Actually all of them. Every step adds up the pull of every planet at the rocket’s current position. Realistic gravity made shots feel unfair, too weak a falloff made them feel floaty. I tried a few versions before landing on something in between.

I'm not sure what you mean.

Are you using F = m * M / r^2 with and tweaked the value of M until it look right?

Or you changed the 2 in the exponent?

Some parts of the trajectories in the demo look weird for plain mM/r^2