+++ Update +++
I made the code more readable and changed my initial approach. I Studied some Geometry:
Polar and Cartesian Coordinates
I looked for the right way to Convert the Polar Coordinates (Angle and Force) to Cartesian Coordinates (VelocityX VelocityY). So when the Spaceship is about to exceed Max_Speed I want to get the Angle of current motion + Acceleratio * dt.
Then use that Angle and set VelocityX VelocityY with new Angle but old Speed.
Here is the CAPX
(at update_Spaceship/Apply_Input marked with comments (3x))
(Use Arrow Keys and Ctrl)
This is my approach:
Accel_Angle seems to not change at all once Max_Speed is reached
Still not sure if I picked the right formulas.