Telescope pointing

jan02

Links:

Description of the model parameters
The model parameter values by receiver.
Pointing models and  measurements.
Steps in making the model
History.
Misc pointing  info
Compute pointing error for various platform motions
platform motions.
motion limits:


The model parameters:  (top)

    The model correction is a function of azimuth and zenith angle. It has 13 coefficients in azimuth and 13 coefficients  in zenith angle. There is also a zenith angle encoder table (for azimuth and zenith angle) that is used to correct for  irregularities in the zenith angle tracks. To use the model correction you:
  1. Convert from the astronomical coordinate system (ra,dec) to az, za.
  2. Evaluate the model correction function at this az, za.
  3. Add the model correction to the az,za computed in 1. Since the model correction is in great circles, you must divide the azimuth model correction by  the sine of the zenith angle before adding it to the azimuth value computed in step 1.
  4. Evaluate the encoder tables for az,za at the current za and add these values to that in 3.
   The model parameters definitions are listed below. There is a separate set for azimuth and za. The values are great circle arc seconds.
 
param name An
constant offset A0
cos(az) A1
sin(az) A2
sin(za) A3
sin(za)^2 A4
cos(3az) A5
sin(3az) A6
sin(za-balance)*cos(3az) ** A7
sin(za-balance)*sin(3az) ** A8
cos(2az) A9
sin(2az) A10
cos(6az) A11
sin(6az) A12
** the balance value is 9.15012 deg. This is the greg za that balances the feed arm when the carriage house is at the stow position (8.183 deg).


The model parameter values by receiver.   (top)

  The values for the model parameters for each receiver are listed in the files below. The file format has the azimuth correction in the left most column, the zenith angle correction in the middle column and then the parameter label in the 3rd column. The top of the file contains the most recent file with older models following. A # in column 1 are comments and should be ignored.

327
430dome
430ch
610
lbw (1.2 to 1.75 Ghz)
alfa (1.22 to 1.52 Ghz)
sbw (1.8 to 3.1 Ghz)
sbn (2.3 to 2.4)
sbh (3 to 4 )
cb   (4 to 6)
cbh (6 to 8)
xb  (8 to 10)


ao observatory position


Pointing models and  measurements:  (top)

171122: model 19 after hurricane maria.
170414: az encoder 1 fails, replaced(water in encoder), reset with pointer
170411: az encoder 1 fails, reset, reset with pointer
01jan17: leap second added . used data 01jan17 thru 01dec17.
02oct16: azimuth encoder 1 fails, replaced. aligned with pointer at 270 degrees.
25may16: controlling the platform height with the tiedowns and distomats.
12jan16: az encoder 1 fails. replaced. aligned with pointer at 270 degrees.
07sep15: using 3 distomats to measure the platform height.
09aug15: pointing errors at noon (for venus run)
22jun15: refit polynomial for utc-ut1 after leap second. 01jul15 -> 30sep15 and 01oct15->15jun16
    --> be sure pointing program gets restarted sometime after 01oct15.
16jul14: refit polynomial for utc-ut1
12mar14: calibration runs made after the m8-4 cable repair. checked pointing.
21oct13: refit polynomial for utc-ut1
10sep13: updated sbw,cb models after reinstalltion following ao19 removal.
05jul13: refit polynomial for utc-ut1
13jan13: updated pointing offsets using jul-dec12 data.
18jun12: Pointing error as we move the platform vertically,.
06jun12: pointing error as we tilt the platform using td12.
05mar12: model 18 after beam repair (a year late!)
28feb12: refit polynomial for utc-ut1 mar12 thru jun12
15,16feb12: tilt sensor azswings to verify "new..11may11" td positions still good.
24oct11: fitting the C0,1az,3az errors for alfa.
08sep11: sbn,alfa pointing check after alfa installed.
30jun11: pointing corrections needed after leveling the platform.
12may11: compute new td positions to level platform.
19apr11: refit polynomial for utc-ut1 apr11 thru apr12
14mar11: correcting pointing offsets of 800 Mhz rcvr
09feb11: pointing errors after the beam reinforcement completed.
22nov10: pointing errors octNov10 with 1,2,3 az fits (after u2-u2l3 repair)
03jun10: updated all models to 1,2,3 az fits.mar10-jun10 data.
08feb10: refit polynomial for utc-ut1 feb10 thru feb11
12dec08: updated utc-ut1 fit for leap second.
20jun08: fit 1az and 3az term to pointing errors to update model.
18jan08: pointing model gradients.
16dec07: model 17 after the painting project.
03may07: modeling the azimuth pointing errors.
30mar07: pointing checks  during the painting setup.
11dec06: fit 1 az and sin(za) terms to pnt errors and update the models.
10dec06: refit UT1 - UTC (dec06 thru jun07).
28nov06: nov06 pointing checks after az encoder failure.
27jan06: check the azimuth error after the nov05 encoder failure.
15mar05: Model16 for the carriage house made.
27may04 : pointing error as we lose tension in the tiedowns.
15may04  : Model15 after kevlar cables, alfa installed, and the dome side rollers tightened.
14oct03   : azimuth encoder jumps.
mar03     :Model14 after shimming and dome move.
15sep02  : azimuth encoder jumped.
jul02        : measuring dome tilt,roll while the tiedowns track the average platform height.
feb02       :How many samples are needed to transfer the model between receivers.
jan02       :Model13 after reflector adjustments.
01aug01  :pointing and gain changes from tertiary motor installation.
24may01: pointing error, gain before and after teritiary platform installed.
feb01       : Model12  after 1st reflector adjusted.
apr01      : platform motion as we pull on the tiedowns.
jan00       : azimuth encoder rack gear error.

Pointing references pages:
apr07 Converting platform rotation to sky rotation
apr07: platform motion, gr pointing error as we move ch 2 to 20 degs za
jul02  : tiedown ramps while tracking do not change pitch, roll.


History: (see also: systemhistory)  (top)


model pointing residuals [asecs]
model
azerr rms
noEncTbl
zaerr rms
noEncTbl
total rms
noEncTbl
azerr rms 
zaerr rms 
total rms 
# of points
oct97 mod 0
           
 
dec97 mod 1
           
 
jan98 mod 7
           
 
apr98 mod 8
 
 
 
 
 
 
 
may98 mod 9
8.02
12.43
14.79
3.82
2.37
4.49
 
jan99 mod 10
8.86
12.59
15.39
5.40
3.05
6.20
 
feb00 mod 11
7.78
6.21
9.96
5.68
3.45
6.65
 
feb01 mod 12
7.57
5.77
9.52
5.61
3.65
6.69
1603
mar03 mod 14
8.98
6.65
11.18
5.38
3.48
6.41
1371
may04 mod15
7.08
6.07
9.33
4.20
2.41
4.84
501
mar05
mod16 (ch)
16.33
13.63
21.27
7.52
8.79
11.57
312
dec07 mod17
8.27
6.30
10.40
4.39
2.99
5.31
480
feb12 mod 18
7.46
5.80
9.45
4.18
2.13
4.69
557
nov17 model 19
7.23
6.02
9.41
4.76
3.06
5.65
435

 comments:


Misc pointing  info    (top)

Fitting for utc-ut1

crossing midnight at the end of the year and leap seconds..

The telescope model.

Taking the data using turret scans.

Definition of the sign of the offsets using turret scans or heiles calib scans:

motions and angles in the focal plane.

Fitting the data

Verifying the model

Turret positions:The turret positions and the corresponding pointing errors

A description of the pointing program and the structure it loads in scramnet.
 

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