From dd@spectra.mit.edu  Thu Apr 27 17:14:00 2000
Date: Thu, 27 Apr 2000 17:13:48 -0400 (EDT)
From: Dan Dewey <dd>
To: sot@head-cfa.harvard.edu
Subject:  simulating the offsets...
Cc: davis, dph, wise


SOT folks, 

 Currently when Chandra "points at" a target that means that the
target is expected to fall in detector coordinates at the
"Image locations" in the table below.  The Chandra optical
axis, however, points at a different region of the sky
given by the "HRMA opt.-axis  intercepts" values in the table
below (all for other offsets = 0.)

 In order to properly simulate an observation with MARX, then,
it is necessary that MARX simulate this difference (some might
say error!) between the optical axis and the target locations
on the detector so that, e.g., simulated chip gaps occurr
where they will with real flight data.      

 --> Are the values below, if implemented by MARX, adequate
and accurate for proposal planning?

  -Dan D for MARX folks...



       Table of "0,0,0,0" Defaults for "Instruments"

    This table summarizes what the result is for a pointing with
    the specified Instrument selected; "0,0,0,0" refers to an
    OR submitted with SIM-Z(trans_offset)=0, SIM-X(focus_offset)=0,
    y_(pointing)offset=0, and z_(pointing)offset=0.
    This is under the assumption of no additional S/C pointing error.


"Instrument"            "0,0,0,0" Result
-----------            ---------------------------------------------
  ACIS-I  
                     Image location centroid at I3 CHIPX =   966
                      (designed: 949, 963)         CHIPY =   956
                     HRMA opt.-axis  intercepts at CHIPX =   984.4 +/-?
                                                   CHIPY =   994.8 +/-?
                     Focus property =         "best aimpoint focus"

  ACIS-S  
                     Image location centroid at S3 CHIPX =   263
                      (designed: 252, 496)         CHIPY =   507
                     HRMA opt.-axis  intercepts at CHIPX =   220.7 +/-?
                                                   CHIPY =   531.8 +/-?
                     Focus property =         "best aimpoint focus"

  HRC-I  
                     Image location  <some HRC-I coord>X = 7667
                                     <some HRC-I coord>Y = 7693
                     HRMA opt.-axis  intercepts at CHIPX = 7529.9 +/-?
                                                   CHIPY = 7745.0 +/-?
                     Focus property =        "best aimpoint focus"

  HRC-S  
                     Image location  <some HRC-S coord>X = 2137
                                     <some HRC-S coord>Y = 8844
                     HRMA opt.-axis  intercepts at CHIPX = 2201.0 +/-?
                                                   CHIPY = 8976.5 +/-?
                     Focus property =        "best focus for LETGS"

  - - -
Useful Conversion factors:

    SIMT (Z)  ODB_TSC_STEPS = 2.51432D-06   meters per motor step

    SIMV (X)  FA            ~ 676 motor steps per mm

"-676 steps/mm is of course a linear approximation appropriate "not
too far" from zero absolute motor steps.  A sixth-order polynomial is
available for better representation (see M. Duncan, Ball System
Engineering Report S98.20874.SYS.386, 2/17/98, "SIM final performance
requirements compliance" pp. 8-9).  Implemented in
/proj/jvrtilek/AXAF_general/sim-focus.exe " - Jan V

 - - - references:
6. Updated optical axis locations from McDowell's March 9th 2000 memo
   "Coordinate Systems Paper 1"
   http://hea-www.harvard.edu/QEDT/jcm/asc/docs
5. HRC "-991" from Schwartz Wed, 10 Nov 1999 11:27:31
4. Updated aimpoints from maxim Wed Nov 10 00:36:21 1999
3. HRC-I updated and converted to other detectors:
    From maxim@head-cfa.harvard.edu  Mon Oct 11 22:41:36 1999
    and added ODB_SI_SIMT and ODB_SI_SIMV values from Schwartz
    (10/22/99) :

 detector    SIM_Z      Opt. axis position      ODB_SI_
             mm         chipx chipy          SIMT     SIMV

 ACIS-I     -233.587     983   992          92905    -536 
 ACIS-S     -190.120     228   523          75620    -468
 HRC-I       126.983    7530  7744         -50505    -716
 HRC-S       250.466    2199  8976         -99612    -991 (with LETG)
                                                    -1065 (no LETG)

The results for instruments other than HRC-I are accurate only to about
10-15" (while for HRC-I it is better than 5"); a more accurate conversion
has to wait for a PIXLIB update.
2. HRC-I info from:
    From maxim@head-cfa.harvard.edu  Tue Oct  5 16:27:03 1999
1. ACIS CHIPX,Y from:
    From maxim@head-cfa.harvard.edu  Fri Aug  6 16:20:36 1999

 - - - end - - -
