RE: [FT] Orbit and FT

Geo-synchronous means you are over the same spot of the planet all the
time.  To achieve this you have to in the orbit radius that gives an
orbit time exactly the same as the length of day of the point on the
planet below.  So GS will depend on the rotation time of the planet
(this gives you the orbit time required), the size of the planet (this
will give the gravity factor to determine what orbit to be in).  Note
that there are certain situations where GS is impossible - large planets
with slow rotations could generate orbits within the planet.  Also GS
can only easily be done across the equator; orbits towards the poles are
more unstable since the orbit is no longer in line with the
gravitational pull.  High tech ships would be able to pull it off since
they can continously apply thrust to counter-act the offset pull of
gravity.

Mass of the ship doesn't matter much.  Mass of the planet determines the
amount of pull gravity has and that determines how fast the orbital
speed will be.

One example to help visualize gravity and orbits.  Take a perfectly
smooth sphere the size and mass of earth with no atmosphere.  If I fire
a bullet horizontally from an altitude of 2 meters at 100 m/s, it will
hit the ground about 60 meters away as gravity pulls it down.  However,
if I fire it at about 8,000 m/s the ground falls away, due to curvature,
at the same rate as the bullet falls - thus "free fall."  Effectively
the bullet is falling at the same rate as the earth is curving away from
it.

As you get farther from the center of mass, the pull of gravity becomes
less.  This is offset slightly by the fact that the curvature of your
orbit is less as you get further out.  But curvature increases linearly
and gravity drops off by the square of the distance so as you get
farther and farther away from the center of gravity of the planet the
less "falling" you have to do to never hit the ground.

To paraphrase the Hitchhiker's Guide to the Galaxy - the art of flying
is throwing yourself at the ground and missing.

--Binhan

> -----Original Message-----
> From: Brian Bilderback [mailto:bbilderback@hotmail.com]
> Sent: Tuesday, March 12, 2002 11:16 AM
> To: gzg-l@csua.berkeley.edu
> Subject: Re: [FT] Orbit and FT
> 
> 
> Brian Bell Wrote:
> 
> 
> >Actually I've used the gravity mechanic for vector movement 
> that others
> >have mentioned.  Determine range bands for the gravitational 
> force, and
> >then apply them to your motion as an additional thrust.  
> Orbit isn't too
> >hard to achieve, you just have to a rough idea how much 
> velocity you have
> >to have at a certain altitude.
> 
> I like this method, but I do have a couple of questions.  
> First off, I 
> always get Geostationary and Geosynchronous mixed up.  Do 
> they mean the same 
> thing?  If not which one means an orbit that keeps you 
> directly over a fixed 
> point on the planet surface (i know, it was mentioned 2-3 
> posts ago, but I 
> already deleted it)?	That's the one I mean, and I'll refer 
> to it as GS for 
> the rest of my comments.
> 
> How would you simulate GS orbit using those rules?  Do you 
> have each band 
> around the planet, instead of having one fixed velocity for 
> orbit, have a 
> range of allowable velocities, with GS somewhere within that 
> range, or do 
> you have one band at which the orbital velocity matches the velocity 
> necessary to maintain GS?  Or is there some direct relationship I'm 
> forgetting between a planets rotational speed and the orbital 
> speed required 
> by it's gravity (being as they are both affected by its mass)?
> 
> 2B^2
> 
> _________________________________________________________________
> Get your FREE download of MSN Explorer at 
> http://explorer.msn.com/intl.asp.
>