The film deals with the moral dilemma of an astronaut who is also a mother of a little daughter, which creates a tension since on one hand it has always been Sara's dream to travel in space and now after she completed the arduous training and was selected to participate in the eponymous Proxima mission, this dream she has had for years may finally come true. However, it means leaving her daughter for over a year (mission plus preparatory training). Sara has to deal with her feelings of missing her daughter, and at the same time prove that she is as good as her male colleagues, sometimes has to face being ridiculed because she is a woman in man's world.
I understand Sara's desire to fulfill her dreams, however I also feel sorry for her daughter Stella, who often looks unhappy and it seems that she considers herself abandoned by her mum, her relationship with Sara is also getting less intense and they may be losing their mother-daughter bond. I guess it must be terrifying for a child to see her mother travel in a space shuffle when it is not certain that she would be able to come back safely. When Sara escaped from the quarantine to show the racket to Stella just as she had promised her, I thought that either she would give up travelling into space, coming to the conclusion that staying with Stella was more important, or that it would be discovered that she broke the quarantine and would not be permitted to leave in the space shuttle, somehow it was a bit disappointing that motherly love did not win over ambition.