we have intersteller spacecraft alredy. but in my new project(sorpendarin project) will shrink the planets to about 15 miles. i need small intersteller spacecraft.
I said it already, but I'm just going to say it again: shrinking the scale is not going to change the behaviour of the orbiter physics engine (not even the behaviour of the camera). I know what you want to do (shrinking scales uniformly to avoid double-precision problems), but I can only repeat myself: It just won't work. 1m will always stay one meter, 1 kg 1 kg, and 1 m/s will always stay 1 m/s, and even if you scale your ship down, that does not mean that the distances will increase. It just doesn't work that way, sorry.
But for what it's worth, there's a very simple solution to prove my point: Spacecraft3 supports scaling, so you can scale down any spacecraft3 vessel by adding the Scale modifier to the .ini file (refer to the spacecraft3 documentation for further details).