[amsat-bb] Re: Geostationary Satellites
bruninga at usna.edu
Tue Oct 11 10:41:37 PDT 2011
>> the risk of collision is more real than one might think.
> I would think the risk of collision is so tiny
> as to be effectively negligible.
I think it is, but when "negligible" incurs about a BILLION$$$ worth of
loss, it magnifies the risk.
> If we position our satellite halfway between two... "slots"
I think that is the problem. One has to stay there. GEO orbits are
impacted by the sun, moon and tides and solar wind. All GEO orbits drift*.
Hence 90% of the mass of these GEO birds are fuel for station keeping. And
that is where the risk comes from. As soon as a spacecraft loses fuel, or
command/control, or any other problem that causes it to no longer keep its
station, it becomes a drifting hazard, moving literally FOREVER along this
extremely narrow orbit, the same orbit that all of these other satellites
are in! It becomes a real hazard to them all.
That is why all nations now subscribe to the requirement that all GEO
spacecraft must have 10% reserve fuel to propel an aging satellite out to
the graveyard orbit. And this must be done before there is loss of
> Is there no clever trick of orbit design
> that can be used to avoid collision?
Not and be geostationary. I think long term drift is the final state of any
GEO orbit. Though there are , I think, *two spots on the entire GEO orcit
which are stable.. but guess what. NO ONE WANTS them, because that is where
all the junk collects and that is where the chances of a collision with all
that junk is highest.
> We can even tolerate some long-term motion...
> Perhaps these extra freedoms would make it possible
> to design an orbit that's close enough to geosynchronous
> for our purposes, but far enough from the commercial orbits to be safe?
I'd guess that being in an orbit closer to earth would be best so that with
time we get further from the GEO arc. But closer in, moves faster and so
all we have to do is chose the DRIFT rate. Let it drift a full cycle once a
year, and the result is that any given country only sees it for 4 months a
year. No matter where we put it, it will be out of view to any one station
2/3rds of the time. But now that it is in its own special orbit, there wont
be any cheap rides to get there...
Our best bet is to piggy back on someone else's bird.
Oh, and it takes almost 10,000 times more power to hit a GEO bird at 22,500
miles away compared to hitting a LEO bird directly overhead (225 miles).
Just my 2 cents
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