Planetary Last Stand

You are the last line of defence orbiting a dying world.

Build your arsenal, upgrade planetary defences, and survive waves of enemies that descend from outer space.

Your ship moves in orbit, automatically firing at visible enemies while defending the planet below.
Collect XP orbs, research upgrades, and unlock new systems to stay alive longer each run.

I'm trying to make a game in one week, so this is the result. If there are enough playing will add in more content, please comment with your suggestions for upgrades!