CSMM Gain Measurement Test

Principal: dmkelly
Deputy: stansber,jkeene
Data Monkey(s): Jane for distortions, Jerry for CSMM expertise
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 96h
Last Updated:

Objective

Obtain baseline data for measuring the gain and the stability of the gain of the scan mirror.

Description

This test consists of two parts. The first is a duplicate of testing performed during ground testing. It involves pointing at moderately bright sky and performing photometry while mapping over the 24um and 70um pickoff mirror edges. The second part of the test involves imaging a point source in 70um WF, 70um NF, and 70um SED modes, all with just CSMM moves and no S/C moves.

Data Collected

mips_sur_C0F2N13; mips_sur_C0F2N8 (x6)


Outline of the AOR:
   Point at a bright calibrator star at an intermediate Galactic latitude (see
   notes below for candidate calibrators).
   PCS_Frame command:   MIPS Frame --> 121 (SED center)
   MIPS_MOBS_PHOT
// COMMENT: Map calibrator star across SED slit, .78 pix step size
// relpos = 369,914,587,1132,805,1350,1023,1568,1241,1786,1459,2004,369
   CESCANPOS '41,"MIPS"'
   CEGERSTCON '10,127,4,"MIPS"'
   CEGESTIM '"AUTO",12,"AON","AON","BOTHOFF",10,10,"MIPS"'
   CESCANCON '"CHOP","FWD",0,260,696,109,511,"MIPS"'
   CEMIPSUR '0x0,0x0,0,"NO_COADD",2,13,"MIPS"'
// COMMENT: Map across SED slit and 24um +Y POM, 3.9 70um pix step size
// relpos = 545,1090,1635,2180,2725,3270,3815,545
   CESCANPOS '36,"MIPS"'
   CEGESTIM '"AUTO",7,"AON","AON","BOTHOFF",10,10,"MIPS"'
   CESCANCON '"CHOP","FWD",0,0,0,545,511,"MIPS"'
   CEMIPSUR '0x0,0x0,1,"NO_COADD,2,8,"MIPS"'
// COMMENT: Map calibrator star across 70um WF mode, 3.9 pix step size
// Make no spacecraft moves -- just move the scan mirror
   CESCANPOS '1,"MIPS"'
   CEMIPSUR '0x0,0x0,2,"NO_COADD,2,8,"MIPS"'
// COMMENT: Map calibrator star across 70um NF mode, 3.9 pix step size
// Make no spacecraft moves -- just move the scan mirror
   CESCANPOS '61,"MIPS"'
   CEMIPSUR '0x0,0x0,3,"NO_COADD,2,8,"MIPS"'
// COMMENT: Map across 70um NF/WF POM edge, 3.9 pix step size
   CESCANPOS '39,"MIPS"'
   CEMIPSUR '0x0,0x0,4,"NO_COADD,2,8,"MIPS"'
// COMMENT: Map across 24um -Y POM edge, 15 pix step size
   CESCANPOS '37,"MIPS"'
   CEMIPSUR '0x0,0x0,5,"NO_COADD,2,8,"MIPS"'
// COMMENT: Map across 70um POM edge, 3.9 pix step size
   CESCANPOS '38,"MIPS"'
   CEMIPSUR '0x0,0x0,6,"NO_COADD,2,8,"MIPS"'
// COMMENT: Restore default settings
   CESCANPOS '0,"MIPS"'
   CEGESTIM '"AUTO",63,"BOTHOFF","BOTHOFF","BOTHOFF",10,10,"MIPS"'
   CESCANCON '"CHOP","FWD",0,2048,2048,0,511,"MIPS"'
   MIPS_BACKTO_MOBS

Data Reformatting Requirements

Array Data Desired:

All Arrays

Data Reformatting Option:

SPECIAL

Special Instructions:
The first set of 13 DCEs should go in one file. Each of the six sets of 8 DCEs should go in a separate file.

Task Dependencies

MIPS-322 (70um First Light)

Calibration Dependencies

70um WF illumination correction
70um NF illumination correction
SED slit illumination correction

Output and Deliverable Products

Centroids for each of the star positions in the 70um WF and 70um NF maps. Brightness vs relpos value for the 70um SED maps. No analysis is needed on the POM edge maps other than to verify that the POM edge is visible. The exception is the map across the 24um -Y POM edge, scanpos 37. That test duplicates the CSMM Gain and Offset Verification test from the MIPS functional, so the location of the POM edge should be determined from these data just as was done in the functional test analysis. If we need to use these data to look for a scan mirror gain change, we will blink-compare these data with the data taken during the retest.

Data Analysis

Step by step analysis:
1) Run mips_sloper and mips_caler on all of the data.  
2) Measure centroids for the star images in the 70um WF and 70um NF maps.
3) Make distortion corrections to the star positions and calculate the
   gain of the scan mirror in relpos counts per pixel.  Compare with
   Jerry Heim's model for how CSMM gain should vary with scan mirror angle.
4) Measure the brightness in the SED slit region for each of the positions
   in the SED map.  Plot brightness versus relpos value and determine the
   relpos value that puts the star in the center of the slit.
5) For each of the pickoff mirror edge maps, examine the data and verify
   that the POM edge is visible and that it is being stepped across the
   array.  Compare these data with the maps taken during the MIPS 
   functional test, which was run during both CTA and ATLO testing,

Software Requirements

mips_sloper, mips_caler, and a tool for measuring centroids.

