Very cool idea, gives me nostalgia of the type of games you'd play in highschool on the computers when the teacher would allow you too . The game is very nicely made although i do feel having the fuel decrease slower when you dont press the up button and faster when you do would be a good idea and having the rocket feel more like a rocket and not so light would be a nice touch, the altitude also i think should be attached to the rockets actual height and not just a number going up because I went down a few times and the altitude still went up.
This game overall is a very cool, the idea was very fun and very original, the artstyle was consistent and suited the overall aesthetic of the game matched with the background music very well and a solid UI to top it off. Good work!