Re: Gravity, Tech & others (was Re: Orbits, etc)

On 10 Jul 98 at 11:01, Andrew Martin, Alex Shvarts & wrote:

> In several SF systems, the writers suggest that FTL drives only work
> in near-flat space. Because a planet is in orbit around a sun, the
> attraction between the sun and the planet would be near neutral
> (near-flat space), at a point proportional to the masses of the sun
> and planet and the distance between them.
> 
> An easy way to under stand this to place two heavy but unequal
> weights on a soft bed. The heavy weight represents a sun, the light
> weight represents a planet. Note that the bed surface curves under
> the weights and changes curvature between the weights. The point
> where the bed surface becomes flat is analogous to a FTL transition
> point in space. If I recall correctly, these are also Lagrange
> points. Around our Earth and Moon, there are, if I recall correctly,
> six L points.

Lagrange points are not actually 'null' gravity points. They are 
places where the orbital period of a body within them is the 
same as that of the orbiting body that they are related to. Some are 
'stable' and actively gather asteroids, the L4 and L5 points, which 
in jupiters case are called the trojan points, have many asteroids 
within their area. The others are less stable, and keeping satellites 
in them is like balancing a ball on the top of a cone, (but still 
requires less thrust for keeping it there than a continual forced 
orbit manuever).

For instance, a satellite in orbit closer to the sun than the earth 
would normally move faster in it's orbit than the earth, and get 
ahead of us. However, in the L1 point between us and the sun, a 
satellite gets just enough pull from the gravity of the earth to keep 
it between us an the sun. In fact we actually have a satellite there. 
SOHO, which monitors the solar wind, and gives us early warning of 
it, since the solar wind is quite a lot slower than light speed. 
(Actually, SOHO just went wrong while having a course correction., oh 
well).

The L points also wobble around due to peturbations from other 
major planetary bodies, in the case of the L4 and L5 points it tends 
to pull the satellites along with it, for the others, the satellites 
'fall off' the L point.

I think there are actually only five L points per orbiting body. For 
earth-sun the are. L1 between earth and sun, close to the earth. L2 
on the other side of the earth. L3 on the other side of the sun, L4 
and L5 leading and trailing the earth by 60 degrees, at the same 
orbital distance of the earth.

> 
> Naturally, as multiple planets move around their sun, these FTL
> transition points move as well. So, you will need a navigator to
> plot and predict where these transition points are. If your
> background allows, this can allow FTL travel between planets in one
> system. It also seems to be the system used in Star Wars.

Shucks, maybe I'll use them anyway, or invent similar points which 
actually /are/ null grav points, and call them Alderson points, or 
something ;)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Richard Slattery	     richard@mgkc.demon.co.uk
In order to fully realize how bad a popular play can be, it is necessary
to see it twice. 
     George Bernard Shaw
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~