Do they plug in the tape and enter a destination, and the computer says - "go here and press jump" or does slotting the tape turn the ship over to computer flight control until the jump is complete? And can they abort if things start going wrong.
It's vague, so the Ref can play it any way he wants, as detailed, or not, as he wants.
My position is that the cartridges are for a specific time. I think a day is good. It's good for a 24 standard hour. Or, if the Ref wants to be colorful, the cartridge is good for a local day.
The cartridge does the work of the Nav computer in generating a flight plan through J-Space. Not only does it figure a path around gravity shadows, but it also figures the explosion of energy needed to put the ship on the right J-Space vector. I like the detailed explanation of how the J-Drive works in the DGP SOP for MT. The ship has a jump grid. Power is fed to this grid, first to generally power up the grid, then, in one big explosion of power, the power is shunted in a specific patter across the grid to open up a route to J-Space. The jump grid, when powered like this, acts like a key. Each vector requires its own specific "key", or pattern of energy on the jump grid.
And, the Nav Comp does this all key to a specific moment in time, in the span of a millisecond. That's a lot of calculations, and the cartridges hold these pre-calced operations for several future moments of one day or span of time.
Some jump cartridges hold only calculations for a jump on the hour for 24 standard hours. A ship must make a particular point in space--the jump point--and jump from that point when it jumps at the specific time it is meant to jump. Therefore, when the ship arrives, it may have to wait for the next hour until the right jump time occurs.
Cartridges tend to cost the same amount--a standard 500 Cr--but how the sellers vary product cost is to limit the number of jumps a cartridge will be used. On a high tech world with a Class A starport, one cartridge could contain a number of jump calculations (let's call them jump packets) that lasts for 24 standard hours, with one jump packet available every 10 seconds of time for that day.
On a lower tech world, with a lower class starport, there might only be one or a few jump packets on the cartridge. And, it is up to the ship's captain to make sure that the vessel is at the jump point at the time designated by the jump packets contained in the cassette.
Miss the last jump time available on the cassette, then Travellers are taking their lives into their own hands if they use old, called "past prime", jump packets.
-- Adventure idea --
Low tech world with Class C starport selling jump cassettes that have only one or two jump packets on them. Then, the starport clerk sells the jump time to local pirates. Along with this, the starport clerk--call him Kickback Jim--will also sell the pirates a manifest of the ship's cargo.
The pirates know exactly how long a ship will be at a jump point before it jumps.
Did someone say Space Battle?
