JWST's Station Keeping Template, available in the Astronomer’s Proposal Tool (APT), is used for JWST orbit maintenance activities.
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. 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.
|assign observation number||number|
|Observation Label||provide observation label||text|
|Observation Comments||provide observation comments||text|
|specify special requirements||choose from list||if needed|
|Template specific information|
|Realtime Duration||specify Realtime Duration||number||must fall within a DSN uplink commanding window|
|Handoff Window Duration||specify Handoff Window Duration||number||optional; defaults to 30 minutes if not specified|
|Initial Setup Duration||specify Initial Setup Duration||number|
|Cleanup Duration||specify Cleanup Duration||number|
|Stored Command Sequence||specify Stored Command Sequence ID||256 – 511|
REALTIME DURATION [RTDURATION] specifies the maximum amount of time needed to complete the Realtime commanding; this value must be in the range 0 to 28800 seconds. This duration must fall within a DSN uplink commanding window.
Handoff Window Duration
HANDOFF WINDOW DURATION [RTHANDOFF] specifies the time during which the S&OC FOT must acknowledge taking observatory control; this value must be in the range 0 to 28800 seconds. Failure to respond within this window results in the Realtime observation being skipped after any cleanup activities are completed. This parameter is optional and will default to thirty minutes by OSS scripts if not specified.
Initial Setup Duration
INITIAL SETUP DURATION [INITDURATION] specifies the amount of time required to complete any initial setup activities; 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 [CLEANDURATION] specifies the amount of time required to complete any cleanup activities; 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; it is an integer with a range from 256 to 511.
Version 3 (April 19, 2019)
- Editorial change (moved change log to main article)
Version 2 (October 5, 2017)
- PR 84147 - revised note on default special requirements
Version 1 (May 22, 2017)
JWST Station Keeping template
JWST Station Keeping template parameters