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 training movie.

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.

    1. 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" option) as 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).




    2. The following steps should be performed for FIXED TARGET observations only.

    3. 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 observation.
    4. 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 ruler 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.









    5. 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).
    6. If any changes have been made to the scheduling requirements, press the Update Display button to get an updated timeline.
    7. 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.
    8. 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 schedulability).



      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.