Re: How many satellites are in geosynchronous orbit by now?

>>From Henry Spencer:
> > It is the round trip taken together, and not the echo itself, that
> >will have a power drop off that tends to decay as the inverse of
> >distance to the fourth power.
>
> Which means that the echo *as received* decays that way, barring the
> special cases that I mentioned. Which is, of course, what matters for
> practical use of radar.
>
> >The problem, as I understand it, is an issue of beam width and angular
> >resolution because the same advantage these orbits have in station
> >keeping works against you in the tracking task. It is because of the
> >lack of relative motion with respect to a ground station that other
> >methods are sought.
>
> Nope. The problem exists even when there is relative motion. And
> relative motion or lack thereof is pretty much irrelevant to radar
> tracking, unless you're using Doppler techniques to pick moving targets
> out of stationary clutter... which is important for aircraft tracking on
> Earth, especially for airborne radars looking down, but is irrelevant to
> space tracking systems looking up.
>
> (I say "pretty much" because there are some space tracking systems that
> point in fixed directions and rely on spacecraft to pass over them... but
> those are LEO-only, irrelevant to high-altitude tracking.)
>
> >A simple way to invalidate the original statement at issue is to
> >consider all of the objects that have been radar tracked at distances
> >far greater than GSO.
>
> This stops looking so simple when you consider the resources that are
> needed to track them. There have been a *few* quite impressive feats of
> spacecraft tracking, notably when it was possible to use Arecibo and
> Goldstone in combination. Those facilities are not available for routine
> spacecraft tracking, or even mildly unusual spacecraft tracking, and
> Arecibo in particular can point at only quite limited areas of the sky.
>
> Note that when Contour was silent after its departure burn, its pieces
> were found optically, not by radar.
>
> As it happens, this is a subject I've been professionally involved in, in
> a small way. Optical tracking is the method of choice for high-altitude
> objects, because radar works poorly at such distances and the resources
> needed to make it work halfway well are not routinely available for
> spacecraft tracking.

I would be very interested to read any reference that anyone would like
to provide that states that the fundamental problem in the orbit
determination of satellites at geostationary distance is the lack of
radar energy.


~ CT

.

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