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.
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