Conjoiner drives were starship engines built by the Conjoiners that used quantum mechanics to propel starships up to relativistic speeds, giving such ships the name "lighthuggers". Conjoiner drives contained a small wormhole linked to the very deep past, through which they draw their propulsion energies from the Quark-gluon plasma created by the Big Bang. The drives had six manual control dials that allowed the power of the engines to be varied. Lighthuggers mounted a pair of Conjoiner drives, both of which were controlled by a disembodied Conjoiner brain that performed rapid calculations to control the internal drive reactions. It should be noted that the Conjoiners did not actually invent the drive themselves, but received the instructions for it via the Exordium Project.
As the drive power was increased, so did the risk of an uncontrolled, ship-destroying explosion. If the turbulence within the drive exceeded the ability of the brain to compensate for, the drive would explode. It would also explode if the gap between the two drives of any one ship grew too large; this occurred because the Conjoiner brain was housed within one of the engines and controlled the other remotely, and thus once the remotely controlled drive passed out of the brain's control, the internal reactions would quickly spiral out of control. The drive was also designed to explode if non-Conjoiners attempted to open it for reverse engineering purposes.
The emission of tau-neutrinos by the drives was eventually found to attract the Inhibitors, and, subsequent to a 100-year suspension of their production, successful experiments resulted in the "quiet" Conjoiner Drive.
- A small part of the workings of the drives is revealed in the short story "Galactic North".