NIRSpec Filter-Grating Wheel Test Template Parameters

JWST's NIRSpec Filter/Grating Wheel Test template, available in the Astronomer’s Proposal Tool (APT), is used for Filter or Grating Wheel Characterization as well as Filter or Grating Wheel Run-In.

Purple text indicates the parameter is Limited Access.

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

(warning)Red text indicates restrictions on a parameter.

(red star) Black text indicates an important note.

Brown text indicates notes for the developers.

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

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

This engineering template supports Filter or Grating Wheel Characterization as well as Filter or Grating Wheel Run-In.

During characterization, the specified wheel is rotated an entire cycle, position by position, with the high capacity telemetry buffer enabled and dumped for each move.

During the run-in test, the specified wheel is rotated an entire cycle from 1 to 100 times as indicated by the NUMBER OF ROTATIONS parameter in order to distribute the lubricant. Each cycle consists of a move of 3 positions in the specified direction, followed by another move of 3 positions and then a move of 2 positions, returning the wheel to its initial position.

Note that this type of observation can never have parallel observations attached to it.

Note to developer: Automatically add a NO PARALLEL special requirement to these observations. If the requirement is removed by the proposer, APT should issue an error. Also add SPECIAL COMMANDING MSA Short Detection.

The following parameters define Filter/Grating Wheel Characterization and Run-In.

General Information
Observation Numberassign observation numbernumber
Observation Labelprovide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Special Requirementsspecify special requirementschoose from listif needed
Template specific information
Wheel Test Typeselect wheel test typeCHARACTERIZE, RUNIN
Wheel Directionselect wheel directionchoose from list
Mechanismselect mechanismFILTER, GRATING
Number of Rotationsspecify number of rotationsnumber

 General information  

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

Wheel Test Type


This parameter specifies whether to run the Filter/Grating Wheel Characterization procedure or the Filter/Grating Wheel Run-In procedure

Wheel Direction


This parameter (used for both mechanisms) specifies whether to rotate the Filter or Grating wheel in the FORWARD, REVERSE, or BOTH directions (forward first, followed by reverse).



This parameter specifies the mechanism to exercise.

Number of Rotations

The NUMBER OF ROTATIONS [NROTATIONS] parameter specifies the number of full rotations of the Filter or Grating wheel to be executed during the Filter/Grating Wheel Run-In procedure.

(warning)This parameter is a positive integer from 1 to 100. If a WHEEL DIRECTION of BOTH is specified, the full number of rotations is applied to each direction.

This parameter is only allowed if WHEEL TEST = RUNIN.

Change log

Version 2 (April 19, 2019)

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

Version 1 (June 15, 2017)

  1. This is the converted Word File from Chapter 39.