Well, golly. I'm going to have to keep an eye on this game. You're on to something very fun.
I hope future development will add an interstellar environment. Warping between planets is fine but warping between stars would be exciting.
I was disappointed to discover that you did not use life-like gravity simulation. I prepared to go into orbit and then scratched my head at what I was seeing instead.
You should add a controls screen asap. I was confused about how the inventory works, and didn't discover the inventory screen until after a 45 minute flight to the moon. A little list of what keys do what things would have made a big difference.
I think you should not make the planets on the star map selectable. It's more fun to look at the map and try to figure out which way to fly. Maybe they should be selectable on a 'easy' difficulty mode.
I made an airlock to protect my ship's oxygen, and then realized that was completely unnecessary because it doesn't work the way I assumed. I think you should make the oxygen machine get destroyed if it is left on while exposed to an un-sealed environment. That would make that aspect of the game more challenging. A short-term oxygen supply inventory item would also be nice, so you don't necessarily have to die because your oxygen machine popped.
I'm sure you have a roadmap laid out already, but I suggest making failure mechanics a priority would be a good idea. I was so careful to land gently every time I moved my ship, then I once crashed and the result was disappointing. Later I flew straight into the star. I mean, I got right in the middle, as close as possible. The result there was also pretty disappointing. So, setting up all the ways the player should die or lose will make a big difference in the experience.
One problem that stood out to me- the adventure sort of defeats itself once you get the stellar drive. It's cool, but it suddenly kills the excitement after about five seconds when you realize it is now super easy to get anywhere. I think progressive levels of propulsion power leading up to the stellar drive would be a good way to go.
I got hours of enjoyment out of this game and I hope I get to see you take it a long way. Good work all around. :)