Jumping near gravity sources.

In regards to the 100 diameter jump guide that I brought up:

First of all I will clarify the situation again.

	1) The whole point of the discussion is not to compe up with a
	   rationaliztion for the rules, rather to figure out an accurate
	   way to caluclate jump distance, so one can use it in unusual
	   circumstances. (eg. Jump distance from an unusually dense world,
	   gas giant, neutron star, or even a Battleship?)

	2) The diameter is a approximation of the mass assuming that
	   all worlds have the same density. The small ones, usually
	   without an iron-nickel core are less dense however.

	3) using 1/r^2 for a large planet (size 8-9, std. density), the
	   attraction of gravity at "100 diameters", is 1/20th the
	   gravity felt by the sun at 1 AU.

The first suggestion proposed by Marty Jarrio, that we use a 1/r^3 method
is reasonable but is handwaving as "according to modern knowledge" gravity
follows a 1/r^2 method.

Calculating the gravity felt by the craft by summing gavity vectors of
significant bodies as Jim Baranski mentioned, has a nice appeal.

First, there will always be points regardless of the masses involved that
the net effect of gravity is less than a certain threshold, by adjusting
the threshold accoringly, we should be able to arrive at a value that will
make safe jumps best at around 100 diameters of the planet.

Second, There will be points, especially in a system with a large moon,
where a jump can be safely made much much closer to the planet, than 100
diameters. These would be small (perhaps even smaller than some ships),
and uncertain to use, which would limit their use. Ships could only use
these on an outbound leg as they would effectively be "islands" of
acceptable gravity level.

Third, in a talk given by Mark Miller, he always intended there to be a
limited (but large) number of points that a ship could jump from/to,
otherwise piracy couldn't exist (qv my other article in this digest).

The only bad part is that the points of low attraction between a habitable
planet and the sun, may also be "islands". Due to the fact that an incoming
ship precipitates out of jump space when it gets to "100 diameters" this
might make leaving quicker than arriving.


				-Dan Corrin