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[McIDAS #QKJ-646440]: GOES-South Antenna Pointing Error

Hi Fred,

First, let me apologize for the tardiness of my reply.  I just returned
from travels where my access to the Internet was sporadic...

> The GOES-South data is consistently missing from 07:15 until 11:45 UTC.
> The GOES-10 data sets from NESDIS do not show this data outage.  The
> GOES-10 orbit is degrading, so the satellite position in the sky makes a
> figure 8 in the sky.  If the antenna beam width is less than the figure
> 8 pattern in the sky, the satellite will go outside the antenna beam,
> causing data loss.  This appears to be happening with the GOES-10 data
> from GOES-South.

Yes, our GOES-10 ingest capability does not yet include tracking.  We have
been investigating an affordable solution to this problem for the past
two months.  We should be working on an implementation for a single axis
"tracking" (vertical only) in the next few weeks.

> If the antenna was exactly centered on the figure 8
> and the figure 8 was bigger than the antenna beam width, data would be
> lost twice per day.  If the antenna is not centered, data will be lost
> just once per day.  This is what appears to be happening.

The dish receiving the GOES-10 data rebroadcast through GOES-12 is also
a fixed mount.

> Was this
> antenna misalignment done on purpose to insure data delivery in the
> middle of the day, or was it inadvertent and could be corrected with a
> simple repositioning of the antenna?

The dish was pointed at the equatorial crossing position of the satellite to
maximize the daily coverage.  Since GOES-10's orbital inclination is now
approx 2.25 degrees, a fixed mount will no longer be able to get all of the
data all of the time.

> Back in the early 90's GOES-7 was the only remaining US geostationary
> satellite, and it had run out of fuel for station keeping.  The figure 8
> pattern grew until it exceeded the beam width of the antenna at the
> NSSFC where I was at the time.  Our GOES antenna was not a tracking
> antenna, but it did have electric motors for positioning the antenna. I
> worked with one of our electronic technicians to develop an automated
> antenna moving process.  I provided him with an formula of figure 8
> growth with time.  He then wrote a simple program to convert this figure
> 8 into the number of pulses needed to move the antenna motors.  He also
> build a D/A converter to convert the digital pulses into electric pulses
> for the motors. This "tracker" arrangement worked quite nicely until
> GOES-8 was launched in 1994 and the "geostationary" satellites when back
> to being geostationary.

This is very interesting indeed.  The GOES-10 dish being used at the moment
is, unfortunately fixed.  The GOES-12 and GOES-11 dishes do have elevation
controls and so could be used in the manner that you used while at NSSFC.
Do you still have the position calculation software around?  I have been
thinking about writing the same kind of software so that we could position
the GOES-10 dish after motorization.

In fact, there is a meeting today among RAL, EOL, and Unidata to discuss
where what should be done to improve the ingest of all three GOES platforms
at UCAR.  I can let you know the outcome of the meeting if you are interested.

Thanks for the note, it was very useful.


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Ticket Details
Ticket ID: QKJ-646440
Department: Support McIDAS
Priority: Normal
Status: Closed

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