Richard Aiken writes:

>	In the series, jump drives do not consume fuel but do require the use of specific
>	jump points, areas where spacetime has been "stretched thin" by interacting gravity
>	fields. These points are the farther edges of stellar systems, many lighthours from
>	the system's primary. Throughout most of the series, these points are fixed and
>	well-known.

I have the same idea IMTU: fixed Jump points which are almost always in deep system orbit
(Kuiper Belt / Oort Cloud distance). The underlying hand-wavy reason is different
(non-linear Jump Space) but the effect is the same. Jump Points have been mapped out over
the millenia by the Scout Service (this is the primary reason they exist), and are quite
reliable. IMTU Jump does use fuel, usually almost all of it.

Here's a little write-up I did for a campaign:
--
Item: How do you navigate in JumpSpace?

Answer: You don't, really. It's "point-and-Jump". People (mainly the Scout Service)
have been mapping out Jump Routes for thousands of years. Unless you're insane,
unlucky, desperate, or being paid a lot, you stick to known Routes. You start out
by being at least 100 diameters from any significant gravity source. EG the diameter
of the Earth is 13000km, more or less, so first you get 1.3 million km away from
the Earth (while making sure you haven't wandered into another gravity well,
such as that of Jupiter), set up to enter JumpSpace in such a way that when you
pop out you'll be in the right place, and off you go. Momentum and kinetic energy
in RealSpace are conserved over a Jump.

Hitting a gravity well (uncharted brown dwarf star is perhaps the most common cause
of this) while in JumpSpace will normally precipitate you straight out of Jump and
back into RealSpace. You are at this point in the middle of nowhere with no fuel,
which is a suboptimal result. Avoiding these is part of the reason why Jump Points
(departure and arrival volumes) may be inconvenient to get to and from.

One side-effect of this is that Jumps almost always happen both in and out of
more-or-less well-known volumes. It's possible to control this somewhat, if you
have a very skilled astrogator and a high-quality drive, but outside the military,
most people don't bother. The volume is likely sextillions of cubic
kilometers, so you don't worry about hitting someone on arrival, but you will
normally depart the arrival volume fairly promptly. Just in case.

Since your ship likely entered JumpSpace with RealSpace velocity, doing nothing will
normally take care of this. The Scouts almost always put Jump arrival volumes out
where there's nothing to easily hit. Typically a system will have a number of Jump
Points, one for each system that you can get to from it, and the Scouts try to set
these up such that your likely RealSpace velocity actually takes you somewhere
useful, such as closer to your destination. This is not always possible.

It is also worthy of note that Jump Points are asymmetric, so that the Jump
Point you arrive in will almost certainly *not* take you back whence you came.
Turning around almost always involves refuelling, manouevring over to the Jump
Point you want to use next, and re-entering JumpSpace.
--

All this has some corollaries. Ships will tend to get to a Jump Point and then "make
the calculations to enter hyperspace" (to borrow a phrase from a well-known movie)
before actually Jumping.

So pirates can hang around here and try to intercept ships while they are relatively
static (at least not accelerating). Conversely, ships arriving at Jump Point X from
system Y will tend to have predictable RealSpace velocities, and so are more easily
closed with and attacked.

Fleet-level military actions will tend to take place around Jump Points.

Arriving ships will turn up with not enough fuel to Jump again, although they will be
able to manoeuvre in-system. The first thing they will want to do is re-fuel (especially
if these are military ships) so they will probably head off to somewhere they can do this:
gas giant, water world, HighPoint/commercial refuelling station, etc. Exploration ships,
e.g. Scouts, will likely use "drop tanks" which will allow them to get out again if the
place they end up in is 'dry'.

I also allow JumpSpace navigation to be more successfully done by psionic talents who
may, and historically would, be unaware of their skills. They are just known as 'really
good navigators'. And, the better your Jump drive, the higher-quality fuel, the more time
you spend 'making the calculations', and the better your navigator, then the better chance
you have of making any Jump, especially an unusual one. Longer Jumps are more hazardous,
but not a lot more.

Not every system is reachable, even if you have a long enough drive. There may simply be
no Jump Point between system X and system Y, even if they are nominally within range.
The further they are apart, the more likely it is that no Jump Route exists (or that
no-one has found it, or it's some big corporate or military secret, etc, etc). The J-5
Route across Riftspan Reaches would be an example of this.

Anyway, hope this is useful or entertaining to someone.

Jonathan