APT Analysis of Scheduling Constraints
This analysis should be performed for all Large
programs, as well as Small/Medium programs that have tight scheduling
constraints (e.g. BETWEENs or AFTER BYs with a range of less than 20
days, ORIENTs with a range of less than 30 degrees).
For a demonstration using a specific example, see the
When determining how tightly to constrain your observations (which
in turn decreases the schedulability of the observations), please
keep the following in mind:
If you require a specific, fixed Orientation, check the
scheduling impact and provide the broadest possible (within
scientific contraints) orientation range for your observation.
If you require a non-specific, fixed Orientation (e.g.
you are mosaicking a large field, and the orientation is strictly to
align the tiles), then use the Orientation plots from the Roll
Range report to estimate the
optimal Orientations (e.g. for a mosaic, +90, +180, and +270 may be
acceptable) that provide the maximum schedulability.
Below are step-by-step instructions for analyzing the schedulability
of your program.
- On the Observation page, fill in the relevant scheduling
requirements (on PRIME observations only; observations with the
Coordinated Parallel flag set can use the "No Scheduling Constraints"
defined in the Call for Proposals. If you have observations of the
same target/configuration that need to occur at different epochs, then
you must include a separate observation for each epoch (with the
appropriate scheduling requirements).
The following steps should be performed for FIXED TARGET observations
- After entering any scheduling requirements, select
the Visit Planner from the
main Toolbar (with the Observation of interest selected in the
Hierarchical (Tree) editor). Note that if you link observations with
the AFTER OBSERVATION BY, then selecting any one of those observations
will cause the Visit
Planner to process all linked observations together (since all
observations impact the total schedulability). Also, selecting the
Observations container will select ALL observations for processing.
After initialization, press the Update Display button to process the
- The Visit Planner
will display the Total Visibility for the Observation
Block. A green check
means the observation is schedulable at some time
during the year, while the red x
means the observation is NOT
schedulable at any time. You can examine the details by clicking on
the key to the left of the /
. These details include:
Sun/Moon - shows when the target is not blocked by the Sun or Moon
Target Visibility - shows when the target is visible
Absolute Orient - shows when the specified orientation is available
Between - shows the specified scheduling window
Low Sky - shows when Low Sky is available
Shadow - shows Shadow is available
Timing Link - shows when timing links (i.e. AFTER OBSERVATION BY) are schedulable
Combined Roll Restriction - no longer required in 3-gyro operations
If the Observation Block is schedulable, placing the cursor on the
black/grey areas in the timeline will provide a tooltip with the exact
dates that are available, while placing the cursor in the white areas
will show when the observations are not schedulable. You can bring
up a ruler by clicking anywhere in the display area. You can then drag the
to where you want (or just click in the display at the position of interest),
and the box will display the Year/Day Number/Time of the ruler location.
You can also type the year and day number into the box and the ruler will
move to that position.
- If the Observation is not schedulable, then examination of the
details will reveal which scheduling requirements are inconsistent
(e.g. the timing link conflicts with the target visibility).
Revise the scheduling requirements to make the observation
schedulable, or in some rare cases, you may need to select a different
target (if possible).
- If any changes have been made to the scheduling requirements, press
the Update Display button to get an updated timeline.
- For CVZ observations (see Observation 3 above), you can easily
determine the number of days that the target is available (which is
required in your proposal) by placing the cursor on all the black
bars and totalling up the number of schedulable days.
- If you started with an unconstrained Observation, and want to
determine which ORIENTs are available with maximum scheduability and/or
on specific dates, you can use the Roll Range Report.
If there are no scientific constraints, select a range that maximizes
schedulability (e.g. 0-120 degrees). Orients with minimal
schedulability (e.g. 150-180 degrees) should only be used if scientifically
necessary (and should be justified in the proposal). Remember that 180
degree flips are possible (e.g. 330-360 degrees, which has good
If your observation is unschedulable due to a conflict between scheduling
constraints (e.g. BETWEEN) and the Target Availability, and you
can't open up the requirement for scientific
reasons, you can increase the schedulability of the observation by
selecting the Increase Scheduling Flexibility flag. Note that this will
DECREASE the amount of orbital visibility you have, which will make
the observation less efficient, and may require additional orbits to
accomplish your program; you should use the Orbit Visiblity for Large
Programs given in the Primer to determine your orbit request.
Note that you can see how much your orbital visibility has been reduced by going
back to the Form Editor.
Last modified: February 7, 2014.