Actions Following Analysis

If necessary, modify the model of CSMM gain versus scan mirror angle and assess the impact on the scanpos table. Make updates to that table if necessary. Forward the results to Chad Engelbracht and Debbie Padgett so that they can consider whether to make changes to any of the AOTs. Generate a report on the results of the test. Archive the data and make sure that the IST understands the test and the results so that they can use these data as a baseline if a check is made later in the mission to see if the scan mirror gain and offset are changing.

Failure Modes and Responses

If the task is not run, use data from the focal plane surveys and from photometry observations to make a scan mirror gain assessment. Try to run this test at a later time since it is the cleanest way of measuring changes in the scan mirror gain.

Additional Notes

Both parts of the test can be performed while pointing at the
same calibrator star field.  The ideal calibrator will be at
intermediate Galactic latitude so that the backgrounds are a
bit higher than normal.  

At Chad's prompting, I did some further work on selecting a target
for these observations.  At 24um, 1 MJy/sr = 14 DN/s.  I prefer a
background of >20 MJy/sr to get at least 1000 DN on the sky.  At
70um NF, 1 MJy/sr = 52 DN/s.  I want at least 10 MJy/sr to get 1500 DN.
For the 70um point source, the saturation limits in 3s are 1.3 Jy in WF,
5 Jy in NF, and 10 Jy at 70um in SED mode.  To get good signal in the
NF and SED modes without saturating in WF mode, I prefer a 70um source
brightness of 0.1-0.6 Jy.  The expected execution time for this task
is somewhere around October 23.  There are a handful of decent candidates, 
listed in order of preference:

   Source      F24   F70   F160     B24   B70   B160   Vis. window
                    (Jy)                (MJy/sr)
   HD 217382   2.2   .26    .05      17    11    51    Aug 12 -- Apr   6
   HD 39425    4.6   .54    .10      18     5     6    Sep  4 -- Dec   5
   HD 189276   2.4   .28    .05      16     6    16    Apr 21 -- Jan  14
   HD 002151   2.0   .24    .05      17     5     8    Apr 16 -- Nov  24
   HD 163588   2.9   .34    .06      16     5     7    Apr 16 -- Dec   1
   HD 180711   3.7   .43    .08      15     5     7    Apr 16 -- Jan  14
   HD 53501    1.2   .14    .03      16     6    15    Apr 16 -- Jan  14

Targets from the April launch window (list retained for reference):
   HD 209750   4.9   .49    .09      41    11    13    May 20 -- June 30
   HD 102647   1.8   .18    .03      43    11     8    May 14 -- June 27
   HD 102870   1.3   .13    .02      51    12     6    May 21 -- July  3
   HD 197989  10.8  1.1     .2       19    11    44    May  7 -- July 14

After the initial S/C moves to put a star in the SED slit, the whole 
sequence is run without further S/C moves.  The star should appear 
in both the 70um WF and 70um NF maps.  The calibrator star should 
never appear on the 160um and 24um arrays; if it does, it will 
indicate a stray light issue.  The scan mirror parameters were 
chosen to match the mapping script used for the 24um POM edges in 
ground testing.  These parameters are good for everything except 
for the 70um SED slit, for which a step size 1/5 as big is used.  
The relpos values for that sequence were chosen to give several 
of the same scanabs values.  The relpos for which a star falls 
in the SED slit is 1088, and the SED map is roughly centered around 
that value.

In scanabs values, here are the CSMM pointings:
Scanpos  Pos1  Pos2  Pos3  Pos4  Pos5  Pos6  Pos7  Pos8  Pos9  P10  P11  P12
   61     687   755   823   891   960  1028  1096   687
   39    1100  1168  1236  1304  1373  1441  1509  1100
   37    1247  1315  1383  1451  1520  1588  1656  1247
    1    1819  1887  1955  2023  2092  2160  2228  1819
   38    2318  2386  2454  2522  2591  2659  2727  2318
   36    3010  3078  3146  3214  3283  3351  3419  3010
   41    3010  3078  3037  3106  3065  3133  3092  3160  3119  3187 3146 3214

These values nearly span the range from the hardstops at 610 and 3486.
These data should be viewed primarily as baseline data for assessing
whether the scan mirror gain is changing.  If that were to occur, the
scan mirror position that places the calibrator star on the SED slit
would no longer put the star at the original position in 70um WF and NF
modes.  The amount of shift would tell us how much the gain had changed.
The change in relpos value needed to put the star in the SED slit would
tell us the change in the scan mirror offset.  In exactly the same manner,
we can use the images of the POM edges to assess the gain and offset.

An assessment was made of the sensitivity of the CSMM gain and
offset values to the telescope temperature.  This analysis showed
that the cooldown that occurs after 70um observations are possible
will have a negligible effect on the CSMM gain and offset.  If we
do this test right after the 24um first light test, we will get
poor numbers due to the subsequent cooling of the scan mirror.