This review began with looking a corrective workaround fix to the "Rogue Jogs" Issue. This is where 1 in 170  centering jogs results in the telescope moving much further than requested and sometimes in the opposite direction. However it has turned in a wider review looking at centering performance which has uncovered a further issue.

Recent Case

• Target 16/22 (Hickson 22) suffered a rogue jog after taking final locate frame (S700).  After taking 3rd locate frame a small jog of 1.28 arc mins was commanded (W= 1.26', N= 0.21') in order to finalise the centering of the target. However later analysis failed to find the target within the field of view of the 5 x 180s images taken. Reviewing the logs showed an anomalous movement of the telescope had occured. The post slew telescope position indicates that the telescope had moved around 36.37 arc mins in the opposite RA direction (W= -36.37', N= 0.01'). This is a known occasional problem and a solution/workaround has been identified.

  Centering 3                           
  Taking 30s image (C)...     Ok        [00700044] 02:51:58 (UT)  Full Locate C
  Linking image (UCA/USNO)... Ok        Stars 11, Scale 1.334, Angle 179.4°
  Linking Time:               Info      3.1s
    Analysing stars ...       Ok        (Stars= 11/11)
    Normalised ZP             20.69     
    Altitude                  17.2      deg (Airmass 3.380)
    Sky Brightness            19.60     ADU/sq.arc sec/sec, bkgd: 1251 ADU, dark: 205.1 ADU(C)
    FWHM                      4.0       arc sec (bright: 4.1, next4: 3.8)
  Reviewing position (3)...   Ok        Pointing Error:  1.28 arc mins (W: -1.26', N: -0.21')  
  Reviewing position (3)...   Ok        Jog Required:    1.28 arc mins (W= 1.26', N= 0.21')
  Jogging ...                 Ok        Est. Scope Change: 36.37 arc mins (W= -36.37', N= 0.01')

03:52:35.40 | Hickson 22                 Try   CalculatePointingErrorQSO | 
03:52:35.40 | Hickson 22                 Info  Pointing Check         | Attempting Pointing Check (CalculatePointingErrorQSO)
03:52:35.40 | Hickson 22                 Data  Target Coords (2000)   | RA= 03 03 31.243 Dec= -15 40 32.60 | Epoch 2000
03:52:35.40 | Hickson 22                 Data  Image Coords (2000)    | RA= 03 03 36.478 Dec= -15 40 45.35 | Epoch 2000
03:52:35.40 | Hickson 22                 Data  Pointing Check (Image) | Object Offset:      [W: -1.26', N: -0.21'] 1.28 arc mins
03:52:35.40 | Hickson 22                 Data  Pointing Check (Image) | Pointing Error:     [W: -1.26', N: -0.21'] 1.28 arc mins
03:52:35.40 | Hickson 22                 Data  Pointing Check (Image) | Correction Required:[W: 1.26', N: 0.21'] 1.28 arc mins
03:52:35.41 | Hickson 22                 Ok    JogQSO                 | IamAlive: Start
03:52:35.41 | Hickson 22                                              | 
03:52:35.41 | Hickson 22                 Data  Jog                    | Net Jog    W: 1.26', N: 0.21'
03:52:35.41 | Hickson 22                 Info  Making Jog             | 1.28 arc mins (W= 1.26', N= 0.21')
03:52:35.41 | Hickson 22                 Ok    JogQSO                 | IamAlive: PreJogPosition, Telescope.GetRaDec
03:52:35.41 | Hickson 22                 Ok    JogQSO                 | IamAlive: Continue
03:52:35.41 | Hickson 22                 Info  Making W Jog           | W= 1.26' (1.31' at Dec -15.6)
03:52:35.41 | Hickson 22                 Ok    JogQSO                 | IamAlive: JogW, Telescope.Jog
03:52:47.11 | Hickson 22                 Ok    JogQSO                 | IamAlive: Continue
03:52:47.11 | Hickson 22                 Info  Jog                    | Sleeping For 2.0 secs
03:52:49.11 | Hickson 22                 Info  Making N Jog           | N= 0.21'
03:52:49.11 | Hickson 22                 Ok    JogQSO                 | IamAlive: JogN, Telescope.Jog
03:53:02.61 | Hickson 22                 Ok    JogQSO                 | IamAlive: Continue
03:53:02.61 | Hickson 22                 Info  Jog                    | Sleeping For 2.0 secs
03:53:04.61 | Hickson 22                 Ok    Jog                    | [W] [N]  Jog Completed 
03:53:04.61 | Hickson 22                 Ok    JogQSO                 | IamAlive: PostJogPosition, Telescope.GetRaDec
03:53:04.61 | Hickson 22                 Ok    JogQSO                 | IamAlive: Continue
03:53:04.61 | Hickson 22                 Data  Scope (Pre-Jog)        | RA= 03 04 29.397  Dec= -15 31 38.94 | Current Epoch
03:53:04.61 | Hickson 22                 Data  Scope (Post-Jog)       | RA= 03 07 00.386  Dec= -15 31 38.21 | Current Epoch
03:53:04.61 | Hickson 22                 Data  Scope Change           | 36.37 arc mins (W= -36.37', N= 0.01')
03:53:04.61 | Hickson 22                 Data  Jog Discrepancy        | 37.63 arc mins (W= -37.63', N= -0.20')

