Technology of the Firmament

The technology of the Firmament is advanced by 21st century standards, but still has a lot of limitations. It’s also very limited outside of the core Foundation worlds. Some examples of the kind of technology available include:

A note on planet killers:

Any society which can accelerate to significant proportions of the speed of light has the ability to create weapons of unavoidable interplanetary destruction. However, this is not fun if you want to have a sci-fi setting where starships aren’t treated as portable WMDs. Relativistic projectiles fired at interplanetary distances are thwarted by the “braker gun”. Usually installed on a moon or orbital station, these enormous emplacements use antigravity technology to nudge relativistic projectiles off their course.

Other forms of WMD are dealt with by a planet’s defensive arrays. Orbital nuclear strikes and kinetic bombardment are trivial to defeat as long as the planet’s defenses are intact - railguns, lasers, missiles, et cetera. Generally speaking, battles for a planet are fought in orbit. Once you’ve overwhelmed a planet’s defenses, the only thing stopping you from scorching the surface with nukes is whatever desire you may have for it to remain inhabitable.

If you’re in the atmosphere, it’s harder to stop you from launching nukes at random. Planetary defenses will be able to shoot down intercontinental missiles, but short-range nukes may get through. There are various precautions to stop this from happening - for example, spacecraft approaching large cities are required to surrender their controls for landing once they get within a few kilometers. Needless to say, nukes and other WMDs are strictly military weaponry that generally aren’t available to the player characters - through legitimate channels, anyway.

Of course, none of this applies to uninhabited worlds, or planets so impoverished that they can’t afford to properly defend themselves. Out on the Rim, anything goes.