APT Visit Planner Constraints

As of APT 2020.2 delivery in March 2020 and following, the constraints shown in the APT Visit Planner have been updated to more understandable names.  Also, the APT GUI now gathers related constraints together in the display for better usability.  Certain constraints that result from use of special requirements now 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.

Default Absolute Constraints

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

Field of Regard

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

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). This reflects the probability of acquisition with the top three guide stars at a given time.

Earth Avoidance

Shows when stray light due to the Earth affects scheduling.  This constraint is hidden unless it is different from Field of Regard. 

Moon Avoidance

Shows when stray light due to the Moon affects scheduling. This constraint is hidden unless it is different from Field of Regard. 

Execution

Shows when the visit executed, or is scheduled to execute. (Only relevant after proposal acceptance.)

Constraints due to user specified special requirements

The effects of user specified scheduling requests are also displayed in the Visit Planner. Most of these constraints have a similar name to the request in the proposal.

Absolute Constraints (ones that affect only one observation):

AFTER <date>

Shows the effect of the After Date special requirement.

BEFORE <date>

Shows the effect of the Before Date special requirement.

BETWEEN

Shows the effect of the Between Dates special requirement.

V3PA RANGE

Shows the additional effect of the Sun on schedulability due to the Aperture PA Range special requirement. Note that it is labeled with the equivalent V3PA Range.  See JWST Position Angles, Ranges, and Offsets for the relationship of V3PA and Aperture PA.

PHASE

Shows the effect of the Phase special requirement.

BACKGROUND LIMITED

Shows the effect of the Background Limited special requirement.  See 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 of all the Observing Windows.


Relative Constraints (ones that link multiple observations):

Visit <> AFTER Visit <> 

Shows the effect of the After Observation Link special requirement.

GROUP Visits <> WITHIN <> 

Shows the effect of the Group Observations Link special requirement. 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 <> 

Shows the effect of the Sequence Observations Link special requirement. 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 <>

Shows the effect of the PA Offset Link  and sometimes the Same Aperture PA Link special requirement.

SAME V3PA Visits <> 

Shows the effect of the Same PA Link special requirement if they are the same in V3 PA. Is 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, V3PA 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 Regard, Guide Star Availability and V3PA 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, Group Observations, Sequence Observations, Same Position Angle and Position Angle Offset. It can also include the relative Implicit Requirements Group/Sequence Visits and Visits Same Position Angle 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 Regard and 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 (V3PA) 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 two ways:

1) You can run your cursor over the time lines to these three constraints. For each schedulable day the allowed V3PA roll range is displayed.

2) You can generate the Visit Planner's visit-level Reports (button at the bottom of the display). These will help if you are investigating an interaction between the Guide Star Availability constraint and V3PA 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)


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