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I have this futuristic setting in which humanity constructs habitable surfaces around the gas giants and ice giants of the Solar System. A similar idea was proposed by Paul Birch which uses dynamic support and has the surfaces outside the planets' atmospheres; however, this version of humanity wants to try something different. They want to have the surfaces inside the atmospheres of the giant planets, supported by atmospheric pressure. This idea was also proposed by Birch, but in the context of colonising Venus.

  • They start by dropping self-replicating factories into the giant planets. These factories deploy balloons of heated hydrogen (one of the only things that can be buoyant in atmospheres that are mostly hydrogen) and stop descending at a certain altitude.
  • The factories replicate themselves, using materials from the surrounding atmosphere and energy from either wind or fusion power, at a rate of once per year.
  • The factories also produce hot hydrogen balloons, again at a rate of once per year, that float up to a higher altitude. The factories and the balloons they make work on the same principle as bubblehabs from Orion's Arm. The balloons are 1 km in diameter and also have smart matter surfaces that can vary their reflectivity to light at multiple wavelengths.
  • The balloons increase in number until they cover the entire surface area of the giant planets. They also vary their reflectivity to control the amount of sunlight absorbed and the amount of infrared radiation emitted by the planets (inspired by Orion's Arm's weather machines). In doing so, they calm the strong winds that are typical of giant planets.
  • Once the atmospheres are calm enough, the balloons start clinging together until they form a continuous solid surface.
  • Now colonisation of the solid surface begins. The surface would be held up by the pressure of all the gas underneath, allowing it to support more weight than the balloons could when they were floating individually. At first, people would live in sealed habitats since the upper atmosphere is still mainly hydrogen with no oxygen.
  • Over a long period of time, the hydrogen is pumped down into the lower atmosphere while oxygen (produced by electrolysis of water from the lower atmosphere) and other gases are added to the upper atmosphere. The end result is a breathable atmosphere of oyxgen and helium (and traces of nitrogen, carbon dioxide, water vapour etc.).

My question is: how long would each of these steps take, assuming realistic or mostly realistic technology (so no teleportation or perpetual motion machines)? From what I can tell, the most time-consuming step would probably be the calming of the atmosphere: this might take centuries or even millennia.

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  • $\begingroup$ One of the main problems is energy. I don't think that sunlight alone will do much more than heating the hydrogen, and may not be enough for that. $\endgroup$
    – NomadMaker
    Commented Nov 27, 2020 at 6:38
  • $\begingroup$ You are not giving any information neither on the surface to be covered, nor on the replication rate. How are we supposed to answer? $\endgroup$
    – L.Dutch
    Commented Nov 27, 2020 at 6:53
  • $\begingroup$ I've now updated the question. And the surface to be covered is roughly equal to the surface area of the planet in question: 61.42 billion km² for Jupiter, 42.7 billion km² for Saturn, 8.083 billion km² for Uranus and 7.618 billion km² for Neptune. $\endgroup$
    – Pitto
    Commented Nov 27, 2020 at 7:06
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    $\begingroup$ Balloons i km. in diameter, 42.7 billion km^2, therefore at least 42.7 billion balloons. 1 balloon made every hour, 42.7 billion hours. 28,076,712 of our centuries. 28,076 of our millenia. If you speed up production to one per minute, just divide that figure by 60. Make them as fast as Apple makes smart phones? Now you are talking. We are down to just a millenia. zdnet.com/article/how-many-iphones-did-apple-sell-every-second $\endgroup$ Commented Nov 27, 2020 at 14:31
  • $\begingroup$ I foresee trouble pumping hydrogen down. In the case of light stuff, what goes down must come up. $\endgroup$
    – Willk
    Commented Nov 27, 2020 at 15:30

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Sorry, it will not work:

They also vary their reflectivity to control the amount of sunlight absorbed and the amount of infrared radiation emitted by the planets (inspired by Orion's Arm's weather machines). In doing so, they calm the strong winds that are typical of giant planets.

Simply will not happen.

The high winds of a Gas Giant planet are caused by the differential temperature between the planet's lower layers(eventually the planet's core), and the upper atmosphere. The energy for these winds do not source from sunlight, as for terrestrial planets, but from the core heat.

The only way to stop these wind would be to either turn the gas giant into a terrestrial world (i.e. freeze the whole thing, which is absurd!) or to remove the temperature differential of the upper atmosphere.

Your setup will do the latter quite well, but.... The core of a gas giant is VERY hot! For the local Gas Giants:
Uranus: 5000K
Neptune core: 7300K
Saturn: 8900K
Jupiter: 24000K !!!!

So conundrum. If you equalize temperatures by insulating heatloss, the atmosphere becomes hotter than the sun surface. If you do not equalize temperatures, you are stuck with enormous winds.

I think you will need to devise a plan that works with/around the winds, rather than calming them.

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  • $\begingroup$ And that's ignoring the pressure of the gas planet. OR the fact that to get the stuff down there, you irradiate any material as you get into a close orbit. $\endgroup$
    – Trish
    Commented Nov 27, 2020 at 8:56
  • $\begingroup$ I tend to agree. Methinks that with the large gas giants, the problem is not about keeping the heat OUT, it would be you are keeping the heat IN. Your insulating blanket of giant balloons would somehow have to allow for heat dissipation OUT from the planet, not IN from the sun. Your blanket would, well, expand like a heated up balloon until it burst. You have created a balloon made of balloons, fully enclosed. pressurized, with the planet inside giving off heat. What could possibly go wrong? $\endgroup$ Commented Nov 27, 2020 at 14:14
  • $\begingroup$ If temperatures and pressures at the core rise to the point where hydrogen fusion occurs, that is when things get really warm. $\endgroup$
    – Willk
    Commented Nov 27, 2020 at 15:33

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