For orbits with physics you can do it using equations of actual orbiting. Some info and capx on it here:
Basically you can do the gravity force with "newton's law of universal gravitation" and set the orbit by setting the velocity to a calculated "mean orbital speed" and set the direction to be perpendicular to the direction from the moon to the planet.
Calculating the impulse to change directions may be doable, just your standard algebra problem, but it's probably simpler to just set the velocity directly.