I really like the concept. There are a few things that could use some improvement:
1. you should be disembarking from your ship when on a planet. would be way more immersive.
2. it's spelled oxygen
3. it took me quite awhile to figure out how to navigate and use the shop. i mean a long long time. it was completely nonobvious that you use the arrow keys to navigate it. i'm sure the majority of people who have rated this poorly had that issue and didn't bother mentioning it. that's kind of my guess but i'd say it's a pretty well educated guess.
4. the first planetoid you fly to has nothing on it... this isn't great design imo. put some stuff there.
that said, i really like the concept. please develop it more. and i'm giving you a 5 because the genre is right up my alley and i'd like to offset the 3 star rating which i believe is a little too low