Nice! You have a really nice balance of difficulty, and I can't help but look at the screenshots and wonder how it feels to get that far, I was expecting Esc to pause and it just closed the whole thing :(
Some things that might help that you might already have in mind:
- Showing HP
- Showing a meter or visual feedback to let players know how hard will they jump
- Updating sprite when Space bar is pressed while not on the ground
And some ideas came to mind, one, making a bit of particles shoot when jumping, this would mean the astronaut is using thrusters on top of their legs, this would also increase the effective distance of the jump (IE being able to propel yourself off walls using the jump by being near the wall but not necessarily touching it), allowing for more advanced movement.
Two, rolling feels like it could be a mechanic by itself and it making you receive damage feels unfair, maybe this is by design, but rolling could be used for more precise positioning, maybe still make bumping your head have some negative effect other than the chance of having to redo the whole level.
And I always love being able to convey ideas and characters with a reduced amount of pixels, well done!