Stability of L points

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

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