I still don't understand why you need to build a Dyson sphere and then transport the energy to where it's needed when you can build decentralized fusion reactors. What am I missing?
The reason to build a Dyson Sphere (or Swarm) is that you want all (or at least a large fraction) of the energy output of a star. To "build decentralized fusion reactors" that can provide the same scale of energy is even less practical than building a shell around a star and would require far more materials! Also, fusion is really simple when the ignition energy is provided for free by the gravitational compression of something the size of a star, and not so simple when you're trying to get it started on a small scale using any other form of energy for ignition. The bottom line is we don't really know if small-scale, controlled, net-energy-positive fusion is possible at all, but if it is it has a lot of overhead costs... you then have to deal with ignition energy, containment, etc. You're trying to make a mini-star and keep it tame. The physics are not favorable to this, they are favorable to star-sized stars, where gravity and fusion energy pressure can balance each other for millions of years.
The concentrated energy of Dyson Sphere can be very useful. Feed some of it into lasers and then launch starships and then slow them down when they get to destination. Not tiny probes with fusion reactors but full size starships.
Feed most of the energy of star to lasers and end up with weapon that will melt planets across the galaxy.
Honestly, don't need to expand across the galaxy if have Dyson Sphere, which could be explanation of Fermi Paradox.
Diffraction limit determines the fundamental beam divergence angle theta = lamda/pi/D, where D is the beam diameter, lamda is wavelegth of elwctromagnetic radiation (eg. light).
To minimize theta, we need to either increase D or decrease lamda.
Lets assume we would be able to make far infrared high power lasers, at say 10,000 nm = 1e-5 m wavelength.
Lets assume we would be able to make D, the diameter of our laser beam, similar to the diameter of a typical planet, for Earth it is ~13,000 km = 13e6 m.
Theta = 1e-5 / 3.14 / 13e6 ~= 1e-13 radians.
Sun is ~ 25,000 light years from the center of our galaxy, ~= 25e3 y 3e8 m/s 31.5e6 s/year ~= 1e20 m.
Laser beam diameter, there far away, would be: 1e-13 *1e20 = 1e7 m, similar to the diameter of Earth, not much further diverged, focused and delivering the wast amount of energy all over the planet thereby evaporating it to a gas.
Indeed, what you say about the melting far away planets is possible, in theory.
Can you build decentralized fusion reactors? This far the most efficient fusion reactor humanity has available to it exists approximately 1 AU away and is rather difficult to relocate.
The technology for a Dyson sphere is primarily the technology for suspension bridges, solar farms, and intensive hydroponics (all well understood) + the technology for the ISS (well understood at this point). The only missing piece there is a fully sustainable (i.e. only energy input) life support system, which we have existence proofs for on Earth but haven't built to reliable engineering standards yet. If we have the material, we could start building it today and get designs that worked well quickly, even if we had to ship in life support maintenance alongside computer chips & pharmaceuticals.
The part we don't know how to do yet is getting the material. Building structures that large in space, the resources for it have to come from space, we cannot lift it off Earth. So we need to figure out how to mine asteroids, and maybe also how to mine Mercury. Either one would be sufficient at the start. Neither of those are a well-understood problem, let alone solved, so that's where you should invest resources if you're a billionaire looking to start a Dyson sphere and think SpaceX is on track for launch cost reduction.
I think in terms of science and engineering difficulty, it's a pretty even race as to which is more difficult between making fusion actually produce net useful energy and being able to mine & refine materials from an asteroid + build a sustainable life support system.
The reason fusion "seems easier" is because it is economically far more achievable, and there's a lot more political will behind it so it feels more possible.
The ceiling on asteroid mining is orders of magnitude higher than anything constrained to earth. Put another way, imagine if you owned Australia because your company built it up off the ocean floor.
The sphere does not need to be built or owned by a single entity. You too can own a single unit of the sphere for the low, low price of $2T. There can be different corporate entities owning different sections and monetizing it in all kinds of ways (e.g. the KY sector is ideal for powering asteroid mining in the Kuiper Belt)
I hear people often talk online saying energy in the future will be either free or very cheap.
Dont know what cheap means for them, but it will never be for free because abundance happens when the supply exceeds demand and I dont see the scenario where the demand for energy is declining in a long run.
Well, I guess the argument would be that a billionaire financing the construction of space habitats could make them effectively company towns, but of a highly educated workforce. Once enough of them are there they'll have their own economy, and whoever owns them/the oxygen supply/whatever would be getting a lot of return. I don't think that's a great argument, though, for multiple reasons. I think it's better to just frame it as building a legacy. Put humans in an entirely new place that many of us desperately want to be, end up having the equivalent of a city named after you.
Are you claiming that it is not possible to put a satellite into an orbit around the Sun? Please take a look at how many times this has been done already: [1]. Now just capture Sun's energy on one and do something useful with it: part of Dyson swarm.
