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

>>From Jonathan Silverlight:
> Stuf4 <tdadamemd-spamblock-@xxxxxxxxxx> writes
> >>From Jim Davis:
> >> Stuf4 wrote:
> >>
> >> >> Radar is not very useful up there -- the strength of a radar
> >> >> echo drops as the distance to the fourth power, barring some
> >> >> special cases.
> >> >
> >> > Actually, the strength of a radar echo drops as the inverse of
> >> > distance *squared*...
> >> >
> >> > But everyone probably knows what was meant!
> >>
> >> No, Henry is correct. Power recieved / power transmitted is
> >> proportional to 1 / (range**4).
> >
> >My feedback was offered in the interest of careful wording. It's easy
> >to have a perfectly accurate thought, but then put that thought into
> >words that are completely inaccurate.
> >
>
> It's even easier to express an inaccurate thought, and it's often better
> not to express a thought..

If anyone would like me to spell it out...

The strength of a radar transmission tends to drop as the inverse of
distance squared. This transmission bounces off an object and the
strength of that echo tends to drop as the inverse of distance squared.
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.

When a person uses appropriate care in how they say something, then it
helps to avoid throwing people off when you make a statement that is
completely inaccurate. While people here may feel like I am pressing a
nit, consider the accuracy of the larger statement that was made:

________

Radar is not very useful up there -- the strength of a radar echo drops
as
the distance to the fourth power, barring some special cases. Most
high-orbit objects are tracked optically. (An ordinary camera with
modest
lens, on a tripod, with the shutter left open a while, will show you a
line of roughly-evenly-spaced dots across the night sky: GSO.)
________


This rationale as to why radar is not very useful up there is presented
unequivocally, yet I see it as completely inaccurate.

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.

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.

....but for some bizarre reason, this forum will swallow invalid
statements made by certain members here and then swarm in support even
after error in such statements has been pointed toward. This
phenomenon strikes me as some kind of implicit appeal to authority.
False statements perpetuate and before long you have the masses
believing in junk like zero gravity in space and radar echos that decay
with the inverse of distance to the fourth power and that there is not
enough radar energy to track satellites in GSO.


In summary, I see it as perfectly accurate to state that optical
tracking is used as an improvement over radar tracking for satellites
out at GSO. What was taken objection to was the reasoning and wording
offered as to why.

(One more plug for avoiding groupthink here at ssh.)


~ CT

.

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