose, and which type of reactor to go along with it?
