At first it was pretty random. Then I took the Kerbal X (stock), made some adjustments, saved it as Kerbal X nonstock, then it got reiterated as X2: Refueled, etc. But as each ship wasn't working right, each name got more frustrated, such as X4: C'mon, X5: You can do eet!, and up to Xex 15: Aaaahahrgh. By then I got annoyed having to scroll all the way to the bottom, so I started over with A1: Starting Over. But eventually I went back to my best performing spacecraft, the ironically called X13: The Lucky One.