Theory time bois:
I'm assuming this story is similar to the movie "Oblivion" starring Tom Cruise where they are living in a sort of dystopian future in which Tom Cruise doesn't realize he is a clone and he is continuing to do work for an alien ship which is disguising itself as the new home for humanity (in this case, the Generic Terra spaceship in the sky). The memories which the Tom Cruise has are suppressed by the aliens until he sees some semblance of past moments with his wife, like how Kujirai is remembering things like habits, and now the photograph.
To cut the explanation short, whatever that "space station" is, it's trying to suppress the main character's humanity and have them do whatever work is needed on the earth below.
Probably way off from what the manga is about, but I thought it could be similar to the plot of that movie hehe