One trick which improves stability heaps is 'tempering' the data to fit the dt. Weve got the verlet integration thing where they say the velocities should be half a step behind before updating forces. I find they should also be reduced a little as objects are cutting through the analog curve of their orbits in the timestep - as a hypotenuse instead of an arc. When I tempered the data like this orbits were all much stabilised. Its required for objects if they are added to the model later too. To have their precise velocities measured while tempered they also need 'de-tempered' to tell where they are going precisely. Just calculate their acceleration move them half step and adjust for ratio of hypot/curve.

"velocity dependent forces" I have been wondering how to implement a sort of quasi-electromagnetic force without the big expense of maintaining a magnetic field. I find the electro-magnetic force mind blowing compared to newtonian gravity. Like charges seem to be able to attract when travelling together, this would seem to produce patterns and structure more readily than gravitation.