Ever notice how space is full of random junk just floating around? It's a hazard to everyone, so it's your job to blast it out of existence and prevent any inadvertent harm coming to the spacebound property of Earth - plus it's a job that comes with the added bonus of being able to vaporize any aliens that get in your way!
Unfortunately cosmic employment law is rather vague, allowing your employer to entirely avoid paying you for your hard work. Instead you'll just have to pick up the coins that are dropped from the various destructible objects you turn into pretty explosions, then use them to upgrade various elements of your ship. See how far you can get and how many points you can accrue!