Alain_Attack: a spaceship is being attacked by little green
men in flying sauces. The ships gun is moved by the arrow
keys and fired by the spacebar a red bolt shows. If an alien
ship is in the cross wires and is hit it spins and dies.
On the ships control panel is a shield status made up of
six bars. Each time an alien scores a hit the ship
superstructure flashes (what not seen star trek!) and one
of the bars disappears and changes from green - orange red.      

Any resemblance to a Beeb game from the early eighties
is purely intentional.