Alcubierre Ring

An Alcubierre Ring can be fitted to a ship to allow anything inside of the Ring to travel faster-than-light by expanding space behind it and contracting space in front of it through the use of Dark Matter. Rather than acting as a type of fuel, the Dark Matter is more like a component that only rarely needs to be replaced. The use and properties of Rings is widely known, however thanks to the near impossibility of obtaining Dark Matter, their construction is reserved for only the most wealthy of governments or corporations.
In early human history, an "Alcubierre Drive" was theorized as a type of faster-than-light travel that instead of moving the ship, thus violating the speed of light, moved the space around that ship. For centuries, research proved fruitless until 390 AE when the Solar Republic siphoned the first Dark Matter deposit. Investigation into the material's properties led to the construction of the first Ring in 393 AE. Later that year, the first starship set sail, traveling from Sol to Alpha Centauri in just over a month. Further investigation and more voyages revealed the most optimal size and usage of a Ring.
The dimensions of Rings are mostly limited, as only certain dimensions can guarantee a successful transit without breakdown. The smallest such "sweet spot" is about six times larger than the largest ship humanity had built before the invention of Rings. The next largest viable size is several orders of magnitude bigger, and thus impractical. The ships built to sit in this narrow window are gargantuan, dwarfing regular sublight ships in comparison. These vessels are denoted as starships. Despite their huge size, starship hulls are only about 30% of the cost, with the Ring frame being another 20% and the Dark Matter that goes inside of the Ring usually 50% of the starship's entire cost. As such, most starships are designed so that the Ring can be detached when the hull is damaged and moved onto a more intact hull.