You can get a lot of upgrades pretty easily using Science, the "Revive" item might also be too busted. Maybe make it single-use and more expensive?
Additionally perhaps you can buy upgrades like "gravity boots" for faster Astronaut speed, something to increase repair speed, research speed, etc.
Pacing-wise I do think it's very solid, it ends when it should as soon as all of the game's content is exhausted and you get in the loop. As a baseline it's very much solid and I see it expanding into something bigger!
I also liked the idea behind the ending, tho yah I wish I saw what was beyond the portal lol. You can also send multiple astronauts thru the door before it lifts away, maybe something bonus could happen if you do that? You can expand a lot on just everything that's in place already without doing too much extra work!