You know, it never even occurred to me that they might have space travel in the present! Surely that would affect something, somewhere in a visible way?

(My headcanon is that after the spaceship came to Haixing back then, there was no further space travel. Possibly the ship wasn't all that spaceworthy any more when it arrived, and everyone settled on Haixing knowing they weren't going to be leaving again. Also possibly Dixing still has the knowledge of how to make spaceships, if not the infrastructure to actually do so - though that knowledge might have been lost with the meteor.)