The zi-Drive was indeed a new kind of hyperdrive, one in which the destination of a hyperspace jump was indeterminate until the exact moment of departure from hyperspace. Until that departure point, a zi-Ship or even an entire battlefleet will remain hidden within a time-dependent topographically expansive hyperspatial zone of possibilities.
A ship with a zi-Drive enters hyperspace in a particular galactic zone. (See the concentric grid map above for a reference on the sizes and relative shapes of galactic zones). Using the powerful zi-Drive:
- Any system within the zone of departure is accessible within 24 hours of entering hyperspace
- Any system within the zone of departure or any contiguous zone is accessible within one week of entering hyperspace
- Any system within the zone of departure, within any contiguous zone, or within any zone that is contiguous with one of the departure-contiguous zones is accessible within two weeks of entering hyperspace
- And so on...
The volume of space that is potentially available as a destination constantly expands with time once the ship enters hyperspace.
It is entirely ambiguous from the perspective of hyperspace topography where a zi-Ship is until it exits hyperspace. This element of uncertainty and surprise is the primary strategic value of the zi-Drive. The Empire's best Mentats have suggested that vessels using this drive enter into a zone of elastically indeterminate hyperspace - one which collapses entirely when a ship exists zi-Space.
But one thing is certain. It is rarely advisable to remain in hyperspace using a zi-Space on for more than two months. Many vessels - and in some cases entire battle fleets - have disappeared forever. It is assumed these vessels exited zi-Space too late perhaps due to errors in subjective time measurement. It is likely these vessels emerged in a damaged state somewhere within the immense intergalactic void.
Of course, it is possible that some of these vessels remain trapped within an ever-expanding bubble of zi-Space like a hyperspatial Flying Dutchman that is simultaneously everywhere and nowhere at once.
To equip a starship with a zi-Drive, select the Stardrive skill and select zi-Drive as one of the ship's Stunts. The zi-Drive stunt allows a vessel to displace itself by one galactic zone for every week (N +1 zones/week, where N is the previous number of weeks in zi-Space). A piloting skill is required to enter zi-Space, and is required to maintain the ship within a stable zi-Space bubble each week.
The Pilot must roll an Effort of Mediocre (0) or higher on their Pilot skill in order to maintain or exit the zi-Space bubble within the same zone/day.
After one day, a weekly roll must be made to maintain the bubble or exit from zi-Space. The Piloting skill required increases by one step on the ladder each week. Failure results in a vessel being marooned in zi-Space or in being ejected at a distance of N zones from the ship's point of entry into zi-Space (where N is equal to the number of weeks the ship has been in hyperspace). The GM will determine which of these results applies and where the ship emerges from zi-Space (if it ever does).
This hyperdrive is based on a movement-based interstellar war game from the 1970s. Does anybody remember the name of this game?