I love the concept of this. There's some refinements that I think you could make, but overall it's a solid evolution of the classic coin-op game.
The player's ship is pretty large for the playfield, but that I think it more a preference thing than an actual design criticism. One design criticism I do have is the mechanism for engaging the ships thrusters. I'd put in both a visual and an audible cue that the engines are on. I'd also like to see a way to identify the astronauts more easily. It's tough trying to isolate white rocks from white astronauts, especially when the playfield gets really crowded. I know you're going for a monochromatic look and feel, so a obviously a different colour wouldn't be the right solution. I'm not sure what would be a good solution. Maybe a periodic speech bubble with an exclamation mark? _(!!!)