I really like the concept my only criticisms are that it's a bit confusing at first with how you can travel between planets, maybe make a tutorial or something. Also when the player loads in there are already enemies shooting at them so what I would recommend is making it so that enemies start spawning a bit after the player has loaded in to give them a bit of time to react.
But I definitely see potential in this becoming a full on game with more polish like lets say a roguelike where you have to jump between planets that all have different terrain and enemies. But in summary this is a fun game that's a bit confusing at first but could definitely work if given polish.