Station Keeping Template Parameters

JWST's Station Keeping Template, available in the Astronomer’s Proposal Tool (APT), is used for JWST orbit maintenance activities.

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.

The Station Keeping visits are used for regular JWST orbit maintenance. When a station keeping activity is necessary the PPS schedules a Station Keeping visit during the contact of interest. The Flight Operation Team (FOT) and PPS operations will agree on a particular contact for the Station Keeping maneuver.

The Station Keeping visit is identified as an FOT engineering visit, which is generated using the Station Keeping visit template and inserted into an Observation Plan that includes normal science operations. In order to minimize the science time lost, the Station Keeping visit will perform preliminary commanding activities and slew to an FOS-computed intermediate attitude still within the science Field of Regard (the burn attitude may be outside the science Field of Regard). Once those steps are completed and after the start of the contact, the OPE enters a fixed-time wait for the FOT to take control of the Observatory. After the FOT takes control, Stored Command Sequences (SCSs) are executed to prepare for the burn, slew to the burn attitude, and perform the burn and related activities. After the burn, the Observatory will slew back to the intermediate attitude under SCS control. The OPE will wait for the FOT to release control, at which point normal science plan execution resumes and it proceeds to the next visit. For more information, refer to the Technical Report "JWST S&OC Station-Keeping Operations Concept" (JWST-STScI-003436).

The Special Requirements NO PARALLEL, REALTIME, REQUIRED, PCS MODE COARSE, and SPECIAL COMMANDING are implied for this template. Special Commanding is required so it will need sign-off by the Commanding team using OPGS. Otherwise, this visit cannot be added to the FLIGHT baseline, since the Special Commanding flag will prevent it from getting onto an OP until approved.

Note for developer: The SPECIAL COMMANDING text field is "Special Commanding Station Keeping".

The target will be automatically set to SK_TARGET . This value indicates that the visit is externally pointed, and requires downstream systems to treat it that way, but also that the exact pointing to be used on orbit will be determined by VSS at scheduling time, based on feedback from Fight Dynamics (FDF) based on the expected momentum profile at the time the Station Keeping visit is to be executed.

The following parameters are used to define Station Keeping observations.

General Information
Observation Numberassign observation numbernumber
Observation Labelprovide observation labeltext
Observation Commentsprovide observation commentstext
Target Namedefault valueSK_TARGET
Special Requirementsspecify special requirementschoose from listif needed
Template specific information
Realtime Durationspecify Realtime Durationnumber must fall within a DSN uplink commanding window
Handoff Window Durationspecify Handoff Window Durationnumberoptional; defaults to 30 minutes if not specified
Initial Setup Durationspecify Initial Setup Durationnumber
Cleanup Durationspecify Cleanup Durationnumber
Stored Command Sequencespecify Stored Command Sequence ID256 – 511

General Information  

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

Realtime Duration

REALTIME DURATION [RTDURATION] specifies the maximum amount of time needed to complete the Realtime commanding. This duration must fall within a DSN uplink commanding window.

(warning) This value must be in the range 1 to 28800 seconds.

(warning)  If HANDOFF WINDOW DURATION is not specified, REALTIME DURATION must be greater than or equal to 1800.

Handoff Window Duration

HANDOFF WINDOW DURATION [RTHANDOFF] specifies the time during which the S&OC FOT must acknowledge taking observatory control. Failure to respond within this window results in the Realtime observation being skipped after any cleanup activities are completed.

(warning)  This parameter is optional but if specified must be in the range 1 to 28800 seconds, and must be less than or equal to REALTIME DURATION

(warning)  If not specified, this parameter will default to thirty minutes (1800 seconds) by OSS scripts

Initial Setup Duration

INITIAL SETUP DURATION [INITDURATION] specifies the amount of time required to complete any initial setup activities; (warning)this value must be in the range 0 to 28800 seconds. For the Station Keeping visit, this time includes 60 to 90 minutes, based on current Operations Concept, of time for the Secondary Combustion Augmented Thruster (SCAT) heaters to reach operating temperature.

Cleanup Duration

CLEANUP DURATION [CLEANDURATION] specifies the amount of time required to complete any cleanup activities; (warning)this value must be in the range 0 to 28800 seconds.

Stored Command Sequence

The STORED COMMAND SEQUENCE ID [SCSID] must be enabled onboard and used to configure the Science Instruments for the Station Keeping visit, if needed, and to ensure integrity of the realtime commanding. The Stored Command Sequence (SCS) will be used to start the SCAT heaters prior to the realtime commanding window, since these need time to reach operating temperature. The SCS ID is used as a pointer in ISIM memory to initiate the SCS ID execution; (warning)it is an integer with a range from 256 to 511.

Change log

Version 4 (February 21, 2022)

  1. PROPINSTJWST-83399 Updated limits and diagnostics for Realtime Duration and Handoff Window duration.

Version 3 (April 19, 2019)

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

Version 2 (October 5, 2017)

  1. PR 84147 -  revised note on default special requirements

Version 1 (May 22, 2017)

  1. This is the converted Word File from Chapter 70.
  2. PR 87714 - Realtime Duration and Handoff Window Duration can't be 0
  3. PR 84174 -  added link to SK-TARGET definition