 

Code Notes (extracts of relative code)

Sub ImageTargetT_CenterTarget (T, ReturnStatus, bExitSub)

    CalculatePointingErrorQSO(T, PointingError_mins, dErrorN, dErrorW, dJogNcorrection, dJogWcorrection)

     If PointingError_mins > SU.MinimumJog Then
       JogQSO(-dErrorN, -dErrorW, T.Dec, Change_Mins)
    End If
End If

Sub CalculatePointingErrorQSO (T ,PointingError_mins  dErrorN , dErrorW , dJogNcorrection , dJogWcorrection )

  Jog Required:              PointingError_mins   (W= -dErrorW,       N= -dErrorN )

Sub JogQSO  (dNorth, dWest,  dDec, Change_Mins)
 
 Est. Scope Change:   Change_Mins            (W=  -Change_W , N= -Change_N)

Review of Rogue Jog Incidences

Problems with E/W jogs have been noted before.   In the current code jog size is specifically checked because "my LX200 can't make West jogs of less than 30 arc secs", if JogW >= 0.5 arc min a normal West Jog of dWest2' is made,  else West  jog of 1.0' is made following by a East Jog of (1.0-dWest2)'

 To what extent does this 'fix' reflecting a previous attempt to workaround the same issue compound the problem.  Should new fix be applied on top of original fix, or a new fix applied to the original state.

3768 jogs were made during obsservatory operations between 2018-08-19 (S621) and 2019-09-28 (S701) of which the incidences with anomalous jog discrepencies are as follows:

2019-09-26 S00700 03:53:04.61 | Hickson 22                 Data Jog Discrepancy        | 37.63 arc mins (W= -37.63', N= -0.20')
2019-09-20 S00697 03:54:09.50 | GCVS NV Ori                Data Jog Discrepancy        | 39.02 arc mins (W= -39.02', N= -0.19')
2019-09-12 S00693 21:37:30.36 | GCVS CY Lyr                Data Jog Discrepancy        | 34.41 arc mins (W= -34.41', N= -0.19')
2019-09-11 S00692 23:37:13.51 | GCVS U Her                 Data Jog Discrepancy        | 19.85 arc mins (W= -0.28', N= 19.85')
2019-09-07 S00691 01:46:04.65 | GCVS BL Lac                Data Jog Discrepancy        | 28.28 arc mins (W= -28.28', N= 0.07')
2019-04-22 S00676 22:55:25.53 | C/2018 Y1 (Iwamoto)        Data Jog Discrepancy        | 31.70 arc mins (W= -31.70', N= -0.11')

2019-02-26 S00669 05:49:14.14 | GCVS HH And                Data Jog Discrepancy        | 30.33 arc mins (W= -29.90', N= -5.07')
2019-02-26 S00669 05:36:03.23 | GCVS SS Cyg                Data Jog Discrepancy        | 651.14 arc mins (W= 0.75', N= -651.14')
2019-02-26 S00669 05:30:22.67 | 61 Cyg                     Data Jog Discrepancy        | 16.49 arc mins (W= -1.02', N= -16.46')
2019-02-26 S00669 05:12:51.99 | GCVS CY Lyr                Data Jog Discrepancy        | 581.81 arc mins (W= 581.68', N= -12.45')
2019-02-26 S00669 04:41:57.34 | GCVS U Her                 Data Jog Discrepancy        | 655.25 arc mins (W= -655.25', N= -0.85')
2019-02-26 S00669 04:17:46.48 | GCVS S Cyg                 Data Jog Discrepancy        | 338.87 arc mins (W= -338.87', N= 0.00')
2019-02-26 S00669 04:10:23.65 | GCVS AM Her                Data Jog Discrepancy        | 417.70 arc mins (W= 417.70', N= -0.36')
2019-02-26 S00669 03:59:11.34 | GCVS R CrB                 Data Jog Discrepancy        | 535.09 arc mins (W= 535.09', N= -0.14')
2019-02-25 S00668 02:04:35.05 | GCVS AM Her                Data Jog Discrepancy        | 24.66 arc mins (W= -24.66', N= -0.17')

2019-02-23 S00667 01:50:58.38 | 46P/Wirtanen               Data Jog Discrepancy        | 26.42 arc mins (W= -26.42', N= 0.18')
2019-02-21 S00666 04:02:01.07 | GCVS ER UMa                Data Jog Discrepancy        | 10.04 arc mins (W= -10.04', N= -0.01')
2019-02-09 S00661 03:01:47.86 | GCVS RZ LMi                Data Jog Discrepancy        | 31.69 arc mins (W= -31.69', N= 0.11')
2019-02-09 S00661 01:43:14.53 | GCVS U Gem                 Data Jog Discrepancy        | 35.48 arc mins (W= -35.48', N= 0.09')

