The Jump Drive opens a transition to jumpspace. Every ship stays in jump for around one week before entering normal space again. Ships in jump are isolated, and can not detect or communicate anything; they are totally isolated in a small bubble of space until they reemerge into out universe again. Even if two ships side by side (far enough apart to avoid field interference) jump at the same instant, they are totally alone. Cases of field overlap (interference) have been known to result in direction error, range error, system damage, or ship destruction, and is advised against. Jump drives rely on the rare earth element Lanthanum.
The distance travelled during this time depends on the jump rating of the drive. A ship with a Jump 1 Drive will travel one parsec, a ship with a Jump 2 Drive two parsecs and so on. The maximum jump rating at the tech level of the Third Imperium is 6. Study of misjump reports suggests that much greater distances are possible, but at present no way to achieve them in a controllable way is known. Research is ongoing on the matter. The maximum misjump reported is 36 parsecs. The average misjump is aproximately 12.25 parsecs, deduced from the study of statistical records. As of present, there is no theoretical limit to jumps in excess of J6, but no working J7 drive is currently manufactured in the Imperium- at least, none is admitted to being manufactured. Armchair theorists speculate that such a drive would be TL16 (TTL) and might be an experimental item in several research centers scattered across the Imperium.
Most civil starships have a jump rating of 1 or 2, with rare vessels equipped for express work carrying systems capable of 3 or 4; such ships operate for premium fees on long routes where speed is of the essence. Long routes tolerating longer delivery times use the usual jump1, but additional tankage to permit crossing voids to other lucrative destinations. It is so uncommon for a civilian ship to mount J5 or J6 that it draws the attention of Imperial authority as a curiosity worthy of review, if not close monitoring- a possible seed for several types of adventure for imaginitive gamesmasters. Ships of lower performance mounting droptank fittings draw at least a cursory inquiry as to why they are required; a simple form explaining the need is usually all the customer needs to file- and this is quietly checked out to see if it looks legitimate. As there are many situations which benefit from long range ships, these are USUALLY approved of. Having a LOW social standing or a criminal background however will result in such special feature applications being declined. USUALLY.
Starships must generate immense amounts of power to jump, and therefore additional fuel must be allocated for employment of the jump drive at the rate of 10% of the ship’s tonnage per parsec to travel via jump. 1% of ship volume per jump number the drive is rated for is dedicated to accumulators, ie jump drive super capacitors. (High Guard, black globe rules declares specifics.)
A significant amount of the fuel consumed during charge to jump is actually used to supercool the reactor while it is in overload mode; more than normal is used as fuel itself, as overload mode is less efficent than normal mode in fuel use, and ship plants are less efficent than stationary power systems to begin with.
Jump distances are calculated in parsecs (3.27 light-years), which therefore is the scale of a subsector mapping grid. Jump-1, for example, indicates the ability to jump one parsec, or one mapping hex. Astrogation maps are based on this fact and are not accurately scaled maps for astronomical purposes.
Although jumps are usually entered at low velocities, the speed and direction which a ship held prior to jump is retained when it returns to normal space. This fact is often employed for tactical purposes. It is not a safe practice, as the emergence point tends to have other ships approaching it for intended use; therefore emergence at speed is known to have resulted in fatal mishaps, and is therefore a serious violation of civil navigation codes with stiff penalties. These do not apply to the navy of course… who tend to place obstacles around possessed jump points with exactly this sort of thing in mind.