Hi, I'd like to suggest a few things related to orbital mechanics with spacecrafts and ask a couple of questions related to their feasibility.
Right now orbit previews for spacecrafts in SE only show the correct prediction when the spacecraft is exclusively in one body's SOI, which leads to wrong predictions when the spacecraft is leaving a body's SOI and you try to preview its orbit around another body (the spacecraft's orbit around the Sun when it is orbiting the Earth for example).
To illustrate, if you are leaving Earth's orbit for a Hohmann transfer to Mars, the orbit's preview will show an apogee for the transfer orbit that is higher than Mars' orbit, which will get lower as you get further away from Earth until you leave its SOI. When you are out of the SOI, only then your true transfer orbit around the Sun will be visible.
As you can see in the images, the orbit changes as you leave Earth's SOI. My suggestion would be to have the final preview, when referencing the Sun, even when inside Earth's SOI, similar to what Kerbal Space Program does (without the added encounter marks to not overcomplicate things).I don't know exactly how hard this would to implement with the current method used to calculate the previews, but it would make playing with the orbital mechanics way easier as you wouldn't have to know the exact amount of deltaV required for a transfer orbit.