*have*to be the same because energy production and the tossing of matter with that energy are in intimate contact and can’t be separated.

Okay, great, so it can shoot matter into other dimensions. But what good is that? The Jump Drive is attached to the ship itself, only the hydrogen goes elsewhere. But by shooting the matter, there is an impulse or reaction similar to bouncing a perfectly spherical rubber ball on the pavement. Our ship shoots up, and lands somewhere else. The hydrogen shoots opposite, and will

*eventually*make its way back into normal space, but it also in a perverse way is “carrying” the ship at the same time. Its trajectory matches in some dimensions with the ship but not others. Also, you'll get only

*one*bounce, not many.

This would be easy to see if you were an 8-dimensional kid with a ball, but not so easy for us navigators. We have to envision it more abstractly, with 8-dimensional matrix algebra, figuring out action and reaction with 8-dimensional geometric vectors we can’t really see directly. Of course, a computer is helping us calculate all that in only a few hours…

We get a certain view as we Jump, but our 3-dimensional brains can only really see "pavement", so the Jumpspace looks to us like a swirly, marbled, mother-of-pearl jumble. It hurts our eyes to look at it for too long.

The math gets weird. If the engines are built for it, if they can convert large masses of fuel at once for more power, you can shoot more fuel, go further. The bounce seems to fix into discrete intervals which more or less fit our parsecs, and curiously matches the general distribution of stars. If you are the proud owner of a Jump-6 drive, you can program jumps of up to 6 parsecs. Strangely, it doesn’t take 6 times as long as a parsec. We would think a ball bounced 6 times higher takes longer to go up and fall down again. But the bounce is more like a swinging pendulum in this respect. Galileo looked idly at a swinging chandelier in a chapel and discovered that, to only small variation, a swing took exactly the same time no matter how wide the swing. This started modern time-keeping. So it turns out we are always talking about a week, give or take.

Of course, things can go wrong. You want to make a nice, perfectly spherical “ball” of hydrogen, and the math says it must also be of “even density” and “smooth”, but I can’t even begin to explain what these 8-dimensional factors mean in real terms. All your calculations are based on shooting a spherical ball of hydrogen behind/next to your ship to control where you are going to rejoin normal space.

But what if that ball is not perfectly “spherical” or “even” or “smooth”? Then, over at universities with nice big calculus difference-engines, you can calculate the variations, small or large, in our return points. In practice on-board we can only do straight navigation and figure out that we veered from our ideal return spot. If the engine sputtered or mis-performed, then the misshapen lump of hydrogen could send our ship to a totally different star or even wreck our ship from sideways torsion. Embarrassing. Probably even fatal. This is where you need your engineer to maintain the engines and avoid such embarrassment. A clean ship is a happy ship!

One extra note: small nicks in the bouncy ball make a ship veer off in another direction, but a gap of hydrogen in the dead center makes the ship go in the right direction but fall short of the mark in a combination of space and time. If the volume of hydrogen is adjusted to make up for the difference in mass, then the ship will bounce to the right spot in space but still with a measurable time difference from the previous predicted time! It takes much more energy to generate a gap of no hydrogen in a sphere and, as the hydrogen reasserts itself, a time-displacement results even if the ship has no net motion. This is more energetic and finicky, and a fledgling Time Corps is being set up to investigate this phenomenon. But so far we are at a primitive stage similar to the earliest days of rocketry. Both launching pads – and astronauts – are blowing up on us.