A hyperdrive ring (also known as a hyperdrive booster ring or hyperspace transport ring) was a mode of faster-than-light travel for spaceships with no onboard hyperdrive.
During the millennia of the Galactic Republic, many starfighters were too small to safely contain a hyperdrive, so in order to travel through hyperspace these ships were required to connect to a Hyperdrive Ring. These rings were usually powered by twin reactors and ion drives; the ring contained hypermatter, providing ballast for the attached starfighter during the jump to hyperspace. Variant models could be equipped with additional acceleration pods, increasing both their sublight and supralight speed. In all cases, once a hyperspace jump was complete, the starfighter disengaged from the booster ring, which remained anchored in space, awaiting the ship's return.
This was seen as a vulnerability by some, for if the booster ring was destroyed, the starfighter would be stranded. Starfighters used by the Jedi Order were equipped with adaptable long-range communication relays, which allowed the pilot to contact the Jedi Temple for assistance in these instances. Some Jedi, like Anakin Skywalker, modified their ships to contain ultra miniaturized-hyperdrives, eliminating the vulnerability, at a cost to the hyperdrive's performance and range.