The explode button has been disabled by the developers shortly for bugfix reasons. Expect it to be readded soon
The accuracy slider is, well, it's hard to explain. So imagine you've got a planet orbiting a star every 3 days, and the simulation measures 6 positions in the orbit. If you increased the accuracy by 100%, it would measure 12 points, if you decreased it by 50%, it would measure three points, and so on and so forth.