In this game, things start getting harder from the 3rd level. There's a way to be invincible on this game. Play using the keyboard. Play the game as usual, docking at all the starbases and destroying the Kingons. When you reach 3.4, press and hold the M key until the warp time runs out. Keep holding it down as you play. As long as the M key is held down, you will remain invincible. If you get tired, just let go of the key.