Slingshotting ships with gravity wells in SJ

Everyone on this list MUST have seen the slingshotting maneouver used in the
Apollo missions, or at least used in 2010.  For those that haven't, it
basically involves "sliding" a ship around the edge of a gravity well of a
planet (or, in SJ, something with gravity), to gain speed for a bit more
"push".  My idea has been that perhaps some ship, specifically those with
non-magical engines, could use this particular maneouver to attain
spelljamming speed.  I am writing up a sphere called Ragespace (visible on
my sphere map if any has had enough interest to take a look), in which the
Order (local human dominant military power, based somewhat on the ideals of
the Whitecloaks from Wheel of Time mixed with the Imperial Order from Sword
of Truth, but also with a great deal of my own terror-DM'ing nature thrown
in) have forbidden the use of magic, and psionics.  This, obviously, would
make spelljamming especially hard, so I am coming up with theories (mainly
because I want a place where my PC's have to think without just going "pfft
magic can fix this/kill this" etc) upon how the order's ships would travel.

Obviously, I had allready decided they used non-magical engines, otherwise
they would be far too hypocritical for me to have fun with, but then the
question of how long would it take them to travel from planet to planet hit
me - bloody ages.  Now, I know 90% of the people on the list would do the
math, and figure it out just to show what they're talking about, but I
really can't be bothered at the moment, and someone else likely will anyway.
In any case, tactical speed is NOT good enough for interplanetary travel,
and is very little good for even planet to moon travel.

I'm thinking of making a system wherein a (tactical speed) ship can spend a
day, navigated correctly, around a body, to get a certain ammount of IS
(interstellar speed).  I'm considering something like 1 day IS for every 12
hours around a body, per size of the body.  Thus, 12 hours spent circling a
size A body would bestow a day of IS speed, while the same ammount of time
around a size B body would give two days of IS speed, right up to 12 hours
worth of travel around a size J body granting 10 days of IS speed.  Do
people think this is a bit excessive, or not enough?  Of course, there would
also be a very hearty navigation check involved, not only for getting into
the orbit correctly, but for charting and successfully taking the course of
the ship required etc etc - and this is not to mention the fact that the
ship is in a little trouble if dropped to tactical speed somehow.  Perhaps
bodies accelerated in this way don't drop to tactical speed, but instead
career through space.  This would make pirate raids on them interesting,
battles at SJ speed!  Obviously, a helm that doesn't drop out of IS speed
when faced with a relevant size body is also going to be something to figure
out, but maybe it just requires a great deal of skill upon the part of the
(attacking) helmsman?

Look, I'd love some feedback on this idea.  It's not that I want to start
bringing proper or high tech into SJ, I just want to use non-magical helms
for this human military group, also to promote Ragespace's feel of an
industrial, grime filled sphere.  Allready, due to a whole lot of stuff, I
have put drifting clouds of noxious gasses and liquids in, and my
description for the main world sounds like it should be a big pile of soot.

Words ne1?

BTW - if ur wondering why I have posted so much in the last day or so, while
I've been relatively silent over the last month or so, it's due to RL,
moving, loss of computer with no warning (note: never borrow your dad's
comp, when he lives half an hour away, and suddenly ssays "im taking it
back), and big brother ;)

Tilaurin
www.planetbaldursgate.com/atreus/index.html
tilaurin@?????????????????.com
"Dying Swans/Twisted Wings,
Bring This Savage Back Home"
Brave New World - Iron Maiden