Pointing errors at noon (for venus run).
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:
The plots show the
pointing results from the runs (.ps) (.pdf):
- 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
- 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.
- When you lose tension in a tiedown, the pointing error
- 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 is 1256.22.. we had ok errors at 1256.1 or even
- 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..
- 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