APT Pointing Model

JWST's Astronomer’s Proposal Tool (APT) estimates duration for each step in the proposal. This page (and its related pages) provide an accounting of duration for each step.

APT has implemented an intermediate Timing model for JWST visits that is being used to calculate times for scheduling, etc right now. Ultimately a lot of these values will need to be enhanced, changed, or gotten from another source, but this documents all the numbers we are using right now, so we can see what needs to be changed and how to come up with values for it. All values are in seconds.

First, a refresher on the APT Pointing Model:

APT will sort through the components that determine the pointing and generate pointings first, then break those pointings into visits based on distance between points, total duration, and total data volume. The order of pointing expansion is:

  1. For each Target in the Observation (supports Target Groups)
  2. For each Mosaic Tile in the Mosaic specification
  3. For each Filter/Grating/ExposureSpecification
  4. For each Dither point (Primary and secondary dithers are expanded first, then the pointing list is iterated. Visits will not be split between secondary dither points, but may be split at a primary dither point.)
  5. Generate the pointing (RA/DEC at a given V2/V3 based on aperture, and mosaic and dither offsets)

There are currently no rules on how to calculate timing for an Internal Engineering visit with no "exposures", per se. They get a time of 0 (to be implemented under PR 72369).

The timing model used by APT does not enforce a particular timing. Because JWST operates in an event-driven model, with each activity starting as soon as a previous activity completes, accurate timing cannot be known. There are several activities that occur within a visit that will take variable time. In most cases, average timing models have been used so that in aggregate, the model will be accurate to within the required specification. Execution times of individual visits and exposures may vary.

Change log

 Click here to expand...

Version 1 (June 6, 2017)

  1. This page and related pages implement PR78448 and PR87643.