The 'Acme Interstellar Transport Company' is delivering spaceship kits to various planets in the solar systems throughout the Galaxy; and as chief test pilot, all you have to do is assemble the rockets and thrust onto your next destination.
But! as you don't often get the chance of a free trip across the Galaxy, and space travel is oh, so expensive, now is your chance to get rich! You might just as well stop off on several planets on your journey, collect the odd sack of precious gems, elements or gold, and take-them back with you.
But before you go and make yourself the richest person in the world, you must remember to refuel your Spaceship every time you land on a planet.