Stability of L points

There is a mission under development to place a solar weather satellite
twice as far, sunward, as L1 by using a solar sail to maintain orbit.
See "Solar Sailing: Technology, Dynamics and Mission Applications,"
Colin R. McInnes and "Space Sailing," Jerome L. Wright for a thorough,
and correct, discussion of these issues.

By the way, it is also possible, with a good solar sail, to hold
communication satellites in geosynchonous orbit above or below the
equatorial plane. This effectively creates new orbit slots in very
lucrative orbital real estate. Unfortunately, for adequate performance
the sails probably have to be made in orbit. They must be so thin that
they probably can't survive launch.

"Combs, Mike" wrote:

>
> From: Bill [mailto:qwerty172@...]
>
> You are both correct.
>
> Well, since Ed is saying that the stable point would be Earthward of
> L1, and I'm saying it would be sunward of L1, I don't think we can
> both be right at the same time.
>
> The stable orbit is further away from the sun
> when light pressure is taken into account, L1, L2, and L3
> are all
> saddle points in the radial direction
>
> The difference in our understanding is that I understand the saddle
> shapes to be in the tangential, not radial, direction. Visualize the
> rubber sheet analogy.
> Another example is O'Neill's mass catcher at the Earth-moon L2 point.
> The constant impact of incoming ore displaces the catcher, but it
> always tends to return. But on the other hand, all it takes is a very
> modest thrust either toward or away from the moon to easily slip off
> the point.
> Wendell Mendell has made an argument for a spaceport at the Earth-moon
> L1 point. The ease with which one could push off either toward the
> Earth or the moon made it an obvious way station to him. Also, if one
> was staging there for a mission to Mars, say, it would be very easy to
> slip off that point toward the Earth, whip around with engines
> thrusting, and thus enjoy a significant kinetic energy advantage.
>
> Regards,
>
> Mike Combs
>

Grab the opportunity to market your company. Choose the
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>

Al Globus
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident.
Maybe we are life's taxi to the stars.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020
goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need
to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid
are
sufficient for orbital colonies with a combined surface area about 500
times
greater than Earth's. Eros alone could make over ten thousand space
colonies,
each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their
colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.