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. All values are in seconds.

APT sorts through the components that determine the pointing and generate pointings first, then expands those pointings into visits based on distance between points, total duration, and total data volume. The order of expansion for all templates (except IFU templates) 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)

For three templates (NIRSpec IFU, NIRSpec Fixed Slit, and MIRI MRS), a Filter First pointing model is used to minimize the number of filter moves required. For Filter First order, the complete mosaic is executed for a filter before moving to the next filter:

1. For each Target in the Observation (supports Target Groups)
2. For each Filter/Grating/ExposureSpecification
3. For each Mosaic Tile in the Mosaic specification
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)

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