Light sail SPS; Sun-Earth L1 (was Correcting my own math -- CORRECTED)

On 4 February 2012 22:20, Frank wrote:

> How would a power sattellite stop that phenomenon?
> After all, a power sattellite is nothing else as a solar sail
> spacecraft, it get's at least half the thrust from solar light pressure
> as a solar sail spacecraft, but it just hasn't the provisions to handle
> this forces by solar sailing.
>

Yes, but your analysis doesn't go far enough. Lightsails actually work by
deliberately tipping themselves to the incident light to give an
acceleration vector along the orbital trajectory, otherwise nothing much
happens.

So the answer to the question is that it doesn't matter. Over the course of
a year, the geosat directly faces the sun at all times, and the sun ends up
having pushed on all sides of the GEO sats orbit around the Earth. The push
deranges the orbit... it will be elliptical... a bit.. at all times..
because of this, but after a year, it's back where it started, the push has
cancelled.

So it's only second order effects that matter, because to first order it
doesn't do anything at all.

If you still don't believe me, consider that the simple lightsail push
effect goes as inverse square law on distance from the sun, but so does
gravity, and it's in the same direction; and I hope you're not claiming
that the Sun's gravity catastrophically destabilises geosats???

These kinds of direct pushes, at right angles to an orbit can normally do
something only if there's a resonance, but a 1 day orbit is not resonant
with the orbital year.

Frank
>

--
-Ian Woollard