I finally found the time to finish it with the help of AI. The basics, like the physics, were already there. Now it has nicer graphics and runs in the browser, on desktop and mobile.
Happy about any feedback, and glad to add more features.
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