If you want to go from point A to point B (or facing A to facing B) in a series of steps, instead of instantly jumping between A and B, that is not hard. The solution involves using interpolation to get a series of in between steps. This process is the same whether you are talking about changing positions, or changing rotations.

There are many different types of interpolation one could use for this process. But the basic idea is that you have a start point and an end point, and a time you want to take to go from start to end. Then you have a number of tween states (probably determined by frame rate, in a game). You then divide the move up into mini-steps, and go step by step till you reach the destination time and end point.

Linear interpolation is the most simple, so I'll start with that as an example. . . Lets say you want your spaceship to turn 60 degrees over 1 second. And to keep the math simple, let us assume that your game is running at 60 frames per second.

So, instead of going from 0 to 60 instantly (in one step), you'd turn the ship 1 degree per frame, and with 60 frame over the course of 1 second, you'd reach your 60 degree goal at the end of 1 second. Of course, things don't usually line up that neatly, but the idea remains the same.

As I mentioned above, there are other ways to generate those tween points besides linear interpolation. . . I recently watched a pretty good youtube video ( here ) on the subject, which you might want to check out.