It’s not quite that bad. Jupiter is 5.2 times as far from the Sun as Earth, so the sunlight intensity is 3.7% of Earth’s.
We actually have sent a solar powered space probe to Jupiter: Juno. However, to get enough power, its solar panels are high efficiency multi-junction cells (about 45% efficiency) and have roughly the cross-section area of a large bus.
I was going to suggest something like that, too (though I don’t know why you’d need mirrors at different altitudes).
Also, you don’t need full Earth levels of sunlight. Some plants on Earth like growing in the shade: Use those (or other plants engineered to be shade-tolerant), and you could get by with a lower collection factor.
At 3%–4% of Earth irradiance, the ambient light at Jupiter would be about the same as pre-dawn or twilight on Earth. While there is no atmosphere to scatter or absorb the near-UV and UVA that is beneficial to plants, this still presents an order of magnitude reduction in light. Even shade-tolerant planets require light which they get from reflected sources, along with nutrients from other plants that use direct sunlight. I can’t think of a primary food-bearing plant which is shade-tolerant to the degree that would be suitable for growth at the solar irradiance at Jupiter orbit without significant concentration.
Stranger
I’ve never watched The Expanse, but are they really limited to solar power? Why don’t they use fusion reactors or whatever sci-fi power source they have to run grow lights. It’s not like we need sunlight to grow plants on Earth - a fission reactor powering UV lamps and you’re not even dependent on the Sun as an ultimate source of power as you would be with solar/wind/hydro/fossil fuel-sourced electricity.
Seems to me like it should be 30,000,000 s (300,000,000 m/s / 10 m/s^2).
As for the mirrors, if the average debris velocity of the pieces is of the same order as the orbital velocity, then there will be a fairly high fraction that falls to the surface. It’ll spread out depending on how much momentum was imparted but as Stranger notes, the pieces will have such a high velocity upon impact with the surface that they can do a lot of damage.
Oh, sure, you’d have a very hard time doing it just with shade-tolerant plants. Realistically, you’d still need big mirrors or some other sort of concentrator. But you could use a smaller concentrator with a shade-tolerant plant than with a sun-lover.
Getting back to the mirror’s orbit question, it could be that they’ve deployed it as a statite:
You’d have to play with the math to see if you could get the vectors to work out right, to both reflect the sunlight to the farm, and use it to maintain the orbit, but it’s not ridiculous on the face of it. And this explains why the mirror falls when it is damaged: Not only does it lose a significant portion of its reflectivity, what’s left will not be properly aligned to stabilize the orbit.
There’s almost certainly some handwaving on the math, but the idea is conceptually sound.
The problem with that is that ‘statite’ like Robert Forward’s “Hovering Hawke” is marginally plausible at great distances (about five times the distance to the Moon) with the solar irradiance at Earth orbit, but at the orbit of Jupiter the amount of thrust per unit area is less than 4%, while there are multiple perturbances from the other moons, and the satellite itself would be in an independent orbit around Jupiter. It would just make more sense to have a solar reflector in a highly inclined synchronous orbit around Jupiter, constantly reorienting to provide light to Ganymede. However, that still wouldn’t explain how large portions of the mirror fall upon Ganymede.
I suspect the authors didn’t really think too much about the orbital mechanics (or of the other issues in living and growing food on Ganymede), and as a reader you are just supposed to accept that this is a workable thing without delving into the details.
Stranger
Once again you are assuming that the effects of low gravity can be extrapolated from the effects of freefall; there must be a relation between microgravity and low gravity, since at some point gravity becomes so low that it has minimal effect. But the details of that relationship have not yet been demonstrated.
Ganymede’s gravity is a seventh of that on Earth, and this may be enough to maintain many human functions at nominal levels.
Fusion power would be a good choice for colonies on Ganymede, Callisto and Europa, assuming we can ever get it to work. The Jupiter system also has a vast magnetic field that could be tapped like a dynamo, allowing the generation of power at a local level.
I do like the concept of beamed power from the inner Solar System, which Stranger has mentioned a few times; but if the Jovian moons can generate their own power locally, they need not be dependent on external factions and factors.
A mirror-swarm would be a reasonable option, I think. Millions of gimballed, open-framework spheres several metres across, each with a flat mirror that can be angled and aimed; orbiting in a swarm of non-intersecting orbits (each orbit offset by a tiny amount, resulting in a thick torus that could collect a significant amount of light). This would be a good option if other, better options (such as fusion, magnetic generation or beamed power) were not available.
