GSFC 12Meter commissioning (2011)

05may21



Intro .. in progress..

    Tapasi received 3 emails from ed himwich back in 2011 related to his commissioning of the goddard gsfc 12meter antenna:

Elevation encoder creep:

    Hi,

The elevation axis continued to show creep this weekend. I have attached
a time-plot of the data which was collected for about 36 hours. The
general impression I get from the plot is that it stable, maybe shifting
up a little, during the first daylight period (first 12 hours
(daylight), then overnight (middle 12 hours) it is shifting rapidly, and
then in the next daylight period (last 12 hours) it is more stable, but
still shifting up a little. It appears to have shifted about 0.1 degrees
in the overnight period.

This is not inconsistent with the idea that something is loose and that
differential contracting with cooling overnight makes it looser. It
isn't obvious though why the change appears to be monotonic, but maybe
there is some feature of the surface contact that makes it ratchet.

The AuScope folks in consultation with Patriot/Cobham have installed ta
"set screw" as described in the e-mail I forwarded separately. They are
tentatively reporting that it may have solved the problem.

It wasn't very cold at GGAO over Saturday night. It got down to about
20C in the Washington area. I have admit I don't understand the
mechanical issues involved, but if the model if differential contracting
is accurate, one might wonder how much worse it might get during the
winter and whether a set screw is sufficient to deal with this or
whether is a different problem. It would be interesting to hear
Patriot's take on this.

Cheers, Ed







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