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When starting to terraform Venus, working people there would have to live first in the upper atmosphere for a long, long time because there are the most Earth like conditions.
But the water there is very scarce and almost only happens in a mixture with sulfuric acid.
Paul Birch suggested to collide one of the ice moons from the outer solar system with Venus for bringing in the needed water, and I would like to get an idea about the feasibility of his plan.
I don't know if, when he wrote this paper, it was already discovered that three Galilean moons also have much ice on their surface.
But it could be they are less suited for ice mining because of their higher surface gravity than the intended moons of Saturn.

Of course, for an energy efficient trajectory gravity assists are essential, but I propose they would not be too much time consuming and a sequence of them would have to happen in a configuration of planets and moons that could happen frequently.

So, launched from Earth with an SLS Block 2 and supplied with as much fuel as possible, how much ice could be mined on an icy moon or moonlet of Saturn or Jupiter by a spacecraft and transported to the upper atmosphere of Venus ?
What would be the most energy efficient trajectory and which of Saturn's or Jupiter's icy moon(let)s would be the most suitable regarding that efficiency ?

I would like to have an answer with the necessary equations and calculations for verification.

Could there be a suitable constellation of planets and moons every 20 years, corresponding to the orbital periods of Jupiter and Saturn ?

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    $\begingroup$ NO limit at all. Because you specify that the rocket can have as much fuel as it wants. If you mean for something we can currently launch from earth, fly to an ice moon, harvest ice, an transport it to Venus, the answer is zero. With a few years of development, a couple of grams. Possibly as much as one kilogram. You really need to place some realistic, numeric parameters for your question. $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 18, 2021 at 20:36
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    $\begingroup$ It is probably easier and energy efficient to direct some TNO or comet to venus $\endgroup$
    – planetmaker
    Commented Jul 19, 2021 at 3:24
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    $\begingroup$ @Cornelis Pick any known with orbits from the minor planet centre: minorplanetcenter.net/data or form one of these lists: en.wikipedia.org/wiki/Lists_of_small_Solar_System_bodies - especially en.wikipedia.org/wiki/List_of_long-period_comets or en.wikipedia.org/wiki/List_of_trans-Neptunian_objects or en.wikipedia.org/wiki/… $\endgroup$
    – planetmaker
    Commented Jul 19, 2021 at 8:43
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    $\begingroup$ If you look at the data, the list of comets on the MPC site has a list of comets with a perihelion inside Earth orbit... it's not too shabby. Also further out doesn't mean you need more energy to get them to Venus... more to the contrary. One surely is not pressured so much by time when terraforming Venus rather than by getting sufficient material (water) to that place. $\endgroup$
    – planetmaker
    Commented Jul 19, 2021 at 10:38
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    $\begingroup$ Apart from the fact that the launch vehicle has little to do with what the spacecraft is capable of, Venus doesn't need water, it needs hydrogen. There's plenty of oxygen there in atmospheric CO2 to make water (and hydrocarbons, carbohydrates, and the bulk of proteins), it doesn't make sense to transport more all the way across the solar system bound up in water, while simultaneously removing it from the atmosphere at great cost. Crack the ice and throw away most of the oxygen, saving some of it to use as reaction mass to transport the ~11% of the ice that's hydrogen. $\endgroup$
    – Christopher James Huff
    Commented Jul 20, 2021 at 21:04

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Almost none, to be honest, using the method you propose. SLS can carry approximately 6 tons to Jupiter using a direct route (Based on Europa Clipper). To then land, cut, and re-launch would lead to a very small amount of ice actually carried to Venus. Not sure of the amount exactly, because it depends on the exact way one makes the spacecraft, but I'm going to say a few kg.

A better way, however, would be to somehow use the ice to make more fuel on said moon, use gravity assists, etc to make the trip easier. SLS should be able to carry closer to 20 tons to a Venus flyby. Landing on an icy moon of Jupiter comes down to maybe 15 tons. Most of that mass would be empty tanks (Not the landing fuel), and power generation, but I imagine a few tons could be lifted.

A MUCH better way to do this would be to find a comet and tweak its orbit slightly to get it to crash in to Venus, using fuel generated from the rocket to get the iceball to Venus. If a proper candidate can be found, it would be possible to launch a spacecraft using SLS and have a small comet crash land on Venus, likely in the tens of thousands of tons, but there would be a limit to how often this could be done.

Lastly, but not least, what would this even accomplish? The atmosphere of Venus is 20 ppm water vapor, with an atmosphere of 92 times that of Earth. That means there is a considerably amount of water vapor on Venus already, it is just too warm to be liquid. Remove the CO2, cool the planet down, and there would be water.

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  • $\begingroup$ The problem with making fuel on a moon of Jupiter is of course the energy source since it's so far from the Sun. Yes, I already pondered if there would be a suitable comet right now to crash it on Venus. Aren't the chances very low that Venus is just in the right position of its orbit and with the speed of the comet to make such slight adjustments of its trajectory. It would be easier of course to give it a try with a chunk of the iceball. $\endgroup$
    – Cornelis
    Commented Jul 20, 2021 at 15:09
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    $\begingroup$ It is, but there's a lot of comets. Surely there are multiple comets out there that a small nudge could get them to collide with Venus. Also, I'm going to add another argument, Venus already has enough water vapor most likely to be Earth-like, it's just too warm. $\endgroup$
    – PearsonArtPhoto ♦
    Commented Jul 20, 2021 at 15:15
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    $\begingroup$ Yes, and according to this question space.stackexchange.com/questions/27467/… there's already 3.10^13 kg water in the clouds, so we just have to extract it from the sulfuric acid there. $\endgroup$
    – Cornelis
    Commented Jul 20, 2021 at 17:46
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Let's compare it to a mission that did almost exactly that:
The OSIRIS-REx asteroid sampling mission.

OSIRIS-REx flew from Earth to a destination closer than any of the possible icy moons or asteroids, but with luck we might locate a suitable ice-bearing target that is as easy to reach. Definitely there are none that are easier, and most are much further away, and in deeper gravity wells.

OSIRIS-REx returns its sample to Earth. You want to go to Venus. Let's be very generous and pretend that Venus is just as easy to reach as Earth. It isn't, but the difference is not that huge.

OSIRIS-REx manages to return a 60g sample.
It was launched on an Atlas V 411, which is good for 12150kg to LEO.
You want to use the much bigger STS Block 2, which is good for 130000kg to LEO. That's a whopping 10.7 times the mass.

As a first estimate, your SLS b2 derived ice miner can deliver 60g * 10.7 = 642 grams of ice to Venus.

This can surely be improved upon, but not using current tech. (as if SLS block 2 is current?)

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  • $\begingroup$ Nice comparison, and without (some) payload of OSIRIS-Rex there could be still more fuel and ice on board ! $\endgroup$
    – Cornelis
    Commented Jul 20, 2021 at 11:30
  • $\begingroup$ @Cornelis Are you being purposefully obtuse? 642 grams. Not even Kg. Even if you were to multiply that by 1000, it is still less than a drop in the bucket as far as a useful amount goes in regards terraforming Venus. $\endgroup$
    – CGCampbell
    Commented Jul 20, 2021 at 13:39
  • $\begingroup$ @CGCampbell I wanted to get an idea about the feasibility of Paul Birch's plan. $\endgroup$
    – Cornelis
    Commented Jul 25, 2021 at 12:58
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    $\begingroup$ @Cornelis give that his plans require some 30 years of sustained 10^18 W of solar power, out around Saturn. Which is 375000 times the current global power production of planet Earth....... I'll not hold my breath. $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 25, 2021 at 13:25

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