APT Visit Planner Constraints

The APT Visit Planner shows constraints with names that indicate the parameter that is being plotted. The APT GUI also gathers related constraints together in the display. Certain constraints that result from use of special requirements only show in the display when relevant. This article provides supporting information on each constraint and its definition.

See also: APT Visit Planner

Figure 1. The VP GUI showing the location of the constraints information

Because visits are the scheduling units for JWST, the constraints are shown at the visit level within an observation. Bars on the timeline show periods when each constraint is satisfied. Hover your cursor over a constraint bar to see the exact start and stop times of the constraint. After running the Visit Planner, the blue links provide direct access to context-sensitive help describing each of the constraints, some of which are roll-ups of various component constraints. This Figure is from APT 2022.1.


Absolute constraints

Words in bold italics are also buttons 
or parameters in GUI tools. Bold 
style represents GUI menus/
panels & data software packages.

The Visit Planner will display timelines to summarize each of the following absolute constraints on schedulability for each visit.

Field of Regard

This shows the effect of the Sun's position on schedulability due to spacecraft pitch (V1 to Sun angle). During schedulable times on the plot, the spacecraft pitch allows sufficient illumination of the solar array and avoids harmfully illuminating the telescope. See the helpful diagram of the field of regard for JWST.

Guide Star Availability

This shows when usable guide stars are available. It is only calculated within the time that the Field of Regard constraint is met. Note that this constraint is the only one that sometimes displays a fractional suitability (the rest are all binary—either schedulable or not). It reflects the probability of acquisition with the top 3 guide stars at a given time.

Earth Avoidance

This shows when stray light due to the Earth impacts scheduling. If it is the same as the Field of Regard constraint, which is often the case, it is not shown.  (See Fig. 1.)

Moon Avoidance

This shows when stray light due to the Moon impacts scheduling. If it is the same as the Field of Regard constraint, which is often the case, it is not shown.  (See Fig. 1.)

Execution

This shows when the visit executed, or is scheduled to execute. (Only relevant after a proposal is accepted and scheduled.)



Constraints due to user-specified observing conditions

The effects of user-specified scheduling requests, called constraints, are also displayed in the Visit Planner. In most cases, these constraints have similar names to the corresponding special requirement in APT that imposed those conditions. Other constraints are named after other types of conditions such as moving targets and implicit requirements.

Absolute constraints (ones that affect only one observation)

AFTER <date>

This shows the effect of the After Date special requirement.

BEFORE <date>

This shows the effect of the Before Date special requirement on schedulability.

BETWEEN

This shows the effect of the Between Dates special requirement on schedulability.

V3 PA RANGE

This shows the additional effect of the Sun on schedulability due to the Aperture PA Range settings in the PA Range special requirement. Note that it is labeled with the equivalent V3 PA range. See JWST Position Angles, Ranges, and Offsets for the relationship of V3 PA and aperture PA.

PHASE

This shows the effect of the Phase special requirement on schedulability.

BACKGROUND LIMITED

This shows the effect of the Background Limited special requirement. Note that specifying the Background Limited special requirement, the user is restricting the scheduling window for the observation as well as the allowed background level allowedSee JWST Background-Limited Observations for when this constraint might be used.

MOVING TARGET

If a moving target observation has one or more Solar System target windows, this constraint will show the combined effect on schedulability for all the observing windows.

Relative constraints (ones that link multiple observations)

Visit <> AFTER Visit <> 

This shows the effect of the After Observation Link special requirement on schedulability.

GROUP Visits <> WITHIN <> 

This shows the effect of the Group/Sequence Observations Link special requirement (with the Non-interruptible option unchecked). It can also display the effect of the "Group Visits within" implicit requirement (which appears automatically on multi-visit observations like mosaics).

SEQUENCE Visits <> WITHIN <> 

This shows the effect of the Group/Sequence Observations Link special requirement with the Non-interruptible option selected. It can also display the effect of the "Sequence Visits within" implicit requirement (which can be placed on multi-visit observations like mosaics).

PA OFFSET Visit <> FROM Visit <>

This shows the effect of the PA Offset Link special requirement, and sometimes the Same PA Link special requirement.

SAME V3 PA Visits <> 

This shows the effect of the Same PA Link special requirement if they are the same in V3 PA. It can also display the effect of the "Visits Same PA" implicit requirement (which appears automatically on multi-visit observations like mosaics). 



Constraints that are combinations of other constraints

The Visit Planner also displays constraints which are actually combinations of other constraints.

Combined Absolute Constraints

Shows the combined effect on schedulability of the following default constraints: Field of Regard, Guide Star Availability, Earth Avoidance, and Moon Avoidance, and all the absolute user-specified constraints: AFTER <date>, BEFORE <date>, BETWEEN, V3 PA RANGE, PHASE, BACKGROUND LIMITED, and MOVING TARGET. 

Combined Absolute Roll Constraints

Shows the combined effect on schedulability of the absolute (non-relative) constraints on position angle. These are: Field of RegardGuide Star Availability, and V3 PA RANGE.

Combined Relative Constraints

This constraint is only shown if there are special requirements (or implicit requirements) linking visits. It shows the combined effect on schedulability of all links. This includes the relative special requirements After Observation Link, Group/Sequence Observations Link, Same PA Linkand PA Offset Link. It can also include the relative implicit requirements "Group/Sequence Visits" and "Visits Same PA" which are added to multi-visit observations like mosaics.



Different ways to view spacecraft roll constraints

In the main Visit Planner display, Guide Star Availability, Field of Regardand Combined Absolute Roll Constraints are expressed in terms of "at what times can it be scheduled?" But they can also be expressed as "at what rolls (V3 PA) can it be scheduled?" This is an important distinction because while time and roll are coupled, a small range of legal rolls are available at each time. You can see this in two ways:

1) You can run your cursor over the timelines for these 3 constraints. For each schedulable day, the allowed V3 PA roll range is displayed.

2) You can generate the Visit Planner's visit level reports (Reports button at the bottom of the display). These will help if you are investigating an interaction between the Guide Star Availability constraint and V3 PA RANGE. The reports are:

  • "Guide Star Availability Analysis" (Different view of the same data in the Guide Star Availability constraint)
  • "Sun Roll Analysis" (Different view of the same data in the Field of Regard constraint)
  • "Total Roll Analysis" (Different view of the same data in the Combined Absolute Roll Constraints)




Latest updates
  •  
    Updated Fig. 1 and minor text clarifications.

  •   
    Minor wording updates for improved clarity.
Originally published