Comment by Cthulhu_

KSP takes some liberties with physics, simplifying things so that e.g. the N-body does not apply (that is, your craft are only affected by one body at once). Other challenges are the scale and number precision. It doesn't get it exactly right either, especially when you use the time accelleration, things can go a bit... weird. See https://wiki.kerbalspaceprogram.com/wiki/Deep_Space_Kraken