I am developing the single player mission so that enemy spaceships fly around the screen and if they spot you they will start shooting at you. These are the outlines for the Missions so far:
Mission 1 Scout- You have been sent to scout the area for enemy ships. Fire at any dangers and report back when you have examined the area. A basic mission in which you fly round the screen and shoot down enemy aircraft if they pop-up. You win if you destroy all the enemy ships in the area and they win if you lose 5 lives.
Mission 2 Defend- The enemy has assembled an assault squad of ships, you must shoot as much of the enemy down as possible without letting too many pass through the bottom to your base. The enemy will fly-around to give the player a chance to hit before passing through the bottom. When you reach a certain amount of kills you will win and when they reach a certain amount of invaded ships you lose.
Mission 3 Destroy the bomb- The enemy has discovered your space base and now they attempt to blow it up by planting a bomb nearby. You must destroy the bomb before the enemy can do harm but beware it is heavily defended. The screen cycles upwards when you have removed enemy from the area and if you fall behind and pass through the bottom screen you respawn and lose a life. If you reach the top then you simply stop moving and the screen scrolling upwards will soon reveal you. The sides wrap around as usual. If you destroy the bomb you win and if you lose 5 lives you lose.
Mission 4 Elemental Battle- Your base is near a newly fought battle between new elemental aliens. Their battle is wreaking havoc in the area and you must destroy them all before they do any damage to your base. Fight hardier enemy ships, some shoot laser beams and other release fireballs that seek out enemy targets. Destroy all the alien ships before you lose 5 lives to win.
Mission Boss- Fight an armoured spacestation with an advanced defence system. Fight through each phase of its attack and destroy it to win. You lose if you lose a certain amount of lives.