Yes, I imagine such a civ would just scoop up hydrogen from the Sun and run something like an artificial CNO cycle in reactors with that fuel. It makes more sense than using a dyson swarm.

What I meant there is that you can out-power the Sun's output easily even without that, by using the fuel on outer gas giants too. So technically you do not need to do anything with the Sun in order to "reach Type II" (it's defined by power generation, regardless of source).

A funny notion concerning Venus, connected to the "necessity of a magnetosphere", is that Venus also happens to have no magnetosphere. Yet it is fully capable of maintaining a thick atmosphere over geological timescales. Despite being hotter and closer to the Sun, its gravity does the job of keeping the atmosphere on the planet. Well, other than H and He, which will be blown away by solar wind (though the Earth loses these over time as well).

Venus doesn't have water, which indeed might be related to its lack of magnetosphere. Water vapor in the upper reaches of the atmosphere can ionize, and the H can be blown off by the solar wind. This might be how Venus lost all its water in the first place, and why it has so much CO2 gas, because without water it won't become bound to rocks like it does on Earth.

So, naturally, the "simple" task of terraforming Venus is probably to "just add water". And yes, you are right, Venus might be a much better early candidate for terraforming due to this. It is closer to the Sun, it has the right gravity etc. Mars is a better candidate for early human (artificial) habitation, but if we can terraform Mars we can probably also terraform Venus and it'd produce better results. And I don't think you really need to accelerate its rotation (unless, again, you're trying to make a magnetosphere perhaps?)

I don't think it's in any way critical to that. Those kinds of harmful waves, from UV to gamma, are mainly helped by having a thick enough atmosphere - its exact composition can matter too though (mainly for UV absorption). But initially all this requires is just dumping a lot of gas of your desired makeup onto Mars. The medium term stability of that atmosphere depends mainly on chemical (and eventually biologically driven) reactions near the surface...

Mars has weaker gravity so it won't be able to help hold onto the thick atmosphere long term. This is where a magnetosphere helps, because it can protect molecules in the upper atmosphere from being ejected by solar rays when in normal conditions they wouldn't reach escape velocity. But Mars' gravity is too low anyway, even with a magnetosphere it wouldn't be able to hold an Earthlike atmosphere forever.

The "easy" solution is to just keep adding required gases into the atmosphere. Which, if you were able to do it the first time, you can probably keep doing. This would still be a matter of millions of years, it's not like your Martian biosphere suddenly runs out of oxygen just because you forgot to add this year's oxygen supply.

Of course all this depends on what "level" civilization we are assuming, i.e. how much energy and what ability to move resources at large scale there are.

To just terraform the surface of Mars we don't need so much. Of course it's huge compared to what we can do now, but it's nowhere near dyson swarm capability levels. Technically it's probably enough to just dump a lot of atmosphere (lots of oxygen of course) plus water (from small icy asteroids e.g.) onto Mars; once it has a thick enough atmosphere with enough water vapor it will warm up through greenhouse effect.

No need for a magnetosphere.

If you still wanted one, even an artificial one, that would take a bit more effort. Not a big deal for a type II civilization, but still you do not need to wait until then to terraform Mars. You can just terraform it the "easy" way as above, even if it's not permanent you don't care, and then you might "fix it" later when you've advanced more - if you even care about it at that point.

To be honest I don't think any self-respecting type II civ would bother with a dyson swarm. That was conceptualized before the notion of nuclear energy was even mainstream understanding. If you're on that level of energy harnessing, using a dyson swarm is pointless; the Sun is an absolutely terrible "fusion reactor". You would instead use artificial fusion yourself. Would take fewer resources than a dyson swarm, you could create as much power as you want (easily more than the Sun itself, even if you just use fuel from Jupiter and leave the Sun alone as a token "natural reserve") and it would be a concentrated, on-demand power source. Of course at this point a project like "terraforming Mars" would become like a school science project.

I understand what you're asking and it's not an artificial field. I don't know how possible it is, but my question is why? An artificial magnetosphere is probably much easier, so why bother with a "terraformed" one?

Better yet, why make one at all? You do not need a magnetosphere to terraform the surface of Mars otherwise. You'd only care about it if you want the changes to become more or less permanent without maintenance. But why would you bother? If we are able to create livable conditions on the Martian surface in the span of centuries only, then we don't care if those conditions are stable over only millions, rather than billions, of years. We can just actively maintain them as needed.

You didn't understand what I said.

What I said is that you could have a power saver state in a modern phone that disables all those sensors, put the processor in a low power state (which is much, much better than those in any old processors), you aren't using your screen because the phone is just standing by not doing anything, and in such a state it should last much longer than an old phone because it would have lower power consumption and a larger battery.

Obviously it's not going to last long if you're using all those features, but it should be able to last long if you aren't. The reason why it doesn't is because even the ultra power saver setting on the phone still leaves things working in the background. Why not have a hyper-super-ultra power saver setting as well that disables them too?

Still it looks like it could be much better. Old phones could last for 2 weeks if not more, in stand by (not turned off - they could receive calls). And they had a much smaller battery and theoretically much less efficient electronics. Seems like the new version is still doing a lot of things in the background. If you wanted to make a true low power stand-by mode for a smartphone it should be lasting weeks, not days. Of course, at least for most phones, you still have the option to just turn it off.

Hmm, I guess it's possible? But then it requires quite a lot of constant fuel for your orbital retrieval vehicle. I suppose you could also "shoot" fuel up with the cannon constantly.

I'm not convinced it could be worth it. From the construction and maintenance of the cannon to the reliability of the method, even if possible, where if you don't catch a payload perfectly it just falls back to earth... rocket launches are probably more worthwhile for all this.

Since you need fuel to get into orbit you're still beholden to the rocket equation where you're using fuel that you catch to put the payload you also catch into orbit... I don't think you're necessarily that far from just using rockets, except the reliability problem.

You have to make a rendezvous with the ISS which means you have to have propulsion on your "vehicle", it can't just be a "cannonball" fired from the ground once. And the engine and other delicate components necessary wouldn't survive being fired out of such a cannon.

To put it simply, you cannot shoot an unpowered object into orbit. Its path intersects the earth again, or it attains escape velocity and leaves earth permanently, but neither path makes an orbit.