I have it loading 17,000 asteroids. Although I knew that a ship going thru the belt may not even see an asteroid it is interesting to zoom out to them and see that even on this small scale there is a lot of space between objects. Doubt I will keep them on all the time but nice to have this option. I had to put my original asteroid file in another location and change the name of this one from astorb.dat to Asteroids.txt. Thanks for this tip.
Asteroid belt IS already available.
But it's not feasible. Each time-step caused several seconds of calculation. But it IS an impressive sight from outer solar system showing up all 17000 objects.