SBMs are Strategic Ballistic Missiles, they're a type of transport that are used mostly to delivery nuclear payloads, but they are also used to make ships go past the planet's orbit. So they're not the weapon, they're the vehicle that leads them to their destination.

In Colonies, the SBMs will also be designed with modules, so there'll be many different types, ones with more stages and more max distance than others. The first stage, the biggest one, will fall to the ground after the second stage kicks in, it'll fall into a random location just below the area where the second stage kicked in. And if the owner doesn't destroy it or collect it, another nation may do so and recover it's research and secrets.

So... everything has a reaction.