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](https://orionsarm.com/fm_store/TerraformingVenusQuickly.pdf), 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](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/Space_Launch_System) and supplied with as much fuel as possible, how much ice could be mined on an [icy moon](https://en.wikipedia.org/wiki/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 ?