SDI, or the Strategic Defence Initiative, to give it its full title, was set up by Ronny Raygun to make sure that the Russkies couldn't attack the good old US of A from space. Now you play the controller of a satellite, armed to the teeth and ready to defend your country.
The game features two distinct phases: offensive and defensive. You start in offensive mode and move both your satellite and its laser beam around the screen in an attempt to destroy the enemy satellites, missiles and weapon pods. At the end of a level the amount of kills are totted up and if you score a perfect 100% across the board you're awarded a 20,000 point bonus and a dancing duck (I kid you not). If you miss any attackers, though, you move into defensive mode and (surprise, surprise) defend your homeland.
Graphically SDI is good, the nicely drawn monochrome sprites zip around the screen and you need a keen eye to shoot them. But sadly the gameplay isn't quite up to scratch. Initially fun to play, SDI soon slides down into the dumper because of its repetitive nature.
Missiles and all sorts of space weaponry in an action-packed snap of SDI.