SDI puts you in control of a satellite, central point of the Strategic Defence Initiative (Wow, this guy really knows his abbreviations - a wealth of suitably impressed readers) as it orbits the Earth and tries to destroy the squillions of nuclear warheads heading America's way.
Luckily, the satellite is fairly manoeuvrable and can zip about the screen pretty sharpish. Missiles, fighters and other killer satellites slide in from all angles. They either attack you, shoot you, or more likely just get in the way. A cursor follows you around and can be trained on any offending space craft to reduce it to ion particles - or whatever laser beams reduce things to.
But all these things are just decoys and distractions to lure you away from the real targets - the nuclear warheads. These glide through the screen silently and insidiously and must be vapourised before you can breathe with relief. If one of them manages to slip past you, then you'll have to play a defensive section and protect the Earth from a shower of splintering warheads.
The graphics are stylish and detailed, and animate very well (rotating, spinning, and gyrating) but they're arthritic when it comes to moving. They jerk across the screen as if pain. Only the warheads move smoothly, but that's because they're so silent and insidious.
Although the satellite responds quickly to your wishes, the switchable cursor moving is very difficult to master and so frustrating.
All this is very straightforward. A simple rejuvenation of the Missile Command game with a few extra pixels added for old times sake. The lure of extra levels, foes and difficulty creates an incentive for a couple of games, but it lacks that magical programming sparkle to make the attraction last any longer.
Detailed by arthritic graphics don't help to alleviate the montony and dullness of this mediocre shoot 'em up.