They do have a super efficient fusion drive system, but I don’t know if that is something that could be sued to produce power or light directly.
There are some downsides to solar, but the upside is that it doesn’t cost any fuel.
In particular, in low (but nonzero) gravity, you could wear a weighted suit to give you approximately the same skeletal loading as on Earth, but with no gravity at all, that’s impossible.
Also, the type of fusion they are using would guzzle lithium or boron by the ton. Both of which are semi-common elements, but not so common that you’d want to be throwing them away needlessly.
I’m pretty sure the fusion they are using uses unicorn farts and rainbow tears.
They regularly accelerate continuously essentially just for passenger comfort, even though a constant acceleration burn is pretty much the least efficient way to get anywhere. Whatever the process is, fuel is not that big a concern. It only really matters when the plot needs it to.
Of course, an engine where you are throwing reaction mass out the back is different from a reactor that produces power, so their epstein drive may not work nearly so well for stationary power production.
Converting either thermal or kinetic energy to electrical power is something we can do efficiently with today’s technology. It beggars belief that a culture with highly efficient fusion propulsion would be incapable of generating electricity via fusion.
Well, ok, I was just using existing knowledge. Which actually says that such an engine would ‘work’. That is, a million ISP isn’t totally unfeasible if the exhaust velocity is 3-4% of the speed of light. And you could fuse hydrogen + lithium, hydrogen + boron, or helium-3, and get charged particles that you could bend with magnets so they fly out the back of the engine at that velocity for that kind of ISP.
The catch - the thing that makes it science fiction, maybe fantasy - is the absurd rates of acceleration they get. To the point that 8+ Gs is something most warships can do, you just have to set the throttle to that. In reality, the problem with such an engine would be that since your drive flare would be releasing terawatts or greater - just absurd quantities of energy - even the tiniest fraction of that terrible flare of fusion flame would require you to mass down the ship with so much required heat radiating capacity, plus magnet mass, and other things, that you’d end up with plausible accelerations measured in maybe micro-Gs…
A “weighted suit” may address the gross musculoskeletal issues with low gravity (although walking around with seven times the mass of your body weight is going to cause a lot of problems with inertia; better start planning to slow down long before you get to a door or you’re going to find yourself thrown right into it) but does not deal with the cellular and fluid distribution problems that affect the body at very fundamental levels. It is true that we don’t have any definitive answers about the effects for a lack of data, but space physiologists expect to see numerous issues with long term habitation in low fractional gravity environments in both childhood and adult development, some of which may not be manageable without significant advances in medical science and genetic modification.
Stranger
Since we aren’t going to be living on Ganymede any time soon, I’d expect that there would be some fairly major advances in medical science and genetics before we are ready to do so. But the prospect of modifying humans to live in an alien environment is something many people might find disturbing. I don’t believe that The Expanse has considered this aspect yet in any detail, but I may be wrong.
Well in a way, it shares the problem all “mid-future” science fiction has. Because the actual way forward is completely obvious.
Develop ever more intelligent machine systems. Integrate them into ever more integrated packages and pools of interlinked subsystems. That is, develop general AI, through methodical and incremental improvements over a period of probably decades, using previous, simpler AI systems to help the engineers who do this solve the technical problems.
Once you have these advanced AIs, chemists and physicists and concrete examples from biology and semiconductor fabs tell us we can probably build circuitry and functional machinery that works at the nanoscale.
And then, eventually, either the AIs will be capable and smart enough to take over from there, or maybe humans will find a way to preserve some of themselves through ripping their brains to pieces and copying them.
All this really should happen within the next century. It might take longer but this seems unlikely because a lot of the processes involved seem to be accelerating.
Once you get all that - where what you have is basically “machine men or man machines”, to borrow a phrase (either computing machinery made of some sort of very dense, molecular scale, 3d circuitry just as good as humans or humans made into such systems, basically no practical difference) - the future is obviously not very interesting to a writer of fiction. It is difficult to grasp what such entities would do, as they would probably not engage in any of the inefficient things that humans even do that make people have personality at all. Though even that’s just speculation.
And for beings made of circuitry, they ain’t gonna be using mirror farms over Ganymede. They won’t need artificial gravity or need to waste fuel on transfers orbits faster than efficient ones.