Handling Multiple Obsids With The Same SI Mode
(like Comet Observations)


From time to time, a load will contain consecutive observations
of the same target, using the same SI Mode, but with changing Obsids.

The first observation in the series should have the normal, with-bias, SI Mode load commands
followed by the usual Start Science commands - but NO Stop Science.
So long as the SI mode remains the same, there should be no parameter
block loads, power commands, or Start or Stop Science commands in the load until the
last observation in the series is complete:

    - Since you are using the same SI mode, you want ACIS to continue to
      use the bias map obtained in the first observation in the series.

Generally, once the observations in the series have begun, the only Stop Science
command should be after the last Obsid in the series has completed.

An Example - The DEC0318 Load

The DEC0318 A and B loads contain a series of observations of comet 46P/Wirtanen.
For all of these observations except the last one, the SI Mode must be TE_0065A.
The last observation in the series uses a different SI mode - TE_005C6. The fact
that the last observation has a different SI mode is specific to this series.

The A load has an error in the comet observation series.

But let's look at how this is properly done - in the B load:

The first observation ( at 2018:337:18:04:54.261) in the series should load the
"with bias" parameter block for that SI Mode - WT0065A034.

And in fact it does:


     ............................................
                                                                      
2018:337:18:05:26.261     831251  ACISPKT     WSPOW1C81E              
                                                                      
  ==> WSPOW COMMAND LOADS: Feps 1 2 3 4;  I3 S2 S3 S4                 
                                                                      
2018:337:18:06:29.261     831497  ACISPKT     WT0065A034              
                                                                      
ACIS PBLOCK LOADS:                                                    
   parameterBlockId           = 0x0065a034                            
   fepCcdSelect               =   10    7    6    3    8   10         
   fepMode                    = 3 # FEP_TE_MODE_EV5x5                 
   bepPackingMode             = 0 # BEP_TE_MODE_FAINT                 
   recomputeBias              = 1                                     
   trickleBias                = 1                                     
   subarrayStartRow           = 0                                     
   subarrayRowCount           = 1023                                  
   primaryExposure            = 31                                    
   secondaryExposure          = 0                                     
   dutyCycle                  = 0                                     
   lowerEventAmplitude        = 20                                    
   eventAmplitudeRange        = 3250                                  
   windowSlotIndex            = 65535                                 
                                                                      
                                                                      
2018:337:18:06:33.261     831512  ACISPKT     XTZ0000005       
   .............................................................

After that, the only "commands" you should see in ACIS-LoadReview.txt
for all subsequent observations - except the last in this case - should be the Obsid change.
That will prompt lr to display the OCAT entries, so you'll see those too.

For the last 46P/Wirtanen observation - Obsid 21993 - it was necessary to use a
different SI Mode - TE_005C6. So we expect to see the stop sciences, power down,
and parameter block load, start science etc. for that Obsid.   And we do:


     ............................................
                                                                      
2018:347:16:41:35.680    4183326  ACISPKT     AA00000000              
                                                                      
2018:347:16:41:39.680    4183342  ACISPKT     AA00000000              
                                                                      
2018:347:16:41:43.680    4183358  ACISPKT     WSPOW00000              
                                                                      
  ==> WSPOW COMMAND LOADS: All Feps down; All vids down               
                                                                      
2018:347:16:42:07.680    4183451  ACISPKT     WSPOW1C00E              
                                                                      
  ==> WSPOW COMMAND LOADS: Feps 1 2 3;  S2 S3 S4                      
                                                                      
2018:347:16:43:10.680    4183697  ACISPKT     WT005C6024              
                                                                      
ACIS PBLOCK LOADS:                                                    
   parameterBlockId           = 0x005c6024                            
   fepCcdSelect               =   10    7    6    8   10   10         
   fepMode                    = 3 # FEP_TE_MODE_EV5x5                 
   bepPackingMode             = 0 # BEP_TE_MODE_FAINT                 
   recomputeBias              = 1                                     
   trickleBias                = 1                                     
   subarrayStartRow           = 0                                     
   subarrayRowCount           = 1023                                  
   primaryExposure            = 31                                    
   secondaryExposure          = 0                                     
   dutyCycle                  = 0                                     
   lowerEventAmplitude        = 20                                    
   eventAmplitudeRange        = 3250                                  
   windowSlotIndex            = 65535                                 
                                                                      
                                                                      
2018:347:16:43:14.680    4183713  ACISPKT     XTZ0000005

     ............................................

But in the A load we caught an error. Again this is something to watch out for whenever
there are consecutive observations of the same target where only the Obsid changes.

The first observation in the series was set up correctly - same as above.
The last observation in the series was set up correctly.

However the second to the last observation - Obsid 21992 - had power down, parameter block
and Start Science commands which were IN ERROR :

                                                                      
LATEST OCAT INFO FOR OBSID 21992:                                     
Target Name: 46P/Wirtanen	SI Mode: TE_0065A

     ............................................
 2018:347:16:03:16.680    4174355  ACISPKT     WSVIDALLDN              
                                                                                       
 2018:347:16:03:34.680    4174425  ACISPKT     WSPOW1C81E              
                                                                      
  ==> WSPOW COMMAND LOADS: Feps 1 2 3 4;  I3 S2 S3 S4                                  
                                                                      
 2018:347:16:04:37.680    4174671  ACISPKT     WT0065B034  
       .......................  
                                                                      
 2018:347:16:04:41.680    4174686  ACISPKT     RS_0000001              
                                                                      
 2018:347:16:04:45.680    4174702  ACISPKT     RH_0000001              
                                                                      
 2018:347:16:05:08.680    4174792  ACISPKT     XTZ0000005              
                                                                      
   ====> CHANDRA STATUS ARRAY=(ACIS-S,HETG-OUT,LETG-OUT,21992,OORMPEN,CSELFMT2,ENAB)
                                                                      
     
       .......................

None of those ACISPKT commands should be there because we wanted to use the
same SI mode and re-use the bias map obtained by the first observation in the series.

So to recap...when you have a load that contains consecutive observations of the
same target, using the same SI Mode, and only the Obsid changes, be on the lookout
for power, parameter block and start/stop science commands that don't belong there.