2019-02-01 S00655 23:39:52.12 | NGC 2628                   Data Jog Discrepancy        | 36.00 arc mins (W= -36.00', N= -0.09')
2019-02-01 S00655 23:21:03.10 | GCVS SU Tau                Data Jog Discrepancy        | 38.12 arc mins (W= -38.11', N= -0.28')
2019-02-01 S00655 21:26:10.81 | GCVS RR Tau                Data Jog Discrepancy        | 36.16 arc mins (W= -36.16', N= -0.22')

2019-01-29 S00652 23:52:57.98 | GCVS CM Tau                Data Jog Discrepancy        | 537.32 arc mins (W= -2.16', N= 537.31')
 (associated with slew discrepencies)
2019-01-29 S00652 20:51:45.79 | GCVS RR Tau                Data Jog Discrepancy        | 35.74 arc mins (W= -35.74', N= -0.11')
2019-01-23 S00650 22:20:51.80 | 46P/Wirtanen               Data Jog Discrepancy        | 21.33 arc mins (W= -21.33', N= -0.11')
2019-01-20 S00648 20:33:21.07 | GCVS BL Lac                Data Jog Discrepancy        | 28.60 arc mins (W= -28.60', N= -0.02')
2018-10-21 S00633 20:16:17.83 | GCVS CI Cyg                Data Jog Discrepancy        | 5.59 arc mins (W= -0.45', N= 5.58')
2018-10-20 S00632 21:28:02.01 | GCVS GK Per                Data Jog Discrepancy        | 463.92 arc mins (W= 463.92', N= -0.13')
2018-09-14 S00629 00:14:19.71 | NGC 5322                   Data Jog Discrepancy        | 19.88 arc mins (W= -19.88', N= -0.05')

2018-09-04 S00626 22:19:44.15 | GCVS S Cyg                 Data Slew Discrepancy       | 3.38 arc min (W= -0.67', N= -3.31')
2018-09-04 S00626 22:20:48.36 | GCVS S Cyg                 Data Jog Discrepancy        | 4.73 arc mins (W= 1.51', N= 4.49')
2018-09-04 S00626 22:22:41.67 | GCVS S Cyg                 Data Jog Discrepancy        | 5.46 arc mins (W= 3.21', N= 4.41')

What we can see is that the instances with rogue jog are
- relatively rare, with usually just a single occurence in 1 out of 5 sessions.
- there is sometimes a run of occurances (S666 - S669),  & S691-S693)
- there are sometimes 3 occurances in one session (S655)
- sometimes a really bad case (S668 with 9 occurances)
- most due to errors in W with values -10 to -40'  , but in one session (S66) with values in range -635 to +535
- there are very case with jog discrepencies in the 3 to 10' range.  (one case S633, 2 cases S626)
- very rare cases where problem is caused by N error with value 19 (S692)

Considering just rogue jogs in the range 5 to 60 arc min there have just 22 incidences amoung the 3768 jogs made between 2018-08-19 and 2019-09-28, that an incidence rate of 1 in 171 jogs. In some cases thesse would have been self correcting but in others the target will have been missed.

The cases with jog discrepencies in excess of 60 arc min (most  300-650 arc min range), nearly all occured on one particular night (S669) and might have a different origin in view of their much higher discrepencies.

Notes:
Data listed from logs file using cmd.ex console

cd  C:\Data\CCD Imaging\Analysis
findstr /s /i /l c:"Jog Discrepancy" *.log  > t.tmp

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/findstr

Focus look at S669

In comparing the requested jog movements with the movements that the telescope actually seemed to make, it is clear that the scope moves to positions 0.5 to 1.5 arc min further east that the commanded jogs
- difference between the commanded and actual jogs in the N-S direction don't show any large deviations or bias, the problem is with jogs in the E-W direction
- the precise difference varies from one jog to the next but the direction of extra movement is always to the east
- its very rare that the scope moves to a position more than 0.1 arc min further west that requested.
- there doesn't seem to be any big difference in discrepency whether the scope is being jogged east or jogged west
  (there may be some bias because any prior bias in the original slew error )
- the average difference doesn't appear to depend on the size of the jogs being made
  (i.e. a jog of 10' and a jog of 0.6' will both showly roughly the same extra movement to the east, say 0.7')
- all the jogs in one session will show roughly the same amount of extra movement,  but session can vary in the amounts of extra movement seen.
  Session S700 shows around 0.5 to 0.75' of extra movement
  Session S678 showed around 1.5' of extra movement

Whilst the cause of this extra movement is unknown, its behaviour is sufficiently well known that the following improvements can be made.

 - the commanded jogs can be modified to take account of the bias in actual RA jog  movements using a JogWAdj (jogW adjustment)
 - machine learning can be used to improve the accuracy of jogs within a session by fine tuning the JogWAdj term depending on errors seen
 - any trends in required JogWAdj term can be spotted to aid diagnosis and make additional improvements.

Fixes to workaround both problems (the rogue jogs and the bias in jog movements) was implement in AstroMain 3.13 (2018-09-30)