Re: [ft] Orbits in Vector

On Sat, 29 Jul 2000 20:28:49 -0400, Laserlight <laserlight@quixnet.net>
wrote:

>     If I understand it correctly, a slingshot starts with the
>ships coming from high in the gravity well.  When it gets to the
>bottom (as close as it's going to get), it burns propellant, and
>the momentum that the propellant acquired by "falling down the
>well" stays with the ship.  

There are two reasons for a "slingshot". One is to allow a ship to
increase
its velocity without using up its fuel. The problem is that whole
conservation
of momentum thing. If you increase velocity dropping into a gravity
well, you
lose it coming out of the gravity well. By, as you point out, you only
gain
from a gravity well because you are burning up fuel mass on the way out.

The other reason for a slingshot is to make abrupt course changes. You
drop
into the gravity well and let the gravity alter your course. This saves
having
to burn a lot of fuel to make a course change. This, in fact, is a very
handy
thing, something NASA uses all the time with their deep space probes. 

I suggest if you want to handle fuel mass consumption that dropping into
a
gravity well could give you a +1 to velocity or something like that on
the way
out to abstractly represent that. If you want to assume that fuel mass
isn't
an issue, don't give the bonus.

Either way, going into a gravity well should give you extra thrust
points
above that rated by the ship's drive, but when you exit you have to
subtract
those thrust points.

At the same time, the gravity well should have a vector towards the
planetary
body. The trick, of course, is how much of a vector would you need? I
answer
this in a reply to Sean.

Allan Goodall		       awg@sympatico.ca
Goodall's Grotto:  http://www.vex.net/~agoodall

"Surprisingly, when you throw two naked women with sex
toys into a living room full of drunken men, things 
always go bad." - Kyle Baker, "You Are Here"