--- In spacesettlers@yahoogroups.com, Al Globus wrote:
> Are you concerned that the sats will eclipse each other during certain parts of the orbit at the equinoxes?

I'm mainly concerned with powersats eclipsing comsats. The comsats will necessarily be near dead center in the middle of the umbras around 6 AM and 6 PM. Even when they are not in the umbras, they can have much of their light blocked. I think people who own the present ~300 solar-powered satellites in GEO would rightly be concerned about the plans of SPS advocates. The idea of "solar rights", though common in Earth-based cities, hasen't yet come up in space, and the reason is that no one has yet been blocking enough sunlight for it to matter. That all changes with the advent of SPS -- especially if it's scaled out to the terawatts.

The powersats will also tend to block *some* light from each other, even when not casting discrete black shadows. This affects the system scalability. the more we try to scale the system, the more light-blocking will occur, reducing predicted scalability. Thus, twice the powersats doesn't mean twice the total power output.

> Wait a minute. The plane of GEO is inclined 22+ degrees to the ecliptic. So how is it that SSPs eclipse each other even at the equinoxes?

At the equinoxes, the satellites at the 6 AM point will be at maximum north. As they pass the 6 AM point, they will fall south at the exact same rate that the satellites approaching the 6 AM point will be rising north, perfectly blocking the sunlight. In a continuous ring of powersats, there would be no point in the orbit, except the 12 noon point, that wouldn't be at least partially blocked of sunlight.

Consider that you are riding in a powersat currently at the 3 AM position. Looking at the sun, you would (at least, if they weren't large enough to cast an umbra that far) see a line of black powersats crossing the sun. By 5 AM, if you're in the center of the powersat, you might be in total darkness.

Again, at the very least, this affects scalability calculations, and should be taken into account when pondering the system's scalability.

> I've runs sims on that [solar light pressure effects]. Most of the acceleration cancels out over a 24 hour period

The light-pressure issues I was concerned about were:

1. bunching up of the powersats in parts of the 24-hour orbit; and
2. dropping below and rising above GEO, and speeding up and slowing down, thus possibly colliding with comsats and with GTO and graveyard-transfer-orbit (or possibly even graveyard orbit itself) traffic.

On Feb 3, 2012, at 11:08 PM, hitssquad wrote:

> --- In spacesettlers@yahoogroups.com, Al Globus wrote:
> > Are you concerned that the sats will eclipse each other during
> certain parts of the orbit at the equinoxes?
>
> I'm mainly concerned with powersats eclipsing comsats. The comsats
> will necessarily be near dead center in the middle of the umbras
> around 6 AM and 6 PM. Even when they are not in the umbras, they can
> have much of their light blocked.

If they aren't in shadow, they're in full sun.

If the orbits were perfect I think this would be a fairly serious
problem, but they aren't. The Moon plays a role, for example. Even
comsats are constantly moving around in their orbit. They don't
really stay over exactly one point.

I think pointing out this issue is a valuable contribution to the
field. I don't think it will be very hard to deal with, if considered
from the beginning. At present there is no law or regulation covering
shadowing of spacecraft as it's not a problem. It seems worth some
serious calculations based on the actual orbits of read spacecraft to
see exactly how much of a problem it is. Certainly worth a paper or
two at AIAA conferences.