[evlatests] 'Missing' panels on ea21

[George Moellenbrock]

Hi Rick-

Your query reminds me of the panel that detached from *ea20* (not ea21) 
back on a windy Oct 28, 2019, during the move into D-array.   One 
wonders if you see a similar drop-out in the holography before (or even 
after) the repair, which was within a week or so, I think. (See photo 
below; I'm not quite sure how to associate your holography coords with 
that pic, though that gap is on the left side looking into the dish from 
above, if the antenna is tilted down.)

Ultimately, the diagnosis was some rusty bolts, and one wonders if there 
are loose edge panels more generally.....  Maybe wind has dislodged (but 
not yet detached) a few panels on ea21....  And maybe a good thing that 
this isn't more common in your holography results?   (Folks walking on 
antenna surfaces should maybe be careful....)

(NB: Lest there be any confusion, when I initially reported the detached 
panel, I mistakenly identified it as ea21 (the one you are describing 
today!) on pad N01, which I thought was the first north arm pad visible 
from the webcam; rather, N01 is behind the whole line of west arm pads 
from that perspective.  The detached panel was ea20 on N02, in fact.   I 
think we have speculated previously, but inconclusively(?), on whether 
or not the possibly tenuous state of that panel would have been evident 
in holography around that time....)

Cheers,
George






On 5/19/21 3:01 PM, rperley via evlatests wrote:
> I'm reviewing all the surface holography taken over the past three 
> years.  The good news is that there is ample evidence that the panels 
> don't change over this period of time, so that once we've made our 
> 'best' adjustments, no more adjustments will be needed for a long time.
>
> The 'bad' news is that something is quite amiss with ea21.  We're 
> getting no signals from two panels - this is seen in both the Jan 2019 
> and May 2020 data.
>
> Of course, these panels cannot be 'gone' (one hopes that somebody 
> would have noticed this, were that the case ...).  What has happened 
> is that the two panels are tilted so much that we don't get a coherent 
> signal over the resolution of the measurements.
>
> The two panels are in the outermost right, and, as seen from the 
> front, looking into the dish, are the top two panels on the right side 
> of the quad leg.
>
> It would be useful for somebody to look at these -- the effect will be 
> very slight, so don't expect an obvious tilt.  It takes only a couple 
> of millimeters of slope, over the extent of the panel, to make it 
> 'disappear'.
>
> Rick
>
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