So, it is in fact an art. I learned, as others have posted here, to add supports in Prusa, slice in Chitu. I manually add supports to corners, beef up the count, sometimes angle the print on relative to the print bed....
You have to really play with it, experiment. Hard-surface models are probably the most unforgiving.
And then there's Blender! That has been a slow learning curve. I expect it to be a year before I feel conformable with it. That being said, I was flailing for the first month — that being several months back now, I confess I have more of an intuitive grasp now on how to approach a model.
But, like the Mars, there were all matter of blind alleys I went down. Often a model that looked fine in Blender failed in Chitu to slice properly: the resulting print that came out of the Mars had seemingly arbitrary layers filled in....
It turns out that making a model "manifold" is pretty important!
As I started feeling my way through Blender I began to be able to imagine a shape, sketch it on a napkin if you like, and then approximate it in Blender. The resulting prints too became better.
Here is a sort of "space radiator" for the top of a scratch-build I am prototyping;
