I'm writing a setting where superEarths abound, frequently with intelligent life, but Earth-size habitable planets are rare, with the focus being on the five intelligent species from Earth-size planets functioning as traders. As per Space.com "No Way Out? Aliens on 'Super-Earth' Planets May Be Trapped by Gravity, the many intelligent species on these superEarths are functionally confined out of space. (That's about relatively heavy superEarths, though the setting says the number of intelligent races trapped on their planets far exceeds those that can build a space program and construct interstellar spaceships.)
This is a fairly hard-science setting; there's subspace handwavium where ships can get from point A to point B through empty-enough space at light speed for a reasonable energy cost, and there probably is limited artificial gravity to avoid rotational issues on small ships or issues of life without gravity. Otherwise, it should all be accord with physics as we know it. Specifically, objects in subspace crossing 1 millibar of atmosphere will immediately self-destruct and exit into real space in the form of subatomic particles, and around the microbar level, would introduce around 1 Gray/microbar to the objects, quickly fatal to computers or living creatures.
If they came across a hostile species, what could that species do to them? I'm trying to be realistic here, but optimally there'd be some danger, but not too much. Eyeballing XKCD on laser pointers a laser weapon might be a risk; thicker atmospheres combine with a much smaller target make taking out a single ship conceivable; anti-laser armor would develop as a defense, to the extent that's possible. It seems unlikely a missile could escape the atmosphere with enough maneuvering fuel to threaten a mobile ship, but possibly if one was clearly negligent in threat awareness. Even without advancement in computer technology, 2020's AI should be enough to give you plenty of warning. And there's Trojan horses—launching objects that are only dangerous if the spacefarers pick them up and open them without precautions. Anything else?