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pntErrs at noon

Pointing errors at noon (for venus run).

08aug15

Intro top

    In aug15 there will be a venus run that starts around midday. During this pass, venus will have a declination of about 7 degrees.
To check the pointing, i did some calibration scans around noon. During these runs i turned off tiedown tracking. The tracking algorithm makes things worse when we loose tension in a tiedown ( it continually tries to push the platform higher, but there is no tension to release in the cable.. this tilts the platform).
    At high za we would loose tension in td 8,12 (rise) and td 12 (setting). This would give errors an az and za. For some of the runs, i pulled the plaform a little lower than ideal, so we would not loose as much tension..

    Data was taken on:

11apr15,18apr15,25apr15,16may15,30may15,06aug15,08aug15

The plots show the pointing results from the runs (.ps) (.pdf):

timing:

the pointing patterns, az pos, pointing error. take about 5.6 minutes each
the platform hght, temp are measured once every 2 minutes
the tiedown tension, position is measured once a second.

page 1: the pointing error for all 7 days.

the srcname has _yymm appended to it.
frame 1,2 za error vs za,az
frame 3,4 az error vs za,az
large errors were seen at rise and set

Page 2-8 .. date from sources on different days..

top: average azimuth position for pattern vs hour of day
2nd: platform (air) temperature for this time
3rd tiedown cable tensions. black:td12, red: td4, green: td8

The vertical scale is blown up to concentrate on when the tiedowns lost tension.
Note: there are 2 cables at each tiedown. for td 12,4,8 i used only cable:[1,2,1]*2 . The other cable had a dc offset.

td 12. cable1 lost tension at .5 kips.
td 8 cable 1 lost tension at .1 kips

4th: tiedown jack position. You can see where i moved the tiedowns and how it affected the height, pointing
5th: average platform height
bottom: pointing error (az,za) in arc seconds

Page 2 J0224+069.. 11apr15

only lost tension at the start. temps were lower.. 78-80.

Page 3: J0224+069 18apr15

had td12 around 7.4 inches pulled down. should have been pulled more to increase the tension.
lost tension td8 at start,
td12 for about 30 minutes at start.and at the end.

the large az error was probably from this.

Page 4: J0224+069 25apr15

td 12 was at 8.5 inches.
tension loss not so bad.
platform height was low, but pnt errors not too bad.

Page 5 J0323+055, j0502_061 30may15

temps warmer 83-87F
had td12 at 7.4 inches again. platform close to focus, but lost tension
should have pulled down more.

Page 6 J1005+077 06aug15

temps around 82
had td12 at 7.5 inches.

plotform close to focus (after start)
lost tension td12,td8 at start and td12 at end
caused large pointing errors when tension lost

Page 7 J0830+077,J1051+061 (last point). 08aug15

temps 81 to 86 F
had td12 at 8.6 inches
platform low, but no tension loss. pointing ok
this data was from transit to set.

Page 8: J1051+061 08aug15

data was rise to near transit.
td12 at 8.6 inches
no tension td 12 at start, platform low
pointing errors not too bad.

Summary:

When you lose tension in a tiedown, the pointing error increases.
You should try and pull down on the platform to get some tension back, even if this causes the platform to be out of focus

focus is 1256.22.. we had ok errors at 1256.1 or even 1256.05..

When you get the tension back (because of lower za ) you can return the platform to the correct height
for the venus run with temps around 80-85, i'd probably run the td with td12 at 8.6 to 9 inches..
Notes:

td12: use cable 1.. hits no tension at .5 kips
td4 : use cable 2
td8: use cable 1 .. hits no tension at .1 kips
td12 around 8.7 inches for ok pointing 80 to 85F

processing: x101/150418/doit.pro

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