It is possible to send a singular satellite pretty much anywhere. It is not possible to build and maintain a Dyson Swarm. At the sizes of modern satellites you'll need trillions of those, which is completely unrealistic with Earth-side launches. This is before we get to doing them any actual dyson swarmy work: so far our probes are only good at communicating and observing.
Dyson Swarm in particular is a megastructure harvesting much of the star energy to the extent its spectrum is dramatically shifted to infrared. I can't stress enough that a lone satellite is not a swarm, Dyson or otherwise.
A dyson swarm is just a bunch of satellites, each harnessing energy from a the same star around which they are more or less are situated (what they do with that energy is up to them). They harvest a proportion of the star's energy anywhere on the range between 0 (non-inclusive) and 100% (inclusive). Your description is one possible end state of a Dyson swarm, and itself includes a subjective measure (what you consider dramatic might not be what I consider dramatic).
Your description of it as a megastructure might explain some of the confusion: it wouldn't be a structure, but rather a formation of satellites not physically connected to each other.
How do you build a swarm of satellites? Well, first you make 1 satellite, then you make another... :)
> Your description is one possible end state of a Dyson swarm, and itself includes a subjective measure (what you consider dramatic might not be what I consider dramatic).
My description is Freeman Dyson's description. Naturally you are allowed to come up with ImPostingOnHN's Swarm, which includes a case of zero satellites and no effect on the star emission whatsoever.
> How do you build a swarm of satellites? Well, first you make 1 satellite, then you make another... :)
Sure and the end state of completing Dyson Swarm in Solar system is not achievable with the technology we have. Now let's move on to discuss if one man with a rifle but no vehicle constitutes a Motor Rifles brigade.
> Sure and the end state of completing Dyson Swarm in Solar system is not achievable with the technology we have.
Sure, for one possible end state.
The point is that we have the technology to start, because we've already started. Thus, it is achievable given enough time and effort with our current level of technological advancement.
How do you get energy from there? How do you deal with waste heat of satellite which is being heated up by sun from one side and heated up by your mode of energy transfer from the other side?
Unless we have some magical solution which can convert waste heat into electricity and thus making such satellite working with 100% effectivity, then such satellite needs to transmit energy with very limited power otherwise it will fry itself up.
Why 100% now? None of those satellites are exploding right now from overheating. Just add a laser on each pointed at somewhere where the energy can be used, done.
None of those satellites are also trying to collect as much energy on one side and beam them on the other side. Notice how those satellite closer to the Sun are wrapped into reflective and isolating materials and only antenna, solar panels and sensors are sticking out.
Additionally high power laser has currently something around 80% of efficiency. So if you have 10kW of input from solar array on one side, then you are transmitting 8kW via laser and 2kW into satellite itself as a heat. And again, we are in vacuum of space, so good luck with radiating 2kW of power into vacuum.
The fact, that you can't get rid of waste heat would need whole satellite to work close to 100% effectivity, which we don't have technology today
Fusion reactors will probably never be economical.
It's the railgun problem: railguns let you trade complicated, unstable ammunition for cheap, stable slugs of metal. But the railgun imposes so much wear on its barrel, and the barrel itself is so much more expensive than in a traditional gun, that you've obliterated your cost savings.
Likewise, it's irrelevant if fusion reactors can provide infinite energy from a single gram of hydrogen, because the reactor housing itself will be an impossibly complex machine with an extremely low lifespan from dealing with the energies involved.
Is fusion possible? Probably. Will it ever be more economical than solar panels? Nope.
Solar panels would be nowhere near as effective far away from a star. Building things as far out as Jupiter or to traverse interstellar areas can't rely on them.
I like the railgun analogy. I think you can stock up on other fusion cost arguments through my article, Engineering and Economic Challenges of Fusion: https://lvenneri.com/blog/ConFusion
I know nothing about railguns, but if they are supposed to launch the projectiles with magnetic force then why do they need to impose any wear on its barrel at all? Couldn't you build a railgun where the projectile never even touches the barrel, being kept at the center by the same magnetic field that accelerates it? Or are we talking about the wear imposed by the magnetic field itself?
If I recall correctly, a "railgun" per se is one that uses the projectile to conduct electricity between the "rails" that direct said projectile. So there's contact, between parts moving hypersonically relative to each other.
It would seem that even without contact there's wear issues with both force exerted on the rails or coils from the magnetic forces and also with creating plasma as the projectile exits?
It's like an 1800s dude thinking aliens would do interstellar travel by having very huge horses, oh no wait...a billion of them (but still somewhat big)
"This is what an advanced race would do...with our current understanding" is an oxymoron
I'm guessing it's more like making a living space in the sphere itself or somewhere nearby and using the energy there (maybe exporting some percentage to Earth).
Because if we're able to build the sphere itself, we probably would already know some way to cool it down in space so it doesn't burn itself, wasting all the money that went to its construction.
