Sub-C Drives power the main thrusters of a ship, usually located in a column at the back of a ship. They operate through a hypergolic fuel that ignites when two chemical mixtures come together. While the drive is running, the radioactive bleed-off from these volatile fuels is fed into a radioisotope thermoelectric generator which then generates energy to feed back into the plasma batteries. It’s easy to think of this as an ‘alternator’ from older models of cars on Earth.
Drives vary in size, and depending on the mass of the ship they’re propelling, can achieve impressive speeds nearing .3C on their own, giving off a large radioactive emission in the process – ships are much easier to spot on scan when they’re going full burn. Once the drives are running, they require little effort to maintain, able to burn on smaller amounts of fuel after the initial injection due to advancements made in the technology over the last century.