Great concept for a game!
Still have some suggestions:
1) Difference between rock planets and gas planets. Which contain different. elements. Gas can be mined faster, but you can't place a base on it for example.
2) Add fuel and travel costs to go between planets. Max travel distance in one time. space stations to place between planets to add fuel to the airship.
3) Add some things to do. For example mini games between traveling (in point 2) like encountering an unexpected group of meteors to avoid, attacking aliens,...
4) like said before upgrades! mining speed; in case of point 2, size of fuel tank; hull of the rocket for mini games in case of point 3; heat resistance to mine planets close to stars;...
5) Earth as start with story to leave Earth would be nice.
Good luck with the rest of the development of the game!
 "Planet Miner - The Search for the Elements of Life")
 "Simple Race")