She came back from space. She didn't come back alone.
Why it is hard sci-fi
An astronaut returns from the ISS after a mid-orbit collision and finds that small details about her family and home are wrong. The show commits to a working rule. There are two parallel branches with overlapping participants, and certain people, including the protagonist, can move between them under specific conditions. The procedural texture is space-program and family drama. The shows engineering interest is in the ISS sequence, which is among the most rigorous orbital portrayals on TV.
Science inside it
A two-branch reality with a working CAL experiment as the in-show physics device, a portrayal of orbital decompression and EVA procedures with real procedural rigour, and a recurring engagement with the medical-and-psychological consequences of being in two states simultaneously. The shows CAL device is a real ISS experiment that the show takes as its physical anchor.