[ExI] The Great Silence again

[spike]

>... On Behalf Of Anders Sandberg
Subject: Re: [ExI] The Great Silence again

>...One problem I see with our starmoving scheme is keeping the Dyson cloud
in orbit. When it reflects the star's light it will also tend to expand/move
ahead, and we need to restore it to it's original position relative to the
star. That seems to require some work.

>A statite will be kept in place by gravity, but that only works for a ring
around the star, not a whole shell. Is there any analysis of closed static
orbits for reflectors reflecting in a particular direction? -- Anders
Sandberg


Nein, Dr. Sandberg.  If you take any orbiting mirror with mass per unit area
sufficient such that the light pressure from the star is smaller than the
gravitational attraction, the Dyson cloud does not need any orbit adjust.  I
can show you the orbit BOTECs Robert and I did on that question, but for now
I will describe it with words instead.  If one imagines the ring of
reflecting nodes orbiting in a plane perpendicular to the acceleration
vector, then the orbit plane is shifted in the direction towards the
acceleration of the star.  The angle from the center of the star to the
reflectors in that plane is proportional to the tangent of the ratio of
light pressure to gravitational attraction.  If we are pulling the star
west, the perpendicular plane is west of the centerline of the star.   That
part is easy.

Now, here's the really wicked cool part: if we look at the nodes orbiting in
a plane parallel to the acceleration vector, the nodes spend more time on
the west side of the star than it spends on the east side of the star.  So
it is gently tugging at the star for more time when it is west than when it
is east.  Kepler's law is violated if light pressure is significant in
comparison to gravity.  (Kewall, huh?  {8^D)

I would like to see some orbit hipsters and general RSPs here to duplicate
those calcs.  My BOTECs from my irresponsible early adulthood showed that
these orbits were all stable, so long as the reflectors were all heavier
than statites, heavy enough that gravity overpowers light pressure.

spike