The ship controls feel very strange and will sometimes get stuck while turning, and I suggest that you list the controls for the game somewhere.

The idea of the game is nice, but as was commented before the controls feel somewhat weird. The help section was useful. It it possibly too easy to place spaceships, for example, pressing space repeatedly works as well. I think that one simple way to improve the game is to end the game when ships collide. Maybe combine it with an explosion?