Not gonna lie I was left confused.
From what I understand I'm the spaceship on the right.
There is some spaceship on the left constantly firing at me, but I can only fire once in a blue moon, because firing again overwrites my shot and makes my previous shot disappear. This also I understood after spending a bunch of time confused why my shots just instantly disappear (because I was mashing fire button).
How exactly am I supposed to earn gold in this game?
At some point I understood that the weird thing flying at the bottom of the screen from time to time is the Mars base, but that was very unclear at the start.
Also, due to the lack of keypad, movement was confusing.