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Let's assume we want to build a Dyson swarm that collects over 90% of the energy from the sun and orbits between the Earth and the sun. Also assume that we want to get none of the resources to build this machine from Earth itself. After the initial mining and construction ship has been launched, it must collect everything it needs from locations outside the Moon's orbit around the Earth. (Thus, you can't touch Earth or the Moon) All other planets and objects are fair game.

Where would be the best places to get the needed materials for construction? You can assume life support and workforce has been taken care of.

Edit: There was some confusion around this so let me clarify. I am asking for where to find enough material that can be used to harvest energy from the sun. If the matter has no known use for this purpose then it should not be mentioned in your answer and there is no handwavium that can convert atoms from one elemental type to another unless it is currently known how we could do so in an energy efficient way. (That is to say it takes less energy than what we would harvest from the sun)

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  • $\begingroup$ We've had a lot of Dyson sphere and swarm questions and while I can't quickly find a question that explicitly answers you, I'm pretty sure this must have been answered somewhere on WB SE. Have you looked through answers to related questions ? $\endgroup$
    – StephenG - Help Ukraine
    Commented Jul 19, 2019 at 21:28
  • $\begingroup$ @StephenG I did and I was super surprised I didn't see any questions asking this. It seems like a really basic thing to ask. If you find one let me know so I can close this one. $\endgroup$
    – Muuski
    Commented Jul 22, 2019 at 15:59
  • $\begingroup$ Mercury $\endgroup$
    – Möoz
    Commented Sep 9, 2020 at 5:03

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Use self-replicating machines to disassemble Mercury, which is made of 30% silicates and 70% metal, so most of it could be used to build the panels that make up the swarm, and the mass is about right to build a swarm at the same distance that Mercury used to orbit. This paper on the Fermi paradox has some rough calculations about the time needed to do this on pages 14-16, assuming that the material that's already been removed from Mercury can be converted into parts of the Dyson swarm and can help provide power to the remaining disassemblers and launchers. They end up concluding that it could be done in only about 31 years!

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    $\begingroup$ Great! Can you include in your answer an estimate of how much coverage one could reasonably expect to have? I can't imagine Mercury having enough mass to block 90% of the sun's energy, though I could be wrong. $\endgroup$
    – Muuski
    Commented Jul 22, 2019 at 16:20
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    $\begingroup$ *Kurzgezagt entered the chat* $\endgroup$
    – Möoz
    Commented Sep 9, 2020 at 5:03
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To get you started, here are some quick 'back of an envelope' calculations:

You could harvest all the material in the solar system, except the Sun, Earth and Moon.

Jupiter is 2.5 times as massive as the rest of the planets put together, so the total mass of the planets is 1.4 x mass of Jupiter = ~2.65 x 10^27 kg. That is about 445 times the mass of the Earth.

If you were to use this material to construct a Dyson sphere 1 AU in radius, it would have a surface area of ~9 x 10^22 m^2.

Putting these two figures together, would give you around 30,000 kg of material for each square metre. That could be used to construct a steel shell around the Sun, but it would be less than 4 m thick.

Alternatively, you could construct 444 more Earths, but I don't think that constitutes a 'swarm' and certainly wouldn't capture 90% of the Sun's output.

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    $\begingroup$ I think a hybrid of your multiple earths and steel shell might solve the 90% capture requirement. Just thin down the shell to the minimum thickness needed for the solar capture, An inch thick membrane supported by a slightly thicker skeleton could fill that need. Then construct as many earths as you can from the remaining material and fix them in orbits under the shell. I don't have the math or the time to figure out the details, but this seems to be a workable compromise. $\endgroup$
    – Henry Taylor
    Commented Jul 19, 2019 at 22:05
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    $\begingroup$ Jupiter is mostly hydrogen and helium though, you'd need large amounts of some other element to create a molecule that would be sold at 1 AU. $\endgroup$
    – Hypnosifl
    Commented Jul 19, 2019 at 22:35
  • $\begingroup$ The OP stated "All other planets and objects are fair game." The implication here is that they have the means to convert matter from one kind to another using some handwaving means to do this on a planetary scale. If they don't have this ability, then there is an awful lot less material available, and they would still need to have a way to get rid of the giant planet's atmospheres. $\endgroup$
    – Nick
    Commented Jul 19, 2019 at 22:55
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    $\begingroup$ I thought "fair game" just meant you are free to mine any usable resources from any planets besides Earth, not that all the material of every planet was automatically usable, but perhaps the OP will clarify. $\endgroup$
    – Hypnosifl
    Commented Jul 20, 2019 at 2:01
  • $\begingroup$ @Hypnosifl you are correct. I am trying to figure out where the usable materials are. I will try to clarify this in the question. $\endgroup$
    – Muuski
    Commented Jul 22, 2019 at 16:07
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You can have a fleet of robots/technicians on the surface of Mercury, which is our best bet judging by how close it is to our target, the sun, no atmosphere, and very low surface gravity, making it easy to launch material. Your fleet may consist of the following machines:

  1. Coring Rovers, they are used to find material in Mercury's crust.

  2. Drilling rovers, used to extract raw material.

  3. Automated material processors, which may be blast furnaces, electric arc furnaces, etc.
  4. Reproducers, produce more machines
  5. Swarm constructors, construct 1 square meter reflective panels and energy harvesters (solar panels and lasers used in conjunction)
  6. Gatling guns, use these to launch the swarm
  7. Solar collectors, harvest the energy of your swarm
  8. Technician habitats, technicians who service machinery live here, each floor spins to generate artificial gravity and are pressurized with $O_2$ and $N_2$ (+ other stuff that living beings need)

That should be about everything for a mostly self sufficient system

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From the star itself.

The Sun is mostly hydrogen, and a fair bit of helium... but the keay word there is mostly. The Sun has a metallicity of 1.2%, which means that it contains approximately 2.39e28kg of heavier elements. That's more than 10 Jupiters of stuff that isn't helium or hydrogen.

So, start with, e.g., Mercury, or the asteroid belt, to get the initial materials to build star lifting equipment, without worrying about whether or not you can build a complete sphere with those materials, and then just collect the rest of the materials for the Dyson sphere by sifting through the material of the Sun itself.

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