We're all aliens, until we get to know one another.
Why it is hard sci-fi
A 1975 series about a lunar research base that is launched out of Earth orbit when a stockpile of nuclear waste explodes on the far side of the Moon. The show commits to the consequence. The Moon is now an interstellar object with a crew of survivors, and each episode is a contact event with whatever the Moon drifts past. The shows physics is broken at the start and the show admits as much in passing, then runs the experiment.
Science inside it
A nuclear-waste-driven impulse as an explicit physics violation, long-duration habitation on a derelict Moon-as-spacecraft, and a recurring contact-with-aliens problem framed as research rather than warfare. The show was made under the production methods of its sister Gerry Anderson series and the procedural details show that lineage.