NIRSpec MSA Short Detection Template Parameters

JWST's NIRSpec Short Detection template, available in the Astronomer’s Proposal Tool (APT), is used to detect and attempt to remedy electrical short-circuits in the micro-shutter assembly (MSA).

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 feature detects MSA electrical shorts and attempts to remedy them by loading updated zero-potential masks to the Micro-shutter Control Electronics (MCE) on board but not in the zero-potential mask files in RAM. In the event that the quadrant current remains elevated, additional short detection is performed via the tri-state masks in the hardware but not in the tri-state mask files in RAM. The masks used when short detection is requested come from the mask files in RAM, not the hardware. If short detection is requested for the same quadrant back to back in a visit file then the found shorts from the first run would be masked in the hardware but then would get overwritten and get lost due to the second run. This feature allows the user to burn off contaminants if desired by doing this in a planned visit.

Note for developer: Add the requirements SPECIAL COMMANDING with a text value of "MSA Short Detection" and the NO PARALLEL.

The following parameters define MSA Short Detection.

General Information
Observation Numberassign observation numbernumber
Observation Labelprovide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Special Requirementsspecify special requirementschoose from listif needed
Template specific information
Error Responseselect error responsePROCEED, SAFE
Region Checkselect to perform brute force methodALL, STANDARD
Quadrantselect quadrantchoose from list
Threshold171specify a Threshold171 parameternumber
Threshold365specify a Threshold365 parameternumber

 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.

Error Response


ERROR RESPONSE specifies the action to take at the end of each MSA Short Detection activity if a high current situation is found in that quadrant. A "high current situation" is defined as when the number of shorts (in rows and columns) exceeds the maximum defined number of shorts allowed. If the action is PROCEED - the next activity will get executed (for the next quadrant in the list). If the action is SAFE - the visit will end prematurely and the NIRSpec subsystems will be commanded into the Preferred Safe state.

Region Check


Specifies the action to take when deciding whether all regions or only suspect regions will be checked.

  • ALLevery row/column of every region to be checked. 
  • STANDARD – only those rows/columns within regions that show an elevated current (short present) will be checked, thus skipping regions that do not show a short is present.


MSA Short Detection will be executed independently on one to four quadrants each with a specified threshold to determine the existence of shorts.



This parameter specifies the quadrants to be analyzed. You may specify one to four unique quadrants. Specifying a list of multiple quadrants will execute the procedure on the quadrants one-by-one in the order specified.

Note for developer: While the quadrants are called QUADRANT1, QUADRANT2, etc. in APT, they should be populated as 1, 2, etc. in the database.


The THRESHOLD171 [THRESHOLD171] parameter specifies the quadrants' 171 side threshold used to determine shorts. (warning)You must specify one 171 side threshold for each requested quadrant; the range is -3.0 to 25.0 mA.


This THRESHOLD365 [THRESHOLD365] parameter specifies the quadrants' 365 side threshold used to determine shorts. (warning)You must specify one 365 side threshold for each requested quadrant; the range is -3.0 to 25.0 mA.

Change log


  1. PROPINSTJWST-91579 Added Region Check section.

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.