The Resistance movement is about to launch a huge offensive against a tyrannical Intergalactic Empire.
In preparation for this mammoth and probably suicidal assault, the Resistance has captured several battle-grade starships, only to discover that they are largely useless in war, as they are lacking the necessary Klystron pods which provide power. The catch is that these pods are only to be found on Empire-owned planets.
A volunteer must be found to steal enough Klystron pods for the mission to go ahead. As you yes, sonny, you are one of the most skilled pilots in the Resistance, just guess who the lucky blighter's going to be. Using all your skills, you must fly to each planet in turn and steal a pod, then drag it out of orbit to where it can be picked up by the Resistance.
Each planet is defended by a battery of limpet guns which are powered by a nuclear plant, and shooting at the plant puts the guns temporarily out of action. The more direct hits scored on the power plant, the longer it takes the limpet guns to recharge. But if too many shots are rained down upon the plant it becomes unstable, and you then have a mere ten seconds in which to grab a pod and pull back before the entire planet self destructs. If you've got away with the pod, then destroying the planet picks up a sizeable reward. Failure to retrieve the pod results in instant mission termination.
Your craft possesses only an upwards thrust, and downwards movements are controlled by gravity. You must constantly thrust away from the planet's powerful gravitational field which drags your craft towards the ground and ultimate destruction.
After each pod has been safely captured you automatically proceed to the next planet, each having its own peculiar characteristics. You will have to contend with reversed gravity and invisible landscapes before the game loops around and starts all over again.
And so, once more, the fate of the galaxy is in your trembling hands. Good luck, and good pod hunting!