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James Webb Space Telescope User Documentation

 

 

JWST's  WFSC Global Alignment Template will be executed several times during commissioning to reduce the observed segment level Wavefront Error by refining the Secondary Mirror position and making coarse corrections for all Primary Mirror Segment Arrays.

Introduction

Wavefront Sensing and Control - Global Alignment will be executed several times during commissioning to reduce the observed segment level Wavefront Error by refining the Secondary Mirror position and making coarse corrections for all Primary Mirror Segment Arrays. Prior to the Global Alignment Measurements, the primary mirror segments are configured so that there is a separate image of the target star for each segment. There will be a total of 18 images per target placed in a pre-determined hexagonal array.

A typical observation will include the following:

  1. Enter FGS guide star tracking on one of the 18 guide star images
  2. Take a NIRCam image
  3. Perform the specified group of mirror moves
  4. Optional Small Angle Maneuver (SAM) to compensate for boresight changes due to the mirror moves
  5. Take another NIRCam image
  6. Take an FGS image to record new guide star PSFs

The following parameters are used to define Wavefront Sensing and Control Global Alignment Operations. A Wavefront Control File (provided by the WFSC Scientist) will be attached to each visit by the PPS Operator.

In addition to the following template parameters, this template will have the Special Requirement WAVEFRONT SENSING added with a default value of SENSING_CONTROL .

Note that this type of observation cannot be obtained with other parallel observations or as a parallel to normal science observations.    

Note for developers: the default PCS MODE should be COARSE. If the user overrides this value, a warning should be given, unless the SEGMENT GUIDE STAR special requirement is used.

The WFSC Global Alignment Template consists of the following parameters:

FieldDetailsValues Notes
General Information   
Observation Numberassign observation number

number


Observation Label 
 
provide observation labeltextoptional
Observations Commentsprovide observation commentstextoptional
Special Requirementsspecify special requirementschoose from listif needed
Template Specific Information   
Global Alignment Iteration Typeselect typechoose from list 
NIRCam Parameters
Moduleselect ModuleA, B
Short Wavelength Filterselect Short FilterF200W, F212N
Option for Long Wavelength Filterselect if Long Wavelength image desiredcheckbox 
Long Wavelength Filterselect long filterchoose from listif Option for Long Wavelength Filter is checked
Readout Patternselect readout patternRAPID, BRIGHT
Number of Groups/Integrationspecify number of groups/integrationnumber
Number of Integrations/Exposurespecify number of integrations/exposurenumber
FGS Parameters


Number of Groups/Integrationspecify number of groups/integrationnumber
Number of Integrations/Exposurespecify number of integrations/exposurenumber

 General Information  

 The following parameters are generic to all templates, and are not discussed in this article: Observation Number, Observation Label, Observations Comments,    and Special Requirements. 

Global Alignment Iteration Type

GA ITERATION TYPE [GATYPE] = ADJUST1, ADJUST2, BSCORRECT, CORRECT, CORRECT+ADJUST

This field specifies the type of Global Alignment operation (see Table 1) to be executed in this observation. Select ADJUST1 or ADJUST2 to obtain more OTE status data. Select BSCORRECT to improve the wavefront error and modify the JWST boresight. Select CORRECT to improve the wavefront error without affecting the JWST boresight. Select CORRECT+ADJUST to improve the wavefront error followed by more OTE status data collection.

If GA ITERATION TYPE = BSCORRECT you will be prompted for the small angle maneuver (Delta X [delta_x] and Delta Y [delta_y] needed to re-center the boresight; each take values from -180 to +180 arcsec). Note that these offsets are in the FGS Ideal Coordinate System.

Table 1. Contents of Wavefront Control (WFC) Files for each GA type

GA TypeWFC file contents
ADJUST1one group of diversity moves
ADJUST2two groups of diversity moves, one positive and one negative
BSCORRECTone group of SM tilt and/or translations and any necessary PMSA moves
CORRECTone group of corrections (not including SM tilt and/or translations)
CORRECT+ADJUSTone group of corrections (not including SM tilt and/or translations) and one group of diversity moves

NIRCam Parameters

The parameters listed below will be used for all NIRCam images in this observation.

Module

MODULE [MODULE] = A, B

This parameter specifies the MODULE to be used to obtain the data.

Short Wavelength Filter

SHORT FILTER  [FILTSHORT] = F200W, F212N

Select the name of the SHORT FILTER [FILTSHORT] you wish to use.

Option for Long Wavelength Filter

Select USE LONG WAVELENGTH CHANNEL if long wavelength images of the sky will also be collected. If not selected, the long wavelength pupil wheel will by default be placed in the FLAT position (as it is for Dark Frames).

Long Wavelength Filter

LONG FILTER  [FILTLONG] = F322W2, F460M, F480M, F323N+F322W2

Select the name of the LONG FILTER you wish to use.

Developer note: In the database the default of FLAT will be stored in PUPILLONG. If long wavelength filter(s) are chosen (including F323N_F322W) they will be stored in the FILTLONG, and the PUPILLONG will be null.

Exposure Duration

For each exposure to be executed, specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION,  and the NUMBER OF INTEGRATIONS/EXPOSURE.

Readout Pattern

READOUT PATTERN [READOUT PATTERN] = RAPID, BRIGHT1

This field specifies the readout pattern to be used to obtain the data.

Number of Groups/Integration

NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration. (warning)The value must be between 1 and 10.

Number of Integrations/Exposure

NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated. (warning)The value must be between 1 and 10.

FGS parameters

The parameters listed below will be used for all FGS images in this observation.

Number of Groups/Integrations

NUMBER OF GROUPS/INTEGRATON [NGROUPS] specifies the number of groups in an integration.

Number of Integrations/Exposure

NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated.

Note for developers: Visits created from this template should be marked as WFS visits by APT and as WFSC visit type in VSS.

Change log

 Click here to expand...

Version 3 (April 19, 2019)

  1. Editorial change (moved change log to main article)


Version 2 (May 7, 2018)

  1. PR 89947 - updated note to developer in Introduction section.


Version 1 (May 8, 2017)

This is the converted Word File from Chapter 60.

Keywords

JWST WFSC Global Alignment template

JWST WFSC Global Alignment template parameters

Format definitions

Boldface italics type indicates the name of an APT parameter or a value for a parameter.

(warning)Red text indicates restrictions on a parameter.

Brown text indicates notes for the developers.

Green text indicates the name of the parameter used by Commanding.

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JWST Proposal Parameters

Change log

Change log